Bupropion plasma levels and CYP2D6 phenotype

Sensitivity, specificity and limitation of in vitro hippocampal slice and neuron-based assays for assessment of drug-induced seizure liability

An effective in vitro screening assay to detect seizure liability in preclinical development can contribute to better lead molecule optimization prior to candidate selection, providing higher throughput and overcoming potential brain exposure limitations in animal studies. This study explored effects of 26 positive and 14 negative reference pharmacological agents acting through different mechanisms, including 18 reference agents acting on glutamate signaling pathways, in a brain slice assay (BSA) of adult rat to define the assay's sensitivity, specificity, and limitations. Evoked population spikes (PS) were recorded from CA1 pyramidal neurons of hippocampus (HPC) in the BSA. Endpoints for analysis were PS area and PS number. Most positive references (24/26) elicited a concentration-dependent increase in PS area and/or PS number. The negative references (14/14) had little effect on the PS. Moreover, we studied the effects of 15 reference agents testing positive in the BSA on spontaneous activity in E18 rat HPC neurons monitored with microelectrode arrays (MEA), and compared these effects to the BSA results. From these in vitro studies we conclude that the BSA provides 93% sensitivity and 100% specificity in prediction of drug-induced seizure liability, including detecting seizurogenicity by 3 groups of metabotropic glutamate receptor (mGluR) ligands. The MEA results seemed more variable, both quantitatively and directionally, particularly for endpoints capturing synchronized electrical activity. We discuss these results from the two models, comparing each with published results, and provide potential explanations for differences and future directions.

Delirium associated with concomitant use of duloxetine and bupropion in an elderly patient

Delirium is common in daily practice. Drug-induced delirium constitutes approximately one-third of all cases of delirium. In cases characterized by the limited efficacy of a single antidepressant, a combination of two antidepressants is required, which may induce a complex drug-drug interaction. We reviewed a case of duloxetine- and bupropion-related delirium in an elderly male patient in our clinical practice. The patient was diagnosed with major depressive disorder and was treated with duloxetine. However, he developed delirium 10 days after bupropion was added to his treatment regimen. Three days after the cessation of bupropion, his delirious condition gradually improved. Duloxetine and bupropion are both cytochrome P450 2D6 inhibitors that may result in a higher level of hydroxybupropion. An increased level of hydroxybupropion may cause the elevation of dopamine and a risk of subsequent delirium. We should be aware of the risk of delirium induced by drug-drug interactions.

Insights into CYP2B6-mediated drug-drug interactions

Mounting evidence demonstrates that CYP2B6 plays a much larger role in human drug metabolism than was previously believed. The discovery of multiple important substrates of CYP2B6 as well as polymorphic differences has sparked increasing interest in the genetic and xenobiotic factors contributing to the expression and function of the enzyme. The expression of CYP2B6 is regulated primarily by the xenobiotic receptors constitutive androstane receptor (CAR) and pregnane X receptor (PXR) in the liver. In addition to CYP2B6, these receptors also mediate the inductive expression of CYP3A4, and a number of important phase II enzymes and drug transporters. CYP2B6 has been demonstrated to play a role in the metabolism of 2%–10% of clinically used drugs including widely used antineoplastic agents cyclophosphamide and ifosfamide, anesthetics propofol and ketamine, synthetic opioids pethidine and methadone, and the antiretrovirals nevirapine and efavirenz, among others. Significant inter-individual variability in the expression and function of the human CYP2B6 gene exists and can result in altered clinical outcomes in patients receiving treatment with CYP2B6-substrate drugs. These variances arise from a number of sources including genetic polymorphism, and xenobiotic intervention. In this review, we will provide an overview of the key players in CYP2B6 expression and function and highlight recent advances made in assessing clinical ramifications of important CYP2B6-mediated drug–drug interactions.

Fluvoxamine-associated oscillopsia and a role for personalized medication dosing

A 60-year-old woman reported horizontal "shimmering" movement while reading crossword puzzles when using fluvoxamine, bupropion, quetiapine, lithium, and levothyroxine. This visual disturbance, likely oscillopsia, started after the fluvoxamine was added and waned as the fluvoxamine was tapered, disappearing after the drug was discontinued. Genetic testing to explore how the patient metabolizes these medications combined with YouScript® interaction analysis suggest that she may have had abnormally high plasma concentrations of fluvoxamine during this time. Oscillopsia may be a novel dose-dependent side effect of fluvoxamine. Genetic testing combined with YouScript has the potential to discover novel drug side effects, elucidate drug interactions and guide future prescribing decisions.

Drug metabolites as cytochrome p450 inhibitors: a retrospective analysis and proposed algorithm for evaluation of the pharmacokinetic interaction potential of metabolites in drug discovery and development

Understanding drug-drug interactions (DDIs) is a key component of clinical practice ensuring patient safety and efficacy of medicines. The role of drug metabolites in DDIs is a developing area of science, and has been recently highlighted in a draft regulatory guidance. The guidance states that metabolites representing ≥25% of the parent drug's area under the plasma concentration/time curve and/or >10% of exposure of total drug-related material should trigger in vitro characterization of metabolites for cytochrome P450 inhibition and propensity for DDIs. The relationship between in vitro cytochrome P450 inhibitory potency, systemic exposure, and DDI potential of drug metabolites was examined using the Pfizer development database to identify compounds with pre-existing in vivo biotransformation data, where circulating metabolites were identified in humans. The database yielded 33 structurally diverse compounds with collectively 115 distinct circulating metabolites. Of these, 52% (60/115) achieved exposures >25% of parent drug levels as judged from mass balance/metabolite identification studies. It was noted that 14 metabolite standards for 12 parent drugs had been synthesized, monitored in clinical studies, and examined for cytochrome P450 inhibition. For the 14 metabolite/parent drug pairs, no clinically relevant DDIs were expected to occur against the major human cytochrome P450 isoforms. A review of the literature for parent/metabolite DDI information was also conducted to examine trends using a larger data set. Leveraging the analysis of both internal and literature-based data sets, an algorithm was devised for use in drug discovery/early development to assess cytochrome P450 inhibitory potential of drug metabolites and the propensity to cause a clinically relevant DDI.

Progressive tremor, truncal ataxia, and acute mental status changes after use of bupropion

An 84-year-old male with stage III chronic kidney disease and a history of multiple psychiatric and medical disorders presented to the emergency department (ED) with new onset proximal leg weakness with tremor upon standing, truncal ataxia, and myoclonic jerks of the upper extremity that had progressively worsened over three weeks. Magnetic resonance imaging and head computed tomography showed no acute change from baseline. After admission, the patient reported visual hallucinations, vertigo, and slurred speech, and displayed nocturnal agitation/delirium. These symptoms were managed with risperidone. Prior to admission, the most recent medication change was the initiation of bupropion 100 mg extended-release twice daily. Bupropion was titrated to 150 mg twice daily over the three weeks prior to the ED visit. Gradual tapering of the bupropion dose was started after admission. Symptoms of agitation, delirium, speech, and motor disturbances decreased 36 to 48 hours after bupropion dose was lowered to 75 mg daily, and risperidone was changed to quetiapine. The patient was discharged to short-term rehabilitation with return of mental status to baseline. Bupropion and quetiapine were discontinued at discharge from the rehabilitation center. Case reports exist for acute psychotic and parkinsonian symptoms after administration of bupropion and bupropion extended-release, but none exist for the combination of focal neurologic deficits and psychotic symptoms found in this patient's presentation. Limited pharmacokinetic data in the elderly and those with renal impairment suggest that this patient population may have reduced clearance of bupropion. Dose adjustment should be considered in such patients and signs of toxicity closely monitored. Adverse reactions to bupropion should be considered if a patient presents with acute neurologic or psychotic symptoms after initiation or dose modification of bupropion.

The impact of CYP allelic variation on antidepressant metabolism: a review

Psychiatric diseases that are treated with antidepressants are the leading causes of morbidity and mortality in humankind. Although antidepressants are generally well tolerated and widely available, they are not equally effective in all patients and only 35 - 45% of patients treated for depression with these drugs recover to premorbid levels of functioning. There is a need for an effective, individualized approach to antidepressant selection. One promising lead in the development of personalized medicine is the emerging field of pharmacogenomics, whereby pharmacologic agents are selected on the basis of the genotype of patients, with particular attention to drug targets and phase I- and phase II-metabolizing enzymes. This review article focuses on phase I antidepressant-metabolizing enzymes (e.g., relevant CYP enzymes). The authors first briefly review CYP nomenclature, the relevant members of the CYP superfamily and their alleles, the metabolic categories and CYP antidepressant substrates, inhibitors and inducers. The literature on the impact of CYP polymorphisms on antidepressant metabolism are also reviewed.

Review of the pharmacology and clinical profile of bupropion, an antidepressant and tobacco use cessation agent

Bupropion hydrochloride ((+/-)-2-tert-butylamino)-3'-chloropropiophenone x HCl) is a nonselective inhibitor of the dopamine transporter (DAT) and the norepinephrine transporter (NET) and is also an antagonist at neuronal nicotinic acetylcholine receptors (nAChRs). In animal models used commonly to screen for antidepressant activity, bupropion shows a positive response. Also using animal models, bupropion has been shown to attenuate nicotine-induced unconditioned behaviors, to share or enhance discriminative stimulus properties of nicotine and to have a complex effect on nicotine self-administration, i.e., low doses augmenting nicotine self-administration and high doses attenuating self-administration. Current studies show that bupropion facilitates the acquisition of nicotine conditioned place preference in rats, further suggesting that bupropion enhances the rewarding properties of nicotine. Bupropion has been shown to attenuate the expression of nicotine withdrawal symptoms in both animal models and human subjects. With respect to relapse, current studies show that bupropion attenuates nicotine-induced reinstatement in rats, but large individual differences are apparent. Clinically, bupropion is used as a treatment for two indications, as an antidepressant, the indication for which it was developed, and as a tobacco use cessation agent. In clinical trials, bupropion is being tested as a candidate treatment for psychostimulant drug abuse, attention-deficit hyperactivity disorder (ADHD) and obesity. Bupropion is available in three bioequivalent oral formulations, immediate release (IR), sustained release (SR), and extended release (XL). Extensive hepatic metabolism of bupropion produces three pharmacologically active metabolites, which may contribute to its clinical profile.

Antidepressant-drug interactions are potentially but rarely clinically significant

The salient pharmacologic features of the selective serotonin reuptake inhibitors (SSRIs) discovered in the late 1980s included an in vitro ability to inhibit various cytochrome P450 enzymes (CYPs). Differences in potency among the SSRIs for CYP inhibition formed the basis of a marketing focus based largely on predictions of in vivo pharmacokinetic drug interactions from in vitro data, conclusions derived from case reports, and the extrapolation of the results of pharmacokinetic studies conducted in healthy volunteers to patients. Subsequently introduced antidepressants have undergone a similar post hoc scrutiny for potential drug-drug interactions. Concern for the untoward consequences of drug interactions led the FDA to publish guidance for the pharmaceutical industry in 1997 recommending that in vitro metabolic studies be conducted early in the drug development process to evaluate inhibitory properties toward the major CYPs. However, the prevalence of clinically significant enzyme inhibition interactions occurring during antidepressant treatment remains poorly defined despite millions of exposures. Although lack of evidence does not equate to evidence of absence, sparse epidemiological and post-marketing surveillance data do not substantiate a conclusion that widespread morbidity results from antidepressant-induced drug interactions. This commentary discusses points of uncertainty and controversy in the field of drug interactions, notes areas where inadequate data exist, and suggests explanations for a low prevalence of serious interactions. The conclusion is drawn that drug interactions from CYP inhibition caused by the newer antidepressants are potentially, but rarely, clinically significant.

The impact of the CYP2D6-polymorphism on dose recommendations for current antidepressants

Cytochrome P450 CYP2D6 represents an extensively characterized polymorphic drug-metabolizing enzyme. The CYP2D6-gene is highly polymorphic and more than 70 different alleles are known currently. The activity of the enzyme markedly varies among individuals from poor to intermediate and extensive up to ultrarapid metabolism on the basis of the polymorphism of the CYP2D6 gene. Association studies provide growing evidence for the clinical importance of the CYP2D6 polymorphism investigating whether the CYP2D6 genotype distribution differs from that of the normal population either in patients with marked adverse effects or in nonresponders during treatment with CYP2D6 substrates. However, these scientifically important studies present less information for dose adjustments necessary to individualize pharmacotherapy in a given clinical case. With respect to psychopharmacological drug metabolism several antidepressants were characterized as being CYP2D6 substrates. Thus, this review summarizes dose recommendations of current antidepressants.

Population pharmacokinetic analysis of drug-drug interactions among risperidone, bupropion, and sertraline in CF1 mice

RATIONALE

Accumulating evidence indicates that modulation of the activity of cytochrome P450 (CYP) enzymes and the multidrug resistance transporter P-glycoprotein (P-gp) is responsible for many drug-drug interactions.

OBJECTIVES

The potential interaction of risperidone (RISP), which is metabolized by 2D6 and transported across the blood brain barrier (BBB) by P-gp, was studied in combination with bupropion (BUP) and also with sertraline (SERT).

METHODS

BUP, SERT, and RISP were administered intraperitoneally into CF1 mice at doses of 100, 10, and 1 microg/g mouse, respectively. Plasma and brain samples were collected at timed intervals from 0.5 to 6 h. A pharmacokinetic analysis was performed using both traditional compartmental modeling and a population pharmacokinetic approach.

RESULTS

BUP increased the RISP plasma (5.9-fold, P<0.01) and brain (2.2-fold, P<0.01) area under the drug concentration vs time curve (AUC), but did not alter the brain-to-plasma concentration ratio. SERT did not significantly change the plasma AUC of RISP and 9-hydroxy-RISP, but increased the brain AUC of RISP and 9-hydroxy-RISP 1.5-fold (P<0.05) and 5-fold (P<0.01), respectively. RISP did not produce significant alterations of plasma or brain concentrations of BUP. It increased the plasma AUC and elimination half-life (T1/2e) of desmethyl-SERT 12.5-fold (P<0.01) and 107-fold (P<0.01), respectively.

CONCLUSIONS

These results suggest that pharmacokinetic interactions exist among these three psychoactive drugs involving inhibition of drug metabolizing enzymes and/or P-gp and other drug transporters present in the BBB. The mechanisms and consequences of these interactions require further study in humans to establish clinical relevance.

Inhibition of CYP2D6 activity by bupropion

The purpose of this study was to assess the effect of bupropion on cytochrome P450 2D6 (CYP2D6) activity. Twenty-one subjects completed this repeated-measures study in which dextromethorphan (30-mg oral dose) was administered to smokers at baseline and after 17 days of treatment with either bupropion sustained-release (150 mg twice daily) or matching placebo. Subjects quit smoking 3 days before the second dextromethorphan administration. To assess CYP2D6 activity, urinary dextromethorphan/dextrorphan metabolic ratios were calculated after an 8-hour urine collection. Thirteen subjects received bupropion, and 8 received placebo. In those receiving active medication, the dextromethorphan/dextrorphan ratio increased significantly at the second assessment relative to the first (0.012 +/- 0.012 vs. 0.418 +/- 0.302; P < 0.0004). No such change was observed in those randomized to placebo (0.009 +/- 0.010 vs. 0.017 +/- 0.015; P = NS). At baseline, all subjects were phenotypically extensive CYP2D6 metabolizers (metabolic ratio <0.3); after treatment, 6 of 13 subjects receiving bupropion, but none of those receiving placebo, had metabolic ratios consistent with poor CYP2D6 metabolizers. Bupropion is therefore a potent inhibitor of CYP2D6 activity, and care should be exercised when initiating or discontinuing bupropion use in patients taking drugs metabolized by CYP2D6.

A case of prolonged seizure activity after combined use of bupropion and clomipramine

A case is reported of seizure development after combined use of bupropion and clomipramine. Electroencephalography revealed frequent generalized spike and wave complexes prominent on both frontal areas. These newly developed epileptiform discharges persisted even after discontinuation of both drugs.

Pharmacogenetics of antidepressants and antipsychotics: the contribution of allelic variations to the phenotype of drug response

Genetic factors contribute to the phenotype of drug response. We systematically analyzed all available pharmacogenetic data from Medline databases (1970-2003) on the impact that genetic polymorphisms have on positive and adverse reactions to antidepressants and antipsychotics. Additionally, dose adjustments that would compensate for genetically caused differences in blood concentrations were calculated. To study pharmacokinetic effects, data for 36 antidepressants were screened. We found that for 20 of those, data on polymorphic CYP2D6 or CYP2C19 were found and that in 14 drugs such genetic variation would require at least doubling of the dose in extensive metabolizers in comparison to poor metabolizers. Data for 38 antipsychotics were examined: for 13 of those CYP2D6 and CYP2C19 genotype was of relevance. To study the effects of genetic variability on pharmacodynamic pathways, we reviewed 80 clinical studies on polymorphisms in candidate genes, but those did not for the most part reveal significant associations between neurotransmitter receptor and transporter genotypes and therapy response or adverse drug reactions. In addition associations found in one study could not be replicated in other studies. For this reason, it is not yet possible to translate pharmacogenetic parameters fully into therapeutic recommendations. At present, antidepressant and antipsychotic drug responses can best be explained as the combinatorial outcome of complex systems that interact at multiple levels. In spite of these limitations, combinations of polymorphisms in pharmacokinetic and pharmacodynamic pathways of relevance might contribute to identify genotypes associated with best and worst responders and they may also identify susceptibility to adverse drug reactions.

Treatment of Anxiety and Depression in Transplant Patients

Depressive and anxiety disorders appear during the transplant process due to psychological stressors, medications and physiological disturbances. Treatment is necessary to prevent impact on patient compliance, morbidity and mortality. Psychotropic medications provide an effective option, although most are only available as oral formulations. Because of this, they are more susceptible to alterations in pharmacokinetic behaviour arising from organ dysfunction in the pretransplant period. Kinetics are also an issue when considering potential drug-drug interactions before and after transplantation. Prior to transplant, organ dysfunction can change the pharmacokinetic behaviour of some psychotropic agents, requiring adjustment of dosage and schedules. Thoracic or abdominal organ failure may reduce drug absorption through disturbances in intestinal motility, perfusion and function. Cirrhotic patients experience increased drug bioavailability due to portosystemic shunting, and thus dosage is adjusted downward. In contrast, dosage needs to be raised when peripheral oedema expands the drug distribution volume for hydrophilic and protein-bound agents. Drug clearance for most psychotropic medications is dependent upon hepatic metabolism, which is often disrupted by endstage organ disease. Selection of drugs or their dosage may need to be adjusted to lower the risk of drug accumulation. Further adjustments in dosage may be called for when renal failure accompanies thoracic or abdominal organ failure, resulting in further impairment of clearance. Studies regarding the treatment of anxiety and depressive disorders in the medically ill are limited in number, but recommendations are possible by review of clinical and pharmacokinetic data. Selective serotonin reuptake inhibitors are well tolerated and efficacious for depression, panic disorder and post-traumatic stress disorder. Adjustments in dosage are required when renal or hepatic impairment is present. Among them, citalopram and escitalopram appear to have the least risk of drug-drug interactions. Paroxetine has demonstrated evidence supporting its use with generalised anxiety disorder. Venlafaxine is an alternative option, beneficial in depression, post-traumatic stress and generalised anxiety disorders. Nefazodone may also be considered, but there is some risk of hepatotoxicity and interactions with immunosuppressant drugs. Mirtazapine still needs to be studied further in anxiety disorders, but can be helpful for depression accompanied by anorexia and insomnia. Bupropion is effective in the treatment of depression, but data are sparse about its use in anxiety disorders. Psychostimulants are a unique approach if rapid onset of antidepressant action is desired. Acute or short-term anxiolysis is obtained with benzodiazepines, and selection of particular agents entails consideration of distribution rate, half-life and metabolic route.

Therapeutic drug monitoring of non-tricyclic antidepressant drugs

Therapeutic drug monitoring (TDM) of many of the tricyclic antidepressants (TCAs) has been demonstrated to be of clear clinical value. This article reviews studies of TDM for the selective serotonin reuptake inhibitors (SSRIs) and other non-tricyclic antidepressants such as venlafaxine, nefazodone, trazodone, mianserin and bupropion. No definitive therapeutic concentrations have been demonstrated for these agents, nor have levels indicative of toxicity been reported. The major benefit of TDM for these agents would appear to be in the assessment of the apparently treatment-refractory depressed patient, to determine whether such lack of response is related to inadequate levels that would suggest either poor compliance, ultra-rapid metabolism, or drug interactions leading to induction of metabolising enzymes. Potential future applications of TDM, in conjunction with genotyping of cytochrome P450 enzymes and pharmacogenomic evaluations, are discussed.

Safety issues in pharmacotherapy for smoking in patients with cardiovascular disease

Twenty percent of patients with cardiovascular disease smoke, and smoking cessation results in a dramatic decline in the relative risk of future cardiovascular events. Questions regarding the safety of nicotine-replacement therapy and bupropion SR for smoking cessation in patients with cardiovascular disease have arisen, in particular because of potential hemodynamic effects of these agents. There have been several randomized, controlled, clinical trials testing the safety of transdermal nicotine in patients with cardiovascular disease that failed to show an increased risk for cardiac events in active treatment conditions compared with placebo. Efficacy trials conducted in other patient populations also support the safety of nicotine-replacement use in cardiac disease patients. To date there is one randomized controlled trial to test bupropion for smoking cessation conducted in this population. Studies to test the efficacy of bupropion for smoking cessation and depression suggest it is safe to use in cardiac disease patients despite recent case reports of adverse events associated with bupropion use. Nicotine-replacement therapy and bupropion significantly increase long-term smoking cessation rates, and the benefits of cessation exceed the risks for pharmacotherapy in patients with cardiovascular disease.

Treatment of nicotine dependence with bupropion SR: review of its efficacy, safety and pharmacological profile

Bupropion hydrochloride, an atypical antidepressant, is the first non-nicotine product that, in its sustained release form (bupropion SR), has been licensed as an aid for smoking cessation. The specialized literature on bupropion SR and smoking cessation is critically reviewed. The pharmacological profile, dosage and administration, contraindications, as well as the clinical efficacy, safety and tolerability data of bupropion are discussed. Recent reports suggest that its mode of actions might be different to what had originally been proposed. When prescribed appropriately, it appears to be a safe, well-tolerated and effective medication in combination with smoking cessation counselling--for a wide range of smokers, as shown in several multicentre double-blind, placebo-controlled clinical trials. Further research is needed on aspects such as the optimal duration of treatment, the potential role of combination therapy with NRT and psychological interventions, and to establish its effectiveness in smokers with other psychiatric disorders or when used with only minimal support by general practitioners.

Clinically significant drug interactions with antidepressants in the elderly

Pharmacological treatment of depression in old age is associated with an increased risk of adverse pharmacokinetic and pharmacodynamic drug interactions. Elderly patients may have multiple disease states and, therefore, may require a variety of other drugs. In addition to polypharmacy, other factors such as age-related physiological changes, diseases, genetic constitution and diet may alter drug response and, therefore, predispose elderly patients to adverse effects and drug interactions. Antidepressant drugs currently available differ in their potential for drug interactions. In general, older compounds, such as tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs), have a higher potential for interactions than newer compounds, such as selective serotonin reuptake inhibitors (SSRIs) and other relatively novel agents with a more specific mechanism of action. In particular, TCAs and MAOIs are associated with clinically significant pharmacodynamic interactions with many medications frequently prescribed to elderly patients. Moreover, TCAs may be susceptible to pharmacokinetic interactions when given in combination with inhibitors or inducers of the cytochrome P450 (CYP) isoenzymes involved in their metabolism. Because of a more selective mechanism of action, newer antidepressants have a low potential for pharmacodynamic drug interactions. However, the possibility of the serotonin syndrome should be taken into account when drugs affecting serotonergic transmission, such as SSRIs, venlafaxine or nefazodone, are coadministered with other serotonergic agents. Newer agents have a differential potential for pharmacokinetic interactions because of their selective effects on CYP isoenzymes. Within the group of SSRIs, fluoxetine and paroxetine are potent inhibitors of CYP2D6, while fluvoxamine predominantly affects CYP1A2 and CYP2C19 activity. Therefore, these agents should be closely monitored or avoided in elderly patients treated with substrates of these isoforms, especially those with a narrow therapeutic index. On the other hand, citalopram and sertraline have a low inhibitory activity on different drug metabolising enzymes and appear particularly suitable in an elderly population. Among other newer antidepressants, nefazodone is a potent inhibitor of CYP3A4 and its combination with substrates of this isoform should be avoided.

The interaction of medications used in palliative care

Palliative care uses several classes of drugs, which are handled by the CYP P450 system. Interaction of drugs in this setting requires ongoing vigilance by the physician. Phenocopying may be more common than previously realized.

Change from the CYP2D6 extensive metabolizer to the poor metabolizer phenotype during treatment With bupropion

Some data indicate that bupropion inhibits the cytochrome P-450 enzyme CYP2D6, but very little published data is available on the extent of this inhibition. The objective of the present study was to quantify this inhibition in a subject treated with bupropion for smoking cessation. Genotypically, the patient was a CYP2D6 homozygous extensive metabolizer (EM). His CYP2D6 phenotype was assessed using the test drug dextromethorphan before, during, and after treatment with bupropion. During treatment with bupropion, he clearly changed from the EM to the poor metabolizer (PM) phenotype. Although the results from a single patient should be interpreted with great caution, the extent of the interaction indicates that bupropion might be a CYP2D6 inhibitor as potent as the most powerful CYP2D6 inhibitors known, such as quinidine and paroxetine.

Drug interactions with patient-controlled analgesia

Patient-controlled analgesia (PCA) has become standard procedure in the clinical treatment of pain. Its widespread use in patients with all kinds of diseases opens a variety of possible interactions between analgesics used for PCA and other drugs that might be administered concomitantly to the patient. Many of these drug interactions are of little clinical importance. However, some drug interactions have been reported to result in serious clinical problems. Drug interactions can either predominantly affect the pharmacokinetics or pharmacodynamics of the drug. Most important pharmacokinetic drug interactions occur at the level of drug metabolism or protein binding. Acceleration of methadone metabolism caused by cytochrome P450 (CYP) 3A4 induction by antiretroviral drugs or rifampicin (rifampin) has caused methadone withdrawal symptoms. Lack of morphine formation from codeine as a result of CYP2D6 inhibition by quinidine results in an almost complete loss of the analgesic effects of codeine. Alterations of methadone protein binding caused by an inhibition of alpha1-acid glycoprotein synthesis by alkylating substances are another possibility for predominantly pharmacokinetically based drug interactions during PCA. Furthermore, inhibition of P-glycoprotein by anticancer drugs could result in altered transmembrane transport of morphine, methadone or fentanyl, although this has not been shown to be of clinical relevance. Synergistic effects of systemically administered opioids with spinally or topically delivered opioids or anaesthetics have been reported frequently. The same is true for the opioid-sparing effects of coadministered non-opioid analgesics. Antidepressants, anticonvulsants or alpha2-adrenoreceptor agonists have also been shown to exert additive analgesic effects when administered together with an opioid. Inconsistent findings, however, are reported regarding the treatment of patients with opioid-induced nausea and sedation, since coadministration of antiemetics either increased or decreased the respective adverse effects or revealed additional unwanted drug effects.

CYP2D6 and CYP2C19 genotype-based dose recommendations for antidepressants: a first step towards subpopulation-specific dosages

OBJECTIVE

This review aimed to provide distinct dose recommendations for antidepressants based on the genotypes of cytochrome P450 enzymes CYP2D6 and CYP2C19. This approach may be a useful complementation to clinical monitoring and therapeutic drug monitoring.

METHOD

Our literature search covered 32 antidepressants marketed in Europe, Canada, and the United States. We evaluated studies which had compared pharmacokinetic parameters of antidepressants among poor, intermediate, extensive and ultrarapid metabolizers.

RESULTS

For 14 antidepressants, distinct dose recommendations for extensive, intermediate and poor metabolizers of either CYP2D6 or CYP2C19 were given. For the tricyclic antidepressants, dose reductions around 50% were generally recommended for poor metabolizers of substrates of CYP2D6 or CYP2C19, whereas differences were smaller for the selective serotonin reuptake inhibitors.

CONCLUSION

We have provided preliminary average dose suggestions based on the phenotype or genotype. This is a first attempt to apply the new pharmacogenetics to suggest dose-regimens that take the differences in drug metabolic capacity into account.

Drug interactions in palliative care

PURPOSE

This review of drug interactions in palliative care examines the relevant literature in this area and summarizes the information on interactions of drugs, nutrients, and natural products that are used in the palliative care setting. Particular emphasis is placed on describing the newer information on the cytochrome P450 (CYP) system and the interactions of opioids, antidepressants, and the antitussive, dextromethorphan.

METHODS

We performed a search of the MEDLINE database of the time period from 1966 until April 1998, using medical subject headings such as the names of selective serotonin reuptake inhibitors and other relevant medications in palliative care. Literature reviewed included both human and animal articles as well as non-English literature. Bibliographies of these articles and the personal libraries of several palliative care specialists were reviewed. Software developed by The Medical Letter-The Drug Interaction Program was also used.

RESULTS

Drug interactions can be categorized in several ways. Drug-drug interactions are the most well known and can be kinetic, dynamic, or pharmaceutical. Pharmacokinetic interactions can involve CYP 2D6, which acts on drugs such as codeine and is responsible for its conversion to morphine. Poor metabolizers, either genotypic or due to phenocopying, are at risk for undertreatment if not recognized. Pharmacodynamic interactions with dextromethorphan may produce serotonin syndrome.

CONCLUSION

Drug interactions are important in palliative care as in other aspects of medicine. These interactions are similar to those seen in other areas of medical care but have significant consequences in pain management. Failure to recognize these interactions can lead to either overdosing or undertreatment.

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.

Effects of SSRIs on sexual function: a critical review

Sexual problems are highly prevalent in both men and women and are affected by, among other factors, mood state, interpersonal functioning, and psychotropic medications. The incidence of antidepressant-induced sexual dysfunction is difficult to estimate because of the potentially confounding effects of the illness itself, social and interpersonal comorbidities, medication effects, and design and assessment problems in most studies. Estimates of sexual dysfunction vary from a small percentage to more than 80%. This article reviews current evidence regarding sexual side effects of selective serotonin reuptake inhibitors (SSRIs). Among the sexual side effects most commonly associated with SSRIs are delayed ejaculation and absent or delayed orgasm. Sexual desire (libido) and arousal difficulties are also frequently reported, although the specific association of these disorders to SSRI use has not been consistently shown. The effects of SSRIs on sexual functioning seem strongly dose-related and may vary among the group according to serotonin and dopamine reuptake mechanisms, induction of prolactin release, anticholinergic effects, inhibition of nitric oxide synthetase, and propensity for accumulation over time. A variety of strategies have been reported in the management of SSRI-induced sexual dysfunction, including waiting for tolerance to develop, dosage reduction, drug holidays, substitution of another antidepressant drug, and various augmentation strategies with 5-hydroxytryptamine-2 (5-HT2), 5-HT3, and alpha2 adrenergic receptor antagonists, 5-HT1A and dopamine receptor agonists, and phosphodiesterase (PDE5) enzyme inhibitors. Sexual side effects of SSRIs should not be viewed as entirely negative; some studies have shown improved control of premature ejaculation in men. The impacts of sexual side effects of SSRIs on treatment compliance and on patients' quality of life are important clinical considerations.