A Novel Method for Studying the Pharmacokinetics of [(14) C]Umeclidinium After Application to the Axilla or Palm of Healthy Male Subjects

Umeclidinium (UMEC), a long-acting muscarinic antagonist approved for chronic obstructive pulmonary disease (COPD), was investigated for primary hyperhidrosis as topical therapy. This study evaluated the pharmacokinetics, safety, and tolerability of a single dose of [(14) C]UMEC applied to either unoccluded axilla (UA), occluded axilla (OA), or occluded palm (OP) of healthy males. After 8 h the formulation was removed. [(14) C]UMEC plasma concentrations (Cp) were quantified by accelerator mass spectrometry. Occlusion increased systemic exposure by 3.8-fold. Due to UMEC absorption-limited pharmacokinetics, Cp data from the OA were combined with intravenous data from a phase I study. The data were described by a two-compartment population model with sequential zero and first-order absorption and linear elimination. Simulated systemic exposure following q.d. doses to axilla was similar to the exposure from the inhaled therapy, suggesting that systemic safety following dermal administration can be bridged to the inhaled program, and offering the potential for a reduced number of studies and/or subjects.

Pharmacometrics: Focus on the Patient

Pharmacometrics, whether using simple or complex models, has contributed to rational and efficient drug development,(1-3) with the main focus on early drug development.(4) This article describes why opportunities more directly focused on the patient abound in late stage development, illustrating the concept with three innovative examples which focus on benefits to patients, enabling drugs that are truly efficacious to reach the market faster in diseases with high unmet medical needs, while maintaining adequate safety.

Population pharmacokinetics of azithromycin in whole blood, peripheral blood mononuclear cells, and polymorphonuclear cells in healthy adults

Azithromycin's extensive distribution to proinflammatory cells, including peripheral blood mononuclear cells (PBMCs) and polymorphonuclear cells (PMNs), may be important to its antimicrobial and anti-inflammatory properties. The need to simultaneously predict azithromycin concentrations in whole blood ("blood"), PBMCs, and PMNs motivated this investigation. A single-dose study in 20 healthy adults was conducted, and nonlinear mixed effects modeling was used to simultaneously describe azithromycin concentrations in blood, PBMCs, and PMNs (simultaneous PK model). Data were well described by a four-compartment mamillary model. Apparent central clearance and volume of distribution estimates were 67.3 l/hour and 336 l (interindividual variability of 114 and 122%, respectively). Bootstrapping and visual predictive checks showed adequate model performance. Azithromycin concentrations in blood, PBMCs, and PMNs from external studies of healthy adults and cystic fibrosis patients were within the 5th and 95th percentiles of model simulations. This novel empirical model can be used to predict azithromycin concentrations in blood, PBMCs, and PMNs with different dosing regimens.

Pharmacokinetics of Alvimopan and Its Metabolite in Healthy Volunteers and Patients in Postoperative Ileus Trials

Alvimopan, a mu-opioid antagonist without anti-analgesic effects, is being developed to manage postoperative ileus. We characterized the population pharmacokinetics of orally administered alvimopan and its primary metabolite in healthy subjects/special populations, and surgical patients at risk for ileus. Models were consistent with known physiology/pharmacology. Alvimopan's model had two compartments with first-order elimination. Metabolite was modeled with a catenary chain and lag for alvimopan's metabolism within the gut followed by absorption, one systemic compartment with first-order elimination. Weight, gender, and renal function did not affect alvimopan or metabolite. Steady-state alvimopan and metabolite concentrations were 87 and 40% higher, respectively, in patients. Alvimopan concentrations were 35% higher in the elderly, but were not affected by race, acid blockers, or antibiotics. Metabolite concentrations were 43 and 82% lower in African Americans and Hispanics, respectively, compared to Caucasians, 49% lower with acid blockers and 81% lower with preoperative antibiotics. Although alvimopan's pharmacokinetics was described with a traditional model, its metabolite required a novel model accommodating gut metabolism.

Pharmacogenetics and disease genetics of complex diseases

Advances in technologies and the availability of a single nucleotide polymorphism (SNP) map are beginning to show the true potential for the human genome project to affect patient healthcare. A whole genome scan, the use of 100000-300000 SNPs across the genome, is now possible. Use of traditional approaches and the whole genome scan will result in identification of disease susceptibility genes and development of many new treatments in the longer term. In the shorter term, the goal will be to predict those patients at risk to experience an adverse reaction or those with a high probability for improved efficacy (i.e. pharmacogenetics). As progress is made in the area of disease genetics and pharmacogenetics, our understanding of disease susceptibility and its interrelationship with drug response will improve, making targeted therapy (i.e. the right drug to the right patient) a reality.

The pharmacokinetics and pharmacodynamics of GW395058, a peptide agonist of the thrombopoietin receptor, in the dog, a large-animal model of chemotherapy-induced thrombocytopenia

GW395058, a PEGylated peptide agonist of the thrombopoietin receptor, stimulates megakaryocytopoiesis and has previously been shown to increase platelet counts in vivo. The pharmacokinetics and pharmacodynamics of GW395058 were characterized using a randomized, crossover study in a large-animal model (dog) of chemotherapy-induced thrombocytopenia. Nine beagle dogs received i.v. carboplatin (350 mg/m(2)) on day 0 and day 28. GW395058 (1.31 mg/kg) (n = 6) or vehicle control (n = 3) was administered on day 1 and day 29 either as an i.v. bolus or s.c. injection. After i.v. administration, peak concentrations of GW395058 occurred rapidly, while the half-life averaged approximately 56 h. Bioavailability (+/- standard deviation) of GW395058 given s.c. was 78.2% (20.9%). GW395058 (i.v. and s.c.) ameliorated the platelet nadir (p = 0.0086) and resulted in a shorter time to recovery compared to the control group. The mean nadir platelet counts following carboplatin administration were 197,000 cells/microl (80,000) for the i.v. GW395058-dose group, 183,000 cells/microl (72,000) for the s.c.-dose group and 71,000 cells/microl (38,000) for the vehicle-alone group. GW395058 reduced the thrombocytopenic effects of carboplatin in dogs. No GW395058-related adverse side effects were observed.

The influence of renal function on the pharmacokinetics and pharmacodynamics and simulated time course of doxacurium

Doxacurium's clearance (C1) is markedly decreased in patients with renal failure undergoing kidney transplantation. However, no studies have determined the influence of renal function (as assessed by creatinine clearance [CrCl]) on its pharmacokinetics in patients without renal failure. We studied 53 patients aged 19-59 yr. During N2O/isoflurane anesthesia, doxacurium was infused over 10 min, plasma was sampled for up to 6 h, and twitch tension was measured. A three-compartment model was fit to plasma concentration data and an effect compartment model to twitch data. Mixed-effects modeling was used to determine the influence of covariates, including CrC1, on doxacurium's pharmacokinetic/pharmacodynamic parameters. Obesity decreased both doxacurium's Cl (1.1% per percent above ideal body weight [IBW]) and its neuromuscular junction sensitivity (0.4% per percent above IBW). Cl increased 0.6% per mL/min increase in CrCl. In addition, the rate constant for equilibration between plasma concentration and effect decreased 46% per 1% increase in isoflurane, central compartment volume decreased 86% per 1% increase in isoflurane concentration, and slow distributional Cl decreased 69% per mg/ 100 mL increase in serum albumin. Simulations showed that the latter two covariates influence the time course of bolus doxacurium administration minimally. Both obesity and renal dysfunction prolong doxacurium's recovery markedly. When dosing is based on IBW, effects of CrCl on neuromuscular recovery are smaller compared with dosing based on actual weight. Therefore, obese patients should be dosed based on IBW. No further dosage adjustment is necessary for patients with renal dysfunction; however, recovery will take longer in patients with moderate-to-severe renal dysfunction.

IMPLICATIONS

We examined the factors influencing doxacurium's pharmacokinetic and pharmacodynamic characteristics. Both creatinine clearance and obesity significantly influence its time course. The effect of obesity is minimized if patients are dosed based on ideal body weight.

Clinical pharmacokinetics of cisatracurium besilate

Cisatracurium besilate, one of the 10 stereoisomers that comprise atracurium besilate, is a nondepolarising neuromuscular blocking agent with an intermediate duration of action. Following a 5- to 10-sec intravenous bolus dose of cisatracurium besilate to healthy young adult surgical patients, elderly patients and patients with renal or hepatic failure, the concentration versus time profile of cisatracurium besilate is best characterised by a 2-compartment model. The volume of distribution (Vd) of cisatracurium besilate is small because of its relatively large molecular weight and high polarity. Cisatracurium besilate undergoes Hofmann elimination, a process dependent on pH and temperature. Unlike atracurium besilate, cisatracurium besilate does not appear to be degraded directly by ester hydrolysis. Hofmann elimination, an organ independent elimination pathway, occurs in plasma and tissue, and is responsible for approximately 77% of the overall elimination of cisatracurium besilate. The total body clearance (CL), steady-state Vd and elimination half-life of cisatracurium besilate in patients with normal organ function are approximately 0.28 L/h/kg (4.7 ml/min/kg), 0.145 L/kg and 25 minutes, respectively. The magnitude of interpatient variability in the CL of cisatracurium besilate is low (16%), a finding consistent with the strict physiological control of the factors that effect the Hofmann elimination of cisatracurium besilate (i.e. temperature and pH). There is a unique relationship between plasma clearance and Vd because the primary elimination pathway for cisatracurium besilate is not dependent on organ function. There are minor differences in the pharmacokinetics of cisatracurium besilate in various patient populations. These differences are not associated with clinically significant differences in the recovery profile of cisatracurium besilate, but may be associated with differences in the time to onset of neuromuscular block.

Dose proportionality of cisatracurium

The dose proportionality of cisatracurium pharmacokinetics was assessed using a population approach by incorporating the collection of sparse blood samples from patients in clinical trials. Plasma concentration-time data from 131 patients with limited concentration-time data and 38 patients with full sampling were pooled and analyzed using nonlinear mixed-effects modeling (NONMEM). Dose proportionality was assessed using dichotomous parameterization and a linear model. The population pharmacokinetic approach revealed that the pharmacokinetics of cisatracurium are independent of dose between 0.1 mg/kg and 0.4 mg/kg, as was expected based on the importance of Hofmann elimination, a chemical process dependent on pH and temperature.

Prospective use of population pharmacokinetics/pharmacodynamics in the development of cisatracurium

PURPOSE

The population PK/PD approach was prospectively used to determine the PK/PD of cisatracurium in various subgroups of healthy surgical patients.

METHODS

Plasma concentration (Cp) and neuromuscular block data from 241 patients in 8 prospectively-designed Phase I-III trials were pooled and analyzed using NONMEM. The analyses included limited Cp-time data randomly collected from 186 patients in efficacy/safety studies and full Cp-time data from 55 patients in pharmacokinetic studies. The effects of covariates on the PK/PD parameters of cisatracurium were evaluated. The time course of neuromuscular block was predicted for various patient subgroups.

RESULTS

The population PK/PD model for cisatracurium revealed that anesthesia type, gender, age, creatinine clearance, and presence of obesity were associated with statistically significant (p < 0.01) effects on the PK/PD parameters of cisatracurium. These covariates were not associated with any clinically significant changes in the predicted recovery profile of cisatracurium. Slight differences in onset were predicted in patients with renal impairment and patients receiving inhalation anesthesia. Based on the validation procedure, the model appears to be accurate and precise.

CONCLUSIONS

The prospective incorporation of a population PK/PD strategy into the clinical development of cisatracurium generated information which influenced product labeling and reduced the number of studies needed during development.

Importance of the organ-independent elimination of cisatracurium

Cisatracurium, one of 10 isomers of atracurium, undergoes pH and temperature-dependent Hofmann elimination in plasma and tissues. The clearance of cisatracurium due to Hofmann elimination and organ elimination was estimated by applying a nontraditional two-compartment pharmacokinetic model with elimination occurring from both compartments to plasma cisatracurium concentration-time data from 31 healthy adult surgical patients with normal renal and hepatic function. The elimination rate constant from the central compartment, intercompartmental rate constants, and the volume of the central compartment were obtained from the model fit. The elimination rate constant from the peripheral compartment could not be independently estimated in vivo and was therefore fixed to the rate of degradation of cisatracurium in human plasma (pH 7.4 and 37 degrees C) and held constant in the model. Total body clearance, Hofmann clearance, organ clearance, and the volume of distribution at steady-state were derived from the model parameter estimates. Renal clearance was calculated from cisatracurium urinary excretion data from 12 of the 31 patients. Clearance values (mean +/- SD) were 5.20 +/- 0.86, 4.00 +/- 1.04, 1.20 +/- 0.71, and 0.85 +/- 0.32 mL.min-1.kg-1 for total body clearance, Hofmann clearance, organ clearance, and renal clearance, respectively. Hofmann clearance accounted for 77% of total body clearance. Organ clearance was 23% of total body clearance. Renal clearance, a component of organ clearance, was 16% of total body clearance. The organ-independent nature of the elimination of cisatracurium was characterized by a relationship between steady-state volume of distribution and total body clearance. The half-life is an independent variable and is not dependent on the total body clearance nor the steady-state volume of distribution. Hofmann elimination is the predominant pathway for cisatracurium elimination in humans.

The effects of epoprostenol on drug disposition. I: A pilot study of the pharmacokinetics of digoxin with and without epoprostenol in patients with congestive heart failure

The influence of epoprostenol on the pharmacokinetics of drugs administered concurrently to patients with congestive heart failure (CHF) receiving epoprostenol was evaluated as a secondary objective of a Phase II pilot study. A total of 278 blood samples were collected from 30 patients with end-stage CHF receiving conventional therapy alone or conventional therapy plus epoprostenol. Estimates of oral clearance (Cl), volume of distribution, and absorption rate constant of digoxin were generated from plasma digoxin concentrations using nonlinear mixed effects modeling, and the effect of epoprostenol on Cl of digoxin was evaluated by univariate analysis. Additional factors that were evaluated by univariate analysis included age, obesity, time since study entry, cardiac output, concomitant use of angiotensin-converting enzyme (ACE) inhibitor, concomitant dobutamine, and estimated creatinine clearance. Backward elimination was used to arrive at a final model that included concomitant epoprostenol as a covariate. The final model revealed an approximate 15% decrease in Cl of digoxin in response to short-term administration of epoprostenol that was no longer apparent by the end of the 12-week treatment phase. Simulations revealed that this effect, although statistically significant, would not be clinically significant in most patients; however, the potential exists for short-term elevation of digoxin concentrations in response to concurrent administration of epoprostenol.

The effects of epoprostenol on drug disposition. II: A pilot study of the pharmacokinetics of furosemide with and without epoprostenol in patients with congestive heart failure

The effect of epoprostenol on the pharmacokinetics of furosemide was investigated in 23 patients with end-stage congestive heart failure (CHF) receiving conventional therapy alone or conventional therapy plus epoprostenol. Estimates of the apparent oral clearance, volume of distribution, and absorption rate constant for furosemide were generated from 198 serum furosemide concentrations using nonlinear mixed effects modeling (NONMEM). Univariate analyses were performed to assess the effects of patient factors on the apparent oral clearance of furosemide. The final multivariate model determined by backwards elimination included concomitant digoxin therapy. When concomitant epoprostenol therapy was included in the final model, there was a 13% decrease in the apparent oral clearance of furosemide in response to short-term administration of epoprostenol. However, the effect of concomitant epoprostenol therapy was not statistically significant and was no longer apparent by the end of the 12-week study. These data suggest that epoprostenol may have a slight short-term effect on the pharmacokinetics of furosemide; the interaction between epoprostenol and furosemide is not clinically significant, however.

Pharmacokinetics of cisatracurium in patients receiving nitrous oxide/opioid/barbiturate anesthesia

BACKGROUND

Cisatracurium, one of the ten isomers in atracurium, is a nondepolarizing muscle relaxant with an intermediate duration of action. It is more potent and less likely to release histamine than atracurium. As one of the isomers composing atracurium, it presumably undergoes Hofmann elimination. This study was conducted to describe the pharmacokinetics of cisatracurium and its metabolites and to determine the dose proportionality of cisatracurium after administration of 2 or 4 times the ED(95).

METHODS

Twenty ASA physical status 1 or 2 patients undergoing elective surgery under nitrous oxide/opioid/barbiturate anesthesia were studied. Patients received a single rapid intravenous bolus does of 0.1 or 0.2 mg x kg-1 (2 or 4 times the ED(95), respectively) cisatracurium. All patients were allowed to recover spontaneously to a train-of-four ratio > or = 0.70 after cisatracurium-induced neuromuscular block. Plasma was extracted, acidified, and stored frozen before analysis for cisatracurium, laudanosine, the monoquaternary acid, and the monoquaternary alcohol metabolite.

RESULTS

The clearances (5.28 +/- 1.23 vs. 4.66 +/- 0.67 ml x min(-1) x kg(-1) and terminal elimination half-lives (22.4 +/- 2.7 vs. 25.5 +/- 4.1 min) were not statistically different between patients receiving 0.1 mg x kg(-1) and 0.2 mg x kg(-1), respectively. Maximum concentration values for laudanosine averaged 38 +/- 21 and 103 +/- 34 ng x ml(-1) for patients receiving the 0.1 and 0.2 mg x kg(-1) doses, respectively. Maximum concentration values for monoquaternary alcohol averaged 101 +/- 27 and 253 +/- 51 ng x ml(-1), respectively. Monoquaternary acid was not quantified in any plasma sample.

CONCLUSIONS

Cisatracurium undergoes Hofmann elimination to form laudanosine. The pharmacokinetics of cisatracurium are independent of dose after single intravenous doses of 0.1 and 0.2 mg x kg(-1).

Intravenous epoprostenol sodium does not increase hepatic microsomal enzyme activity in rats

Previous studies have indicated that epoprostenol may increase hepatic microsomal enzyme activity both in animals and humans. However, interpretation of the results of these studies may be confounded by the route of epoprostenol administration or small sample sizes. The primary objective of the present investigation was to evaluate the effects of epoprostenol (given as a continuous intravenous infusion) on hepatic microsomal enzyme activity in rats. Male Sprague Dawley rats (220-290 g) received infusions of either vehicle (glycine buffer, 1 mL/hr) or 0.2 microgram/kg/min epoprostenol through a jugular vein cannula for 24 hr or 7 days. At the end of the infusion, a 25 mg/kg i.v. bolus of antipyrine was administered and blood samples were collected over 6 hr. Serum antipyrine concentrations were determined by HPLC. Twenty-four hr post-infusion, hepatic microsomes were prepared, and cytochrome P-450 content was determined by difference spectroscopy. Cytochrome P-450 content and antipyrine clearance values determined from serum antipyrine concentration-time profiles were not significantly different between treatment groups. Antipyrine clearance [mean (SD)] in the 24-hr vehicle-treated group was 3.68 (0.49) mL/min/kg versus 4.35 (1.1)mL/min/kg in the epoprostenol-treated group. In the 7-day vehicle-treated rats, antipyrine clearance was 5.43 (1.0) mL/min/kg compared to 4.68 (0.61) mL/min/kg in epoprostenol-treated rats. A statistically significant effect of infusion duration was observed in the control group, i.e., antipyrine clearance in rats treated with vehicle for 7 days was significantly greater than that observed in rats treated with vehicle for 24 hr. However, the increase was less than 50%. These data suggest that when epoprostenol is administered as an intravenous infusion to rats, no significant alterations in hepatic microsomal enzyme activity occur. Based on these data, long term changes in hepatic metabolism in response to chronic epoprostenol administration are not expected.

The pharmacokinetics and pharmacodynamics of the stereoisomers of mivacurium in patients receiving nitrous oxide/opioid/barbiturate anesthesia

BACKGROUND

Mivacurium consists of a mixture of three stereoisomers: cis-trans (34-40%), trans-trans (52-60%), and cis-cis (4-8%). These isomers differ in potency (the trans-trans and the cis-trans isomers are equipotent and the cis-cis isomer is 1/13th as potent a neuromuscular blocking agent) and in rates of in vitro hydrolysis (in vitro half-lives are less than 2 min for the cis-trans and trans-trans isomers and 276 min for the cis-cis isomer). The current study was undertaken to determine the pharmacokinetic profile of the individual stereoisomers of mivacurium, to evaluate the dose-proportionality of the more potent trans-trans and cis-trans isomers, and to evaluate the pharmacodynamics of mivacurium in healthy adult patients receiving a consecutive two-step infusion of mivacurium.

METHODS

Eighteen ASA physical status 1 or 2 adult male patients undergoing elective surgery under nitrous oxide/oxygen/fentanyl anesthesia were studied. Neuromuscular function was monitored using a mechanomyograph at a frequency of 0.15 Hz. An infusion of mivacurium was begun at 5 micrograms.kg-1.min-1. Sixty minutes later, the infusion rate was doubled to 10 micrograms.kg-1.min-1, and, 60 min after that, the infusion was discontinued. All patients were allowed to recover spontaneously from mivacurium-induced neuromuscular block. Venous blood samples were drawn for the determination of the plasma concentrations of each isomer of mivacurium by a stereospecific high performance liquid chromatographic method. Pharmacokinetic parameters were determined using noncompartmental analysis.

RESULTS

During the 5-micrograms.kg-1.min-1 infusion, patients developed 83.2 +/- 13.6% neuromuscular block. Increasing the infusion to 10 micrograms.kg-1.min-1 increased the depth of block to 99.0 +/- 2.0%. After discontinuation of the infusion, patients returned to 25% of their baseline muscle strength in 9.3 +/- 3.7 min and had 25-75% and 5-95% recovery indexes of 7.2 +/- 1.8 and 16.8 +/- 3.7 min, respectively. The volumes of distribution (V beta) of the cis-trans, trans-trans, and cis-cis isomers were 0.29 +/- 0.24, 0.15 +/- 0.05, and 0.34 +/- 0.08 l/kg, respectively. During the 5-micrograms.kg-1.min-1 infusion, the steady-state clearances of the potent cis-trans and trans-trans isomers were 106 +/- 67 and 63 +/- 34 ml.min-1.kg-1, respectively; the clearance of the less potent cis-cis isomer was 4.6 +/- 1.1 ml.min-1.kg-1. The elimination half-lives of the cis-trans and trans-trans isomers were 1.8 +/- 1.1 and 1.9 +/- 0.7 min, respectively, and that of the cis-cis isomer was 52.9 +/- 19.8 min. Clearance of the cis-trans and trans-trans isomers did not vary with infusion rate.

CONCLUSIONS

The short elimination half-lives and high metabolic clearances of the potent cis-trans and trans-trans isomers are consistent with the short duration of action of mivacurium. The cis-cis isomer does not appear to produce significant neuromuscular block as evident by the return of twitch height to baseline despite persistent cis-cis isomer concentrations.

Population pharmacodynamics of doxacurium

The nonlinear mixed-effects modeling (NONMEM) computer program was used to investigate the variability in the duration of doxacurium-induced neuromuscular block in 408 patients enrolled in phase II and phase III clinical trials of doxacurium. Spontaneous recovery data in the 10% to 90% block range from all patients were pooled and fitted to a linear model. Two parameters were estimated: (1) the slope, which is related to the pharmacokinetics and to the steepness of the dose-response curve, and (2) the intercept, which is linearly related to dose but has no physiologic meaning. The primary goal was to determine the factors affecting the slope by use of univariate and multivariate analyses techniques. Estimates of the slope ranged from 0.67% to 1.1% block/min (interindividual variability, 39%). Factors with clinically significant effects on the slope included the following: age, obesity, and anesthesia type. Thus these factors influence the time course of doxacurium-induced block and may require individualization of dose.

Alprazolam in end-stage renal disease. II. Pharmacodynamics

The sensitivity to the psychomotor and memory effects of alprazolam was evaluated in 12 normal subjects and 12 dialysis patients (seven patients receiving hemodialysis and five patients receiving continuous ambulatory peritoneal dialysis). Subjects received a single oral dose of 0.5 mg alprazolam, 2 mg alprazolam, and placebo in a double-blind, placebo-controlled, balanced, three-way crossover study with a Latin square design. After administration of the test drug, blood was obtained for alprazolam concentration and protein-binding determinations, and psychomotor performance, memory, and sedation were assessed. The maximum psychomotor impairment corrected for free alprazolam concentration was 5.0%, 8.2%, and 10.1% per nanogram per milliliter in normal subjects, patients receiving hemodialysis, and patients receiving continuous ambulatory peritoneal dialysis, respectively (p less than 0.01), after administration of 2 mg alprazolam. Free alprazolam concentrations at which 50% of maximum effect is elicited for psychomotor impairment were 10, 7.40, and 5.31 ng/ml in normal subjects, patients receiving hemodialysis, and patients receiving continuous ambulatory peritoneal dialysis, respectively. The maximum memory impairment corrected for the maximum free alprazolam concentration was 4.4%, 7.2%, and 8.9% per nanogram per milliliter, respectively (p less than 0.09), after administration of 2 mg alprazolam. Thus our group of patients receiving dialysis showed enhanced sensitivity to some psychomotor and memory effects of alprazolam.

New high-performance liquid chromatographic method for the determination of alprazolam and its metabolites in serum: instability of 4-hydroxyalprazolam

A high-performance liquid chromatographic method was developed for the determination of alprazolam (ALP) and its active metabolites, alpha-hydroxyalprazolam (AOH) and 4-hydroxyalprazolam (4OH) in human serum. During assay development, the instability of 4OH was revealed. Factors affecting stability of 4OH were then investigated. In this report, the assay methodology for the determination of ALP and AOH, the instability of 4OH, subsequent interference of 4OH breakdown products with AOH quantification, and factors affecting 4OH stability are described. The clinical significance of our findings are reported.

Alprazolam in end-stage renal disease: I. Pharmacokinetics

In a double-blind, randomized, placebo-controlled study, the pharmacokinetics of alprazolam and its active metabolite, alpha-hydroxyalprazolam, were determined in 12 normal subjects and 12 dialysis patients [7 hemodialysis (HD) patients and 5 continuous ambulatory peritoneal dialysis (CAPD) patients]. Blood samples were collected over 48 hours after alprazolam 0.5 mg and alprazolam 2 mg administration. Alprazolam and alpha-hydroxyalprazolam concentrations and alprazolam free fraction were determined. The pharmacokinetics of alprazolam were similar in normal subjects and HD patients with the exception of higher free fraction in HD patients. Differences were detected, however, in the pharmacokinetics of alprazolam in CAPD patients when compared with normal subjects and HD patients. These differences included a higher free fraction and a lower apparent oral clearance and free clearance in CAPD patients than in normal subjects or in HD patients. There was also a tendency for a later Tmax and a longer elimination half-life in CAPD patients than in normal subjects or HD patients. Alpha-hydroxyalprazolam concentrations were less than 15% of corresponding alprazolam concentrations in normal subjects and dialysis patients. Thus, end-stage renal disease is associated with changes in absorption, distribution, and/or elimination of alprazolam.