Alprazolam as a probe for CYP3A using a single blood sample: pharmacokinetics of parent drug, and of α- and 4-hydroxy metabolites in healthy subjects

Objectives (1) To determine the pharmacokinetic parameters of alprazolam and its two metabolites in plasma from healthy volunteers; (2) to identify a suitable single time point to take a plasma sample for CYP3A phenotyping.Methods Twelve healthy Swedish volunteers received a single oral dose of 1 mg alprazolam. Blood samples were collected before drug intake and frequently up to 72 h thereafter. A liquid-chromatography/mass-spectrometry (LC/MS) method was used for the quantification of alprazolam, and 4- and -hydroxyalprazolam.Results The interindividual variation in the area under the concentration–time curve (AUC) was two, three and fourfold for alprazolam, 4-hydroxyalprazolam and -hydroxyalprazolam, respectively. Plasma concentration ratios collected between 1 h and 48 h for both alprazolam/4-hydroxyalprazolam and alprazolam/-hydroxyalprazolam correlated significantly to the corresponding AUC_(0–) ratios.Conclusions The metabolic ratios of alprazolam to respective metabolite in a single plasma sample at 3–24 h are suggested to reflect the alprazolam 4- and -hydroxylation activities. In future, it will be important to study these activities in populations where CYP3A5, in addition to CYP3A4, is expressed at a high frequency and to clarify the relative importance of the two enzymatic pathways for in vivo clearance of alprazolam.     

Influence of dosing regimen on alprazolam and metabolite serum concentrations and tolerance to sedative and psychomotor effects

The relationships between alprazolam and metabolite concentrations and CNS effects were determined in a double-blind placebo controlled four-way crossover trial in 16 normal male volunteers. Active drug treatments consisted of 4-day regimens of 4 mg alprazolam PO daily as 2 mg bid., 1 mg qid, and 0.25 mg each hour. On days 1 and 4, the kinetics, sedative and psychomotor effects were evaluated. Plasma concentrations of the 4- and α-hydroxy metabolites of alprazolam were less than 10% of unchanged alprazolam levels on both days. Accumulation of these metabolites and alprazolam was dependent on alprazolam half-life (11.6 h). Acute and chronic tolerance to the sedative and psychomotor effects was observed with all active drug treatments. All alprazolam treatments resulted in significantly greater sedation than placebo on days 1 and 4. However, on day 4, sedation was 16–36% less than observed on day 1, despite plasma concentrations 1.4–2.76 times the day 1 concentrations. Sedation from alprazolam was reduced in each successive study phase, suggesting a tolerance which was sustained during the 10-day washout between phases. By day 4, psychomotor performance was not different from placebo, indicating more complete development of tolerance than occurred for the sedative effect. Sedation and psychomotor impairment on day 1 were greatest with 2 mg alprazolam bid. During the initiation of therapy, the patient will likely experience less sedation and psychomotor impairment with smaller, more frequent doses. Since tolerance develops to these effects, the advantage of more frequent dosing regimen dissipates by the 4th day.     

Effects of repeated ingestion of grapefruit juice on the single and multiple oral-dose pharmacokinetics and pharmacodynamics of alprazolam

The effects of repeated ingestion of grapefruit juice, an inhibitor of cytochrome P450 3A4 (CYP3A4), on the pharmacokinetics and pharmacodynamics of both single and multiple oral doses of alprazolam, a substrate of CYP3A4, were examined. In study 1, eight healthy volunteers ingesting 600 ml/day water or grapefruit juice for 10 days took a single oral 0.8-mg dose of alprazolam on the eighth day. Plasma drug concentrations were monitored up to 48 h after alprazolam dosing together with evaluation of psychomotor function. Grapefruit juice altered neither the plasma concentrations of alprazolam at any time points, any pharmacokinetic parameters, nor the majority of psychomotor function parameters in subjects. In study 2, 11 patients with anxiety disorders receiving alprazolam (0.8-2.4 mg/day) ingested grapefruit juice (600 ml/day) for 7 days. Blood samples were collected before and during grapefruit juice ingestion and 1 week after its discontinuation together with an assessment of clinical status. Grapefruit juice altered neither the steady-state plasma concentration of alprazolam nor the clinical status in patients. The present study shows that grapefruit juice is unlikely to affect pharmacokinetics or pharmacodynamics of alprazolam due to its high bioavailability.     

Effect of Carbamazepine on the Single Oral Dose Pharmacokinetics of Alprazolam

The effect of carbamazepine, an inducer of cytochrome P450 (CYP) 3A4, on the single oral dose pharmacokinetics of alprazolam was examined in a double-blind, randomized crossover study with two phases. Seven healthy male subjects took carbamazepine 300 mg/day or matched placebo orally for 10 days, and on the 8th day they took a single oral 0.8 mg dose of alprazolam. Blood samples were taken and psychomotor function was assessed by the Digit Symbol Substitution Test, Visual Analog Scale, and UKU Side Effect Rating Scale up to 48 h after alprazolam dosing. Carbamazepine significantly (p < .01 to .001) decreased the plasma alprazolam concentrations during the elimination phase. Carbamazepine significantly (p < .001) increased the apparent oral clearance (0.90 ± 0.21 vs. 2.13 ± 0.54 ml/min/kg) and shortened the elimination half-life (17.1 ± 4.9 vs. 7.7 ± 1.7 h), with no significant effect on the peak plasma concentration (11.7 ± 1.5 vs. 13.0 ± 3.5 ng/ml). The majority of psychomotor function parameters during the carbamazepine treatment were not significantly different from those during the placebo treatment, probably because of the sedative effect of carbamazepine itself. The present study suggests that carbamazepine decreases plasma concentration of alprazolam by inducing its metabolism. It also supports the previous studies, suggesting that alprazolam is metabolized predominantly by CYP3A4.     

Differences in pharmacodynamics but not pharmacokinetics between subjects with panic disorder and healthy subjects after treatment with a single dose of alprazolam

The pharmacokinetics and pharmacodynamics of the benzodiazepine alprazolam (1 mg, administered orally) were compared between eight patients with panic disorder and eight age- and sex-matched healthy volunteers. Subjects received orally administered placebo and alprazolam in a randomized, double-blind, single-dose crossover study. The elimination half-life, time of maximum plasma concentration, maximum concentration, volume of distribution, and clearance of alprazolam were similar for both groups. For each cohort, alprazolam treatment (vs. placebo) produced significant changes in typical benzodiazepine agonist effects, such as increased sedation and impaired cognitive performance on the digit-symbol substitution test. For the panic disorder group only, there was a significant increase in the subjective rating of"contented" and a reduction in the rating of "easily irritated." For the healthy volunteer group, alprazolam produced increases in ratings of "fatigued" and "slowed thinking," but also increases in ratings of "relaxed." In each group, alprazolam significantly increased the electroencephalographic (EEG) measure of relative beta amplitude (range, 13-30 Hz) compared with placebo. Concentration-EEG response curves fit a sigmoid E(max) model, and there was greater sensitivity to EEG effects, as measured by a 28% reduction in the EC50 value, in the panic disorder group compared with healthy control subjects. After alprazolam treatment, there was increased sensitivity to EEG and mood effects and fewer aversive effects in the panic disorder group compared with healthy subjects. There were no differences in the pharmacodynamic measures of sedation and cognition or differences in pharmacokinetics between the two groups.     

Pharmacokinetics and pharmacodynamics of liposomal mifamurtide in adult volunteers with mild or moderate hepatic impairment

Aims

To evaluate the pharmacokinetics and pharmacodynamics after a single dose of liposomal mifamurtide (liposomal muramyl tripeptide phospatidyl ethanolamine; MEPACT®) in adult subjects with mild (Child-Pugh Class A) or moderate (Child-Pugh Class B) hepatic impairment in comparison with age-, weight- and sex-matched healthy subjects with normal hepatic function.

Methods

Subjects received a 4 mg dose of liposomal mifamurtide via 1 h intravenous infusion. Blood samples were collected over 72 h for pharmacokinetic and pharmacodynamic assessments (changes in serum interleukin-6, tumour necrosis factor-α and C-reactive protein).

Results

Thirty-seven subjects were enrolled: nine with mild hepatic impairment, eight with moderate hepatic impairment and 20 matched healthy subjects. Geometric least-square mean ratios of total mifamurtide AUC_inf for the mild hepatic impairment and moderate hepatic impairment groups vs. matched healthy subjects were 105% (90% confidence interval, 83.6–132%) and 119% (90% confidence interval, 94.1–151%), respectively, which are below the protocol-specified threshold (150%) to require development of dose-modification recommendations. Pharmacodynamic parameters for changes in serum interleukin-6 and tumour necrosis factor-α concentrations were generally similar across hepatic function groups. Mifamurtide-induced increases in serum C-reactive protein were attenuated in the moderate hepatic impairment group, consistent with the liver being the major organ of C-reactive protein synthesis. No grade ≥3 adverse events were seen in subjects administered mifamurtide (4 mg).

Conclusions

These results support the conclusion that mild or moderate hepatic impairment does not produce clinically meaningful effects on the clinical pharmacokinetics or pharmacodynamics of mifamurtide; no dose modifications are needed in these special patient populations based on clinical pharmacological considerations.     

The relationship of alprazolam dose to steady-state plasma concentrations

Alprazolam is a widely used antianxiety agent, yet relatively little is known about the relationship between chronic oral doses and steady-state plasma levels. This study examines the relationship over a wide range of therapeutic doses. We conducted a parallel, double-blind, placebo-controlled study in 36 patients with agoraphobia with panic attacks, or panic disorder with limited phobic avoidance based on DSM-III criteria. Patients received alprazolam (N = 25) or placebo (N = 11) beginning at 1 mg/day and increased weekly until either a maximum tolerated dose or 10 mg/day was achieved. Dosages were then gradually tapered according to a predetermined schedule. The entire study period lasted 14 weeks. Laboratory and clinical assessments were conducted weekly. Doses up to 6 mg/day were tolerated by 80% of patients on alprazolam and doses of 10 mg/day were tolerated by 40% of patients. Twenty-seven percent of the placebo patients reached 10 tablets/day. In the alprazolam group, the principal cause of intolerance was sedation. Throughout the study no significant changes in vital signs or laboratory parameters were observed. Steady state alprazolam, 4-hydroxy alprazolam, and alpha-hydroxy alprazolam plasma levels were linearly related to dose. A 1 mg dosage increment produced, on the average, a corresponding 10 ng/ml increase in steady state level of the parent drug. Significant response was observed in subjects who achieved concentrations greater than 20 ng/ml, with a maximum of 81% of the samples classified as responders within the 60 ng/ml and above group.(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of continuous venovenous haemodialysis on the pharmacokinetics of multiple oral moxifloxacin administration to patients with severe renal dysfunction

What is already known about this subject

• Although renal excretion is one important route of excretion of moxifloxacin and its metabolites, moxifloxacin pharmacokinetics are similar in patients with varying degrees of renal impairment (but not on dialysis) and in healthy subjects.

What this study adds

• This study showed that moxifloxacin pharmacokinetics are comparable in patients with severe renal failure requiring haemodialysis and in healthy subjects and patients with impaired renal function not on dialysis.
• No dose adjustments are required for haemodialysis patients on oral moxifloxacin therapy.

Aim

We investigated single dose and steady-state pharmacokinetics of moxifloxacin in eight venovenous haemodialysis patients.

Methods

Plasma, dialysate and urine pharmacokinetic parameters for moxifloxacin and its main metabolites were calculated after single and multiple (7 days) dosing with 400 mg day⁻¹.

Results

Moxifloxacin pharmacokinetics after a single dose and at steady state (multidose day 7) were comparable in patients with impaired renal function and healthy subjects (geometric mean/%CV AUC mg l⁻¹ h single dose 37.0/24.3 in haemodialysis patients vs. 29.8/22.6 in healthy subjects, 95% CI for ratio of haemodialysis patients to healthy subjects 99.34%, 154.60%; steady state 40.4/29.1 haemodialysis patients vs. 33.9/20.1 in healthy subjects, 95% CI for ratio of haemodialysis patients to healthy subjects 90/39%, 156.93%). In haemodialysis patients plasma concentrations of moxifloxacin at steady-state were elevated compared with those after a single 400 mg dose (AUC mg l⁻¹ h, geometric mean/%CV, 40.4/29.1) compared with 37.0/24.3; 95% CI for ratio of steady-state to single dose 87.29%, 136.52%, as were concentrations of metabolite M1 3.21/34.6 compared with 2.02/45.3, 95% CI for ratio of steady state to single dose 14.21%, 175.07%. Haemodialysis cleared about 9% of the dose as unchanged moxifloxacin.

Conclusions

No dose adjustments are required for venovenous haemodialysis patients on oral moxifloxacin therapy.     

Dose-response evaluation of the interaction between sertraline and alprazolam in vivo

In vitro data show the inhibition of alprazolam metabolism by sertraline via CYP3A4; therefore, using a randomized, double-blind, placebo-controlled design, the authors conducted this study to assess the potential for similar in vivo inhibition in humans. Ten healthy volunteers participated in two test sessions (placebo/alprazolam 1 mg orally) before the initiation of sertraline treatment. Blood samples were obtained over a 32-hour period and pharmacodynamic measures (sedation, psychomotor performance, memory function) were obtained over an 8-hour period. After a minimum of 2 weeks of daily sertraline self-administration (50, 100, or 150 mg/day), test sessions were repeated. Alprazolam concentrations (N = 6, 4, and 6 at sertraline doses of 50, 100, and 150 mg/day, respectively) showed no significant changes based on peak concentration (Cmax), time to maximum concentration (Tmax), elimination half-life (t1/2[beta]), and area under the concentration-time curve (AUC(0-8)), with the exception of a reduced Cmax in the 50 mg/day group. Similarly, dynamic data showed no significant variations based on peak effect, Tmax, and AUC(0-infinity), with the exception of increased peak impairment in one measure of psychomotor performance. No differences were detected between placebo alone and placebo plus sertraline. These findings suggest that sertraline (50-150 mg/day) does not alter the single-dose kinetics or dynamics of alprazolam; therefore, the combination may be prescribed without an increased risk of alprazolam toxicity.     

Steady-state pharmacokinetics of nefazodone in subjects with normal and impaired renal function

The steady-state pharmacokinetics of nefazodone (NEF) and its metabolites hydroxynefazodone (HO-NEF) and m-chlorophenylpiperazine (mCPP) were compared in subjects with normal and impaired renal function. Patients: The Study was of parallel group design which included 7 subjects with normal (NOR) renal function, CL_CR72 ml·min^–1·1.73 m^–2, 6 with moderate (MOD) renal impairment, CL_CR 31–60 ml·min^–1·1.73 m^–2 and 9 with severe (SEV) renal impairment, CL_CR30 ml·min^–1·1.73 m^–2. Subjects in each renal function group received a 100-mg oral dose of nefazodone hydrochloride BID for 7 days and a single morning dose on day 8. Starting 48 h after the last 100-mg dose, 200-mg doses were administered on a similar schedule to 3, 4 and 3 subjects from each renal function group (NOR, MOD and SEV, respectively). Single trough blood samples just prior to each morning dose (C_min) and serial samples after the dose on day 8 were obtained at each dose level for pharmacokinetic analysis. Plasma samples were assayed by a specific HPLC method for NEF, HO-NEF and mCPP.The CMIN data indicated that steady state was attained by the third day of BID administration of both the 100- and 200-mg doses of nefazodone, regardless of degree of renal function. Both NEF and HO-NEF attained steady-state C_max within 2 h after administration of nefazodone; t_max for mCPP was less defined and more delayed. HO-NEF and mCPP plasma levels were about 1/3 and <1/10 those of NEF, respectively, regardless of the status of renal function. Steady-state systemic exposure of NEF and HO-NEF, as reflected by AUC and C_max, and elimination t_1/2 values did not differ significantly among renal function groups. Conclusion: The study results suggest that dose adjustments may not be necessary, but nefazodone should be used with caution in the presence of severe renal impairment.     

An overdose death involving the insufflation of extended-release oxymorphone tablets

Two cases are reported involving the abuse of extended-release oxymorphone hydrochloride tablets (Opana? ER) in combination with alprazolam (Xanax?). Two juvenile females were discovered unresponsive and hypoxic by a male acquaintance. The trio had reportedly crushed and snorted Opana ER tablets and consumed Xanax for recreational purposes. Emergency personnel were able to stabilize one female. The second female was pronounced dead at the scene. Blood and urine samples from the surviving female were collected at the trauma center between 48 and 96 h post incident. Toxicology results showed the presence of oxymorphone, doxylamine, dextromethorphan, alprazolam, α-hydroxyalprazolam, oxazepam, and temazepam in her urine. No drugs were detected in her blood. Toxicology on the deceased female revealed the presence of 0.13 mg/L oxymorphone and 0.04 mg/L alprazolam in her blood. Gastric contents contained 0.25 and 0.93 mg/L of oxymorphone and alprazolam, respectively. Oxymorphone, alprazolam, and α-hydroxyalprazolam were present in her urine. Quantitative results were achieved by gas chromatography-mass spectrometry monitoring selected ions for the oxime-oxymorphone-trimethylsilyl derivative, alprazolam, and the α-hydroxyalprazolam tert-butyldimethylsilyl derivative. The established linearity ranges for the opiate and benzodiazepine methods were 0.050-3.000 and 0.025-1.000 mg/L, respectively. The cause of death was reported as multiple drug toxicity, and the manner of death was accidental.     

Effect of itraconazole on the single oral dose pharmacokinetics and pharmacodynamics of alprazolam

To assess the effect of itraconazole, a potent inhibitor of cytochrome P450 (CYP) 3A4, on the single oral dose pharmacokinetics and pharmacodynamics of alprazolam, the study was conducted in a double-blind randomized crossover manner with two phases of treatment with itraconazole-placebo or placebo-itraconazole. Ten healthy male subjects receiving itraconazole 200?mg/day or matched placebo orally for 6 days took an oral 0.8?mg dose of alprazolam on day 4 of each treatment phase. Plasma concentration of alprazolam was measured up to 48?h after alprazolam dosing, together with the assessment of psychomotor function by the Digit Symbol Substitution Test, Visual Analog Scale and Udvalg for kliniske undersøgelser side effect rating scale. Itraconazole significantly (P?相似文献   

Influence of CYP2C19 polymorphism on the pharmacokinetics of nelfinavir and its active metabolite

AIMS

This study reports the pharmacokinetics of nelfinavir, its active metabolite, M8, and active moiety (nelfinavir + M8) in volunteers genotyped for CYP2C19 as extensive metabolizer (*1*1; n = 38), heterozygous poor metabolizer (PM) (*1*2; n = 22) and homozygous PM (*2*2; n = 6).

METHODS

Subjects received nelfinavir at normal dose (3.5 days of 1250 mg q12h) or high dose (1250 mg q12h for 3 days and single dose of 3125 mg on day 4). Steady-state plasma samples were analysed by high-performance liquid chromatography/ultraviolet assay to determine pharmacokinetics.

RESULTS

At steady state, the mean C_max was 42% [95% confidence interval (CI) 19, 69] and 63% (95% CI 20, 122) higher, and mean AUC was 51% (95% CI 24, 83) and 85% (95% CI 32, 159) higher for *1*2 and *2*2 compared with *1*1 subjects, respectively. For M8, the mean C_max and AUC were 35% (95% CI 6, 55) and 33% (95% CI −3, 56), respectively, lower for *1*2 compared with *1*1 subjects. M8 was not detectable in *2*2 subjects. The mean C_max and AUC values for the active moiety were higher by 30–35% for the *1*2 and *2*2 compared with *1*1 subjects.

CONCLUSIONS

Mutation in CYP2C19 increased the systemic exposure of nelfinavir and reduced the exposure of M8. No significant differences were noted among the heterozygous (*1*2) and homozygous (*2*2) PMs. These changes are not considered to be clinically relevant and hence the use of nelfinavir does not require prior assessment of CYP2C19 genotype.     

Single-dose pharmacokinetics of nefazodone in healthy young and elderly subjects and in subjects with renal or hepatic impairment

The single-dose pharmacokinetics of nefazodone (NEF) and its metabolites hydroxynefazodone (HO-NEF) and m-chlorophenylpiperazine (mCPP) were examined in 12 healthy younger subjects 55 years of age (YNG), 12 elderly subjects 65 years of age (ELD), 12 patients with biopsy proven hepatic cirrhosis (HEP) and 12 patients with moderate renal impairment (REN), Cl_CR 20–60 ml·min^–1. The study was of parallel group design, with each of the four subject groups receiving escalating single oral doses of 50, 100 and 200 mg of nefazodone at 1 week intervals. Serial blood samples for pharmacokinetic analysis were collected for 48 h following each dose and plasma samples were assayed for NEF, HO-NEF and mCPP by a validated HPLC method.Single oral doses up to 200 mg of nefazodone were well tolerated by all subjects. Maximum plasma levels of NEF and HO-NEF were generally attained within 1 h after administration of nefazodone. HO-NEF and mCPP plasma levels were about 1/3 and <1/10 those of NEF, respectively. There were no apparent gender-related pharmacokinetic differences in any group of subjects. NEF and HO-NEF pharmacokinetics were dose dependent in all four subject groups; a superproportional increase in AUC and an increase in t_1/2 with increasing dose was obtained, indicative of nonlinear pharmacokinetics. Relative to normal subjects, elderly and cirrhotic subjects exhibited increased systemic exposure to NEF and HO-NEF, as reflected by AUC, at all doses of nefazodone; subjects with moderate renal impairment did not.Elderly and cirrhotic patients may require lower doses of NEF to achieve and maintain therapeutic effectiveness.     

Differential effects of misoprostol and ranitidine on the pharmacokinetics of diclofenac and gastrointestinal symptoms

1. The effects of oral misoprostol (800 microg day(-1)) and ranitidine (300 mg day(-1)) on the pharmacokinetics of diclofenac (100 mg) were assessed in a three-way randomized crossover study in 18 healthy male subjects. 2. Subjects were studied over three 8 day periods, during which they received twice-daily placebo, misoprostol, or ranitidine. A single dose of diclofenac was given orally on days 1 and 8, and plasma diclofenac concentrations were measured by h.p.l.c. over 24 h. 3. Misoprostol caused a non-significant 19% increase in the mean Cmax value of diclofenac on both days 1 and 8. After 8 days of dosing with misoprostol there was a significant (P = 0.04) 20% decrease in the AUC of diclofenac. 4. Ranitidine had no statistically significant effects on the pharmacokinetics of diclofenac. 5. Co-administration of misoprostol and diclofenac was associated with a higher frequency and severity of gastrointestinal symptoms and frequency of bowel opening, and a decrease in faecal consistency when compared with either placebo or ranitidine plus diclofenac (P < 0.01).     

Pharmacokinetic pharmacodynamic evaluation of the combined administration of alprazolam and fluoxetine

The pharmacokinetic and pharmacodynamic effects of concomitant administration of alprazolam and fluoxetine were studied in this double-blind parallel study in 80 healthy, male volunteers. Subjects were randomly assigned to one of four treatment groups. Drug treatments consisted of 4-day regimens of 1 mg alprazolam four times daily, 60 mg fluoxetine every morning, 1 mg alprazolam four times daily and 60 mg fluoxetine every morning, and placebo four times daily. Psychomotor performance, mood status, and degree of sedation were evaluated at designated times. Combined administration of alprazolam and fluoxetine resulted in an approximate 30% increase in plasma alprazolam concentrations relative to plasma concentrations following the administration of alprazolam alone. There were no significant differences in fluoxetine or norfluoxetine plasma concentrations between the alprazolam/fluoxetine and fluoxetine treatments. Psychomotor decrements increased when fluoxetine was administered with alprazolam relative to alprazolam administration alone. Psychomotor performance of the fluoxetine treatment group was not significantly different from that of the placebo group. No significant changes were observed in mood status, and sedation was minimal in all treatment groups. As when any two psychoactive drugs are administered together, increased patient monitoring and patient education is recommended when alprazolam and fluoxetine are prescribed concurrently.     

Multiple-dose, linear, dose-proportional pharmacokinetics of retigabine in healthy volunteers

Retigabine, a first-in-class selective M-current potassium channel opener, is a novel antiepileptic compound currently in clinical development. The purpose of this randomized placebo-controlled study was to assess retigabine oral safety and pharmacokinetics in healthy male volunteers (N = 45). Subjects received one dose on day 1 and doses every 12 hours for the next 14 days. Fixed doses were given to the first four groups (200, 400, 500, and 600 mg per day). Titrated doses were given to group 5 in 100 mg increases every 4 days, achieving 700 mg per day on day 15. Serial blood samples were collected on days 1 and 15. Pharmacokinetic parameters were compared between days and among dose groups. After administration of a single dose, retigabine was rapidly absorbed, with maximum concentrations of 387 ng/ml (normalized to a 100 mg dose) occurring within 1.5 hours. Retigabine was eliminated with a mean terminal half-life of 8.0 hours and an apparent oral clearance of 0.70 L/h/kg in white subjects. In black subjects, retigabine clearance and volume of distribution were 25% and 30% lower, respectively, after normalizing by body weight, leading to higher exposure in this population. Retigabine's pharmocokinetics was linearly dose proportional. Steady-state pharmacokinetics was in agreement with single-dose pharmacokinetics, and the accumulation ratio was about 1.5. Retigabine and AWD21-360 trough evening concentrations were significantly lower (about 30% to 35%) than morning values. The titration regimen allowed for higher doses to be tolerated compared to the fixed-dose regimen. In conclusion, the pharmacokinetics of retigabine is linearly dose proportional for daily doses of 100 to 700 mg and is not modified on multiple administrations.     

The pharmacokinetics and pharmacodynamics of sublingual and oral alprazolam in the post-prandial state

Summary We gave 12 healthy male volunteers 1 mg of alprazolam or placebo on three occasions after a standard breakfast in a double-blind, randomized, single-dose, three-way crossover study.The three trials were: (a) oral alprazolam and sublingual placebo; (b) oral placebo and sublingual alprazolam; (c) placebo by both routes.Plasma alprazolam concentrations during 24 h after each dose were measured by electron-capture gas-liquid chromatography.Peak plasma concentrations were reached later after sublingual than oral dosage (2.8 vs 1.8 h, P<0.01). Other kinetic variables were not significantly different: peak plasma concentration, 11.3 vs 12.0 ng·ml^–1; elimination half-life, 12.5 vs 11.7 h; and total area under the plasma concentration versus time curve, 197 vs 186 h·ng·ml^–1.Pharmacodynamic measures showed that sublingual and oral alprazolam both produced sedation, fatigue, impaired digit symbol substitution, slowing of reaction time, and impairment of the acquisition and recall of information. These changes were initially observed at 0.5 h after dosage and lasted up to 8 h.In general the two routes were significantly different from placebo but not from each other.     

The effect of mild and moderate hepatic impairment on the pharmacokinetics of valdecoxib, a selective COX-2 inhibitor

Purpose This study evaluated the effects of varying degrees of hepatic impairment on the pharmacokinetics and safety of valdecoxib following single and multiple dosing.Methods This was an open-label, randomised, parallel group study in 12 subjects with mild hepatic impairment (Child-Pugh Class A) and in 13 with moderate hepatic impairment (Child-Pugh Class B) matched for age, weight, sex, and smoking status; there were two control groups of 12 healthy volunteers, one for each study group. All subjects received a single dose of valdecoxib 20 mg on day 1 and valdecoxib 20 mg twice daily on days 4–7, followed by a single morning dose on day 8. Plasma concentrations of free (unbound) and total valdecoxib and its active hydroxylated metabolite (SC-66905) were measured following single and multiple dosing (day 1 and day 8). Additionally, all subjects received a single intravenous dose of lidocaine 60 mg during the pretreatment period to determine plasma concentrations of monoethylglycinexylidide (MEGX) as a marker of hepatic CYP3A4 activity.Results The mean apparent oral clearance of free valdecoxib in plasma at steady state decreased by 22–25% in those with mild to moderate impairment (corresponding to a 28–33% increase in the AUC of free valdecoxib and a 19–23% decrease in the AUC of total SC-66905). The mean free fraction of valdecoxib in plasma increased by 9–38%, resulting in a mean decrease in apparent oral clearance of total valdecoxib in plasma of 0–15% (corresponding to a 0–17% increase in the AUC of total valdecoxib). Individual AUCs for free valdecoxib and total SC-66905 did not correlate well with AUCs for MEGX, indicating that decreases in intrinsic clearance of valdecoxib in those with hepatic impairment could not solely be explained by decreased CYP3A4 expression in hepatic impairment.Conclusions In our small study sample, mild and moderate hepatic impairment appeared to have only a modest effect on valdecoxib and SC-66905 pharmacokinetics. The adjustment of valdecoxib dose or dosing regimen does not appear mandatory in subjects with mild or moderate hepatic impairment, although caution is necessary during treatment of these patients with valdecoxib.     

Pharmacokinetics and safety of ebastine in patients with impaired hepatic function compared with healthy volunteers: a phase I open-label study

OBJECTIVE: To assess the differences between patients with hepatic insufficiency and healthy subjects with regard to the pharmacokinetics, cardiac safety and overall safety of ebastine and its active metabolite carebastine. DESIGN: Open-label parallel-group study. PARTICIPANTS: 24 patients with varying degrees of hepatic insufficiency, as categorised by the Child-Pugh classification, and 12 healthy volunteers. METHODS: Healthy subjects and patients with Child-Pugh class A (n = 8) or B (n = 8) received ebastine 20 mg once daily for 7 days. Patients with Child-Pugh class C (n = 8) [single or repeated dose] received ebastine 10 mg. Plasma concentrations of ebastine and carebastine were determined for 23.5 hours following the initial dose on day 1 and for 96 hours following the dose on day 7 by using a sensitive liquid chromatography-tandem mass spectrometry assay with a minimum quantifiable limit of 0.05 microg/L for ebastine and 1.00 microg/L for carebastine. Hepatic function was assessed by blood clearance of indocyanine green 0.5 mg/kg administered intravenously on day 2. Cardiac and overall safety parameters were monitored. RESULTS: Overall, the pharmacokinetics of ebastine were not modified by hepatic impairment. No correlation between ebastine pharmacokinetics and hepatic function, as expressed by indocyanine green clearance, was observed. Comparison of the effective half-life of ebastine and carebastine between groups did not show relevant differences. Therefore, no apparent accumulation of ebastine occurred, and steady-state concentrations of ebastine and carebastine were predictable from single-dose pharmacokinetics both in healthy subjects and in hepatically impaired patients. Finally, no apparent difference was noted in the safety of ebastine between patients with hepatic insufficiency and healthy subjects as assessed by evaluation of adverse events, vital signs and laboratory parameters. CONCLUSION: Ebastine can be safely administered to patients with impaired hepatic function, as no clinically important differences can be anticipated from the pharmacokinetics and safety profile of ebastine/carebastine as compared with healthy subjects. Nevertheless, the dosage used in severely impaired patients (10mg daily) was half that used in patients with mild to moderate impairment, and any comedication did not include drugs affecting liver function; in clinical practice, both these factors should be taken into account.