The bioequivalence and therapeutic efficacy of generic versus brand-name psychoactive drugs

BACKGROUND: For the purposes of drug approval, the interchangeability of a generic drug and the corresponding brand-name drug is based on the criterion of "essential similarity," which requires that the generic drug have the same amount and type of active principle, the same route of administration, and the same therapeutic effectiveness as the original drug, as demonstrated by a bioequivalence study. However, bioequivalence and therapeutic effectiveness are not necessarily the same. OBJECTIVE: This review summarizes available data comparing the bioequivalence and therapeutic efficacy of brand-name psychoactive drugs with those of the corresponding generic products. METHODS: Relevant information was identified through searches of MEDLINE, Current Contents/Clinical Medicine, and EMBASE for English-language articles and English abstracts of articles in other languages published between 1975 and the present. The search terms used were generic drug, branded drug, safety, toxicity, adverse events, clinical efficacy, bioequivalence, bioavailability, psychoactive drugs, and excipients. RESULTS: Few publications compared the bioequivalence and efficacy of brand-name and generic psychoactive drugs. Those that were identified revealed differences in the efficacy and tolerability of brand-name and generic psychoactive drugs that had not been noted in the original bioequivalence studies. Specifically, l study found that plasma levels of phenytoin were 31% lower after a switch from a brand-name to a generic product. Several controlled studies of carbamazepine showed a recurrence of convulsions after the shift to a generic formulation. After a sudden recurrence of seizures when generic valproic acid was substituted for the brand-name product, an investigation by the US Food and Drug Administration found a difference in bioavailability between the 2 formulations. Statistically significant differences in pharmacokinetic variables have been reported in favor of brand-name versus generic diazepam (P < 0.001). Finally, a case report involving paroxetine mesylate cast doubt on the tolerability and efficacy of the generic formulation. CONCLUSION: The essential-similarity requirement should be extended to include more rigorous analyses of tolerability and efficacy in actual patients as well as in healthy subjects.     

Bioequivalence of two film-coated tablets of imatinib mesylate 400 mg: A randomized,open-label,single-dose,fasting, two-period,two-sequence crossover comparison in healthy male South American volunteers

Background: Imatinib is a tyrosine kinase inhibitor that has been established as a highly effective therapy for chronic myelogenous leukemia and gastrointestinal stromal tumors. A new generic, once-daily 400-mg tablet of imatinib has been developed by a pharmaceutical company in Argentina, where the regulatory standard for marketing authorization of an imatinib generic is in vitro dissolution testing.Objective: The aim of this study was to assess the bioequivalence of a new generic film-coated test tablet formulation versus a film-coated reference tablet formulation of imatinib 400 mg. The local manufacturer seeks to validate the in vitro performance of this new formulation with a bioequivalence study.Methods: A randomized, open-label, single-dose, fasting, 2-period, 2-sequence crossover design with a 2-week washout period was used in this study. The study population consisted of healthy male South American (Uruguayan) volunteers, who were assigned in a 1:1 ratio to a randomized sequence (test-reference or reference-test). In each period, the test or reference formulation was administered after an overnight fast. During the 72-hour follow-up period, participants were monitored for vital signs and symptoms. Blood samples were collected at 15 time points, including baseline, until 72 hours. Physical examination and laboratory tests (blood, urine) were repeated 1 week after study completion. A noncompartmental model was used to determine the pharmacokinetic parameters of imatinib. The 90% CIs of the test/reference ratios for AUC_0-∞ and C_max were determined; the test and reference formulations were considered bioequivalent if the 90% CIs were between 0.80 and 1.25. Adverse events were assessed by a nurse who administered a questionnaire while the healthy volunteers were admitted in the unit.Results: The bioequivalence study was conducted in 30 Uruguayan male volunteers. Demographic characteristics (mean [SD]) included age, 27.8 (6.5) years; weight, 71.2 (9.8) kg; height, 1.71 (0.09) m; and body mass index, 24.3 (3.0) kg/m2. The mean (SD) of AUC_0-∞ was 38,179 (15,504) ng/mL · h^?1 for the test formulation and 40,554 (17,027) ng/mL · h^?1 for the reference formulation. The mean of Cmax for the test formulation was 2472 (933) ng/mL, and the mean Tmax was 3.28 (0.93) hours. The mean of Cmax for the reference formulation was 2566 (963) ng/mL, and the mean T_max was 3.63 (1.20) hours. The point estimates (90% CIs) for the test/reference ratios of the log-transformed AUC- and C_max mean values were 0.95 (0.87–1.03) and 0.97 (0.89–1.05), respectively, which met the regulatory criteria for bioequiv-alence. Thirty-four mild to moderate adverse events were reported (13 with the test formulation and 21 with the reference formulation), and no serious or unexpected adverse events were observed during the study. The adverse events included 16 cases of headache, 13 cases of nausea, 4 cases of vomiting, and 1 episode of diarrhea.Conclusions: The results of this study suggest that the test formulation of imatinib met the regulatory criteria for bioequivalence to the reference formulation in these healthy fasting male volunteers. Both formulations were generally well tolerated and appeared to have a similar adverse-event profile.     

Bioequivalence of two oral formulations of tebipenem pivoxil hydrobromide in healthy subjects

Tebipenem pivoxil hydrobromide (TBP‐PI‐HBr) is a novel oral carbapenem prodrug of tebipenem (TBP), the active moiety, currently in development for treating serious bacterial infections. This study assessed the bioequivalence (BE) of the clinical trial and registration tablet formulations of TBP‐PI‐HBr and evaluated the effect of food on the pharmacokinetics (PKs) of tebipenem. This was a single center, open‐label, randomized, single‐dose, three‐sequence, four‐period crossover, BE, and food‐effect study. Subjects received single 600 mg oral doses of TBP‐PI‐HBr as the reference clinical trial tablet (treatment A) and test registration tablet (treatment B) formulations in alternating sequence while fasting, and then the test formulation under fed conditions. Whole blood samples were collected predose and at specified intervals up to 24 h postdose to evaluate TBP PK parameters. Safety and tolerability were monitored. Thirty‐six healthy, adult subjects were enrolled and completed the study. The criteria for BE were met for the TBP‐PI‐HBr test (registration tablet) and reference (clinical trial tablet) formulations as the 90% confidence intervals for the geometric mean ratios for TBP area under the curve (AUC)_0‐t , AUC_0‐inf, and maximum plasma concentration (C _max) fell within the established 80% to 125% BE limits. Dosing with food had no meaningful effect on TBP PK parameters. Five (14%) subjects reported adverse events (AEs) of mild severity. No deaths, serious AEs, or discontinuations due to AEs were reported, and no clinically relevant electrocardiograms, vital signs, or safety laboratory findings were observed. The study results demonstrate the BE of oral TBP‐PI‐HBr registration and clinical trial tablet formulations and indicate that TBP‐PI‐HBr can be administered without regard to meals.

Study Highlights WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC? Tebipenem pivoxil hydrobromide (TBP‐PI‐HBr) prodrug was developed as the first oral carbapenem for treatment of serious bacterial infections due to gram‐positive and gram‐negative bacteria, including drug‐resistant pathogens. The TBP‐PI‐HBr formulation was developed for use in phase I and phase III clinical studies during clinical development. However, the oral tablet formulation was modified for registration purposes. Because the registration formulation had differences than the formulation used in early clinical development, a bioequivalence (BE) study was conducted and, within the same study, a food effect evaluation arm also was included. WHAT QUESTION DID THIS STUDY ADDRESS? This study evaluated the BE of a 300 mg TBP‐PI‐HBr registration tablet (test) formulation developed for commercial use (i.e., the intended marketed formulation) and the 300 mg clinical trial tablet formulation (reference) in healthy adults under fasting conditions and the effect of food on tebipenem (TBP) pharmacokinetics (PKs) for the registration tablet formulation. WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE? Clinical study and registration tablet formulations of oral TBP‐PI‐HBr were bioequivalent and administration of the registration tablet with food had no clinically relevant effect on the PK profile of TBP. HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE? The registration tablet formulation of oral TBP‐PI‐HBr is comparable to the clinical study formulation and can be administered without regard to meals for the treatment of serious bacterial infections.     

Bioequivalence of single 100-mg doses of two oral formulations of topiramate: An open-label,randomized-sequence,two-period crossover study in healthy adult male Mexican volunteers

Background: The proprietary form of topiramate is indicated in Mexico as an antiepileptic agent and in the prophylaxis of migraine headaches. However, before generic topiramate is placed on the market, pharmacokinetic studies investigating the bioequivalence of generic and branded formulations are needed.Objective: The aim of this study was to compare the bioequivalence and tolerability of a generic (test) and a branded (reference) formulation of topiramate 100 mg in healthy Mexican volunteers.Methods: This open-label, randomized-sequence, 2-period crossover study was conducted at Ipharma SA de CV, Monterrey, Mexico. Eligible subjects were healthy male Mexican volunteers aged 18 to 45 years. Participants were randomly assigned to receive 100 mg of the test or reference formulation, followed by a 3-week washout period and administration of the alternate formulation. Doses were administered after a 12-hour overnight fast. For analysis of pharmacokinetic properties, including C_max, AUC_0-t, and AUC_0-∞, blood samples were obtained over a 144-hour period after dosing. The formulations were to be considered bioequivalent if calculations of a 90% CI for the ratio of the means of the measures for the test and reference formulations fell within bioequivalence limits, 80% to 125%, for logarithmic (log) transformation of C_max and AUC, and if two 1-sided t tests showed P < 0.05. Tolerability was assessed using vital sign measurement (blood pressure, body temperature, heart rate, and respiratory rate), laboratory analysis (hematology, blood biochemistry, hepatic function, and urinalysis), and subject interview.Results: Twenty-eight men (mean age, 22.21 years [range, 18–28 years]; mean weight, 75.04 kg [range, 62–96 kg]; mean height, 177 cm [range, 163–192 cm]) were enrolled in this study, and 28 (14 each randomized to receive the test or reference formulation first) completed it. No period or sequence effects were observed. The 90% CIs for the log-transformed C_max, AUC_0-t and AUC_0-∞ were 94.70 to 112.05, 98.88 to 105.16, and 98.80 to 105.28, respectively (all, P < 0.05). No adverse events were reported by the volunteers or found on clinical laboratory testing during the study.Conclusions: This study did not find any statistically significant differences in C_max or AUC values between the test and reference formulations of oral topiramate 100 mg in this population of healthy adult male Mexican volunteers. On that basis, and according to both the rate and extent of absorption, the test and reference formulations met the regulatory criteria for bioequivalence. Both formulations were well tolerated.     

A pharmacokinetic and clinical review of the potential clinical impact of using different formulations of cyclosporin A. Berlin,Germany, November 19, 2001

A meeting of 14 transplant and pharmacokinetic specialists from Europe and North America was convened in November 2001 to evaluate scientific and clinical data regarding the use of different formulations of cyclosporin A (CsA). The following consensus was achieved. (1) CsA is a critical-dose drug with a narrow therapeutic window. Clinical outcomes after transplantation are affected by the pharmacokinetic properties of CsA, particularly by its bioavailability, and by intrapatient variability in CsA exposure. (2) Standard bioequivalence criteria do not address differences in CsA pharmacokinetics between transplant recipients and healthy volunteers, or between subpopulations of transplant recipients. (3) In some circumstances, currently available formulations of CsA that meet standard bioequivalence criteria are likely to be nonequivalent with respect to pharmacokinetic characteristics. (4) The choice of CsA formulation can affect the short- and long-term clinical outcome. Currently, there is a lack of clinical comparisons between generic CsA formulations and the Neoral formulation (Novartis Pharmaceuticals Corporation, East Hanover, New Jersey). Initial retrospective data from the Collaborative Transplant Study suggest that use of generic CsA formulations may result in reduced graft survival at 1 year. (5) Management of transplant recipients by monitoring Neoral concentrations 2 hours after dosing (C(2)) reduces the incidence and severity of acute rejection compared with monitoring of trough concentrations with no increase in toxicity. C(2) monitoring has been developed based on the pharmacokinetics of Neoral only and has not been evaluated or validated for generic formulations of CsA. (6) The major costs of care after transplantation relate to the management of poor clinical outcomes and toxicity. CsA formulations with different pharmacokinetic properties may be associated with varying clinical outcomes, which would be expected to affect total health care costs. (7) The transplant physician is responsible for selecting immunosuppressive agents and formulations for his or her patients. Any switch between CsA formulations in a particular patient should take place only in a controlled setting with adequate pharmacokinetic monitoring.     

Sex Effect on Average Bioequivalence

Purpose

Generic formulations are by far the most prescribed drugs. This scenario is highly beneficial for society because medication expenses are significantly reduced after expiration of the exclusivity period conceded to the branded name drug. Correspondingly, these formulations must be adequately evaluated to avoid drug inefficacy and toxicity in the overall patient population. Bioequivalence studies are the only in vivo evaluation that a generic drug must overcome to reach the market. These clinical trials have not been exempt from underrepresentation of female subjects and a lack of sex-based analysis. Frequently, conclusions obtained in men are extrapolated to women. Furthermore, the obtained results are not analyzed to determine sex differences. The aim of this study was to discuss the effect that male and female differences in gastrointestinal physiology can have on bioequivalence conclusions and to show why a sex-based analysis must be conducted in these studies to improve the evaluation of generic drugs.

Relative fasting bioavailability of two formulations of nateglinide 60 mg in healthy male Chinese volunteers: an open-label, randomized-sequence, single-dose, two-way crossover study

BackgroundNateglinide, N-(trans-4-isopropylcyclohexyl-carbonyl)-d-phenylalanine, is a potent insulin secretagogue designed to restore early-phase insulin secretion. It increases pancreatic insulin secretion by competitively binding to sulfonylurea receptors inhibiting adenosine triphosphate–sensitive potassium channels and thus reducing blood glucose levels. The drug has a rapid onset (causing immediate insulin release) and a short duration (allowing insulin to return to baseline levels between meals) of insulinotropic action.ObjectiveTo meet the requirements for marketing a new generic product, this study was designed to compare the pharmacokinetic parameters and relative fasting bioavailability of new generic (test) formulation of nateglinide with the reference formulation of nateglinide in healthy Chinese male volunteers.MethodsThis open-label, single-dose, randomized-sequence, 2-way crossover study was performed at Nanjing First Hospital of Nanjing Medical University. Eligible subjects were healthy male volunteers who were randomly assigned in a 1:1 ratio to receive a single 60-mg (0.88 mg/kg) dose of the 2 formulations, followed by a 1-week washout period and then administration of the alternate formulation. Study drugs were administered after a 10-hour overnight fast. Concentrations of nateglinide were determined by using a validated LC-MS method. For analysis of pharmacokinetic properties, including C_max, AUC_0–10, and AUC_0–∞, blood samples were obtained at intervals over the 10-hour period after study drug administration. As established by the State Food and Drug Administration, the formulations were assumed bioequivalent if 90% CIs for the test/reference ratios of ln-transformed values of C_max and AUC (obtained by using ANOVA) were within the predetermined equivalence range (80%–125%). Tolerability was assessed by monitoring vital signs and laboratory tests (hematology, blood biochemistry, hepatic function, and urinalysis) and by questioning subjects about adverse events.ResultsThe 90% CIs for nateglinide were as follows: C_max, 98.4% to 118.6%; AUC_0–10, 99.5% to 110.3%. Both C_max and AUC_0–10 met the predetermined criteria for assuming bioequivalence. The relative bioavailability of the test formulation was estimated to be 102.1% (13.5%). One volunteer (5%) experienced a headache after administration of the test formulation. This resolved spontaneously within 1 hour and was considered by the investigators to be mild. No serious adverse events were reported. No period or sequence effects were observed.ConclusionsIn this study of healthy Chinese male volunteers, a single 60-mg dose of nateglinide (test formulation) met the regulatory criteria for assuming bioequivalence to the established reference formulation. Both formulations were well tolerated. Chinese Clinical Trials registration number: ChiCTR-TRC-11001754.     

Pharmacodynamic bioequivalence testing

What is known and Objective: The assessment of bioequivalence of drugs intended for local action/targeted delivery and with poor systemic absorption presents unique challenges. Approaches such as pharmacodynamic (PD) bioequivalence testing have been proposed as alternatives to pharmacokinetic (PK) bioequivalence studies. Our objective is to comment on when PD bioequivalence testing might be considered appropriate and whether the acceptance criteria for bioequivalence could be adjusted based on observed variability in PD response. Comment: Pharmacokinetic bioequivalence studies are generally conducted to evaluate the rate and extent of drug absorption of a test drug as compared to a reference drug. However, this may not be appropriate for locally acting drugs, when the plasma drug concentrations, if measurable, are not correlated with the clinical therapeutic effect. Systemic absorption may in fact be undesirable for such drugs. The US Food and Drug Administration (FDA) recommends alternative approaches for evaluating the bioequivalence of acarbose, including a bioequivalence study with a PD endpoint. For the evaluation of therapeutic equivalence of highly variable drugs, adjusting the acceptance interval for the PK parameters has been discussed by the FDA and the European Medicines Agency (EMEA). However, it is still not clear whether the newly proposed methodology is applicable to PD bioequivalence testing. What is new and Conclusion: Although no consensus has been reached on the criteria for PD bioequivalence testing, various approaches are currently being investigated. Further studies should be performed to assess whether an adjustment of the acceptance intervals is appropriate based on the within-subject variability of PD responses. This may potentially minimize the unnecessary exposure of a large number of subjects to the test drugs.     

Bioequivalence and other unresolved issues in generic drug substitution

BACKGROUND: Substitution of generic drugs for brand-name products is highly controversial and often is met with suspicion by health care providers and patients. Historically, the debate has focused on the issue of bioequivalence, and clinical practice has identified a number of drug classes for which generic substitution should be approached with caution. Current bioequivalence requirements are based on a measure of average bioequivalence; however, there are fears that use of this measure may be inappropriate in the case of a drug with a narrow or wide therapeutic range or high intrasubject or intersubject variability. Under these circumstances, measures of individual and population bioequivalence are proposed to be more accurate than measures of average bioequivalence. OBJECTIVE: This paper addresses issues of bioequivalence and other concerns with generic drug substitution. METHODS: I conducted a MEDLINE search of the English-language literature containing the key terms generic, multisource, quality, and brand and published between 1973 and 2003. The names of branded pharmaceuticals whose patents had recently expired (eg, Ventolin HFA, Adalat, Capoten, Tagamet HB 200, and Valium) also were used to search for articles on generic substitution. Reference lists of relevant articles also were searched. Bioequivalence issues are presented together with more general concerns over generic drug substitution, such as consumer perception of risk, differences in product and packaging appearance, and differences in excipients. RESULTS: The literature reviewed act to highlight a number of different drug categories and patient subpopulations for which generic substitution can still prove to be problematic. CONCLUSION: I recommend that health care providers continue to exercise caution in the consideration of generic drug substitution under certain circumstances.     

Pharmacokinetic and bioequivalence evaluation of two formulations of 100 mg trimebutine maleate (Recutin and Polybutin) in healthy male volunteers using the LC-MS/MS method

BACKGROUND: Trimebutine maleate is a prokinetic agent that acts directly on the smooth muscle of the GI tract. A bioequivalence (BE) study of 2 oral formulations of 100 mg trimebutine maleate (TMB) was carried out in 24 healthy male Korean volunteers according to a crossover-randomized design. METHODS: Subjects were given a single dose of 2 100 mg tablets of each formulation. The test and reference formulations were Recutin (Hutax Co., South Korea) and Polybutin (Samil Co., South Korea), respectively. Each set of tablets was administered with 240 ml of water to subjects after 10 h overnight fasting on 2 treatment days separated by a 1 week washout period. After dosing, serial blood samples were collected for a period of 36 h. Plasma was analyzed for the main metabolite of TMB, N-monodesmethyl trimebutine (nor-TMB), by a validated LC with MS/MS detection capacity for nor-TMB in the range 5-1500 ng/ml, with a lower limit of quantification (LLOQ) of 5 ng/ml. Several pharmacokinetic (PK) parameters (including AUC(t), AUC(infinity), C(max), T(max), T(1/2), and K(e)) were determined from the plasma concentrations of nor-TMB of both formulations. AUC(t), AUC(infinity), and C(max) were tested for BE after log-transformation of the data. RESULTS: No significant difference was found based on ANOVA; 90% confidence intervals (98.98%112.03% for AUC(t); 98.60%-113.20% for AUC(infinity); 90.85%-107.87% for C(max)) for the test and reference were found within KFDA acceptance range of 80-125%. CONCLUSIONS: Based on these statistical inferences, it was concluded that Recutin is bioequivalent to Polybutin and can be used interchangeably in a clinical setting.     

Bioavailability and pharmacokinetic comparison between generic and branded azithromycin capsule: a randomized, double-blind, 2-way crossover in healthy male Thai volunteers

BACKGROUND: Azithromycin is a semisynthetic azalide antibiotic with extensive tissue penetration and a prolonged t(12). It is used once daily for 3 days in the treatment of a number of bacterial infections. However, based on a literature search, information concerning its pharmacokinetic properties, including the relative bioavailability of a newly developed generic capsule formulation compared with an established branded one in the Thai population, has not been reported. OBJECTIVE: The aim of this study was to compare the relative bioavailability and other pharmacokinetic properties of a newly developed generic capsule formulation of azithromycin with those of an established branded formulation in healthy male volunteers in Thailand. METHODS: A randomized, double-blind, 2-way crossover study was performed in healthy male Thai volunteers under fasting conditions with a washout of 30 days between the study periods. A single dose of 2 x 250-mg azithromycin capsules was orally administered, and blood samples were collected over a period of 120 hours. Plasma azithromycin concentrations were determined using a validated high-performance liquid chromatography method with fluorescence detection after derivatization with 9-fluorenylmethyloxycarbonyl chloride. A plasma concentration-time curve was generated for each volunteer from which the C(max), T(max), AUC(0-Iast), AUC(0-infinity), t(1/2), and kappa(e) were determined using noncompartmental analysis. Bioequivalence was defined using regulatory requirements set forth by Thailand, Association of Southeast Asian Nations, and the US Food and Drug Administration (bioequivalence acceptance range, 0.80-1.25). RESULTS: A total of 14 volunteers completed the study. The mean age of volunteers was 20.8 years (range, 19-23 years), and the mean body weight was 62.8 kg (range, 50.6-70.0 kg). The mean (SD) T(max), C(max), AUC(0-last), and AUC(0-infinity) values after administration of the generic and branded formulations were 1.46 (0.41) versus 1.54 (0.41) hours, 425.23 (208.45) versus 431.75 (198.16) ng/mL, 3919.77 (1549.65) versus 4344.79 (1654.98) ng . h/mL, and 4027.05 (1839.13) versus 4515.53 (2203.87) ng . h/mL, respectively. The relative bioavailability of the generic and branded formulations were 1.00 (0.17). The mean (SD) t1/2 values after administration of the generic and branded formulations were 26.43 (10.92) and 28.10 (13.13) hours, respectively. The analysis of variance results of the natural logarithm (In) -transformed values found no significant effect of formulation, period, or sequence on the studied pharmacokinetic parameters. The 90% CIs of the treatment ratios for the Intransformed values of C(max), AUC(0-last), and AUC(0-infinity) were 0.82 to 1.11, 0.91 to 1.06, and 0.91 to 1.08, respectively. All were within the standard bioequivalence acceptance range of 0.80 to 1.25. No adverse events were reported in this study. CONCLUSIONS: In this small study in a selected population of healthy male Thai volunteers, the C(max) and AUC were not statistically significantly different between generic and branded formulations of a single, 2 x 250-mg dose of azithromycin capsules. The generic and branded formulations were found to be bioequivalent. Both formulations were well tolerated.     

Bioequivalence Comparison of Two Drug-in-Adhesive Transdermal Nitroglycerin Patches

Plasma concentrations of nitroglycerin, 1,2-dinitroglycerin and 1,3-dinitroglycerin in 50 healthy male subjects who received single 24-h applications of two 0.6 mg/h drug-in-adhesive transdermal nitroglycerin patch formulations were compared for the purpose of establishing bioequivalence. The rates of appearance and elimination of nitroglycerin and both dinitro metabolites were the same for both patch treatments. The pharmacokinetic and statistical analyses indicated that the 20-cm(2) test patch met the current two one-sided t-test criteria for bioequivalence with the 30-cm(2) reference patch for nitroglycerin and both dinitro metabolites, even though the reference patch was 50% larger in size and contained 120% more nitroglycerin than the test patch. A likely explanation for the equivalence in drug delivery with a smaller patch is that the test patch maintained more intimate skin contact than did the reference patch. This study shows that strict bioequivalence criteria can be met with a highly variable drug such as nitroglycerin.     

Case reports of the reemergence of psychotic symptoms after conversion from brand-name clozapine to a generic formulation.

BACKGROUND: The use of generic drugs has resulted in considerable cost savings; however, whether all generics are truly bioequivalent to their brand-name counterparts is questionable. Although the efficacy of clozapine in the management of treatment-resistant schizophrenia has been well established, reports of relapse after conversion to a generic formulation are becoming more common. OBJECTIVE: This article presents 7 case studies of patients in a long-term residential care facility who experienced a relapse of psychotic symptoms when the pharmacy inadvertently switched their therapy from brand-name clozapine to a generic formulation. Neither patients, physicians, nor staff of the facility were aware of this switch. Possible reasons for the apparent increased risk of relapse in some patients switched to the generic formulation of clozapine are explored, with reference to US Food and Drug Administration bioequivalence standards and reports. RESULTS: All 7 patients, whose condition had been well stabilized with brand-name clozapine, experienced a rapid and profound deterioration after the switch to the generic formulation. Five patients required hospitalization. All patients responded well when brand-name clozapine was reinstated. CONCLUSION: The findings suggest that brand-name clozapine and the generic formulation may display important clinical differences, and a comparable therapeutic response may not be achievable despite adequate monitoring. Large, controlled, prospective trials are needed to clarify the potential for treatment failure with the use of generic clozapine.     

Benzathine penicillin G: a model for long‐term pharmacokinetic comparison of parenteral long‐acting formulations

What is known and Objective:  Long‐acting intramuscular penicillin G injection is an important product for the management of some severe infections. However, testing the bioequivalence of such long‐acting formulations is difficult. Our aim was to undertake such a test using a generic formulation containing 1 200 000 IU of benzathine penicillin G powder and an innovator’s product (Retarpen^® 1·2 million units; Sandoz, Switzerland). Methods:  In an open, double‐blind, randomized, two‐periods, two‐group crossover study, 12 healthy male volunteers received both formulations of benzathine penicillin G on two different days with a 5‐month washout period between the doses and a sampling period of over 500 h. A simple, sensitive and rapid high‐performance liquid chromatography (HPLC)‐UV method was developed and validated for determination of penicillin G plasma concentrations and other pharmacokinetic (PK) parameters. Results and Discussion:  The analytical method used produced linear responses within a wide analyte concentration range with average within‐run and between‐run variations of below 15% with acceptable recovery, accuracy and sensitivity. The primary PK parameters we used were maximum plasma concentration (C_max), time to reach the maximal concentration (T_max) and the area under the plasma concentration vs. time curve from time zero to the last sampling time (AUC_0→t) using a standard non‐compartmental approach. Based on these parameters, the two formulations were bioequivalent. What is new and Conclusion:  We illustrate the bioequivalence testing of a very long‐acting product. The data indicate that the generic test formulation and the branded reference formulation were bioequivalent in fasting healthy Iranian male volunteers.     

Bioequivalence and pharmacokinetic comparison of a single 200-mg dose of meclofenoxate hydrochloride capsule and tablet formulations in healthy Chinese adult male volunteers: a randomized sequence, open-label, two-period crossover study

BACKGROUND: Meclofenoxate hydrochloride is a psychostimulant in the nootropic agent group available in capsule and tablet formulations approved for traumatic cataphora, alcoholic poisoning, anoxia neonatorum, and children's enuresis in China. Although these 2 generic formulations are marketed in China, information regarding their pharmacokinetics and bioequivalence in humans has not been published. OBJECTIVE: The aim of this study was to compare the pharmacokinetic properties and bioequivalence of the capsule (test) and tablet (reference) formulations of meclofenoxate hydrochloride 200 mg in healthy Chinese volunteers. METHODS: This single-dose, randomized-sequence, open-label, 2-period crossover study was performed at the Nanjing First Hospital of Nanjing Medical University, Nanjing, China. Eligible subjects were healthy male volunteers who were randomly assigned at a 1:1 ratio to receive a single 200-mg dose of the test or reference formulation, followed by a 1-week washout period and administration of the alternate formulation. The study drugs were administered after a 12-hour overnight fast. As a prodrug, meclofenoxate is hydrolyzed into 4-chlorophenoxyacetic acid and is not detected in plasma. The active metabolite of meclofenoxate, chlorophenoxyacetic acid, was assayed using a high-performance liquid chromatography method. For analysis of pharmacokinetic properties, including Cmax, AUC0-24, and AUC0-infinity, blood samples were obtained at 0.33, 0.67, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 10, 14, and 24 hours after administration. The formulations were considered bioequivalent if the log-transformed ratios of Cmax and AUC were within the predetermined equivalence range (80%-125%) as established by the US Food and Drug Administration (FDA). Subjects were interviewed concerning the occurrence of adverse events including excitement, insomnia, lassitude, and headache. Tolerability was assessed at baseline (before administration) and at 1, 2, 6, and 12 hours after administration by monitoring vital signs and laboratory tests (hematology, blood biochemistry, hepatic function, and urinalysis). RESULTS: Twenty-four Chinese male subjects (mean [range]age,23.5[22-30]years;weight,63.3[56-68]kg; height, 171 [165-184] cm) were enrolled; all completed the study. No period or sequence effect was observed. The 90% CIs for the log-transformed ratios of chlorophenoxyacetic acid Cmax, AUC0-24, and AUC0-infinity were 95.7 to 122.9, 97.6 to 111.9, and 97.8 to 111.7, respectively (all, P>0.05). Similar results were found for the data without log-transformation. No adverse events were reported or observed during this single-dose study. CONCLUSIONS: In this small study in healthy Chinese adult male volunteers, a single 200-mg dose of the capsule formulation was found to be bioequivalent to a single 200-mg dose of the tablet formulation based on the US FDA's regulatory definition (rate and extent of absorption). Both formulations were well tolerated.     

A multiple-dose safety and bioequivalence study of a narrow therapeutic index drug: a case for carbamazepine

BACKGROUND AND OBJECTIVES: Carbamazepine is among those drugs that have been considered to have a narrow therapeutic plasma concentration range, that is, a narrow therapeutic index. Although the US Food and Drug Administration has approved new generic products based on standard single-dose bioequivalence studies, several state formularies, including the New Jersey Drug Utilization Review Council, have recently established additional criteria for acceptance of bioequivalence of narrow therapeutic index drugs, limiting the use of some approved generic drugs in specific states. To further validate the adequacy of single-dose studies for the determination of bioequivalence of narrow therapeutic index drugs, a multiple-dose study was conducted that more closely reflected therapeutic use. METHODS: A single-center, multiple-dose, randomized, open-label, 2-way crossover bioequivalence study was conducted in 32 fasting volunteers at steady state. Subjects received the test and reference products as a 200 mg carbamazepine tablet 3 times a day in a crossover fashion. Concentrations of carbamazepine and carbamazepine-10,11-epoxide in plasma were measured by a validated specific HPLC method. RESULTS: A total of 28 subjects completed the study. Pharmacokinetic parameters and measures of fluctuation for both products at steady state were similar, with 90% and 95% confidence intervals falling within 90% and 110%. CONCLUSION: The multiple-dose study provided reliable safety and bioequivalence data under rigorous statistical conditions and confirmed bioequivalence of test and reference products determined by a single-dose study.     

Assessing equivalence of innovator and generic formulations of betamethasone dipropionate cream and ointment.

A series of tests was used to compare two formulations of the topical steroid beta-methasone dipropionate, Diprolene (manufactured by the innovator, Schering Corp.) and Topilene (a generic formulation, manufactured by Technilab). Cream and ointment formulations produced by both manufacturers were compared with respect to physicochemical characteristics, skin sensitivity in rabbits, and a vasconstrictor assay indicative of topical availability in man. The physicochemical tests revealed no differences between innovator and generic ointment formulations, whereas excipients varied widely for the cream products. Similarly, the ointment formulations were comparable on the skin sensitivity tests in rabbits, whereas the generic cream product was much more irritating than the innovator cream in this test. On the vasoconstrictor assay in man the ointments were comparable, while the activity of the generic cream was much lower (approximately 30%) than that of the innovator cream; this difference was highly statistically significant. The difference in vasoconstrictor activity of the two cream products is discussed in relation to the differences in their physicochemical properties. It is concluded that the generic Topilene cream is not interchangeable with the innovator Diprolene cream, and that both pharmacists and physicians should be very careful when substituting one topical steroid formulation for another.     

Comparative Fasting Bioavailability of 2 Bepotastine Formulations in Healthy Male Chinese Volunteers: An Open-Label,Randomized, Single-Dose, 2-Way Crossover Study

Background

Bepotastine is a second-generation histamine₁ receptor antagonist that is used in the treatment of allergic rhinitis, urticaria, and pruritus associated with skin disease. A new generic formulation of bepotastine has been developed in China, and information concerning bioavailability and pharmacokinetic properties in the Chinese population has not been reported.

Objective

The aim of the present study was to compare the bioavailability and pharmacokinetic properties of 2 tablet formulations of bepotastine, the 10-mg generic formulation (test) and a branded formulation (reference), in healthy male Chinese volunteers to obtain registration approval of the test formulation.

Methods

A single-center, open-label, randomized, 2-way crossover study with a 1-week washout period was conducted in 24 healthy male volunteers. Blood samples were collected for 16 hours after a single dose of the 10-mg bepotastine test formulation or the reference formulation. Plasma bepotastine concentrations were determined using a validated LC-MS/MS method. C_max, T_max, AUC_0–t, AUC_0–∞, and t_½ were determined using noncompartmental analysis. The formulations were considered bioequivalent if the 90% CIs for the log-transformed C_max and AUC values were within the predetermined interval of 75% to 133% and 80% to 125%, respectively, according to the guidelines of the China Food and Drug Administration.

Results

No significant differences were found in mean (SD) pharmacokinetic parameters between the test and reference drugs, including C_max (74.81 [9.91] ng/mL vs 78.60 [29.58] ng/mL), AUC_0–t (295.55[115.29] ng·h/mL vs 299.17[109.29] ng·h/mL), and AUC_0-∞ (305.28 [118.50] ng·h/mL vs 310.90 [112.20] ng·h/mL). The mean (SD) t_½ values of the test and reference formulations were 2.53 (0.50) hours and 2.62 (0.41) hours, respectively. The 90% CIs of the treatment ratios for the logarithmic transformed values of C_max, AUC_0–t, and AUC_0–∞ were 86.96% to 101.80%, 93.22% to 104.13%, and 92.66% to 103.30%, respectively. All values were within the predetermined bioequivalence range. Two adverse events were reported as neutropenia (1 volunteer [4.2%]) and neutrophilia (1 volunteer [4.2%]). Both adverse events were transient and considered mild by physicians.

Conclusion

The test and reference tablets met the regulatory criteria for bioequivalence as defined by the China Food and Drug Administration. Both formulations were well tolerated. Chinese Clinical Trials Registry identifier: ChiCTR-TTRCC-13003723.     

Comparison of Scaled-average,Population, and Individual Bioequivalence on 2 Tablets of Pitavastatin Calcium: A 3-Period,Reference-replicated,Crossover Study in Healthy Chinese Volunteers

Background

Pitavastatin, a fully synthetic β-hydroxy-β-methylglutaryl–coenzyme A reductase inhibitor, is potent for the treatment of primary hyperlipidemia and mixed dyslipidemia. Recently, the original product and some generic products of pitavastatin calcium have become available in China. However, the intrasubject variability and interchangeability of this newly developed generic product and the branded innovator product have rarely been investigated in the Chinese population.

Purpose

The aim of this study is to develop and compare the scaled-average, population, and individual bioequivalence (BE) of pitavastatin calcium tablets in healthy Chinese volunteers. This study will be used to allow for the interchangeability (switchability and prescribability) of the 2 products in clinical medication in China.

Methods

A single-dose, reference-replicated, 3-period crossover BE study was conducted in 36 healthy male volunteers. Plasma samples were collected before and after oral administration of 2-mg test or reference tablets. A LC-MS/MS method was used to determine the concentration of pitavastatin calcium. A noncompartmental method was used to investigate the pharmacokinetic parameters. The ANOVA and 90% CIs of ln(AUC_0–t) and ln(C_max) were used for statistical analysis of scaled-average BE. A nonparametric test (Wilcoxon signed rank test) was performed to T_max. The analyses of population BE and individual BE were used to assess the switchability and prescribability of the 2 products.

Findings

Thirty-six volunteers were enrolled in this clinical research; 33 volunteers completed the 3 treatment periods. The mean (SD) relative bioavailability calculated from the ratios (T/R) of AUC_0–t was 101.3% (19.7%). The mean ln(AUC_0–t) and ln(C_max) were 98.64 (90% CI, 93.44–104.13) and 98.68 (90% CI, 91.88–105.99) within previously stipulated ranges recommended by the US Food and Drug Administration and the China Food and Drug Administration (CFDA). The intrasubject %CVs of AUC_0–t and C_max were 12.0% and 18.0% for the reference tablet and 13.0% and 17.0% for the test tablet. No significant differences were found among T_max (0.742 ± 0.276, 0.674 ± 0.202, and 0.689 ± 0.226, respectively) for reference tablet 1, reference Supplemental Table II in the online version at 10.1016/j.clinthera.2014.06.21, and test tablet by a Wilcoxon test (P > 0.05). For ln(AUC_0–t) and ln(C_max), the statistical test-reference ratios were 99.13% and 98.95%, respectively. After inspecting the results for reference and mixed scaling, all the upper confidence limits were <0; therefore, population and individual BE were given.

Implications

In the healthy Chinese males, the generic and branded name tablets of pitavastatin calcium are bioequivalent at the rate and extent of absorption after a comparison of scaled-average, population, and individual BE and thus may be used interchangeably. Both the formulations are generally well tolerated. Chinese Clinical Trial identifier: ChiCTR-TTRCC-13003973.