Comparison of fluorescence polarization immunoassay and high performance liquid chromatography for the quantitative determination of phenytoin, phenobarbitone and carbamazepine in serum

The Abbott TDx fluorescence polarization immunoassay (FPIA) system has been evaluated and compared with well-established high performance liquid chromatography (HPLC) for the determination of three anticonvulsant drugs: phenytoin, phenobarbitone and carbamazepine. These assays were evaluated for precision, calibration curve stability, specificity and accuracy. Within-run precision studies using control samples (n = 15) in the subtherapeutic, therapeutic, and toxic concentrations, resulted in coefficients of variation in the range of 1.79-3.99% (FPIA) and 1.16-2.52% (HPLC), respectively. Between-run precision ranged from 2.32-6.34% for FPIA and from 2.04-3.38% for HPLC. Comparison of 122 patient samples assayed with both methods indicated an extremely good analytical correlation (r = 0.96) for all three comparisons. The FPIA method offers significant advantages in calibration curve stability while maintaining accuracy and precision comparable with those of established HPLC procedures.     

Measurement of cyclosporine in plasma of cardiac allograft recipients by fluorescence polarization immunoassay

The Abbott TDx fluorescence polarization immunoassay (FPIA) procedure for measuring cyclosporine A (CsA) was evaluated and compared with the Sandoz polyclonal radioimmunoassay (CsA RIA kit) method. This drug assay was evaluated for precision, calibration, stability, and accuracy. Within-run precision studies utilizing 25 replicate analyses of the three control preparations (containing CsA in the 60-800 ng/ml range) resulted in coefficients of variation (CV) ranging from 1.0 to 9.1%. The CVs of between-run precision determined by assaying the same control drug levels for five consecutive working days ranged from 3.9 to 4.6%. Calibration curve stability was assessed by examining the drift in control values over a 2-week period. Maximum plasma ranged from 82.6 to 108.2%. Four hundred plasma samples were obtained from 30 heart-transplant patients during the first 6 months of CsA therapy and each sample was analyzed simultaneously by TDx and RIA. Linear regression analysis of the results obtained for each patient (x = RIA, y = FPIA) revealed the following mean values: r = 0.87, (CV = 13.7%), slope = 1.47 (CV = 39.2%). Moreover, the concentration of CsA was determined in 35 patient samples both by TDx and high-performance liquid chromatography (HPLC). FPIA results up to 12 times higher than HPLC results have been noted.     

Evaluation of fluorescence polarization immunoassay for determination of cyclosporin in plasma

The fluorescence polarization immunoassay (FPIA) method for determination of cyclosporin in plasma was evaluated and compared with the high-performance liquid chromatography (HPLC) and the radioimmunoassay (RIA) methods. The coefficients of variation for the within-run and between-run precision were less than 5 and less than 8%, respectively, for samples ranging in concentration from 50 to 600 ng/ml. Recoveries were determined by adding cyclosporin at concentrations from 25 to 1,000 ng/ml to patient plasma; they were, on average, 98.5%. The calibration curve was stable throughout a 10-week study period. There was no clinically significant interference due to hemolysis, icterus, lipemia, or other commonly used drugs. There was considerable variation of the ratio of the FPIA result to the HPLC result, whereas there was a good correlation between the FPIA and the RIA results (r = 0.975, n = 25, y = 1.2x - 36.4), when evaluated using specimens from renal transplant patients receiving cyclosporin orally. It was concluded that the FPIA is an appropriate, rapid method for patient cyclosporin analysis in plasma and serves as a practical alternative to the RIA.     

Pharmacokinetics of canrenone after oral administration of spironolactone and intravenous injection of canrenoate-K in healthy man

Five healthy male volunteers received canrenoate-K 200 mg (Sincomen pro injectione) by intravenous injection and one week later spironolactone 200 mg (Sincomen-100) orally. Plasma levels and urinary excretion of unchanged canrenone were determined up to 24 h by a specific HPLC method. Following intravenous administration, the maximum plasma level of 2066 +/- 876 ng/ml was found after 29 +/- 15 min and thereafter the concentration declined with a half-life of 3.7 +/- 1.2 h. Total clearance was 4.2 +/- 1.7 ml/min . kg. After oral ingestion, the maximum concentration of 177 +/- 33 ng/ml was observed at 4.4 +/- 0.9 h. The absolute bioavailability of canrenone was 25 +/- 9%. Within 24 h, respectively 0.4 and 0.6 mg, canrenone were excreted by the kidney after intravenous and oral administration. The half-life of elimination was 4.9 +/- 1.8 h (i.v.) and 3.9 +/- 1.2 h (p.o.).     

The effect of quinidine, used as a probe for the involvement of P-glycoprotein, on the intestinal absorption and pharmacodynamics of methadone

AIMS: There is considerable unexplained interindividual variability in the methadone dose-effect relationship. The efflux pump P-glycoprotein (P-gp) regulates brain access and intestinal absorption of many drugs. Evidence suggests that methadone is a P-gp substrate in vitro, and P-gp affects methadone analgesia in animals. However the role of P-gp in human methadone disposition and pharmacodynamics is unknown. This investigation tested the hypothesis that the intestinal absorption and pharmacodynamics of oral and intravenous methadone are greater after inhibition of intestinal and brain P-gp, using the P-gp inhibitor quinidine as an in vivo probe. METHODS: Two randomized, double-blind, placebo-controlled, balanced crossover studies were conducted in healthy subjects. Pupil diameters and/or plasma concentrations of methadone and the primary metabolite EDDP were measured after 10 mg intravenous or oral methadone HCl, dosed 1 h after oral quinidine (600 mg) or placebo. RESULTS: Quinidine did not alter the effects of intravenous methadone. Miosis t(max) (0.3 +/- 0.3 vs 0.3 +/- 0.2 h (-0.17, 0.22)), peak (5.3 +/- 0.8 vs 5.1 +/- 1.0 mm (0.39, 0.84)) and AUC vs time (25.0 +/- 5.7 vs 26.8 +/- 7.1 mm h (-6.1, 2.5)) were unchanged (placebo vs quinidine (95% confidence interval on the difference)). Quinidine increased (P < 0.05) plasma methadone concentrations during the absorptive phase, decreased t(max) (2.4 +/- 0.7 vs 1.6 +/- 0.9 h (0.33, 1.2)), and increased peak miosis (3.2 +/- 1.5 vs 4.3 +/- 1.6 mm (-1.96, -0.19)) after oral methadone. The C(max) (55.6 +/- 10.3 vs 59.4 +/- 14.1 ng ml(-1) (-8.5, 0.65)) and AUC of methadone (298 +/- 46 vs 316 +/- 74 ng ml(-1) h (-54, 18)) were unchanged, as were the EDDP : methadone AUC ratios. Quinidine had no effect on the rate constant for transfer of methadone between plasma and effect compartment (k(e0)) (2.6 +/- 2.6 vs 2.5 +/- 1.4 h(-1) (-3.5, 4.2)). CONCLUSIONS: Quinidine increased the plasma concentrations of oral methadone in the absorptive phase and the miosis caused by methadone, suggesting that intestinal P-gp affects oral methadone absorption and hence its clinical effects. Quinidine had no effect on methadone pharmacodynamics after intravenous administration, suggesting that if quinidine is an effective inhibitor of brain P-gp, then P-gp does not appear to be a determinant of the access of methadone to the brain.     

Pharmacokinetics of D(+)-usnic acid in rabbits after intravenous and oral administration.

The pharmacokinetics of D(+)-usnic acid--a lichen antitubercular, antitumor, and enzyme-inhibiting agent--was studied in rabbits following intravenous or oral administration of 5 and 20 mg/kg body weight doses, respectively. Plasma samples were collected at different time intervals, and usnic acid was determined by HPLC. Plasma usnic acid levels following intravenous administration showed a triexponential elimination with a mean +/- SD terminal half-life of 10.7 +/- 4.6 hr. The volume of distribution of the central compartment and systemic clearance were 43.9 +/- 21.3 ml/kg and 12.2 +/- 3.0 ml/hr/kg, respectively. Pharmacokinetic parameters obtained, based on compartmental and noncompartmental approaches, were comparable. Plasma concentration data obtained after oral administration were analyzed using a noncompartmental method. Peak plasma level (Cmax) of 32.5 +/- 6.8 micrograms/ml was achieved in 12.2 +/- 3.8 hr (tmax). Mean absolute bioavailability of usnic acid following oral administration was 77.8%.     

Monitoring of plasma methadone: intercorrelation between immunoassay and gas chromatography-mass spectrometry

Determination of plasma methadone is essential in connection with dose adjustments for patients participating in methadone maintenance programs. We successfully adapted the existing fluorescence polarization immunoassay (FPIA) kit intended for urinary methadone to plasma assays. A concentration interval of 50-900 ng/ml could be covered. The coefficient of variation was less than 7%, and the limit of detection below 50 ng/ml. The intercorrelation between the immunoassay and a specific gas chromatographic-mass spectrometric (GC-MS) method was studied in samples from 19 heroin addicts in methadone maintenance treatment. A total number of 97 plasma samples with a concentration range of 31-842 ng/ml were used. The slope and intercept of the regression line (CFPIA = 0.93 X CGC-MS + 15) was in good agreement with the theoretical relation (CFPIA = CGC-MS), with a coefficient of correlation of 0.978. The mean ratio, in quantitative result, between the techniques (CFPIA/CGC-MS) was 1.03 +/- 0.01 (SEM). We conclude that the immunoassay proposed in this study can be safely used in patients participating in methadone maintenance programs.     

Clinical estimation of vancomycin measurement method on hemodialysis patient

The fluorescence polarization immunoassay (FPIA) method is used to perform measurement of vancomycin hydrochloride (VCM) at many institutions. However, the values measured by the FPIA method are more vulnerable to overestimation than the high performance liquid chromatography (HPLC) method. In particular, it was not reported to perform exact therapeutic drug monitoring (TDM) measurement. Since overestimation is likely in patients with renal dysfunction, the HPLC method is preferable for TDM measurement. This study investigates the clinical conditions that lead to overestimation in the FPIA method, paying attention to the relation of clinical laboratory data inspection values and the existence of hemodialysis (HD). Overestimation in the evaluation of TDM using the FPIA method was clinically examined with 116 serum samples obtained from 18 cases medicated with VCM. The relevance between overestimation of patients who had not had HD performed was 72.7 +/- 61.7% (means +/- SD). In short, the overestimation was greatest in HD patients. Since overestimation did not affect the evaluation of clinical TDM, such as an effect and a side-effect, the TDM of VCM was shown to be satisfactorily evaluated by the simple FPIA method.     

A sensitive HPLC-MS-MS assay for quantitative determination of midazolam in dog plasma

The clinical pharmacokinetics of midazolam have been extensively studied, due to its high clearance by CYP3A4 and sensitivity to drug-drug interactions. In order to investigate the potential to model drug-drug interactions with midazolam in the dog, a selective and sensitive high performance liquid chromatography-tandem mass spectroscopy (HPLC-MS-MS) method has been developed, with sufficient sensitivity to allow analysis of dog plasma samples generated following administration of a clinically relevant dose. The method involves extraction of midazolam and internal standard (flunitrazepam) from dog plasma, using 96-well Oasis MCX solid phase extraction plates. The assay has been validated over a concentration range of 0.1-10 ng/ml and its specificity, accuracy and precision demonstrated. The relative bias of the assay was within +/-15% for all standards with intra- and inter-assay precision (coefficient of variation-%CV) of less than 15%. The assay was applied to the analysis of plasma samples (0.2 ml), generated following intravenous or oral administration of midazolam to male beagle dogs, at a dose level of 0.05 mg/kg, and pharmacokinetic parameters were derived from the resulting data.     

Evaluation of fluorescence polarization immunoassay for quantitation of serum salicylates

A fluorescence polarization immunoassay (FPIA) for serum salicylates that has been developed for use with the Abbott TDx analyzer is evaluated with regard to precision, accuracy, and stability of the standard curve. The FPIA method is also compared with a well-established high performance liquid chromatography (HPLC) technique in a clinical laboratory environment. The FPIA demonstrates excellent precision, and the standard curve is sufficiently stable to perform reproducible measurements over a 29-day period without recalibration. Superior accuracy of the FPIA method is indicated for salicylate concentrations between 50 and 800 micrograms/ml by recovery studies and by favorable comparison with the reference method. The performance of the FPIA for salicylate concentrations between 0 and 50 micrograms/ml is somewhat less favorable and should be used with caution in this range. The present method is more appropriate than HPLC for the management of patients receiving chronic high doses of salicylates or in cases of acute salicylate overdose and is also more rapid.     

Determination of N-desmethylmethsuximide serum concentrations using enzyme-multiplied and fluorescence polarization immunoassays

N-Desmethylmethsuximide (NDM), the active metabolite of the antiepileptic agent methsuximide, has been analyzed by gas-liquid chromatography and high-performance liquid chromatography (HPLC) in the past. This study compares methods using two commercially available immunoassays for ethosuximide, the enzyme multiplied immunoassay technique (EMIT) and fluorescence polarization immunoassay (FPIA), with an HPLC method for the measurement of NDM concentrations in serum. Within-day precision studies, utilizing low therapeutic (15.0 mg/L) and toxic (45.0 mg/L) NDM concentrations (n = 20), resulted in coefficients of variation (CVs) of 4.6 and 4.2%, respectively, for EMIT and 5.4 and 3.2%, respectively, for FPIA. Day-to-day precision studies (n = 10) resulted in CVs of 7.6 and 5.5%, respectively, for EMIT and 3.5 and 2.4%, respectively, for FPIA. No interference was observed from toxic concentrations of acetaminophen, caffeine, carbamazepine, methsuximide, phenobarbital, phensuximide, phenytoin, primidone, salicylate, and valproic acid in the EMIT and FPIA procedures. There was good linear correlation between EMIT and HPLC NDM determinations of 50 patient samples (r = 0.970; y = 0.96 x + 0.03), and a similar correlation between FPIA and HPLC NDM determinations in 48 patient samples (r = 0.975; y = 0.91 x + 1.24). Using ethosuximide reagents, both EMIT and FPIA systems can be adapted to reliably measure NDM serum concentrations.     

Evaluation of a fluorescence polarization immunoassay procedure for quantitation of isepamicin, a new aminoglycoside antibiotic

A fluorescence polarization immunoassay (FPIA) procedure for measuring isepamicin, a new aminoglycoside antibiotic, was evaluated. The range of the assay studied was from 0.3-50 micrograms/ml and the calibration curve can be stored for at least 32 days. There was no interference from hemoglobin (up to 400 mg/dl) and bilirubin (up to 20 mg/dl). Within-run precision on each 20 replicates at 5, 15, and 25 micrograms/ml yielded a coefficient of variation (CV) of 1.44-2.52%; between-run precision on analyses at 5, 15, and 25 micrograms/ml over five periods yielded a CV of 1.26-1.59%. Cross-reactivities of the assay system with tobramycin and amikacin were null, but that with gentamicin, of which isepamicin is a derivative, was approximately 14-29%. Data obtained by microbiological assay and FPIA and by high-performance liquid chromatography and FPIA correlated significantly, with coefficients of correlation being 0.980 (n = 70) and 0.965 (n = 39), respectively. The FPIA offers a rapid, efficient, and accurate system for therapeutic monitoring of isepamicin plasma levels.     

沙丁胺醇气雾剂在健康受试者体内的药物动力学和相对生物利用度

目的:研究沙丁胺醇气雾剂在健康受试者的药物动力学和生物利用度.方法:十名健康男性志愿者单剂量吸入1.2 mg沙丁胺醇气雾剂或口服沙丁胺醇水溶液.用HPLC法测定人血浆中沙丁胺醇浓度.以非房室模型计算药物动力学参数,计算气雾剂相对水溶液的生物利用度.结果:气雾剂和口服溶液的药物动力学参数如下:T_(max)(0.22±0.07)和(1.8±0.6)h,C_(max)(3.4±1.1)和(3.9±1.4)μg·L~(-1),T_(1/2)(4.5±1.5)和(4.6±1.1)h,AUC_(0-20min)(0.9±0.3)和(0.16±0.10)μg·h·L~(-1).两种给药途径的T_(max)和AUC_(0-20 min)之间差异显著(P<0.01).AUC_(0-20min)(nihal)为 AUC_(0-20 min)(po)的 8倍.沙丁胺醇气雾剂相对口服溶液的生物利用度为 57％±24％.结论:沙丁胺醇气雾剂在人体的吸收过程与口服溶液差异有显著性.     

Evaluation of a mouse monoclonal antibody for the determination of serum theophylline by fluorescence polarization immunoassay

Theophylline concentrations in spiked human serum and serum specimens obtained from patients with normal and impaired renal function were measured by fluorescence polarization immunoassay (FPIA) using a mouse monoclonal antitheophylline antibody. The interday coefficients of variation of the assay after 14 days were 4.2, 3.3, and 2.4% at serum theophylline concentrations in pooled human serum of 7.1, 12.2 and 26.9 mg/L. Theophylline concentrations determined by FPIA and high performance liquid chromatography (HPLC) were used to generate the following linear regression equations relating the corresponding theophylline concentrations measured by each method in serum specimens from 50 patients with normal renal function (FPIA = 1.00 HPLC + 1.01, r = 0.98) and 50 patients with end-stage renal disease (FPIA = 1.04 HPLC + 0.08, r = 0.99). In contrast to previous studies performed with a polyclonal antitheophylline antibody, the precision, accuracy, and specificity of the FPIA were adequate for analysis of theophylline in serum specimens obtained from patients with end-stage renal disease.     

Pharmacokinetics of morphine and its surrogates. VII: High-performance liquid chromatographic analyses and pharmacokinetics of methadone and its derived metabolites in dogs

Reversed-phase HPLC assays with on-column UV detection and post-column fluorescent detection of ion pair-extracted material were developed and used for the quantitative assay of methadone, its presumed metabolites, and acid- and alkali-hydrolyzable conjugates of these metabolites in biological fluids with assay sensitivities of 10-20 ng/mL. Plasma, urine, and bile were monitored in dogs after intravenous bolus administration of 0.8, 1.0, 2.0, and 2.2 mg/kg methadone hydrochloride. Plasma-time data showed two sequential half-lives of 8.3 +/- 3.4 (SEM) and 128 +/- 37 min, with apparent dose-independent pharmacokinetics in the studied dose range. Total body clearances were 899 +/- 103 (SEM) mL/min. Renal clearances (6-82 mL/min) of methadone were highly variable within and among studies but showed no significant variation with urinary pH or flow rate. The percentages of the dose excreted in the urine as methadone and (+)-2-ethyl-1,5-dimethyl-3,3-diphenylpyrroline (2) were 3.6 +/- 0.5% (SEM) and 4.1 +/- 0.4% (SEM), respectively, but there were no significant concentrations of 2 in plasma. The presumed metabolites 2-ethyl-5-methyl-3,3-diphenyl-1-pyrroline (3), 1,5-dimethyl-3,3-diphenyl-2-pyrrolidone (4), (-)-alpha-N-normethadol (7), 4-dimethylamino-2,2-diphenylvaleric acid (8), p-hydroxymethadone (9), and (-)-alpha-methadol (10) were not observed in the plasma of dogs given methadone. Quantities of presumed metabolites 3, 4, 7, 8, 9, and 10 were negligible in urine (less than 0.03% of dose). No acid-hydrolyzable conjugates, or generators on acidification, of 3, 4, 7, 8, or 10 were detectable in urine. No alkali-hydrolyzable conjugates, or generators on alkalinization, of 3, 4, 8, or 10 were detectable in urine. There was no significant biliary secretion of unchanged methadone; 2 in bile amounted to only 2% of the dose. In bile and urine, 50% and 17-27%, respectively, of the radiolabeled dose was not extractable into hexane. In a non-bile-cannulated dog, 35% of the total radiolabeled intravenous dose was present in the feces. As much as 88% of an intravenous radiolabeled dose could be accounted for, even though only small amount of methadone was disposed through the metabolic routes claimed in the literature. The intravenous administration of 2 resulted in two sequential half-lives of 3 and 270 min and no apparent pharmacokinetic dose dependency. Amounts of 2 excreted unchanged in urine and bile were 23% and 5-16% of the dose, respectively. Renal and total body clearances were 170 and 1150 mL/min.(ABSTRACT TRUNCATED AT 400 WORDS)     

Sex differences in the pharmacokinetics, oxidative metabolism and oral bioavailability of oxycodone in the Sprague-Dawley rat

1. The pharmacokinetics and oxidative metabolism of oxycodone were investigated following intravenous and oral administration in male and female Sprague-Dawley (SD) rats. 2. High-performance liquid chromatography (HPLC)-electrospray ionization (ESI)-tandem mass spectrometry (MS-MS) was used to quantify plasma concentrations of oxycodone and its oxidative metabolites noroxycodone and oxymorphone following administration of single bolus intravenous (5 mg/kg) and oral (10 mg/kg) doses of oxycodone. 3. The mean (+/-SEM) clearance of intravenous oxycodone was significantly higher in male than female SD rats (4.9 +/- 0.3 vs 3.1 +/- 0.3 L/h per kg, respectively; P < 0.01). Mean areas under the plasma concentration versus time curves (AUC) for oxycodone were significantly higher in female than male SD rats following intravenous (approximately 1.6-fold; P < 0.01) and oral (approximately sevenfold; P < 0.005) administration. 4. The oral bioavailability of oxycodone was low (at 1.2 and 5.0%, respectively) in male and female SD rats, a finding consistent with high first-pass metabolism. Noroxycodone : oxycodone AUC ratios were significantly higher in male than female SD rats after intravenous (approximately 2.4-fold; P < 0.005) and oral (approximately 12-fold; P < 0.005) administration. 5. Circulating oxymorphone concentrations remained very low following both routes of administration. Noroxycodone : oxymorphone AUC ratios were greater in male than female SD rats after intravenous (approximately 13- and fivefold, respectively) and oral (approximately 90- and sixfold, respectively) administration. 6. Sex differences were apparent in the pharmacokinetics, oxidative metabolism and oral bioavailability of oxycodone. Systemic exposure to oxycodone was greater in female compared with male SD rats, whereas systemic exposure to metabolically derived noroxycodone was higher in male than female SD rats. 7. Oral administration of oxycodone to the SD rat is a poor model of the human for the study of the pharmacodynamic effects of oxycodone.     

Bioavailability and pharmacokinetic studies of eurycomanone from Eurycoma longifolia

A validated HPLC analysis of eurycomanone (1), a bioactive quassinoid, in rat plasma following oral and intravenous administration of Eurycoma longifolia Jack extract was developed for pharmacokinetic and bioavailability studies. Relatively high plasma eurycomanone concentrations were detected after an intravenous injection of 10 mg/kg extract F2 containing 1.96 mg/kg of the quassinoid. However, it declined rapidly to zero after 8 h. Its mean elimination rate constant (k(e)), biological half-life (t(1/2)), volume of distribution (V(d)) and clearance (CL) were 0.88 +/- 0.19 h (-1), 1.00 +/- 0.26 h, 0.68 +/- 0.30 L/kg and 0.39 +/- 0.08 L/h/kg, respectively. Following oral administration of eurycomanone, its Cmax and Tmax values were detected as 0.33 +/- 0.03 microg/mL and 4.40 +/- 0.98 h, respectively. The plasma concentration of the quassinoid after oral administration was much lower than after intravenous application in spite of the oral dose being 5 times higher. The results indicate that eurycomanone is poorly bioavailable when given orally. A comparison of the AUC (0-->infinity) obtained orally to that obtained after an intravenous administration (normalized for dose differences) revealed that the absolute bioavailability of the compound was low with 10.5 %. Furthermore, the compound appeared to be well distributed in the extravascular fluids because of its relatively high V(d) value. The poor oral bioavailability was not attributed to instability problems because eurycomanone has been shown to be stable under different pH conditions. Thus, its poor oral bioavailability may be due to poor membrane permeability in view of its low P value and/or high first-pass metabolism.     

Absolute bioavailability and absorption profile of cyanamide in man

A pharmacokinetic study of cyanamide, an inhibitor of aldehyde dehydrogenase (EC1.2.1.3) used as an adjuvant in the aversive therapy of chronic alcoholism, has been carried out in healthy male volunteers following intravenous and oral administration. Cyanamide plasma levels were determined by a sensitive HPLC assay, specific for cyanamide. After intravenous administration cyanamide displayed a disposition profile according to a two-compartmental open model. Elimination half-life and total plasma clearance values ranged from 42.2 to 61.3 min and from 0.0123 to 0.0190 L.kg-1.min-1, respectively. After oral administration of 0.3, 1.0, and 1.5 mg/kg x +/- SEM values of Cmax, tmax (median) and AUC were 0.18 +/- 0.03, 0.91 +/- 0.11, and 1.65 +/- 0.27 micrograms.ml-1; 13.5, 13.5, and 12 min; and 8.59 +/- 1.32, 45.39 +/- 1.62, and 77.86 +/- 17.49 micrograms.ml-1.min, respectively. Absorption was not complete and the oral bioavailability, 45.55 +/- 9.22, 70.12 +/- 4.73, and 80.78 +/- 8.19% for the 0.3, 1.0, and 1.5 mg/kg doses, respectively, increased with the dose administered. The models that consider a first-order absorption process alone (whether with a fixed or variable bioavailability value as a function of dose) or with loss of drug due to presystemic metabolism (with zero-order or Michaelis-Menten kinetics) were simultaneously fitted to plasma level data obtained following 1 mg/kg i.v. and 0.3, 1.0, and 1.5 mg/kg oral administrations. The model that best fit the data was that with a first-order absorption process plus a loss by presystemic metabolism with Michaelis-Menten kinetics, suggesting the presence of a saturable first-pass effect.     

Intravenous pharmacokinetics, oral bioavailability and dose proportionality of ragaglitazar, a novel PPAR-dual activator in rats

Pharmacokinetics of ragaglitazar (a novel phenoxazine derivative of aryl propanoic acid), a potent insulin sensitizing and lipid-lowering compound was studied in Wistar rats. A single dose of 1, 3 or 10 mg/kg of ragaglitazar was given orally to male rats (n=4 per dose level) to evaluate dose proportionality. In another study, a single intravenous bolus dose of ragaglitazar was given to rats (n=4) at 3 mg/kg dose following administration through the lateral tail vein in order to obtain the absolute oral bioavailability and clearance parameters. Blood samples were drawn at predetermined intervals and the concentration of ragaglitazar in plasma was determined by a validated HPLC method. Plasma concentration versus time data were generated following oral and intravenous dosing and pharmacokinetic analysis was performed using non-compartmental analysis. The results revealed that Cmax and AUC(0-infinity) increased more than proportionally to the administered oral doses. As dose increased in the ratio of 1:3:10, the mean Cmax and AUC(0-infinity) increased in the ratio of 1:3.2:13 and 1:3.2:16, respectively. After intravenous administration the systemic clearance and volume of distribution of ragaglitazar in rats were 139+/-30 ml/h/kg and 463+/-51 ml/kg, respectively (mean+/-SD). Plasma concentrations declined mono-exponentially following intravenous administration and elimination half-life (t1/2) was about 2.6 h and not significantly different (p > 0.05) from the value from oral administration. Mean residence time (MRT) values for ragaglitazar were found to be 4.15+/-0.52 h (3.5 to 4.6 h). Absolute oral bioavailability of ragaglitazar across the doses tested was in the range of 68%-93%. In conclusion, ragaglitazar exhibits promising pharmacokinetic properties in rats.     

The use of polymeric solid phase extraction and HPLC analysis for the determination of ranitidine in routine plasma samples obtained from paediatric patients

A sensitive HPLC method for the determination of ranitidine in small-volume (0.5 mL) paediatric plasma samples is described. Plasma samples were extracted using a simple, rapid solid phase extraction (SPE) technique developed using disposable copolymer packed SPE cartridges. Chromatographic separation was achieved by reverse-phase HPLC with isocratic elution using a microBondapak C18 column and a phosphate buffer (10 mM, pH 3.75)-acetonitrile (87:13 v/v) mobile phase with UV detection at 313 nm. The HPLC system exhibited linearity in the range 8-800 ng mL(-1). Intraday % CV and % bias values were in the range 1.28-8.09% (% bias -4.33 to -0.87) and interday % CV and % bias values were in the range 0.73-15.28% (% bias -1.80 to + 1.65). The limits of detection and quantitation obtained were 2 ng mL(-1) and 8 ng mL(-1), respectively, and ranitidine extraction recoveries from plasma ranged from 92.30 to 103.88%. In this study, the developed HPLC and SPE methodologies have been successfully applied to the determination of ranitidine concentrations in 68 paediatric plasma samples. The sampled population was drawn from patients already receiving the study drug therapeutically. Patients recruited had received ranitidine by two main routes - oral and intravenous. The plasma concentrations of ranitidine encountered in paediatric samples following oral or intravenous administration of a range of prescribed doses are presented graphically. These profiles are based on analysis of the first 68 plasma samples obtained from the first 35 patients recruited to the study receiving ranitidine by the oral or intravenous route.