Cytochrome P450 enzymes: interpretation of their interactions with selective serotonin reuptake inhibitors. Part I

Fundamental Pharmacokinetic Concepts and Their Clinical Relevance: Clearance, Zero Versus First Order and Nonlinear Pharmacokinetics

In response to a question posed by a valued colleague, this column will discuss 4 fundamental pharmacokinetic concepts: (1) What does the term clearance encompass? (2) What do the terms first order and second order pharmacokinetics mean? (3) What does the term nonlinear pharmacokinetics mean and is it just a synonym for zero order pharmacokinetics? (4) What is the clinical relevance, if any, of these concepts and why? In addition, this column cites several earlier columns that are relevant to aspects of each of the answers. Thus, readers interested in more details can refer to these earlier publications that include case examples and figures that further illustrate various points. In considering the clinical relevance of these pharmacokinetic concepts, this column discusses relative binding affinity for targets and the concept of selective versus nonselective drugs, which are foundational cornerstones for understanding and optimally using currently available psychopharmaceutical agents.

Controlling for caffeine in cardiovascular research: A critical review

Caffeine, the most widely consumed drug in the world, exerts numerous effects on cardiovascular activity. Thus, it is important and advisable to control for caffeine consumption in studies examining caffeine and/or cardiovascular activity and reactivity. This paper 1) reviews the literature concerning caffeine's effects on cardiovascular parameters; 2) summarizes the widely varying protocols used to control for the drug in extant cardiovascular literature, and 3) provide guidelines for caffeine control procedures to minimize potentially confounding acute and withdrawal effects of the drug. An abstention period equal to the average half-life of the drug is recommended for creation of methodological controls for caffeine. Additional methodological recommendations are described concerning factors that moderate the half-life of caffeine. When feasible, researchers should consider and aim to control for caffeine's acute and extended psychophysiological effects. This understudied issue has fundamental implications for caffeine-related investigations and research in psychophysiology and behavioral medicine.

Selective Serotonin Reuptake Inhibitors

The first antidepressants were created by chance but brought the idea that central serotonin agonism produced an antidepressant effect. SSRIs were the first class of psychotropic medications to be rationally designed, meaning that researchers intended to utilize a specific mechanism of action while avoiding adverse effects. In this way, SSRIs were created to be safer and more tolerable than previous antidepressants. SSRIs share many similarities, but differ in terms of pharmacokinetics and effects on CYP450 enzymes, which is detailed in this chapter. Further information will be provided regarding safety, clinical indications/uses, and dosing recommendations.

Antidepressants relevant to oral and maxillofacial surgical practice

Background:

Depression is commonly associated with a high-carbohydrate diet, lack of interest in proper oral hygiene and xerostomia connected to the use of antidepressants. Patients often consult their dentists as a result of changes affecting the hard dental substance and the soft-tissues.

Aim:

The aim of this study was to identify adverse drug interactions between the antidepressants and medications commonly administered in dentistry in order to give practicing dentists an overview of the scientific literature.

Objective:

The objective is to identify the adverse drug interactions between antidepressants and medication commonly administered in dentistry.

Study Design:

The literature search was performed using PubMed, Cochrane and the specific search items. The review (1984-2009) focused on medicines used in dental practice (vasoconstrictors, non-opioid analgesics, non-steroidal anti-inflammatory drugs, antibiotics, antifungals and benzodiazepines).

Results:

There are various drug interactions between antidepressants and medicines used in dentistry. When two or more drugs are co-administered, a drug interaction must always be anticipated though many of the interactions are potential problems, but do not seem to be real clinical issues.

Conclusion:

The probability of a drug interaction can be minimized by careful history-taking, skillful dose adjustment and safe administration of the therapeutic agent.

Understanding the pharmacokinetics of anxiolytic drugs

INTRODUCTION

Anxiety disorders are considered the most common mental disorders and they can increase the risk for comorbid mood and substance use disorders, significantly contributing to the global burden of disease. For this reason, anxiolytics are the most prescribed psychoactive drugs, particularly in the Western world.

AREAS COVERED

This review aims to analyze pharmacokinetic profile, plasma level variations so as the metabolism, interactions and possible relation to clinical effect of several drugs which are used primarily as anxiolytics. The drugs analyzed include benzodiazepines, anticonvulsants (pregabalin, gabapentin), buspirone, β-blockers and antihistamines (hydroxyzine). Regarding the most frequently used anxiolytic benzodiazepines, data on alprazolam, bromazepam, chlordesmethyldiazepam, chlordiazepoxide, clotiazepam, diazepam, etizolam, lorazepam, oxazepam, prazepam and clonazepam have been detailed.

EXPERT OPINION

There is a need for a more balanced assessment of the benefits and risks associated with benzodiazepine use, particularly considering pharmacokinetic profile of the drugs to ensure that patients, who would truly benefit from these agents, are not denied appropriate treatment. An optimal pharmacological approach involving an integrative pharmacokinetic and pharmacodynamic optimization strategy would ensure better treatment and personalization of anxiety disorders. So it would be desirable for the development of new anxiolytic drug(s) that are more selective, fast acting and free from the unwanted effects associated with the traditional benzodiazepines as tolerance or dependence.

Psychiatric symptomatologies and disorders related to epilepsy and antiepileptic medications

INTRODUCTION

Psychiatric comorbidities (such as depression, anxiety, psychosis, inattention, obsession, personality traits, aggression and suicide) are frequent in patients with epilepsy and have a significant impact on medical management and quality of life.

AREAS COVERED

A literature search was performed in MEDLINE for epidemiological, longitudinal, prospective, double-blind clinical trial studies published between 1990 and 2011 using the following words: epilepsy, antiepileptic drugs (AEDs), behavioral/emotional/psychiatric comorbidities, suicide and aggression. In this review, the author discusses: i) the characterization and prevalence of behavioral disturbances associated with epilepsy, ii) variables correlated with behavioral comorbidities which include: psychosocial-, clinical- and treatment-related variables, iii) the complex mechanisms of behavioral comorbidities associated with epilepsy, which include both psychosocial (functional) and organic; the process of epileptogenesis, neuronal plasticity, abnormalities in hypothalamic-pituitary axis and neurotransmitters and pathways are fundamental determinants, iv) the negative psychotropic effects of AEDs and their mechanisms and v) the suggested biopsychosocial model of management (pharmacological and non-pharmacological).

EXPERT OPINION

The relationship between psychiatric disorders and epilepsy has relevant therapeutic implications which should be directed towards a comprehensive biopsychosocial approach that focuses on the whole person rather than simply on the disease process.

Venlafaxine vs. paroxetine in the acute phase of treatment for major depressive disorder among Han Chinese population in Taiwan

PURPOSE

Clinical studies have suggested that venlafaxine induces a higher remission rate than paroxetine. However, very few studies have evaluated relapse episodes over treatment periods longer than a few weeks, and the cut-off score of 7 on the Hamilton Rating Scale for Depression (HRSD) often used to define remission is too high. This score is associated with the high rates of social function impairment. We report on a single centre, open-label, prospective 24-week study to investigate the comparative efficacy of acute treatments with venlafaxine and paroxetine, using different definitions of response and remission rates.

METHODS

Outpatients satisfying DSM-IV criteria for major depression with a baseline HRSD17 score of at least 16 were eligible. Following baseline evaluations, the patients were assigned to receive venlafaxine 75-225 mg/day with the mean dosage 141.35 +/- 26.98 (SD) mg/day (n = 78), or paroxetine 20 mg/day (n = 92) for 24 weeks. Efficacy was assessed using the mean change in HRSD(17) score from baseline, the response rate and the remission rates based on different criteria for remission (HRSD(17) score < or = 7 or 5).

RESULTS

One hundred and seventy patients were evaluated for efficacy; 78 treated with venlafaxine and 92 with paroxetine. Over the treatment period, venlafaxine was comparable with paroxetine on most outcome measures, whereas paroxetine produced significantly higher remission rates at weeks 4, 8, 16, 20 and 24 weeks when the lower cutoff of 5 was used.

CONCLUSIONS

Venlafaxine treatment was similar to paroxetine according to the typical efficacy measures for treating outpatients with major depression. However, based on the stricter remission criterion, paroxetine might be superior to venlafaxine.

Metabolism of N-methyl, N-propargylphenylethylamine: studies with human liver microsomes and cDNA expressed cytochrome P450 (CYP) enzymes

1. We used an in vitro screening procedure and studies with individual human liver microsomes and cDNA-expressed CYP enzymes to investigate the metabolism of the putative neuroprotective drug N-methyl,N-propargyl-2-phenylethylamine (MPPE) to N-methylphenylethylamine (N-methylPEA) and N-propargylphenylethylamine (N-propargylPEA). 2. An electron-capture gas chromatographic procedure previously developed in our laboratories was used to measure the quantities of N-methylPEA and N-propargylPEA formed in the experiments with a single donor human liver microsome panel and cDNA expressed single CYP enzyme systems. The data were fitted to nonlinear regressions using Prism to determine kinetic constants. The results from a fluorogenic screen determined which cDNA-expressed single CYP enzymes were investigated. 3. CYP2B6, CYP2C19, and CYP2D6 all contributed to the formation of N-methylPEA, while only CYP2B6 catalyzed the formation of N-propargylPEA. The K (M) and V (max) values for N-propargylPEA formation were 290 +/- 70 microM and 139+/-16 ng/mL/min. The values for formation of N-methylPEA were not determined from these experiments due to the complexity of fitting the data to a three-variable equation, but data on the time course of N-methylPEA formation are presented. 4. Catabolism of MPPE to N-methylPEA and N-propargylPEA is catalyzed by CYP enzymes. CYP2B6, 2C19 and 2D6 all contribute to the depropargylation of the parent compound, but only CYP2B6 also catalyzes demethylation. CYP2C19 was found to be the most active with respect to generation of N-methylPEA.

The potential for clinically significant drug-drug interactions involving the CYP 2D6 system: effects with fluoxetine and paroxetine versus sertraline

BACKGROUND

Patients taking antidepressants are more likely to also be taking multiple medications, increasing the risk of adverse drug-drug interactions (DDIs). Because of substantial inhibition of one or more cytochrome P450 (CYP) enzymes at therapeutic doses, the selective serotonin reuptake inhibitors fluoxetine, fluvoxamine, and paroxetine have a higher risk of CYP-mediated DDIs than citalopram, escitalopram, and sertraline, which do not substantially inhibit any CYP enzyme.

METHODS

Prescribing patterns in 2,779 Veterans Affairs (VA) patients who had a prescription for an antidepressant in the preceding year and a current prescription for at least one systemically active drug were analyzed to determine 1) prevalence of drug combinations with potential to cause CYP-mediated DDIs, 2) frequency of combinations of fluoxetine, paroxetine, or sertraline with drugs whose metabolism is principally dependent on CYP 2D6, and 3) use of reduced doses of CYP 2D6 substrate/drugs with narrow therapeutic indices in patients on fluoxetine or paroxetine compared with sertraline.

RESULTS

In 2,779 patients, 55 pairs of drugs with the potential to cause CYP-mediated DDIs occurred in 300 patients (11%), but only 26 of the patients and 6 of the drug pairs were identified by the VA Drug Alert System. Of the 461 patients receiving fluoxetine and/or paroxetine, 39 (8%) were also receiving a CYP 2D6-model substrate/drug with a narrow therapeutic index, 14 (36%) of whom were receiving high enough doses to be at moderate to high risk of a serious DDI.

CONCLUSIONS

VA patients on fluoxetine, paroxetine, and sertraline were equally likely to be on drugs whose metabolism is dependent on CYP 2D6, including drugs with narrow therapeutic indices. No differences were found in doses of tricyclic antidepressants (i.e., "victim" drugs), which have narrow therapeutic indices and serious dose-dependent toxicity, when co-prescribed with fluoxetine or paroxetine versus sertraline (i.e., "perpetrator" drugs), despite predictable differences in CYP 2D6-mediated clearance of these drugs.

Heart and mind: (2) psychotropic and cardiovascular therapeutics

There is a plausible biological basis for the association between psychiatric morbidity and cardiovascular disease. Anxiety, panic disorder, and depression are common in patients with coronary heart disease and hypertension. Despite this evidence there is poor recognition of anxiety disorders and depression in primary care and hospital medical practice. Concern also surrounds the use of psychotropic drugs in patients with cardiovascular disease. In the first of the two articles on this subject, we highlighted the current evidence regarding the association between cardiovascular and psychotropic conditions. In this second article, we discuss the interaction of the drugs used in the management of these two varied but commonly coexistent group of diseases as well as their relative effects on either system. Finally, we summarise the data regarding the safe use of these medications based on the recommendations from the currently available evidence.

Paradigms for pharmacologic use as a treatment component in feline behavioral medicine

Veterinary behavioral medicine remains an under-supported, under-appreciated, and under-taught specialty within veterinary medicine. Neuropsychopharmacology is the aspect that has provided the field with the most scientific legitimacy, but is also one of the most hotly debated. Paradigms for use of pharmacologic intervention include firstly ruling out any underlying medical cause. If a behavioral diagnosis can be made, treatment with psychotropic medication may be considered, although their use is most effective as part of an integrated treatment program that includes behavior modification. Used without an understanding of the mechanism of action, pharmacologic intervention may only blunt or mask behavior without altering processes or environments that produced the behavior. This paper reviews specific drugs, mechanism of action of those drugs, and relevant uses are reviewed for cats. Future advances in treatment in veterinary behavioral medicine will be pharmacological and neurophysiological. As the field of veterinary behavioral medicine expands, its paradigm will enlarge to include routine combination therapy and the implementation of neuropharmacological intervention as a diagnostic tool.

Selectivity of SSRIs: individualising patient care through rational treatment choices

Despite a common mode of action [inhibition of the 5-hydroxytryptamine (5-HT) neuronal reuptake transporter], proven antidepressant efficacy and a similar range of indications (depression and a variety of anxiety disorders), the unique secondary binding properties of each selective serotonin reuptake inhibitor (SSRI) account for clinically significant differences in tolerability and side-effect profiles, particularly in some patients. Secondary properties within the class of SSRIs include some combination of actions at noradrenergic, dopaminergic, muscarinic cholinergic, histaminergic and sigma receptors. In addition, most SSRIs inhibit at least one of the cytochrome P450 enzymes, resulting in potential pharmacokinetic interactions with co-prescribed drugs. Although secondary properties of SSRIs can be associated with side effects, sometimes these same actions can be harnessed to good therapeutic effect through rational, informed treatment choices. In this way, agents that more consistently cause central nervous system activation (such as fluoxetine and sertraline) can be used to boost energy in patients whose depression is accompanied by fatigue and apathy, while the anxiolytic, sedative properties of others (particularly paroxetine and fluvoxamine) can be beneficial in patients with insomnia and agitation. When secondary properties are experienced as undesirable side effects, agents with greater selectivity for the serotonin transporter and without significant secondary binding properties, such as citalopram and escitalopram, may be desirable. This article explains how an understanding of the secondary binding properties of the SSRIs can guide individualised treatment across the spectrum of depressive and anxious states.

Transient neurologic deficits associated with carbamazepine-induced hypertension

Carbamazepine is a well-established, effective treatment of complex partial seizures and is well tolerated in most patients. The adverse effects of carbamazepine include aplastic anemia, agranulocytosis, pancytopenia, bone marrow depression, thrombocytopenia, cardiac conduction abnormalities, congestive heart failure, and peripheral edema. Hypertension or hypotension has also rarely been documented in patients with either therapeutic or toxic blood levels of carbamazepine. It is possible that carbamazepine-induced hypertension in those with therapeutic blood levels is rarely seen because most of the patients who begin treatment are young and do not have baseline hypertension. The authors describe a patient of African-American descent with a history of controlled essential hypertension who developed severe uncontrolled hypertension when started on carbamazepine. Treatment with additional antihypertensive medications did not reduce his blood pressure. In addition, he developed two episodes of transient neurologic deficits, the symptoms of which consisted of dysarthria, vertigo, and unstable gait. A substantial reduction of his carbamazepine dose resulted in the control of his blood pressure and no recurrence of his symptoms.

Role of pharmacogenomics in individualising treatment with SSRIs

The introduction of the SSRIs has significantly transformed the pharmacological treatment of a range of psychiatric disorders. In particular, individuals affected by depression, panic disorder, obsessive-compulsive disorder and social phobia have benefited substantially from their use. Compared with the previous generation of psychotropic drugs, SSRIs offer an improved tolerability to therapy while maintaining a high level of efficacy. Nevertheless, despite these advantages, not all patients benefit from treatment; an appreciable proportion do not respond adequately, while others may react adversely. This necessitates a review of the initial treatment choice, often involving extended periods of illness while a more suitable therapy is sought. Such a scenario could be avoided were it possible to determine the most suitable drug prior to treatment. Several factors are postulated to influence outcome of drug therapy; most recently, pharmacogenetic studies have demonstrated a significant influence of genetic mechanisms on the efficacy of clinically prescribed drugs. This contribution, which is primarily a reflection of alterations in genes that encode drug-metabolising enzymes, drug receptors, transporters and second messengers, may be pertinent to the success of SSRI therapy. Attesting to this potential, studies to elucidate the influence of genetic processes on SSRI efficacy now represent a major focus of pharmacogenetics research. Current evidence emerging from the field suggests that gene variants within the serotonin transporter and cytochrome P450 drug-metabolising enzymes may bear a particular importance, though further corroboration of these findings is still warranted. At the same time, it appears likely that further key participating genes remain to be identified. By comprehensively delineating these genetic components, it is envisaged that this will eventually facilitate the development of highly sensitive protocols for individualising SSRI treatment.

Pharmacologic management in veterinary behavioral medicine

As our knowledge expands, behavioral pharmacology plays an increasingly important role in behavioral medicine. Drugs traditionally categorized as anxiolytics, antidepressants, anticonvulsants, and hormones may be used to help manage a range of animal behavioral problems. Knowledge of how these agents act in the body and interact with other agents is imperative for safe and efficacious use.

In vitro inhibition of pimozide N-dealkylation by selective serotonin reuptake inhibitors and azithromycin

Pimozide is often coprescribed with serotonin reuptake inhibitor (SSRI) antidepressants to treat depression in patients with Tourette's syndrome. In human liver microsomes (HLMs), the inhibition of the primary route of pimozide metabolism, N-dealkylation to 1,3-dihydro-1-(4-piperidinyl)-2H-benzimidazol-2-one (DHPBI), by four SSRIs (fluoxetine, sertraline, paroxetine, and fluvoxamine) and azithromycin was tested. Inhibition constants (K(i) values) were estimated from Dixon plots (three HLMs for each inhibitor) using the appropriate enzyme inhibition model by nonlinear regression. At 10 microM paroxetine, sertraline, fluoxetine, or fluvoxamine, the formation of DHPBI from pimozide (10 microM) in HLMs was inhibited by an average (three HLMs) of 7%, 7.7%, 8%, and 16%, respectively, whereas this inhibition did not exceed 55% at the maximum concentrations (100 microM) of the SSRIs tested. Azithromycin had negligible effect on pimozide (10 microM) N-dealkylation (19% at 100 microM azithromycin). These inhibition data were compared with ketoconazole, which was included as a positive control of CYP3A inhibition. At 0.1 microM and 0.5 microM ketoconazole, the formation of DHPBI from 10 microM pimozide was inhibited by 32% and 62%, respectively. The K(i) values (+/- SD) of ketoconazole, sertraline, fluvoxamine, azithromycin, fluoxetine, and paroxetine were 0.07 microM, 89 +/- 44 microM, 89 +/- 24 microM, 103 +/- 52 microM, 117 +/- 27 microM, and 129 +/- 33 microM, respectively. These values are least 100-fold higher than the expected plasma concentrations after the usual daily doses of the SSRIs and azithromycin, suggesting that coadministration of SSRIs and azithromycin are unlikely to markedly diminish the elimination of pimozide in patients. However, in vivo predictions from in vitro data are not always perfect. In vivo, the SSRIs or azithromycin may concentrate in the liver relative to plasma. In addition, the possibility that these drugs could alter pimozide disposition through effects on transport proteins or via promoter repression cannot be ruled out.

Differential time course of cytochrome P450 2D6 enzyme inhibition by fluoxetine, sertraline, and paroxetine in healthy volunteers

The selective serotonin reuptake inhibitors (SSRIs) paroxetine, sertraline, and fluoxetine have varying degrees of potency in inhibiting the hepatic cytochrome P450 (CYP) 2D6 enzyme. However, the time course for maximum inhibition to occur or for inhibition to dissipate when dosing is discontinued, requires clarification. In an open label, parallel group study of 45 healthy volunteers, the time course of CYP2D6 inhibition of the above SSRIs was evaluated. Subjects were randomized to receive paroxetine at 20 mg/day for 10 days; sertraline at 50 mg/day for 3 days, followed by sertraline at 100 mg/day for 10 days; or fluoxetine at 20 mg/day for 28 days. CYP2D6 activity was assessed using the dextromethorphan metabolic ratio (DMR) on antidepressant days 5 and 10 for sertraline and paroxetine and at weekly intervals for fluoxetine. Following SSRI discontinuation, calculation of a CYP2D6 inhibition half-life (t(1/2)inh) revealed the time course of fluoxetine inhibition (t(1/2)inh = 7.0 +/- 1.5 days) to be significantly longer than either paroxetine (t(1/2)inh = 2.9 +/- 1.9) or sertraline (t(1/2)inh = 3.0 +/- 3.0) (p < 0.01), but the latter were not significantly different from each other (p > 0.05). Time for the extrapolated DMR versus time log-linear plots to return to baseline was significantly different between fluoxetine (63.2 +/- 5.6 days) and both paroxetine (20.3 +/- 6.4 days) and sertraline (25.0 +/- 11.0 days) (p < 0.01), making the rank order (from longest to shortest) of time for CYP2D6 inhibition to dissipate: fluoxetine > sertraline >or= paroxetine. Differences between mean baseline DMR values and measured values obtained after drug discontinuation for each drug group became nonsignificant on discontinuation day 5 for both paroxetine and sertraline and on discontinuation day 42 for fluoxetine. These data define the time course of a persistent effect that fluoxetine, sertraline, and paroxetine have on CYP2D6 following drug discontinuation and should be considered when initiating therapy with a CYP2D6 substrate.

Antidepressant Drug Interactions

Second-generation antidepressants are more selective in their pharmacological mechanisms and offer fewer side effects and a safer toxicological profile than cyclic antidepressants and monoamine oxidase inhibitors. While the risk for pharmacodynamic interactions is more limited than with older agents with broader receptor effects, the risks for pharmacokinetic interactions is greater. The capacity of selective serotonin reuptake inhibitors to inhibit the metabolic activity of cytochrome P450 isozyme system has spurred over a decade of intense psychopharmacological and pharmacogenetics research to better the understanding of the significance of these interactions. Clinicians have had to increase their knowledge and understanding of drug interaction potential to better manage patients receiving these newer antidepressants. The following is a review of both pharmacodynamic and pharmacokinetic drug-drug interactions with antidepressants.

Pharmacotherapy of depression in older patients: a summary of the expert consensus guidelines

Depression in older adults increases disability, medical morbidity, mortality, suicide risk, and healthcare utilization. Most studies of antidepressants are conducted in younger adults, and clinicians often have to extrapolate from findings in populations that do not present the same problems as older patients. Older patients often have serious coexisting medical conditions that may contribute to or complicate treatment of depression; they tend to take multiple medications, some of which may contribute to depression or interact with antidepressants; and they metabolize medications slowly and are more sensitive to side effects than younger patients. To address clinical questions not definitively answered in the research literature, the authors surveyed 50 experts on the pharmacotherapy of depressive disorders in older patients. The survey contained 64 questions with 857 options: 618 of the options were scored using a modified version of the RAND 9-point scale for rating appropriateness of medical decisions; for the other 239 options, the experts were asked to write in answers or check a box. The experts reached consensus on 89% of the options rated on the 9-point scale. Categorical rankings (first line/preferred, second line/alternate, third line/usually inappropriate) were assigned to each option based on the 95% confidence interval around the mean rating. Guideline tables indicating preferred treatment strategies were then developed for common and important clinical scenarios. The authors summarize the expert consensus methodology and the experts' recommendations and discuss how they relate to research findings. The experts recommend including both antidepressant medication and psychotherapy in treatment plans for nonpsychotic unipolar major depressive disorder of any severity, as well as for dysthymic disorder or persistent minor depressive disorder. They would also consider using either medication or psychotherapy alone for milder depression. For unipolar psychotic major depression, the treatment of choice is an antidepressant plus one of the newer atypical antipsychotics, with electroconvulsive therapy another first-line option. If the patient has a comorbid medical condition that is contributing to the depression, the experts recommend treating both the depression and the medical condition from the outset. The SSRIs were the top-rated antidepressants for all types of depression, with highest ratings for efficacy and tolerability given to citalopram and sertraline. Paroxetine was another first-line option, and fluoxetine was rated high second line. The preferred psychotherapy techniques for treating depression in older patients are cognitive-behavioral therapy, supportive psychotherapy, problem-solving psychotherapy, and interpersonal psychotherapy. The experts also recommended use of psychosocial interventions (e.g., psychoeducation, family counseling, visiting nurse services) in addition to pharmacotherapy and psychotherapy. Within limits of expert opinion and with the expectation that future research data will take precedence, these guidelines provide direction concerning common clinical dilemmas in older patients. They cannot address the complexities of each individual patient's care and can be most helpful in the hands of experienced clinicians.

Depression in patients with cardiac disease: a practical review

Some degree of depression affects at least 30% of hospitalized patients with coronary artery disease (CAD), and is associated with increased risks of mortality and continuing depression over at least the first year following hospital discharge. Despite its consequences for prognosis and quality of life, depression is underrecognized and undertreated in cardiac patients. The diagnosis of depression is complicated in patients with medical illness. Their symptoms can reflect physical as well as psychological complaints. Many CAD patients resist the idea of additional medications, and drug interactions can be problematic for those willing to accept antidepressant treatment. Finally, depression tends to recur. Its successful treatment requires a long-term commitment from both physician and patient. This article examines the special challenges involved in diagnosing depression in patients with CAD, outlines available psychotherapeutic and pharmacological treatments, and considers the issues involved in deciding which patients to treat, with what approach, and for how long.

Clonazepam and sertraline: absence of drug interaction in a multiple-dose study

Thirteen subjects (seven men, six women) completed a placebo-controlled, randomized, double-blind, crossover study to determine whether an interaction occurs between clonazepam and sertraline. Ten days of once-daily doses of either clonazepam 1 mg and placebo (CZ + PL) or clonazepam 1 mg and sertraline 100 mg (CZ + SR) were administered; there was an 11-day washout period. Sertraline did not significantly affect the pharmacokinetics of clonazepam (p > 0.13). Clonazepam apparent oral clearance, volume of distribution, and half-life were 3.9 +/- 0.2 L/hr, 233 +/-11 L, and 40.5 +/- 0.3 hours, respectively. The kinetics of the inactive metabolite 7-aminoclonazepam were marginally affected by sertraline, with a 21% decrease in the elimination half-life (p = 0.03) relative to CZ + PL and no significant difference between treatments in area under the curve or metabolite ratio. Card sorting (CS), digit-symbol substitution test (DSST), nurse-rated sedation scale (NRSS), and self-rated sedation scores were assessed four times daily on days -1 (PL + PL), 1, 4, 7, and 10. There were no differences between treatments in area under the effect curve or maximum observed effect for CS, DSST, or NRSS. Maximum impairment on all assessment days was low, with a less than 10% change from the drug-free values for CS and DSST. Despite higher clonazepam concentrations, predose (time 0) psychomotor and sedation scores did not differ among days -1, 1, 4, 7, and 10 or between treatments. These results in healthy volunteers indicate that sertraline does not affect the pharmacokinetics or pharmacodynamics of clonazepam.

Pharmacokinetics of selective serotonin reuptake inhibitors

The five selective serotonin reuptake inhibitors (SSRIs), fluoxetine, fluvoxamine, paroxetine, sertraline, and citalopram, have similar antidepressant efficacy and a similar side effect profile. They differ, however, in their pharmacokinetic properties. Under steady-state concentrations, their half-lives range between 1 and 4 days for fluoxetine (7 and 15 days for norfluoxetine) and between 21 (paroxetine) and 36 (citalopram) hr for the other SSRIs. Sertraline and citalopram show linear and fluoxetine, fluvoxamine, and paroxetine nonlinear pharmacokinetics. SSRIs underlie an extensive metabolism with high interindividual variability, whereby cytochrome P450 (CYP) isoenzymes play a major role. Therefore, resulting blood concentrations are highly variable between individuals. Except for N-demethylated fluoxetine, metabolites of SSRIs do not contribute to clinical actions. Therapeutically effective blood concentrations are unclear so far, although there is evidence for minimal effective and upper-threshold concentrations that should not be exceeded. Paroxetine and, to a lesser degree, fluoxetine and norfluoxetine are potent inhibitors of CYP2D6 and fluvoxamine of CYP1A2 and CYP2C19. This can give rise to drug-drug interactions that may have no effect, lead to intoxication, or improve the therapeutic response. These different pharmacokinetic properties of the five SSRIs, especially their drug-drug interaction potential, should be considered when selecting a distinct SSRI for treatment of depression or other disorders with a suggested dysfunction of the serotonergic system in the brain.

Citalopram and desmethylcitalopram in vitro: human cytochromes mediating transformation, and cytochrome inhibitory effects

BACKGROUND

Biotransformation of citalopram (CT), a newly available selective serotonin reuptake inhibitor antidepressant, to its principal metabolite, desmethycitalopram (DCT), and the capacity of CT and DCT to inhibit human cytochromes P450, were studied in vitro.

METHODS

Formation of DCT from CT was evaluated using human liver microsomes and microsomes from cDNA-transfected human lymphoblastoid cells. Cytochrome inhibition by CT and DCT in liver microsomes was studied using isoform-specific index reactions.

RESULTS

Formation of DCT from CT in liver microsomes had a mean apparent K(m) of 174 mumol/L. Coincubation with 1 mumol/L ketoconazole reduced reaction velocity to 46 to 58% of control values, while omeprazole, 10 mumol/L, reduced velocity to 80% of control. Quinidine produced minimal inhibition. DCT was formed from CT by heterologously expressed human P450-2D6, -2C19, -3A4. After accounting for the relative abundance of individual cytochromes, 3A4 and 2C19 were estimated to make major contributions to net reaction velocity, with a possible contribution of 2D6 at therapeutic CT concentrations. CT and DCT themselves produced negligible inhibition of 2C9, 2E1, and 3A, and only weak inhibition of 1A2, 2C19, and 2D6.

CONCLUSIONS

Formation of DCT from CT is mediated mainly by P450-3A4 and 2C19, with an additional contribution of 2D6. CT at therapeutic doses in humans may produce a small degree of inhibition of P450-1A2, -2C19, and -2D6, but negligible inhibition of P450-2C9, -2E1, and -3A.

Metabolism of some "second"- and "fourth"-generation antidepressants: iprindole, viloxazine, bupropion, mianserin, maprotiline, trazodone, nefazodone, and venlafaxine

1. This review summarizes the major known aspects of the metabolism of second-generation (iprindole, viloxazine, bupropion, mianserin, maprotiline, and trazodone) and fourth-generation (nefazodone and venlafaxine) antidepressants. 2. Discussions about specific enzymes involved and about possible pharmacokinetic drug-drug interactions, particularly as they relate to cytochrome P450 enzymes, are provided.

Metabolism and pharmacokinetics of selective serotonin reuptake inhibitors

1. Five drugs with the predominant pharmacologic effect of inhibiting the neuronal reuptake of serotonin are available worldwide for clinical use. This class of psychoactive drugs, known as selective serotonin reuptake inhibitors (SSRIs), is comprised of fluoxetine, sertraline, paroxetine, fluvoxamine, and citalopram. 2. The SSRIs appear to share similar pharmacodynamic properties which translate to efficacy in the treatment of depression and anxiety syndromes. The drugs are differentiated by their pharmacokinetic properties with regard to stereochemistry, metabolism, inhibition of cytochrome enzymes, and participation in drug-drug interactions. Studies focusing on the relationship of plasma drug concentration to therapeutic and adverse effects have not confirmed the value of plasma concentration monitoring. 3. This review summarizes the metabolism and relevant pharmacokinetic properties of the SSRIs.

Metabolism of anxiolytics and hypnotics: benzodiazepines, buspirone, zoplicone, and zolpidem

1. The benzodiazepines are among the most frequently prescribed of all drugs and have been used for their anxiolytic, anticonvulsant, and sedative/hypnotic properties. Since absorption rates, volumes of distribution, and elimination rates differ greatly among the benzodiazepine derivatives, each benzodiazepine has a unique plasma concentration curve. Although the time to peak plasma levels provides a rough guide, it is not equivalent to the time to clinical onset of effect. The importance of alpha and beta half-lives in the actions of benzodiazepines is discussed. 2. The role of cytochrome P450 isozymes in the metabolism of benzodiazepines and in potential pharmacokinetic interactions between the benzodiazepines and other coadministered drugs is discussed. 3. Buspirone, an anxiolytic with minimal sedative effects, undergoes extensive metabolism, with hydroxylation and dealkylation being the major pathways. Pharmacokinetic interactions of buspirone with other coadministered drugs seem to be minimal. 4. Zopiclone and zolpidem are used primarily as hypnotics. Both are extensively metabolized; N-demethylation, N-oxidation, and decarboxylation of zopiclone occur, and zolpidem undergoes oxidation of methyl groups and hydroxylation of a position on the imidazolepyridine ring system. Zopiclone has a chiral centre, and demonstrates stereoselective pharmacokinetics. Metabolic drug-drug interactions have been reported with zopiclone and erythromycin, trimipramine, and carbamazepine. Reports to date indicate minimal interactions of zolpidem with coadministered drugs; however, it has been reported to affect the Cmax and clearance of chlorpromazepine and to decrease metabolism of the antiviral agent ritonavin. Since CYP3A4 has been reported to play an important role in metabolism of zolpidem, possible interactions with drugs which are substrates and/or inhibitors of that CYP isozyme should be considered.

Polymorphic cytochromes P450 and drugs used in psychiatry

1. The cytochrome P450 monooxygenases, CYP2D6, CYP2C19, and CYP2C9, display polymorphism. CYP2D6 and CYP2C19 have been studied extensively, and despite their low abundance in the liver, they catalyze the metabolism of many drugs. 2. CYP2D6 has numerous allelic variants, whereas CYP2C19 has only two. Most variants are translated into inactive, truncated protein or fail to express protein. 3. CYP2C9 is expressed as the wild-type enzyme and has two variants, in each of which one amino acid residue has been replaced. 4. The nucleotide base sequences of the cDNAs of the three polymorphic genes and their variants have been determined, and the proteins derived from these genes have been characterized. 5. An absence of CYP2D6 and/or CYP2C19 in an individual produces a poor metabolizer (PM) of drugs that are substrates of these enzymes. 6. When two drugs that are substrates for a polymorphic CYP enzyme are administered concomitantly, each will compete for that enzyme and competitively inhibit the metabolism of the other substrate. This can result in toxicity. 7. Patients can be readily phenotyped or genotyped to determine their CYP2D6 or CYP2C19 enzymatic status. Poor metabolizers (PMs), extensive metabolizers (EMs), and ultrarapid metabolizers (URMs) can be identified. 8. Numerous substrates and inhibitors of CYP2D6, CYP2C19, and CYP2C9 are identified. 9. An individual's diet and age can influence CYP enzyme activity. 10. CYP2D6 polymorphism has been associated with the risk of onset of various illnesses, including cancer, schizophrenia, Parkinson's disease, Alzheimer's disease, and epilepsy.

Metabolism of monoamine oxidase inhibitors

1. The principal routes of metabolism of the following monoamine oxidase inhibitors (MAOIs) are described: phenelzine, tranylcypromine, pargyline, deprenyl, moclobemide, and brofaromine. 2. Acetylation of phenelzine appears to be a minor metabolic pathway. Phenelzine is a substrate as well as an inhibitor of MAO, and major identified metabolites of phenelzine include phenylacetic acid and p-hydroxyphenylacetic acid. Phenelzine also elevates brain GABA levels, and as yet unidentified metabolites of phenelzine may be responsible for this effect. beta-Phenylethylamine is a metabolite of phenelzine, and there is indirect evidence that phenelzine may also be ring-hydroxylated and N-methylated. 3. Tranylcypromine is ring-hydroxylated and N-acetylated. There is considerable debate about whether or not it is metabolized to amphetamine, with most of studies in the literature indicating that this does not occur. 4. Pargyline and R(-)-deprenyl, both propargylamines, are N-demethylated and N-depropargylated to yield arylalkylamines (benzylamine, N-methylbenzylamine, and N-propargylbenzylamine in the case of pargyline and amphetamine, N-methylamphetamine and N-propargylamphetamine in the case of deprenyl). These metabolites may then undergo further metabolism, e.g., hydroxylation. 5. Moclobemide is biotransformed by C- and N-oxidation on the morpholine ring and by aromatic hydroxylation. An active metabolite of brofaromine is formed by O-demethylation. It has been proposed that another as yet unidentified active metabolite may also be formed in vivo. 6. Preliminary results indicate that several of the MAOIs mentioned above are substrates and/or inhibitors of various cytochrome P450 (CYP) enzymes, which may result in pharmacokinetic interactions with some coadministered drugs.

Metabolism of tricyclic antidepressants

1. Despite the considerable advances in the treatments available for mood disorders over the past generation, tricyclic antidepressants (TCAs) remain an important option for the pharmacotherapy of depression. 2. The pharmacokinetics of TCAs are characterized by substantial presystemic first-pass metabolism, a large volume of distribution, extensive protein binding, and an elimination half-life averaging about 1 day (up to 3 days for protriptyline). 3. Clearance of tricyclics is dependent primarily on hepatic cytochrome P450 (CYP) oxidative enzymes. Although the activities of some P450 isoenzymes are largely under genetic control, they may be influenced by external factors, such as the concomitant use of other medications or substances. Patient variables, such as ethnicity and age, also affect TCA metabolism. The impact of gender and related reproductive issues is coming under increased scrutiny. 4. Metabolism of TCAs, especially their hydroxylation, results in the formation of active metabolites, which contribute to both the therapeutic and the adverse effects of these compounds. 5. Renal clearance of the polar metabolites of TCAs is reduced by normal aging, accounting for much of the increased risk of toxicity in older patients. 6. Knowledge of factors affecting the metabolism of TCAs can further the development and understanding of newer antidepressant medications.

Systematic review and guide to selection of selective serotonin reuptake inhibitors

A meta-analysis of 20 short term comparative studies of 5 selective serotonin reuptake inhibitors (SSRIs; citalopram, fluoxetine, fluvoxamine, paroxetine and sertraline) has shown no difference in efficacy between individual compounds but a slower onset of action of fluoxetine. There were suggestions that fluoxetine caused more agitation, weight loss and dermatological reactions than the other SSRIs. More patients discontinued fluvoxamine and fewer patients stopped sertraline because of adverse effects than their comparator SSRIs. The most common adverse reactions to the SSRIs were gastrointestinal (especially nausea) and neuropsychiatric (particularly headache and tremor). Data from the Committee on Safety of Medicines showed more reports of suspected reactions (including discontinuation reactions) to paroxetine, and of gastrointestinal reactions to fluvoxamine and paroxetine, than the other SSRIs during their first 2 years of marketing. Prescription-event monitoring revealed a higher incidence of adverse events related to fluvoxamine than its comparators. There were higher incidences of gastrointestinal symptoms, malaise, sedation and tremor during treatment with fluvoxamine and of sedation, tremor, sweating, sexual dysfunction and discontinuation reactions with paroxetine. Fluoxetine was not associated with a higher incidence of suicidal, aggressive and related events than the other SSRIs. Patients have survived large overdoses of each of the compounds, but concern has been expressed over 6 fatalities following overdoses of citalopram. Drug interactions mediated by cytochrome P450 enzymes are theoretically less likely to occur during treatment with citalopram and sertraline, but there is a sparsity of clinical data to support this. Methodological difficulties and price changes do not allow choice for recommendations on the choice of SSRI based on pharmacoeconomic data. Taking into account the strengths and weaknesses of the methods used to compare drugs, guidelines to the selection of individual SSRIs in clinical practice are proposed. Citalopram should be avoided in patients likely to take overdoses. Fluoxetine may not be the drug of first choice for patients in whom a rapid antidepressant effect is important or for those who are agitated, but it may have advantages over other SSRIs in patients who are poorly compliant with treatment and those who have previously had troublesome discontinuation symptoms. Fluvoxamine, and possibly paroxetine, should not be used as first choice in patients especially prone to SSRI-related adverse reactions, while paroxetine should be avoided if previous discontinuation of treatment was troublesome. When in doubt about the risks of drug interactions, citalopram or sertraline should be considered given the lower theoretical risk of interactions.

Debate resolved: there are differential effects of serotonin selective reuptake inhibitors on cytochrome P450 enzymes

In 1993, it was first proposed that an important difference between selective serotonin reuptake inhibitors (SSRIs) was the degree of inhibition of the cytochrome P450 (CYP) enzyme 2D6 that they produced under usually dosing conditions (Preskorn, 1993). Specifically, fluoxetine and paroxetine, in contrast to sertraline, were identified as causing substantial increases in the plasma levels of coadministered drugs, which were principally dependent on CYP 2D6 for their metabolism. Over the next 5 years, this position was hotly contested (Preskorn and Nemeroff, 1997). However, an extensive body of research has now accumulated, which incontrovertibly supports the original position. This paper will reviews this research and extends the discussion to all five SSRIs and four other important CYP enzymes: 1A2, 2C9/10, 2C19, and 3A3/4.

Appetite suppressant drugs as inhibitors of human cytochromes P450: in vitro inhibition of P450-2D6 by D- and L-fenfluramine, but not phentermine

The activity of D-fenfluramine, L-fenfluramine, and phentermine as inhibitors of five human cytochromes P450 was evaluated using human liver microsomes in vitro. All three compounds produced negligible inhibition of P450-1A2, -2C9, -2E1, and -3A. Phentermine also did not inhibit P450-2D6. However, D- and L-fenfluramine significantly inhibited P450-2D6 activity as measured by dextromethorphan O-demethylation, with mean 50% inhibitory concentrations (15.1 microM) within one order of magnitude of that for fluoxetine (2.7 microM). Findings from the in vitro assay are consistent with clinical studies showing significant inhibition of desipramine clearance by coadministration of fenfluramine.

Psychotropic drug metabolism in the cancer patient: clinical aspects of management of potential drug interactions

An overview of drug metabolism, with particular focus on the cytochrome p450 system, is provided in this review. To date, there has been a growing body of literature concerning the cytochrome p450 enzyme, drug-drug interactions and the role of psychotropic medications when co-administered with medications prescribed in the medically ill population. The article provides an ability to cross-reference commonly prescribed medications to their known involvement as substrates, inhibitors or inducers of p450 enzymes. This information will permit the clinician working in an oncologic setting to better predict potential interactions based on available in vitro and in vivo data and choose psychotropics analytically when confronted with a situation of polypharmacy. A knowledge of drug interactions will decrease the uncertainty in prescription of multidrug therapies and minimize the likelihood of diminished drug efficacy or toxic reactions.

Economic consequences of selective serotonin reuptake inhibitor use with drugs also metabolized by the cytochrome P-450 system

Administration of selective serotonin reuptake inhibitors (SSRIs) may increase plasma concentrations of concomitant medications that are also metabolized by the cytochrome P-450 system (CYP-450), in particular by the 2D6 and 3A4 isoenzymes. This may lead to side effects or other clinical events that might be expected to incur higher health-care expenditures. The purpose of this study was to assess whether there was a difference in expenditures during the first 90 days of SSRI therapy with paroxetine or sertraline versus fluoxetine in patients who were also receiving a stable dosage of a nonpsychiatric drug also metabolized by the CYP-450 2D6 or 3A4 isoenzyme systems. A sample of 2445 patients who initiated therapy with an SSRI while receiving a stable dosage of a nonpsychiatric drug was obtained from a private insurance claims database. Multivariate regression techniques were used to estimate total health-care expenditures in the first 90 days after receiving a prescription for an SSRI. After adjusting for nonrandom SSRI prescription patterns and controlling for observable and unobservable characteristics that might correlate with SSRI selection, total health-care expenditures were 95% higher for patients initiating SSRI therapy with sertraline or paroxetine compared with fluoxetine. Results suggest that there are cost differences between SSRIs during concomitant therapy with drugs also metabolized by the CYP-450 system. To determine whether there are additional differences in expenditures across SSRIs, future research should focus on (1) simultaneous initiation of SSRI therapy and a nonpsychiatric drug also metabolized by the CYP-450 enzyme system, and (2) addition of nonpsychiatric drug therapy to stable SSRI therapy. Relationships between additional expenditures, drug interactions, and clinical outcomes should also be assessed directly using medical records and patient interview data that are not available in claims-based files.

Pharmacokinetic interactions involving clozapine

BACKGROUND

Metabolism of clozapine is complex and not fully understood. Pharmacokinetic interactions with other drugs have been described but, in some cases, their mechanism is unknown.

METHOD

Published trials and case reports relevant to the human metabolism of clozapine and to suspected pharmacokinetic interactions were reviewed.

RESULTS

Metabolism of clozapine appears to be largely controlled by the function of the hepatic cytochrome p450IA2 (CYPIA2). Compounds which induce CYPIA2 activity (carbamazepine, tobacco smoke) may reduce plasma clozapine levels. Inhibitors of CYPIA2 (caffeine, erythromycin) have the opposite effect. Drugs which inhibit the hepatic cytochrome p4502D6 (CYP2D6) have also been reported to elevate plasma clozapine levels. The mechanism of this interaction is unclear.

CONCLUSIONS

The co-administration of clozapine and compounds reported to alter its metabolism should be avoided where possible. A host of other interactions can be predicted and so caution should be exercised when co-administering drugs which affect the function of CYPIA2 and CYP2D6. The pharmacokinetics of clozapine require further investigation so that its safe use can be assured.

The clinical relevance of preclinical data: mirtazapine, a model compound

This paper discusses how in vitro and preclinical in vivo studies might be of help for the interpretation and prediction of possible clinically relevant effects. The examples given refer to the data obtained with mirtazapine, a novel antidepressant with a dual mechanism of action, which can be best summarized as a noradrenergic and specific serotonergic antidepressant. Preclinical data on mirtazapine have shown that (i) its binding to plasma proteins is relatively low and non-specific; (ii) the contribution of its metabolites to the pharmacologic effect is negligible; (iii) it possesses high bioavailability, resulting in a low variance between individuals; (iv) it has no inducing or inhibiting effects on hepatic P450 enzymes; (v) it has a very low potential for clinically relevant pharmacokinetic interactions with other drugs; and (vi) its disposition is independent of polymorphic CYP2D6 activity. The available preclinical data on mirtazapine could be used to advise clinicians and to guide clinical practice.