Effect of ketoconazole on venlafaxine plasma concentrations in extensive and poor metabolisers of debrisoquine

OBJECTIVE

To study the influence of CYP3A4 inhibition by ketoconazole on the disposition of venlafaxine in individuals with different CYP2D6 pheno- and genotypes.

METHODS

In an open two-phase study, 21 healthy volunteers with known CYP2D6 pheno- and genotype [14 extensive metabolisers (EMs), 7 poor metabolisers (PMs)] were given a single oral dose of venlafaxine (50 mg to EMs and 25 mg to PMs). Plasma and urine levels of venlafaxine and its three metabolites were measured and the pharmacokinetics of venlafaxine were determined. After a 2-week washout period, subjects were treated for 2 days with ketoconazole (100 mg twice daily) starting 1 day before the administration of venlafaxine; and the same parameters as for the administration of venlafaxine only were measured.

RESULTS

Data were evaluated from 20 subjects (14 EMs and 6 PMs) who completed the study. The dose-corrected AUC of venlafaxine was on average 2.3 times higher ( P<0.01) and that of its active metabolite O-desmethylvenlafaxine 3.4 times lower ( P<0.0001) in PMs than EMs. There was a good correlation between the debrisoquine metabolic ratio and the ratio between the AUC of venlafaxine and that of O-desmethylvenlafaxine ( Rs=0.93, P<0.002). The majority of subjects showed higher plasma levels of venlafaxine and O-desmethylvenlafaxine upon co-administration of ketoconazole. AUC of venlafaxine significantly increased by 36% and that of O-desmethylvenlafaxine by 26% ( P<0.01). C(max) values increased by 32% and 18%, respectively. The elimination half-life of venlafaxine was unaltered. Three of the PMs displayed marked increases in AUC (81, 126 and 206%) and C(max) (60, 72, 119%) of venlafaxine while the other three showed small or no changes.

CONCLUSIONS

Ketoconazole consistently affected the disposition of venlafaxine in EMs of debrisoquine while the response in PMs was erratic. The precise mechanisms underlying this interaction remain to be elucidated.

Decreased lymphocyte 3H-paroxetine binding in obsessive-compulsive disorder

The pathophysiology of obsessive-compulsive disorder (OCD) is mainly focused on the serotonin (5-HT) system and transporter. The presence of this structure in blood lymphocytes prompted us to investigate it, by means of the specific binding of (3)H-paroxetine ((3)H-PAR), in a group of drug-free OCD patients as compared with healthy control subjects matched for sex and age. Lymphocyte membranes and (3)H-PAR binding were carried out according to standard protocols. The results showed that the patients had a statistically significant lower density of (3)H-PAR-binding sites than the control subjects. On one hand, this finding confirms previous data of an abnormal platelet 5-HT transporter in OCD, on the other it provides the possibility to explore the regulation of this structure in this and other disorders, since lymphocytes are nucleate cells.

Nefazodone poisoning: toxicokinetics and toxicodynamics using continuous data collection

Nefazodone overdose has been reported infrequently. The commonest effects reported are drowsiness, nausea, dizziness, and vomiting, less commonly hypotension and bradycardia. We report a case of single-agent nefazodone poisoning. Serial drug concentrations were taken for quantification of parent drug and metabolites. Clinical findings were documented every 1 to 2 hours. We modeled both the toxicokinetics of nefazodone and correlated this with clinical effects and electrocardiograph (ECG) abnormalities. A 16-year-old female took 2.4 g of nefazodone. She had significant drowsiness in the first 6 hours, associated with hypotension (systolic BP < 90 mmHg; lowest BP 70/30 mmHg) for 18 hours, and mild bradycardia (slowest rate of 56 bpm). She had a prolonged QT/QTc which normalized over 24 hours. She was given charcoal and intravenous fluids and was observed carefully, recovering with no problems. The terminal elimination half-life for nefazodone was 8.3 hours, and its metabolite hydroxy(OH)-nefazodone was 14.6 hours. BP-time curves demonstrated an 18-hour period of hypotension. There was a significant correlation between systolic BPand OH-nefazodone (R2 = 0.602). HR remained between 56 and 66 bpm for 30 hours despite hypotension. QT was significantly correlated with nefazodone (R2 = 0.911) and OH-nefazodone (R2 = 0.797), but no significant relationship between QTc and drug concentrations. The case demonstrates that nefazodone may potentially cause cardiac toxicity, which appears to be concentration-dependent. Although QT was concentration-dependent, this would need confirmation with other cases. Bradycardia, hypotension, and drowsiness are the most significant effects and are maximal in the first 12 hours when parent and metabolite concentrations are high.

Effects of orlistat, a lipase inhibitor, on the pharmacokinetics of three highly lipophilic drugs (amiodarone, fluoxetine, and simvastatin) in healthy volunteers

To investigate the effect of orlistat on the pharmacokinetics of three highly lipophilic drugs (amiodarone, fluoxetine, and simvastatin), the authors performed double-blind, placebo-controlled, randomized two-period crossover (for fluoxetine and simvastatin) or parallel (for amiodarone) studies in healthy volunteers ages 18 to 65 years of a body mass index between 18 and 30 kg/m2. During treatment with orlistat or matching placebo for 5 to 13 1/3 days, a single oral dose of highly lipophilic drug was administered, followed by obtaining serial blood samples for measuring plasma (for fluoxetine and simvastatin) or serum (for amiodarone) concentrations of the lipophilic drug and its active metabolite. Treatments were compared for the pharmacokinetic parameters AUC0-infinity, Cmax, tmax, and t 1/2 of highly lipophilic drugs and active metabolites. Analysis of variance was performed to assess the significance of the sequence effect and provide the variance estimate for the 90% confidence intervals. Subjects were also evaluated for adverse events, vital signs, and clinical and laboratory safety. The absorption of amiodarone (and active metabolite) was significantly reduced by approximately one-quarter using parameters of Cmax and AUC, while no inhibition of absorption was observed for fluoxetine and simvastatin as well as their active metabolites. There were no clinically significant differences in t 1/2 and tmax for all three drugs tested. Due to expected gastrointestinal adverse events known to occur with orlistat, there was a higher incidence of adverse events under regimen B (highly lipophilic drugs and orlistat) than under regimen A (highly lipophilic drugs and placebo). Other adverse events were sporadic and unremarkable. There were no clinically relevant changes in vital signs or laboratory values. In conclusion, except for amiodarone, there was no effect of orlistat on the pharmacokinetics of highly lipophilic drugs when these drugs were taken concomitantly with orlistat.

An evaluation of the potential for pharmacokinetic interaction between escitalopram and the cytochrome P450 3A4 inhibitor ritonavir

BACKGROUND

Depression often coexists with a number of disease states, and patients with a diagnosis of depression often receive multiple medications. Thus, it is desirable to avoid coadministration of agents that have a potential for drug interactions in these patients. Although escitalopram and its metabolites are weak to negligible inhibitors of the cytochrome P450 (CYP) 3A4 isozyme and are therefore unlikely to affect plasma concentrations of ritonavir (a CYP3A4 substrate and prototype CYP3A4 inhibitor), ritonavir may potentially affect plasma concentrations of escitalopram, as CYP3A4 is partially responsible for conversion of escitalopram to its major metabolite, S-demethylcitalopram (S-DCT).

OBJECTIVES

The aim of this study was to investigate the potential for pharmacokinetic interaction between escitalopram and ritonavir after concomitant administration of a single dose of each in healthy young subjects.

METHODS

In this single-center, randomized, open-label, 3-way crossover study, subjects received each of the following: a single dose of escitalopram 20 mg, a single dose of ritonavir 600 mg, and single doses of both escitalopram 20 mg and ritonavir 600 mg. Blood was collected and plasma was analyzed for the pharmacokinetic parameters (maximum plasma concentration [C(max)], time to C(max) [T(max)], area under the plasma concentration-time curve, plasma elimination half-life, oral clearance, and apparent volume of distribution) of escitalopram, S-DCT, and ritonavir.

RESULTS

Of 21 subjects (11 men, 10 women; mean [SD] age, 28.4 [4.4] years) who were enrolled, 18 completed the study. After concomitant administration of escitalopram and ritonavir, no statistically significant differences were noted in the pharmacokinetics of escitalopram, with the exception of apparent volume of distribution, which was reduced by approximately 10% (P < 0.001). The pharmacokinetics of S-DCT were unaffected by coadministration of ritonavir, with the exception of T(max), which was increased in the presence of ritonavir. The pharmacokinetic parameters of ritonavir were also unaffected by coadministration of escitalopram.

CONCLUSION

In general, no pharmacokinetic interaction was observed between escitalopram and ritonavir in the present study.

Pharmacokinetics, drug interactions, and tolerability of paroxetine and paroxetine CR

The development of paroxetine hydrochloride began in the late 1970s. An abundance of data have been accumulated from clinical investigations demonstrating the efficacy of paroxetine in the treatment of major depression and anxiety disorders. The published literature contains a substantial amount of supportive data documenting the safety, tolerability, and pharmacokinetic and pharmacodynamic properties of paroxetine. The role of paroxetine in clinically significant drug-drug interactions, especially involving metabolic inhibitory effects on the substrates of cytochrome p450 2D6, has long been suspected, but only isolated cases provide any evidence. Published data for widespread patient morbidity from drug interactions with paroxetine are almost nonexistent. Considerations of the pharmacokinetic properties of paroxetine support a rationale for the development of new dosage forms that maintain the efficacy yet improve the tolerability profile of the selective serotonin reuptake inhibitors. Paroxetine controlled-release is an enteric-coated formulation with release features that may enhance clinical outcome by modifying absorption-related pharmacokinetics, improving tolerability, and maintaining therapeutic benefits

Focus on paroxetine

This review of paroxetine is based on Medline and PsycLit searches and a manual search of the available research literature. It aims to cover the pharmacology of this frequently prescribed SSRI antidepressant in terms of its indications, efficacy and adverse effects. Overall, paroxetine is a well-tolerated and safe first-line SSRI antidepressant with anxiolytic qualities. It has been found useful in depression, anxiety and other conditions such as obsessive compulsive disorder and post-traumatic stress disorder. The antidepressant has some advantages over earlier tricyclic medication in terms of a lack of cardiovascular side-effects and relative safety in overdose. Cessation of use, however, is associated with withdrawal or discontinuation symptoms and patients should be counselled as to how these might be avoided. A 3- or 4-week graded withdrawal regimen, perhaps with concomitant fluoxetine to cover serotonergic discontinuation symptoms, may be advisable.

An open pilot study of nefazodone in depression with anger attacks: relationship between clinical response and receptor binding

Nefazodone has been widely used as an antidepressant, but it has not been tested for depression with anger attacks. In an open study, we administered nefazodone (maximum 600 mg/day) for 12 weeks to 16 outpatients who had major depression with anger attacks. Assessment instruments comprised the Structured Clinical Interview for DSM-IV (SCID), Anger Attacks Questionnaire (AAQ), 17-item Hamilton Rating Scale for Depression (HAM-D-17), Clinician Global Impression Scale (CGI), Symptom Questionnaire (SQ), Modified Overt Aggression Scale (MOAS), and MOAS-Self-Rated. Three subjects underwent positron emission tomography (PET) with [18F]-setoperone for 5-HT2 binding potential (BP) and [11C]-SCH-23,390 for D1 BP, both at baseline and after 6 weeks of treatment. Eight subjects underwent PET with [18F]-setoperone and with [11C]-SCH-23,390 at baseline only. In an examination of whether D1 and 5HT2 (data available in six subjects) receptor BP predicted treatment response, we found significant decreases in the HAM-D-17, CGI-S, weighted MOAS, MOAS verbal scale, OAS Self-Rated verbal, SQ Depression and Anger/Hostility scales after nefazodone; 50% responded to nefazodone (defined as >or=50% decrease in HAM-D-17 score), and 44% reported disappearance of anger attacks. A statistically significant percentage decrease in 5HT2 BP was observed for the right mesial frontal and left parietal regions after 6 weeks of treatment. No significant change was observed in D1 BP in any region. Although CGI-I scores correlated significantly with D1 BP in the left thalamic region, the correlation was not significant after Bonferroni correction. The effectiveness of nefazodone for depression with anger attacks may be related to widespread changes in 5HT2 receptor BP.

Alternative venlafaxine kinetics in overdose

The pharmacokinetics of venlafaxine in therapeutic doses is well established. It is metabolized by the cytochrome P450 enzymes including CYP2D6. The toxicokinetics in overdose is less well known.

CASE REPORT

A 33-year-old Caucasian female who ingested 3.0 g venlafaxine, and 210 mg zolpidem. The patient remained symptomatic for the following 24 h. Plasma pharmacokinetic analysis demonstrated a prolonged elimination half-life of venlafaxine, estimated to be 15.3 h. We postulate that the patient was a slow metabolizer of substrates for CYP2D6, an enzyme known to exhibit polymorphism.

Pharmacokinetically induced benzodiazepine withdrawal

Pharmacokinetic interactions between medications can have clinically significant effects. Concern usually arises when a medication is added to a continuing regimen, though discontinuation of a medication can also have an impact. A case is presented of a patient who experienced benzodiazepine withdrawal symptoms on discontinuation of nefazodone, an antidepressant that inhibits the cytochrome P450 3A4 isoenzyme. Plasma levels of alprazolam, a substrate for the 3A4 isozyme, fell rapidly when nefazodone was discontinued, presumably because of renewed 3A4 isoenzyme activity. The management of the patient's withdrawal symptoms is described.

A pharmacokinetic drug-drug interaction study of venlafaxine and indinavir

Depression is a common occurrence in the human immunodeficiency virus (HIV)-infected population. Complications in treating depressed HIV-infected individuals include the use of multiple medications, additive side effects, and potentially significant drug-drug interactions. Based on the pharmacologic characteristics of venlafaxine and indinavir, we hypothesized that significant pharmacokinetic drug-drug interactions would not occur when these drugs where taken concurrently. Nine healthy adult subjects were given a single 800 mg oral dose of indinavir and serial blood samples were collected for measurement of plasma drug concentrations. Over the next 9 days, venlafaxine was administered at a dosage of 50 mg every 8 hours following a brief titration. A venlafaxine trough plasma concentration and serial concentrations following venlafaxine administration were obtained on day 10. On day 11, venlafaxine and indinavir were administered together and serial blood sampling was repeated. Indinavir had no effect on venlafaxine plasma concentrations but resulted in a 7% decrease in plasma concentrations of O-desmethyl-venlafaxine (ODV)(P = 0.028). This effect is unlikely to be clinically significant. Venlafaxine coadministration resulted in a 28% decrease in the area under the concentration time curve (AUC) of plasma indinavir (P = 0.016) and a 36% decrease in its maximum plasma concentration (Cmax; P = 0.038). As the plasma concentration of protease inhibitors is a critical factor in maintaining efficacy and minimizing the potential for viral resistance, the decrease in both AUC and Cmax of indinavir from coadministration of venlafaxine is of concern. The clinical significance of these results obtained from a small number of healthy volunteers is unknown. Further studies are needed to substantiate or refute this apparent drug-drug interaction. Until such time, venlafaxine should be used cautiously in patients receiving indinavir.

Zyban-- is there a cause for concern?

Bupropion hydrochloride is a monocyclic antidepressant which is used in a slow-release formulation as a smoking cessation aid. Its side effects include insomnia and dry mouth with seizures occurring in 1 in 1000 patients. In overdose, it can cause tachycardia, conduction defects and convulsions. It is, however, effective in smoking cessation in approximately 20% of patients and may be more effective if combined with nicotine replacement therapy. The key question is whether the risks associated with the drug are justified by the obvious benefits to health from smoking cessation.

Escitalopram

Escitalopram oxalate (S-citalopram, Lexapro), a selective serotonin re-uptake inhibitor antidepressant which is the S-enantiomer of citalopram, is in clinical development worldwide for the treatment of depression and anxiety disorders. Preclinical studies demonstrate that the therapeutic activity of citalopram resides in the S-isomer and that escitalopram binds with high affinity to the human serotonin transporter. Conversely, R-citalopram is approximately 30-fold less potent than escitalopram at this transporter. Escitalopram has linear pharmacokinetics, so that plasma levels increase proportionately and predictably with increased doses and its half-life of 27 - 32 h is consistent with once-daily dosing. In addition, escitalopram has negligible effects on cytochrome P450 drug-metabolising enzymes in vitro, suggesting a low potential for drug-drug interactions. The efficacy of escitalopram in patients with major depressive disorder has been demonstrated in multiple short-term, placebo-controlled clinical trials, three of which included citalopram as an active control, as well as in a 36-week study evaluating efficacy in the prevention of depression relapse. In these studies, escitalopram was shown to have robust efficacy in the treatment of depression and associated symptoms of anxiety relative to placebo. Efficacy has also been shown in treating generalised anxiety disorder, panic disorder and social anxiety disorder. Results also suggest that, at comparable doses, escitalopram demonstrates clinically relevant and statistically significant superiority to placebo treatment earlier than citalopram. Analysis of the safety database shows a low rate of discontinuation due to adverse events, and there was no statistically significant difference between escitalopram 10 mg/day and placebo in the proportion of patients who discontinued treatment early because of adverse events. The most common adverse events associated with escitalopram which occurred at a rate greater than placebo include nausea, insomnia, ejaculation disorder, diarrhoea, dry mouth and somnolence. Only nausea occurred in > 10% of escitalopram-treated patients.

Enantiomers' potential in psychopharmacology--a critical analysis with special emphasis on the antidepressant escitalopram

Stereochemistry is now influencing most areas of pharmacotherapy, with a growing awareness in the field of psychiatry and, more specifically, depression. This is due to the fact that the enantiomers of many chiral drugs may have distinct pharmacological, pharmacokinetic and/or pharmacogenetic profiles. Consequently, in some instances there may be an advantage in using a single enantiomer over the racemic form-thus providing a basis for the development of new therapeutic agents, as well as the potential to improve current treatments. This review highlights some of the potential advantages and disadvantages that using single enantiomers might offer. The principles are exemplified through reference to the stereoselective properties of several established chiral psychotropic drugs, including thioridazine, methadone, trimipramine, mianserin, mirtazapine, fluoxetine and citalopram. Emphasis is given to the treatment of depression and how the potential of one pure enantiomer-escitalopram, the S-enantiomer of the selective serotonin reuptake inhibitor citalopram-appears to be fulfilling its preclinical promise in the clinic.

Relationship between CYP 2D6 metabolic status and sexual dysfunction in paroxetine treatment

This article describes the incidence of sexual dysfunction in 30 patients subjected to long-term treatment by paroxetine in dependence on the P 450 CYP 2D6 isoenzyme metabolic status. Measured on the Arizona Sexual Experience Scale (ASEX; McGahuey, Delgado, & Gelenberg, 1999), the incidence of sexual dysfunction in patients converted to CYP 2D6 poor metabolizers was markedly higher compared with patients who had no history of such conversion, a difference that reached the level of statistical significance. Our article discusses the incidence of sexual dysfunction in connection with reduced CYP 2D6 capacity.

Venlafaxine: a new class of antidepressant

Venlafaxine represents a new class of antidepressant, the serotonin and noradrenaline re-uptake inhibitor (or SNRI). This article discusses its evolution, pharmacological properties and role in the treatment of depression and related disorders, beginning with an outline of the biology of depression.

Estimates of nursing infant daily dose of fluoxetine through breast milk

BACKGROUND

This study compared three methods of estimating the daily dose of fluoxetine to nursing infants and the relationship between these estimates and infant serum concentrations.

METHODS

Breast milk and infant serum concentrations of fluoxetine and norfluoxetine were obtained from 10 nursing mother-infant pairs. Quantification of daily infant dose was determined by three methods: 1) collection of the total volume of breast milk over 24 hours and determination of the average breast milk concentration (Baby's Total Daily Dose); 2) determination of the maximum and minimum breast milk concentrations during 24 hours and an estimated milk consumption of 150 mL/kg/day (Atkinson Model); and 3) determination of the gradient of excretion of medication into breast milk at a specified time after the maternal dose, applying this gradient to each nursing collection and summing the values for 24 hours (Mathematical Model). The relationship between the 24-hour medication dose, obtained from each method, and the infant serum concentrations was examined.

RESULTS

A total of 177 breast milk and 10 infant serum samples were collected. An estimate of the infant daily medication dose obtained by the Mathematical Model was the best predictor of total infant serum concentration.

CONCLUSIONS

Breast milk analysis may allow one to determine whether medication concentrations will be detectable in an infant, eliminating the need for an infant serum concentration. Although the Mathematical Model seems to reflect infant serum concentration most accurately, all three methods suggest that the maximum dose that a nursing child receives over the course of a year equals as much as 120 mg, or 160 +/- 47% of the maternal daily dose.

Steady-state concentration of venlafaxine enantiomers: model-based analysis of between-patient variability

OBJECTIVE

To investigate patients treated for depression with respect to steady-state concentration of venlafaxine enantiomers, to quantify within- and between-subject variability and to study the possible influence of individual characteristics such as gender and age.

METHODS

Thirty-five inpatients received venlafaxine orally at a fixed 300-mg daily dose. Blood samples were taken on day 14 and day 28 for therapeutic drug monitoring purposes. All measurements reflected steady-state trough values. In a first stage, plasma concentrations of racemic venlafaxine (V) and O-desmethylvenlafaxine (ODV) were measured using a gas chromatography method. In a second stage, (+)/(-) enantiomeric ratios for V and ODV were determined using a stereoselective capillary electrophoresis method.

RESULTS

Interindividual variability was 77% and 33% for concentrations of racemic V and ODV, respectively. Intraindividual variability was below 20% for both compounds. Enantiomeric ratios did not statistically differ from unity, with median (+)/(-) ratios of 1.14 for V and 0.97 for ODV. ODV/V metabolite formation ratios for the (+) and (-) enantiomers did not significantly differ from each other (median values 2.85 and 2.37, respectively). However, reduced ODV/V ratio for the (-) enantiomer was strongly associated with decreased (+)/(-) ratio for V (r(S)=0.71, P<0.001) and increased (+)/(-) ratio for ODV (r(S)=-0.79, P<0.001). In contrast, ODV/V ratio for the (+) enantiomer did not significantly correlate with parent compound (+)/(-) ratio and correlated only weakly with metabolite (+)/(-) ratio (r(S)=-0.38, P<0.05). When compared with males, females displayed a significantly lower ODV/V ratio for the (-) enantiomer (median values 1.42 vs 5.08 on day 14, P<0.05) but not for the (+) enantiomer (median values 2.36 vs 3.27, n.s.). Analysis did not reveal any significant association between ODV/V ratios and age, weight, height, creatinine clearance, smoking or co-medication. A pharmacokinetic model at steady state was developed that postulated two different enzyme systems to contribute to O-desmethylation. ODV(-) formation was supposed to largely depend on a single pathway, possibly impaired in a patient subpopulation. ODV(+) formation was postulated to rely on both pathways to a similar extent. Model predictions were in close agreement with observations in patients.

CONCLUSION

Observations, together with model-based simulations, suggested that marked stereoselectivity in a patient subgroup may be related with impairment of O-desmethylation greater for (-) than (+) venlafaxine. This hypothesis requires testing against phenotypic and genotypic characteristics of patients.

Citalopram in pregnancy and lactation

BACKGROUND

Although citalopram has gained wide acceptance in the treatment of depression and anxiety disorders, its use during pregnancy and lactation has been poorly characterized. The aim of this study was to examine the efficacy and safety of citalopram in relation to concentrations of citalopram and its metabolites during pregnancy and lactation.

METHODS

Eleven mothers taking citalopram and their infants were enrolled in the study, and a control group of 10 women who were not taking medication were prospectively matched for confounding obstetric characteristics at the time of delivery. Plasma and breast milk samples were collected from mother/infant pairs during pregnancy, at delivery, and for up to 2 months after delivery. Trough plasma and breast milk concentrations of citalopram, desmethylcitalopram, and didesmethylcitalopram were measured by HPLC. The pregnancy outcome was recorded, and the neurodevelopment of children was monitored for up to 1 year.

RESULTS

Although the citalopram dose of 20 mg to 40 mg once daily resulted in low maternal trough plasma concentrations (range, 46-214 nmol/L) and metabolites during pregnancy, only one subject required an increase of daily dose. The mean didesmethylcitalopram-desmethylcitalopram metabolic ratio was significantly higher during pregnancy (54%, P <.001) than at 2 months after delivery, indicating induction of cytochrome P450 (CYP) 2D6 during pregnancy. At delivery, the trough plasma citalopram, desmethylcitalopram, and didesmethylcitalopram concentrations in the infants were 64%, 66%, and 68% of the maternal concentrations, respectively. The citalopram and metabolite concentrations in the milk were 2- to 3-fold higher compared with maternal plasma concentrations, but the infant citalopram and metabolite plasma concentrations were very low or undetectable. The delivery outcome and the neurodevelopment of all infants up to the age of 1 year were normal.

CONCLUSION

Even though the sample size was limited, results from this prospective clinical trial suggest uncomplicated pregnancy outcome in mothers using citalopram during pregnancy and minimal exposure of the infants to citalopram during lactation. However, maternal therapeutic drug monitoring of citalopram should be recommended to minimize fetal exposure.

Postmortem concentrations of citalopram

The postmortem concentrations of citalopram in blood, bile, liver, and vitreous humour were investigated in 14 cases using a specially developed high performance liquid chromatography assay. Concentrations from drug and non-drug related deaths were categorized to determine a postmortem therapeutic and toxic range. Therapeutic citalopram concentrations for blood, bile, liver, and vitreous humour ranged to 0.4 mg/L, 2.1 mg/l, 6.6 mg/kg, and 0.2 mg/L, respectively. In one potentially fatal response to citalopram, concentrations were 0.8 mg/L, 6.0 mg/L, 0.3 mg/L for blood, bile and vitreous humour, respectively.

Prevention of the serotonin reuptake inhibitor discontinuation syndrome

Prevention of the serotonin reuptake inhibitor discontinuation syndrome (SRIDS) is an important issue. The author suggests: (1) serotonin reuptake inhibitors (SRIs) should be used only when they are necessary. Sometimes tablets should be replaced with other treatment modalities; (2) patients should be given the lowest dosage of SRIs possible; (3) patients who have a history of medication noncompliance, who have experienced the discontinuation symptoms in the past, or who have treatment-emergent anxiety are at highest risk for experiencing the SRIDS and need closer monitoring; (4) SRIs should be tapered prior to stoppage; (5) generic drugs are allowed up to a 20% difference in bioequivalence from the brand original. Patients should receive continuity of supply from the dispenser, with no intermanufacturer switching; (6) patients and healthcare professionals should be educated to ensure that SRIs are not stopped abruptly; (7) neonatal SRIDS can follow maternal use of antidepressants during pregnancy and possibly breast feeding. The patient and physician should take this into consideration when making treatment decision.

Efficacy of venlafaxine in patients with major depressive disorder who have unsustained or no response to selective serotonin reuptake inhibitors: an open-label, uncontrolled study

BACKGROUND

Approximately half of patients who are prescribed selective serotonin re-uptake inhibitors (SSRIs) either do not respond to treatment or do not experience a sustained response.

OBJECTIVE

The purpose of this study was to assess the efficacy of venlafaxine immediate-release (IR) and extended-release (XR) in outpatients who either did not respond to SSRI treatment or did not maintain a sustained response.

METHODS

Outpatients who met the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria for major depressive disorder who were previously treated with an SSRI (fluoxetine > or = 20 mg/d; sertraline > or = 50 mg/d; paroxetine > or = 20 mg/d) for > or = 6 weeks, but demonstrated an inadequate or unsustained response, were switched to venlafaxine (IR or XR formulation, 50-400 mg/d, titrated from 37.5 mg/d) for > or = 6 weeks. Response at 6 to 8 weeks was defined as total score < or = 10 on the modified 25-item Hamilton Depression (HAM-D25) rating scale or total score > or = 5 on the 21-item Patient Global Improvement (PGI-21) scale. Remission was defined as a HAM-D25 total score < or = 8 or PGI-21 score > or = 7. Tests were administered by an unblinded, board-certified psychiatrist.

RESULTS

A total of 73 patients (54 women, 19 men; mean age, 38.6 years) were enrolled and treated with venlafaxine IR (n = 63) or venlafaxine XR (n = 10); 33 were SSRI nonresponders and 36 had an unsustained response to SSRI treatment. Four patients receiving venlafaxine IR discontinued due to drug-related adverse events (agitation, sedation, or nausea). Data from these patients were excluded from the analysis. After 6 to 8 weeks of treatment, 94.2% (65/69) of patients were considered responders (HAM-D25 or PGI-21 criteria); 91.3% (63/69) of patients responded to treatment as assessed by both measures. Eighty-seven percent (60/69) and 85.5% (59/69) of patients achieved remission based on HAM-D,5 and PGI-21 criteria, respectively. Response/remission rates were comparable among patients treated with SSRIs, regardless of whether patients had failed to respond to treatment with 1 or 2 SSRIs.

CONCLUSION

Venlafaxine IR/venlafaxine XR may be effective in outpatients with major depressive disorder who do not respond or have an unsustained response to SSRIs. However, randomized, controlled trials are needed before any conclusions can be drawn about the efficacy of this agent in this population.

[Second generation SSRIS: human monoamine transporter binding profile of escitalopram and R-fluoxetine]

BACKGROUND

Single isomers of the selective serotonin reuptake inhibitors citalopram (escitalopram, S-citalopram) and fluoxetine (R-fluoxetine) are currently under development for the treatment of depression and other psychiatric disorders. Previous studies conducted in laboratory animals have revealed that the biological effects on serotonin reuptake for citalopram reside in the S enantiomer. In contrast, both enantiomers of fluoxetine contribute to its biological activity.

METHODS

In the present study, the potency and selectivity of escitalopram, R-fluoxetine, and all of the other currently available selective serotonine reuptake ihibitors were compared for binding affinity at the human serotonin, norepinephrine, and dopamine transporters and several select neurotransmitter receptors using radioligand binding assays.

RESULTS

Both escitalopram and R-fluoxetine were potent inhibitors of the serotonin transporter (Ki=1,1 and 1,4 nmol/L, respectively). escitalopram was the most serotonin transporter-selective compound tested and was approximately 30 fold more potent than R-citalopram.

CONCLUSIONS

As noted previously, paroxetine and sertraline possess moderate affinity (<50 nmol/L) for the human norepinephrine transporter and dopamine transporter, respectively. R-fluoxetine, unlike the other selective serotonin reuptake inhibitors, possesses moderate affinity (Ki=64 nmol/L) for the serotonin 2C receptor. Potential clinical correlates of these unique attributes of escitalopram and R-fluoxetine are discussed. (Biol Psychiatry 2001; 50: 345-350 " 2001 Society of Biological Psychiatry).

[Delirium during withdrawal of venlafaxine]

A 35-year-old man with anxiety and depression who was treated with venlafaxine, 300 mg a day, developed severe withdrawal symptoms in the form of a delirium during gradual tapering of the dosage. The symptoms resolved when the dosage was kept constant and did not recur when the dosage was reduced more gradually. Withdrawal symptoms are common during discontinuation of antidepressants, particularly after prolonged use of agents with a short half-life. The symptoms are usually mild and transient, especially in the case of selective serotonin reuptake inhibitors and venlafaxine. The occurrence of delirium as a result of the withdrawal of venlafaxine has not been reported previously. Even when antidepressants are being withdrawn with care, one should remain alert to the possible development of severe withdrawal symptoms.

[Metabolic interaction between psychopharmaceuticals. Probable cause of exacerbation of hypothyroidism according to a case report]

Little is known about how psychotropic drugs influence thyroid function in man, but it has been reported that sertraline decreases the efficacy of levothyroxine in patients treated for hypothyroidism. Most psychotropic drugs are metabolized in the liver by cytochrome P450. Sertraline is metabolized by cytochrome P450 CYP 2D6, CYP 3A4, and CYP 2C19. Mianserin is metabolized by CYP 2D6, and to some extent also by CYP 3A4. Since both substances, at least in part, are metabolized by the same liver enzymes, drug interactions can be expected. In this article we describe such a possible interaction between sertraline and mianserin in a patient treated with levothyroxine for hypothyroidism (Hashimoto's thyroiditis). She displayed both clinical symptoms and laboratory data typical of hypothyroidism when long-term antidepressive sertraline therapy (100 mg/day) was transiently supplemented with mianserin (30 mg/day). All symptoms and signs of hypothyroidism disappeared completely when the mianserin treatment was discontinued. These findings imply that unexpected drug effects may occur in depressed patients with primary hypothyroidism if they are treated with both sertraline and mianserin. In such situations thyroid function should be checked carefully.

Pharmacology and pharmacokinetics of milnacipran

Milnacipran is a dual-action antidepressant drug with equivalent inhibitory action at noradrenaline and serotonin neuronal reuptake systems. This dual action has been demonstrated in vitro and in vivo in experimental animals, and ex vivo in man. Milnacipran has no relevant affinity for any neurotransmitter receptor studied, in particular postsynaptic adrenergic, muscarinic and histamine receptors, and is therefore expected to be devoid of the prominent side-effects of many earlier antidepressants. Studies in human volunteers have not demonstrated any impact of milnacipran on cognitive function, consistent with its lack of anticholinergic properties. These pharmacodynamic properties are well preserved in vivo in humans, because milnacipran is only metabolized to a limited extent, and therefore circulates in the body principally as the unchanged parent drug, which is the only pharmacologically active compound at clinical doses. The pharmacokinetic profile of milnacipran is characterized by rapid absorption, high bioavailability, low protein binding, and rapid elimination, both by hepatic glucuronidation and renal excretion. This gives milnacipran certain pharmacokinetic advantages, such as low inter-individual variation in plasma levels, low potential for drug interactions, and limited impact on hepatic cytochrome P450 systems. These pharmacokinetic properties differentiate milnacipran from most other antidepressant drugs and contribute to the good safety profile of milnacipran and allow it to be used simply and flexibly in clinical practice.

Disposition of venlafaxine enantiomers in rats with hepatic encephalopathy after chronic drug treatment

Portacaval shunted (PCS) rats, a model of hepatic encephalopathy, and control animals were administered racemic venlafaxine for 14 days (10 mg/kg). The levels of the S- and R-enantiomers and the S/R-enantiomer ratios of venlafaxine and its metabolites were assessed by an enantiomer-selective chromatographic assay in serum, brain parenchyma, and brain dialysate of both groups. Higher levels of the S- and R-enantiomers of venlafaxine were found in serum and brain of PCS vs. normal rats (median values of S- and R-venlafaxine in serum: 290 and 201 nM in PCS; 97 and 66 nM in normal rats; median values of S- and R-venlafaxine in cortex: 956 and 939 nM in PCS; 357 and 318 nM in normal rats). Interestingly, similar S/R-venlafaxine ratios were observed in PCS and normal rats both in serum (S/R = 1.4) and brain compartments (S/R = l.0-1.1). These findings may have clinical relevance for the safety of venlafaxine in chronic hepatic encephalopathy.

The amount of fluvoxamine in milk is unlikely to be a cause of adverse effects in breastfed infants

The aim of this study was to characterize milk/plasma (M/P) ratio, as well as relative infant dose and well-being, in 2 breastfeeding women taking fluvoxamine. The women (37 and 34 years old) and their infants (26 and 0.75 months old) were studied over a 24-hour dose interval at steady state. Fluvoxamine concentrations were measured by high-performance liquid chromatography. Infant exposure was measured as concentration in milk multiplied by an estimated milk production of 0.15 L/kg/d and normalized to the weight-adjusted maternal dose. M/P values of 1.34 and 1.21 were calculated for subjects 1 and 2, respectively, and relative infant doses were estimated to be 1.38% and 0.8%, respectively. No adverse effects in the infants were detected by the mother or on clinical examination, and fluvoxamine was not detected in the infants' plasma (limit of detection 2 micrograms/L). These limited data support the prescription of fluvoxamine to breastfeeding mothers after a careful, individual risk/benefit analysis is undertaken.

Paroxetine: an update of its use in psychiatric disorders in adults

Paroxetine is a selective serotonin reuptake inhibitor (SSRI), with antidepressant and anxiolytic activity. In 6- to 24-week well designed trials, oral paroxetine 10 to 50 mg/day was significantly more effective than placebo, at least as effective as tricyclic antidepressants (TCAs) and as effective as other SSRIs and other antidepressants in the treatment of major depressive disorder. Relapse or recurrence over 1 year after the initial response was significantly lower with paroxetine 10 to 50 mg/day than with placebo and similar to that with imipramine 50 to 275 mg/day. The efficacy of paroxetine 10 to 40 mg/day was similar to that of TCAs and fluoxetine 20 to 60 mg/day in 6- to 12-week trials in patients aged > or =60 years with major depression. Paroxetine 10 to 40 mg/day improved depressive symptoms to an extent similar to that of TCAs in patients with comorbid illness, and was more effective than placebo in the treatment of dysthymia and minor depression. Paroxetine 20 to 60 mg/day was more effective than placebo after 8 to 12 weeks' treatment of obsessive-compulsive disorder (OCD), panic disorder, social anxiety disorder (social phobia), generalised anxiety disorder (GAD) and post-traumatic stress disorder (PTSD). Improvement was maintained or relapse was prevented for 24 weeks to 1 year in patients with OCD, panic disorder, social anxiety disorder or GAD. The efficacy of paroxetine was similar to that of other SSRIs in patients with OCD and panic disorder and similar to that of imipramine but greater than that of 2'chlordesmethyldiazepam in patients with GAD. Paroxetine is generally well tolerated in adults, elderly individuals and patients with comorbid illness, with a tolerability profile similar to that of other SSRIs. The most common adverse events with paroxetine were nausea, sexual dysfunction, somnolence, asthenia, headache, constipation, dizziness, sweating, tremor and decreased appetite. In conclusion, paroxetine, in common with other SSRIs, is generally better tolerated than TCAs and is a first-line treatment option for major depressive disorder, dysthymia or minor depression. Like other SSRIs, paroxetine is also an appropriate first-line therapy for OCD, panic disorder, social anxiety disorder, GAD and PTSD. Notably, paroxetine is the only SSRI currently approved for the treatment of social anxiety disorder and GAD, which makes it the only drug of its class indicated for all five anxiety disorders in addition to major depressive disorder. Thus, given the high degree of psychiatric comorbidity of depression and anxiety, paroxetine is an important first-line option for the treatment of major depressive disorder, OCD, panic disorder, social anxiety disorder, GAD and PTSD.

PET evaluation of a tetracyclic, atypical antidepressant, [N-methyl-11C]mianserin, in the living porcine brain

We synthesized [N-methyl-11C]mianserin by alkylation of N-desmethyl mianserin with [11C]methyl iodide followed by HPLC purification. We used PET for determining the regional cerebral pharmacokinetics of the radiotracer in anesthetized swine. [N-methyl-11C]Mianserin entered most brain regions readily (range of K1 values: 0.66-1.13), reaching highest levels in the basal ganglia and thalamus. The binding potential of [N-methyl-11C]mianserin was relatively low (range: 0.07-0.50), but regional differences were nonetheless observed, with highest values in the temporal cortex and lowest values in the brainstem. These PET findings, which are the first ones for a tetracyclic, antidepressant drug, show that [N-methyl-11C]mianserin has only a limited degree of regional specificity of binding in the living brain.

Pharmacology of antidepressants: focus on nefazodone

The past decade has witnessed the introduction of a diverse group of antidepressants from a variety of distinct chemical classes, each with their own specificity for neurochemical transmitters, receptors, and cytochrome P450 isozymes. This review focuses on nefazodone, a distinct antidepressant with efficacy for the treatment of depression with depression-related anxiety symptoms, an established tolerability profile, and a multimodal mechanism of action. Relevant pharmacologic and pharmacodynamic effects are summarized that support nefazodone as an attractive choice for both the short- and long-term treatment of depression.

[Treatment of nicotine addiction. Drug therapy for smoking cessation]

Most Danish smokers are addicted to nicotine. Treatment with nicotine replacement therapy or bupropion doubles the one-year success rate after cessation of smoking. Pregnant smokers who are unable to stop smoking without medical treatment can safely be offered nicotine replacement therapy. The health risk of smoking is particularly high in patients with cardiovascular disease. Reluctance to use nicotine products for patients with heart disease is not supported by scientific evidence, and either bupropion or nicotine products can safely be administered to them.

Combining bupropion SR with venlafaxine, paroxetine, or fluoxetine: a preliminary report on pharmacokinetic, therapeutic, and sexual dysfunction effects

BACKGROUND

This study was designed to evaluate the effect of combining bupropion sustained release (SR) with venlafaxine, paroxetine, or fluoxetine in patients who reported unacceptable sexual dysfunction when treated with monotherapy with the latter 3 agents.

METHOD

Following a minimum of 6 weeks of antidepressant treatment with a selective serotonin reuptake inhibitor (SSRI) or venlafaxine (a serotonin-norepinephrine reuptake inhibitor), eligible subjects received a further 8 weeks of monitored combination therapy with bupropion SR at a dose of 150 mg/day with no alterations to index antidepressant dosing.

RESULTS

There was a clinically significant benefit in 14 (78%) of 18 partial responders or nonresponders, and 33% (N = 6) achieved a full response (chi2= 8.06, df = 2, p = .017). Sexual dysfunction, particularly a decrease in orgasmic delay, was also significantly improved with combination therapy (men: paired t = -2.1, df = 6, p = .08; women: paired t = -3.0, df = 7, p = .02). Plasma monitoring of drugs and their metabolites revealed a statistically significant increase in venlafaxine levels (F = 6.89, df = 4,24; p = .001) accompanied by a decrease in O-desmethylvenlafaxine (F = 14.26; df = 4,24; p < .0005) during combined treatment with bupropion SR. There were no statistically significant changes in plasma levels of SSRIs (paroxetine and fluoxetine) during the trial.

CONCLUSION

Bupropion had an effect on the pharmacokinetics of venlafaxine but not those of the SSRIs. Further investigation of combination treatments under randomized, double-blind conditions is recommended.

Interaction between fluvoxamine and cotinine or caffeine

We examined the relationships between plasma fluvoxamine concentrations and plasma levels of cotinine and caffeine, respectively, under steady-state conditions in 30 patients who met DSM-IV criteria for a major depressive disorder and who were being treated with fluvoxamine. The daily dosages of fluvoxamine ranged from 50 to 200 mg (mean +/- SD 108 +/- 42 mg). Eleven patients were smokers and the remaining 19 were nonsmokers. The plasma fluvoxamine concentrations were significantly higher in nonsmokers (0.92 +/- 0.40 ng/ml/mg) than in smokers (0.56 +/- 0.28 ng/ml/mg); in addition, a trend towards negative correlations was observed between the plasma fluvoxamine concentrations and the plasma cotinine levels, although it was not significant. Significant positive correlations were found between the plasma fluvoxamine concentrations and the plasma caffeine levels. These findings are compatible with those in earlier reports that cytochrome P450 1A2 plays a major role in fluvoxamine metabolism.

Once-weekly fluoxetine

The relatively long half-life of the selective serotonin reuptake inhibitor fluoxetine has allowed the development of a delayed-release (enteric-coated) formulation containing 90 mg fluoxetine per capsule for once-weekly oral administration. The cumulative relapse rate in patients switched to once-weekly fluoxetine 90 mg for 25 weeks (after responding to 13 weeks of fluoxetine 20 mg/day) was similar to that in patients continuing to receive fluoxetine 20 mg/day and significantly lower than seen in patients switched to placebo. The efficacy of the once-weekly formulation was also similar to that of the daily formulation in other assessment parameters (modified 17-item Hamilton Rating Scale for Depression, Clinical Global Impressions - Severity of Illness Scale). Patient compliance (measured using an electronically monitored tablet bottle) was maintained at 87.5% in evaluable patients receiving once-weekly fluoxetine 90 mg for 12 weeks from a baseline of 85.4% after responding to 4 weeks of fluoxetine 20 mg/day; in contrast, compliance declined significantly (from 87.3% at baseline to 79.4%; p < 0.001) in patients continuing to receive 20 mg/day for 12 weeks. Once-weekly fluoxetine is well tolerated, with a tolerability profile similar to that of the immediate-release formulation.

Pharmacokinetic interactions between cyclosporine and bupropion or methylphenidate

A 10-year-old boy with a history of heart transplantation had a potentially life-threatening decrease in his cyclosporine (CSA) blood levels during administration of bupropion. Subsequently he had an increase in CSA levels while receiving methylphenidate. These occurrences represent potential drug-drug interactions in children not previously documented in the literature. The CSA-bupropion and CSA-methylphenidate interactions merit further investigation, particularly because psychotropic agents are often prescribed in combination with immunosuppressants in transplantation patients of all ages.

Selective serotonin reuptake inhibitors for late-life depression: a comparative review

Late-life depression is a serious health problem that is challenging to manage but generally responds well to pharmacotherapy. Selective serotonin (5-hydroxytryptamine: 5-HT) reuptake inhibitors (SSRIs), the most commonly prescribed antidepressants, are usually used as first-line agents for elderly patients with depression. Like most drugs, SSRIs have not been widely tested in clinical trials that approximate 'real-life' geriatric situations. However, studies completed to date provide valuable information about the efficacy, safety and tolerability of this class of antidepressants among older patients with depression, including those with depression secondary to stroke or dementia and those with other comorbid physical disorders. Although one SSRI may be more efficacious or better tolerated by elderly patients than another, existing data do not support such claims. However, other distinguishing features may influence the choice of agent. For example, fluoxetine, fluvoxamine and paroxetine are more likely to be involved in significant drug-drug interactions than are citalopram or sertraline. In contrast to the other SSRIs, fluoxetine has a half-life well in excess of 1 day, which can be an advantage when weaning the patient off therapy in that it may reduce the incidence of discontinuation symptoms, but a significant disadvantage if the patient cannot tolerate the drug or experiences an adverse drug-drug interaction.

Influence of antidepressant pharmacotherapy on behavioral treatment adherence and smoking cessation outcome in a combined treatment involving fluoxetine

The authors examined whether serum fluoxetine levels influence behavioral treatment adherence and smoking cessation outcome. Nondepressed smokers (N = 989) from 16 centers were randomized on a double-blind basis to receive either fluoxetine (30 or 60 mg) or placebo plus 9 sessions of behavioral smoking cessation treatment. Fluoxetine and norfluoxetine blood levels were assayed 1 week after the quit date. Logistic regression was used to predict treatment completion and cessation outcome, controlling for gender, age, treatment site, and degree of nicotine dependence. Higher steady-state fluoxetine blood levels (fluoxetine + norfluoxetine) predicted less likelihood of dropping out, chi2(1, N = 820) = 3.9, p < .05, and more likelihood of being abstinent, chi2(1, N = 513) = 18.1, p < .001. Attaining a higher fluoxetine blood level improved the likelihood of completing behavioral treatment and increased the probability of achieving abstinence.

Postmortem tissue concentrations of venlafaxine

Venlafaxine is a phenethylamine antidepressant which inhibits both serotonin and norepinephrine reuptake and is structurally unrelated to the serotonin reuptake inhibitors (SSRIs). Its major metabolite, O-desmethylvenlafaxine (ODV), also inhibits serotonin reuptake. Although metabolized by the cytochrome P-450 (CYP) system, venlafaxine inhibits CYP 2D6 and 3A4 to a far lesser extent than do the SSRIs. Mechanisms of drug action are reviewed and evaluated in the investigation of 12 fatalities occurring over a 6-month-period where venlafaxine was detected.Venlafaxine and ODV were identified by liquid chromatography-mass spectrometry (LC-MS) using atmospheric pressure ionization (API) electrospray in positive mode following an n-butyl chloride extraction. Postmortem tissue concentrations studied in each of 12 postmortem cases for venlafaxine and ODV, were 0.1-36 and <0.05-3.5mg/l (peripheral blood), <0.05-22 and <0.05-9.9mg/kg (liver), <0.05-10 and <0.05-1.5mg/l (vitreous), <0.05-53 and <0.05-6.8mg/l (bile), <0.05-55 and <0.05-21mg/l (urine), respectively, and 0.1-200mg of venlafaxine in the gastric contents. Venlafaxine was typically present with other drugs, including other antidepressants, alcohol, and benzodiazepines. The potential for interaction with each drug is discussed. Over the 6-month-period of this study, there were no deaths ascribed solely to venlafaxine intoxication.

[14C]Serotonin uptake and [O-methyl-11C]venlafaxine kinetics in porcine brain

As part of our program of developing PET tracers for neuroimaging of psychotropic compounds, venlafaxine, an antidepressant drug, was evaluated. First, we measured in vitro rates of serotonin uptake in synaptosomes prepared from selected regions of porcine brain. Then, we determined the pharmacokinetics of venlafaxine, [O-methyl-11C]-labeled for PET. Synaptosomal studies showed that the active uptake of [14C]5-HT differed markedly between brain regions, with highest rates in hypothalamus, raphé region, and thalamus, and lowest rates in cortex and cerebellum. PET studies showed that the unidirectional rate of uptake of [O-methyl-11C]venlafaxine from blood to brain was highest in the hypothalamus, raphé region, thalamus and basal ganglia and lowest in the cortex and cerebellum. Under normal physiological conditions, the capillary permeability-surface area (PS) product for [O-methyl-11C]venlafaxine could not be estimated, because of complete flow-limitation of the cerebral uptake. Nevertheless, a correlation occurred between the apparent partition volume of the radiotracer and the rate of active uptake of 5-HT in selected regions of the porcine brain. During hypercapnia, limitations of blood-brain transfer were observed, giving PS-products for water that were only ca. 50% higher than those of venlafaxine. Thus, under normal physiological conditions, the rate of uptake of venlafaxine from blood into brain is completely flow-limited.

Serotonin syndrome in HIV-infected individuals receiving antiretroviral therapy and fluoxetine

OBJECTIVE

To describe HIV-infected individuals taking antidepressants who developed the serotonin syndrome due to drug--drug or drug--food interactions.

DESIGN AND SETTING

Case studies carried out at the HIV Outpatient Clinic, Atlanta Veterans Affairs Medical Center.

PARTICIPANTS AND INTERVENTIONS

HIV-positive patients who were receiving antiretroviral and antidepressant therapies and presented with symptoms consistent with the serotonin syndrome. Their antidepressants were discontinued or the doses reduced in order to resolve the symptoms.

RESULTS

Five cases of serotonin syndrome developed after patients who were taking antidepressants ingested P450 inhibitors.

CONCLUSIONS

Serotonin syndrome should be suspected in patients on serotonergic medications who present with mental status change, autonomic dysfunction, and neuromuscular abnormalities. Suspicion should be heightened in those who are ingesting substances known to inhibit P450 enzymes, such as protease inhibitors, non-nucleoside reverse transcriptase inhibitors, and grapefruit juice.

Single-dose pharmacokinetics of bupropion in adolescents: effects of smoking status and gender

Sustained-release (SR) bupropion (Zyban) is approved as a smoking cessation aid for adults. Since smoking often begins in adolescence, we determined the single-dose pharmacokinetics of bupropion SR in 75 adolescent subjects ranging from 13 to 18 years old. Subjects self-reported their smoking status. Urinary cotinine concentration was used to verify smoking status. Thirty-seven subjects (18 males, 19 females) were classified as cigarette smokers and 38 were nonsmokers (19 males, 19 females). Fasted subjects received one tablet (150 mg) of bupropion SR, and plasma samples were collected before (0) and 1/2, 1, 2, 3, 4, 6, 8, 24, 48, and 72 hours after dosing. Plasma samples were analyzed for bupropion and its three major metabolites (hydroxybupropion and the aminoalcohol isomers, erythrohydrobupropion plus threohydrobupropion, expressed as a composite) by solid-phase extraction, followed by LC/MS/MS. Factorial analysis of variance (ANOVA) was used to evaluate the effects of smoking and gender on pharmacokinetic parameters. Smokers and nonsmokers differed significantly (p < 0.05) in age and urinary cotinine (p < 0.01) concentration but did not differ significantly in mean weight, height, body surface area, or body mass index. The pharmacokinetic (PK) parameters for bupropion and hydroxybupropion did not differ between smokers and nonsmokers, but differences were found between male and female subjects. Mean values for area under the plasma concentration versus time curve (AUC0-->infinity), volume of distribution (Vd beta) normalized to body weight, maximum plasma concentration (Cmax), and elimination half-life (t1/2 beta) for bupropion were significantly (p < 0.05) greater in females than males, while clearance of bupropion normalized to body weight (CL/f) did not differ between males and females. Females also exhibited significantly (p < 0.05) larger values for hydroxybupropion mean AUC0-->infinity and Cmax than males. The mean ratio of hydroxybupropion to bupropion AUC for adolescents was approximately 4 to 5, which is lower than that previously reported for adults. In conclusion, smoking status does not affect the single-dose pharmacokinetics of bupropion SR in adolescents. However, females differ from males in several potentially important PK parameters for bupropion and its major metabolite, hydroxybupropion.

KW-6002 (Kyowa Hakko Kogyo)

Kyowa Hakko is developing KW-6002, an adenosine A2A receptor antagonist, for the potential treatment of Parkinson's disease (PD) [183211]. The company subsequently began evaluating the compound for depression, and in June 2000 initiated a phase II trial for this indication. Good results have been obtained in a preclinical depression model and Kyowa Hakko hopes that KW-6002 will be representative of a new class of antidepressants [376107]. KW-6002 is undergoing phase II trials for PD in Japan [343257] and in Europe, including the UK 1271929], [321641], [402754]. As expected, KW-6002 entered phase II trials for PD in the US in October 1999 [321640], [342643], [360980], [402754]. The drug is of particular interest due to the absence of the involuntary movement adverse effects characteristic of L-DOPA therapy [271929]. Roche was to codevelop KW-6002 with Kyowa in the US and Europe, but withdrew from the development of this drug in April 1999 [321640]. Kyowa will continue with the drug's development in the US [321640]. NDAs are estimated to be filed around the end of 2001 and the drug is expected to be launched in Western Europe during 2002. An NDA is expected to be filed in Japan approximately three to four years later than in Western Europe [271929].

Effect of venlafaxine versus fluoxetine on metabolism of dextromethorphan, a CYP2D6 probe

Two antidepressants, venlafaxine and fluoxetine, were evaluated in vivo for their effect on cytochrome P450 2D6 (CYP2D6) activity, measured by the ratio of dextromethorphan, a sensitive CYP2D6 marker, to its metabolite dextrorphan (i.e., DM:DT) excreted in urine after DM coadministration. Twenty-eight healthy extensive metabolizers of CYP2D6 received either venlafaxine (37.5 mg bid for 7 days, then 75 mg bid until Day 28) or fluoxetine (20 mg daily for 28 days); 26 completed the study. Plasma concentrations of both drugs and their active metabolites were determined. DM:DTs were evaluated at baseline (Day 0), on Days 7 and 28 of dosing, and 2 weeks after drug discontinuation (Day 42). Steady-state drug and metabolite levels were achieved in both groups by Day 28. Mean DM:DTs for venlafaxine and fluoxetine differed statistically significantly (p < 0.001) on Days 7, 28, and 42. Comparisons of DM:DT as a percentage of baseline values showed that DM:DT increased 1.2-fold for venlafaxine and 9.1-fold for fluoxetine on Day 7 (p < 0.001) and increased 2.1-fold for venlafaxine and 17.1-fold for fluoxetine on Day 28 (p < 0.001). Inhibition of CYP2D6 metabolism persisted for 2 weeks after discontinuation of fluoxetine, unlike the case with venlafaxine. These in vivo results confirm in vitro data demonstrating significantly weaker inhibition of CYP2D6 with venlafaxine than with fluoxetine. This suggests that clinically significant interactions involving CYP2D6 inhibition could occur between fluoxetine and drugs metabolized by CYP2D6 but may be less likely to occur with venlafaxine.