Alprazolam in end-stage renal disease: I. Pharmacokinetics

Systematic and quantitative assessment of the effect of chronic kidney disease on CYP2D6 and CYP3A4/5

Recent reviews suggest that chronic kidney disease (CKD) can affect the pharmacokinetics of nonrenally eliminated drugs, but the impact of CKD on individual elimination pathways has not been systematically evaluated. In this study we developed a comprehensive dataset of the effect of CKD on the pharmacokinetics of CYP2D6‐ and CYP3A4/5‐metabolized drugs. Drugs for evaluation were selected based on clinical drug–drug interaction (CYP3A4/5 and CYP2D6) and pharmacogenetic (CYP2D6) studies. Information from dedicated CKD studies was available for 13 and 18 of the CYP2D6 and CYP3A4/5 model drugs, respectively. Analysis of these data suggested that CYP2D6‐mediated clearance is generally decreased in parallel with the severity of CKD. There was no apparent relationship between the severity of CKD and CYP3A4/5‐mediated clearance. The observed elimination‐route dependency in CKD effects between CYP2D6 and CYP3A4/5 may inform the need to conduct clinical CKD studies with nonrenally eliminated drugs for optimal use of drugs in patients with CKD.

The solvation structure of alprazolam

Alprazolam is a benzodiazepine that is commonly prescribed for the treatment of anxiety and other related disorders.

Psychotropic drugs and renal failure: translating the evidence for clinical practice

INTRODUCTION

The kidney is a primary route of drug elimination; abnormal kidney function is predicted to alter the pharmacokinetics of agents metabolized and/or excreted predominantly through this route. The high prevalence of mental disorders associated with psychotropic drug use in individuals with deteriorating renal function suggests there is a need to investigate the effects of renal failure on psychotropic pharmacokinetics. The aim of this review is to provide a clinically accessible overview of the effect of chronic renal failure on the pharmacokinetics for each of the major classes of prescribed psychotropic agents.

METHODS

All English language articles published between 1977 and 2008 were searched through PubMed, using the following keywords: "renal," "kidney," "pharmacokinetics," "renal impairment," "renal insufficiency," and "renal failure." Each of these search words was cross-referenced with the non-proprietary name of each psychotropic agent. The manufacturer's product insert was also reviewed for some agents for updated dosing. Owing to the lack of adequately powered studies, an inclusive manner was used.

RESULTS

Chronic renal failure variably affects the pharmacokinetic parameters of psychotropic drugs. A review of each psychotropic drug is provided, with an emphasis on the individual pharmacokinetic parameters and recommended dosing.

CONCLUSIONS

The adjudication of safe and effective doses for any psychotropic agent needs to be individualized. Tactics including dosage adjustment, slow titration, and careful monitoring for serious adverse events should be incorporated into practice.

Psychiatric issues in renal failure and dialysis

This article aims to bring to the fore, issues regarding the interface of psychiatry and renal failure. Depression, anxiety, suicide and delirium are common complications observed in patients with renal failure. Pharmacological management of these problems need stringent monitoring on part of the psychiatrist. This article examines the various complications that may be observed in patients with renal failure while discussing treatment approaches and also emphasizing the need for interdisciplinary team work in improving the quality of life of patients with renal failure and those on dialysis.

Alprazolam induced conformational change in hemoglobin

Alprazolam (ALP) is a widely prescribed sedative and antidepressant benzodiazepine group of drugs. The wide uses of this drug lead us to investigate its possible interaction with hemoglobin (Hb). Spectrophotometric and spectofluorimetric studies showed strong binding of ALP with Hb. Circular dichroic spectra showed that alpha-helical structure of Hb-subunits has been largely changed. On ALP treatment partial pressure of O(2) is increased in the blood indicating release of O(2) from erythrocytes. Further, the binding of ALP-induced conformational changes in Hb resulting in larger Hb particle size was demonstrated by dynamic light scattering experiment. Thus, the present study unambiguously raises question of danger of random usage of ALP, which binds with and changes the function of Hb.

Update on Psychotropic Medication Use in Renal Disease

Renal failure is a common medical condition, and many patients have comorbid psychiatric disorders. In this review, which is intended as a resource for consultation psychiatrists, the authors discuss pharmacokinetic considerations and provide information about the use of individual psychotropic medications in patients with renal disease. Most psychotropic medications are fat soluble, easily pass the blood-brain barrier, are not dialyzable, are metabolized primarily by the liver, and are excreted mainly in bile. Consequently, the majority of these drugs can be safely used with the end-stage renal disease population.

Clinical pharmacology, clinical efficacy, and behavioral toxicity of alprazolam: a review of the literature

Alprazolam is a benzodiazepine derivative that is currently used in the treatment of generalized anxiety, panic attacks with or without agoraphobia, and depression. Alprazolam has a fast onset of symptom relief (within the first week); it is unlikely to produce dependency or abuse. No tolerance to its therapeutic effect has been reported. At discontinuation of alprazolam treatment, withdrawal and rebound symptoms are common. Hence, alprazolam discontinuation must be tapered. An exhaustive review of the literature showed that alprazolam is significantly superior to placebo, and is at least equally effective in the relief of symptoms as tricyclic antidepressants (TCAs), such as imipramine. However, although alprazolam and imipramine are significantly more effective than placebo in the treatment of panic attacks, Selective Serotonin Reuptake Inhibitors (SSRIs) appear to be superior to either of the two drugs. Therefore, alprazolam is recommended as a second line treatment option, when SSRIs are not effective or well tolerated. In addition to its therapeutic effects, alprazolam produces adverse effects, such as drowsiness and sedation. Since alprazolam is widely used, many clinical studies investigated its cognitive and psychomotor effects. It is evident from these studies that alprazolam may impair performance in a variety of skills in healthy volunteers as well as in patients. Since the majority of alprazolam users are outpatients, this behavioral impairment limits the safe use of alprazolam in patients routinely engaged in potentially dangerous daily activities, such as driving a car.

Human variability in CYP3A4 metabolism and CYP3A4-related uncertainty factors for risk assessment

CYP3A4 constitutes the major liver cytochrome P450 isoenzyme and is responsible for the oxidation of more than 50% of all known drugs. Human variability in kinetics for this pathway has been quantified using a database of 15 compounds metabolised extensively (>60%) by this CYP isoform in order to develop CYP3A4-related uncertainty factors for the risk assessment of environmental contaminants handled via this route. Data were analysed from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration-time curve (AUC)] and acute exposure (Cmax). Interindividual variability in kinetics was greater for the oral route (46%, 12 compounds) than for the intravenous route (32%, 14 compounds). The physiological and molecular basis for the difference between these two routes of exposure is discussed. In relation to the uncertainty factors used for risk assessment, the default kinetic factor of 3.16 would be adequate for adults, whereas a CYP3A4-related factor of 12 would be required to cover up to 99% of neonates, which have lower CYP3A4 activity.

In vitro/in vivo scaling of alprazolam metabolism by CYP3A4 and CYP3A5 in humans

We attempted to predict the in vivo metabolic clearance of alprazolam from in vitro metabolic studies using human liver microsomes and human CYP recombinants. Good correlations were observed between the intrinsic clearance (CL(int)) for 4-hydroxylation and CYP3A4 content and between the CL(int) for alpha-hydroxylation and CYP3A5 content in ten human liver microsomal samples. Using the recombinant CYP isoforms expressed in insect cells, the CL(int) for CYP3A4 was about 2-fold higher than the CL(int) for CYP3A5 in the case of 4-hydroxylation. However, the CL(int) for CYP3A5 was about 3-fold higher than the CL(int) for CYP3A4 in the case of alpha-hydroxylation. The metabolic rates for 4- and alpha-hydroxylation increased as the added amount of cytochrome b(5) increased, and their maximum values were 3- to 4-fold higher than those without cytochrome b(5). The values of CL(int), in vivo predicted from in vitro studies using human liver microsomes and CYP3A4 and CYP3A5 recombinants were within 2.5 times of the observed value calculated from literature data. The average CL(int) value (sum of 4- and alpha-hydroxylation) obtained using three human liver microsomal samples was 4-fold higher than that obtained using three small intestinal microsomal samples from the same donors, indicating the minor contribution of intestinal metabolism to alprazolam disposition. The area under the plasma concentration-time curve (AUC) of alprazolam is reported to increase following co-administration of ketoconazole and the magnitude of the increase predicted from the in vitro K(i) values and reported pharmacokinetic parameters of ketoconazole was 2.30-2.45, which is close to the value observed in vivo (3.19). A quantitative prediction of the AUC increase by cimetidine was also successful (1.73-1.79 vs 1.58-1.64), considering the active transport of cimetidine into the liver. In conclusion, we have succeeded in carrying out an in vitro/in vivo scaling of alprazolam metabolism using human liver microsomes and human CYP3A4 and CYP3A5 recombinants.

Clinical pharmacokinetics of reboxetine, a selective norepinephrine reuptake inhibitor for the treatment of patients with depression

Reboxetine is a novel selective norepinephrine inhibitor that has been evaluated in the treatment of patients with depression. Reboxetine is a racemic mixture, and the (S,S)-(+)-enantiomer appears to be the more potent inhibitor. However, the ratio of the areas under the concentration-time curves of the (S,S)-(+)- and (R,R)-(-)-enantiomers in vivo is approximately 0.5. There is no evidence for chiral inversion. Differences in the clearances of the 2 enantiomers may be explained by differences in protein binding. The pharmacokinetics of reboxetine are linear following both single and multiple oral doses up to a dosage of 12 mg/day. The plasma concentration-time profile following oral administration is best described by a 1-compartment model, and the mean half-life (approximately 12 hours) is consistent with the recommendation to administer the drug twice daily. Reboxetine is well absorbed after oral administration. The absolute bioavailability is 94.5%, and maximal concentrations are generally achieved within 2 to 4 hours. Food affects the rate, but not the extent, of absorption. The distribution of reboxetine appears to be limited to a fraction of the total body water due to its extensive (>97%) binding to plasma proteins. The primary route of reboxetine elimination appears to be through hepatic metabolism. Less than 10% of the dose is cleared renally. A number of metabolites formed through hepatic oxidation have been identified, but reboxetine is the major circulating species in plasma. In vitro studies show that reboxetine is predominantly metabolised by cytochrome P450 (CYP) 3A4; CYP2D6 is not involved. Reboxetine plasma concentrations are increased in elderly individuals and in those with hepatic or renal dysfunction, probably because of reduced metabolic clearance. In these populations, reboxetine should be used with caution, and a dosage reduction is indicated. Ketoconazole decreases the clearance of reboxetine, so that the dosage of reboxetine may need to be reduced when potent inhibitors of CYP3A4 are coadministered. Quinidine does not affect the in vivo clearance of reboxetine, confirming the lack of involvement of CYP2D6. There is no pharmacokinetic interaction between reboxetine and lorazepam or fluoxetine. Reboxetine at therapeutic concentrations has no effect on the in vitro activity of CYP1A2, 2C9, 2D6, 2E1 or 3A4. The lack of effect of reboxetine on CYP2D6 and CYP3A4 was confirmed by the lack of effect on the metabolism of dextromethorphan and alprazolam in healthy volunteers. Thus, reboxetine is not likely to affect the clearance of other drugs metabolised by CYP isozymes.

Pharmacokinetics of alprazolam in elderly patients with multiple diseases

The pharmacokinetics of alprazolam (1 mg p.o.) were investigated (using a new developed HPLC-assay) in 10 multimorbid elderly patients (five female, five male; mean age 72.8 +/- 8.2 years, creatinine clearance 63.6 +/- 25.9 ml/min, weight 68.9 +/- 13.9 kg). Compared with young and elderly volunteers from other studies peak plasma concentrations of alprazolam were decreased while peak time and elimination half-life were increased. 'Second peak' plasma levels (correlated with age and creatinine clearance) occurred in eight of 10 elderly patients. The variability associated with the pharmacokinetic parameters in the multimorbid elderly patients was far greater than that observed in young and old healthy volunteers. Mean alprazolam concentrations in multimorbid patients aged 72 years or more were elevated as compared to 'younger' patients (age range: 63-71 years). Dose reduction should be considered in the older multimorbid patients.