Effect of alosetron on the pharmacokinetics of fluoxetine

Lotronex (alosetron hydrochloride) is a 5-HT3 receptor antagonist indicated for the treatment of irritable bowel syndrome (IBS) in females whose predominant bowel habit is diarrhea. Alosetron is extensively metabolized by multiple cytochrome P450 (CYP) enzymes, including CYP2C9 and CYP3A4. Fluoxetine is an antidepressant that is administered as a racemic mixture of equipotent R- and S-enantiomers. Fluoxetine metabolism involves CYP2D6 and CYP2C9 in the formation of its major metabolite, norfluoxetine. This metabolite is also present as two enantiomers, of which only the S-enantiomer exhibits comparable antidepressant activity. This study was conducted to assess the potential for an effect of alosetron on the pharmacokinetics of fluoxetine. This was an open-label, two-period, nonrandomized, crossover study in 12 healthy female and male volunteers. The pharmacokinetics for both enantiomers of fluoxetine and norfluoxetine were examined following single oral doses of 20 mg fluoxetine, given alone and in combination with alosetron 1 mg twice daily for 15 days. The results showed small delays in peak concentration but no clinically significant effect of alosetron on the pharmacokinetics of S- and R-fluoxetine or S- and R-norfluoxetine. Coadministration of alosetron and fluoxetine was well tolerated by all subjects.

Diphenhydramine alters the disposition of venlafaxine through inhibition of CYP2D6 activity in humans

CYP2D6 is the major enzyme involved in the metabolism of venlafaxine. Subjects with a low CYP2D6 activity have increased plasma concentrations of venlafaxine that may predispose them to cardiovascular side effects. In vitro and in vivo studies showed that diphenhydramine, a nonprescription antihistamine, can inhibit CYP2D6 activity. Therefore, the authors investigated in this study a potential drug interaction between diphenhydramine and venlafaxine. Fifteen male volunteers, nine with the extensive metabolizer (EM) and six with the poor metabolizer (PM) phenotype of CYP2D6, received venlafaxine hydrochloride 18.75 mg orally every 12 hours for 48 hours on two occasions (1 week apart): once alone and once during the concomitant administration of diphenhydramine hydrochloride (50 mg every 12 hours). Blood and urine samples were collected for 12 hours under steady-state conditions. In EMs, diphenhydramine decreased venlafaxine oral clearance from 104+/-60 L/hr to 43+/-23 L/hr (mean +/- SD; p < 0.05) without any effect on renal clearance (4+/-1 L/hr during venlafaxine alone and 4+/-2 L/hr during venlafaxine plus diphenhydramine). In PMs, coadministration of diphenhydramine did not cause significant changes in oral clearance and partial metabolic clearances of venlafaxine to its various metabolites. Diphenhydramine disposition was only slightly affected by genetically determined low CYP2D6 activity or concomitant administration of venlafaxine. In conclusion, diphenhydramine, at therapeutic doses, inhibits CYP2D6-mediated metabolism of venlafaxine in humans. Clinically significant interactions could be encountered during the concomitant administration of diphenhydramine and other antidepressant or antipsychotic drugs that are substrates of CYP2D6.

Sustained administration of the antidepressant venlafaxine in rats: pharmacokinetic and pharmacodynamic findings

Rats were administered venlafaxine (10 mg/kg per day) for 14 days by using subcutaneously implanted osmotic minipumps. The present study assessed the distribution of VEN in different compartments, whether the VEN concentration in the compartments correlated, the effect of VEN on dialysate monoamine levels and on the spontaneous open-field behavior, and possible relations between the pharmacokinetic and pharmacodynamic parameters. The venlafaxine level in serum after sustained treatment was about 25% of the concentration in brain parenchyma and much higher than in brain dialysate. There was a clear correlation between venlafaxine concentrations in blood and brain compartments. The sustained venlafaxine challenge resulted in higher neocortical concentration of serotonin and noradrenaline, lower 5-hydroxyindole-3-acetic acid levels and increased locomotor activity in the central part of the test arena as compared to controls. No correlations were found between the venlafaxine concentration and brain monoamine parameters or the open-field behaviors. We conclude that, although species differences in pharmacokinetic properties for venlafaxine between rat and man exist, the pharmacokinetic correlations found after sustained treatment add information to the in vivo nature of the drug. Also, more studies like the present need to be performed to find the pharmacokinetic/pharmacodynamic interrelations for drugs like VEN.

Fluoxetine in depressed patients on dialysis

OBJECTIVE

To test the safety and efficacy of fluoxetine in patients with renal failure on dialysis.

METHOD

Fourteen patients with major depression and end stage renal disease on hemodialysis were randomized into two groups for an eight-week study. Subjects as well as investigators were blinded as to which subject received fluoxetine and which placebo. Patients were carefully monitored concerning adverse events, serum fluoxetine and norfluoxetine levels, and psychological measurements of degree of depression.

RESULTS

No patients discontinued treatment because of adverse events, all of which were minor. All psychological tests showed improvement in depression at the four-week and eight-weeks point, although statistical significance could only be demonstrated at the fourth week of this study. All patients in the active group had serum plasma concentrations of fluoxetine and norfluoxetine less than 250 ng/ml at eight weeks, similar to levels in patients with normal renal function in a previous open label study.

CONCLUSIONS

This study confirms the relative safety of fluoxetine in depressed patients in renal failure on hemodialysis. It also suggests that fluoxetine may be efficacious in depressed patients on dialysis.

Gender-specific aging effects on the serotonin 1A receptor

The effects of age on serotonergic function have been hypothesized to underlie age-related changes in mood and behaviors such as sleep and eating. Of particular interest is the serotonin type-1A (5-HT1A) receptor, due to its putative role in mediating the therapeutic efficacy of antidepressant treatment. Using positron emission tomography (PET) and [11C--carbonyl] WAY100635, we assessed 5-HT1A receptor binding in 21 healthy subjects (10 men, 11 women) ranging in age from 21 to 80 years. Regional binding potential values were generated using a reference tissue model and corrected for partial volume effects. We observed an inverse relationship between age and binding of [11C--carbonyl] WAY100635 to the 5-HT1A receptor in men, but not women. This finding is in accord with observations reported in the postmortem literature. Gender-specific effects of age on central serotonergic function may relate to differences between men and women in behavior, mood, and susceptibility to neuropsychiatric disease across the adult lifespan.

Venlafaxine occupation at the noradrenaline reuptake site: in-vivo determination in healthy volunteers

Venlafaxine, a serotonin and noradrenaline reuptake inhibitor, is an effective antidepressant at doses of 75 mg p.o. daily and above. Preclinical and healthy volunteer studies have demonstrated that venlafaxine is more potent at the serotonin than at the noradrenaline reuptake site, with noradrenergic blocking effects being observed at doses >75 mg p.o. in man. We used the Multiple Organs Coincidences Counter and [11C] meta hydroxy ephedrine (MHED) to test whether significant occupation of cardiac sympathetic neurones was achieved in man in vivo after the acute administration of venlafaxine 75 mg p.o. in nine healthy volunteers. MHED is a tracer which binds at the noradrenaline reuptake site. This study demonstrates that the [11C]MHED signal is significantly reduced after the administration of venlafaxine 75 mg p.o. thus showing that noradrenaline reuptake blockade is observable at this dose. This effect is predominantly seen in volunteers who received > 1 mg/kg venlafaxine.

Paroxetine: a review

Paroxetine is a potent and selective serotonin reuptake inhibitor (SSRI) with currently approved indications for the treatment of depression, obsessive-compulsive disorder, panic disorder and social phobia. It is also used in the treatment of generalized anxiety disorder, post traumatic stress disorder, premenstrual dysphoric disorder and chronic headache. Paroxetine, a phenylpiperidine derivative, is the most potent inhibitor of the reuptake of serotonin (5-hydroxytryptamine, 5-HT) of all the currently available antidepressants including the class of SSRIs. It is a very weak inhibitor of norepinephrine (NE) uptake but it is still more potent at this site than the other SSRIs. The selectivity of paroxetine, i.e., the ratio of inhibition of uptake of norepinephrine to serotonin (NE/5-HT) is amongst the highest of the SSRIs. Paroxetine has little affinity for catecholaminergic, dopaminergic or histaminergic systems and by comparison with tricyclic antidepressants (TCAs) has, therefore, a reduced propensity to cause central and autonomic side effects. Paroxetine exhibits some affinity for the muscarinic cholinergic receptor but much less than the TCAs. In addition, the adaptive changes of somatodendritic (5-HT(1A)) and terminal (5-HT(1B/1D)) autoreceptors observed with paroxetine are different to those observed with TCAs; it also inhibits nitric oxide synthase. It is both a substrate and an inhibitor of cytochrome isoenzyme P450 2D6. Paroxetine is well absorbed orally and undergoes extensive first pass metabolism that is partially saturable. Its metabolites are pharmacologically inactive in vivo. Steady state levels are achieved after 4-14 days and an elimination half-life of 21 h is consistent with once-daily dosing. There is wide inter-individual variation in the pharmacokinetics of paroxetine in adults as well as in the young and the elderly with higher plasma concentrations and slower elimination noted in the latter. Elimination is also reduced in severe renal and hepatic impairment. Serious adverse events are, however, extremely rare even in overdose. In summary, paroxetine is well tolerated and effective in the treatment of both depressive and anxiety disorders across the age range.

Loratadine and terfenadine interaction with nefazodone: Both antihistamines are associated with QTc prolongation

BACKGROUND AND OBJECTIVE

Nefazodone inhibits CYP3A; therefore coadministration with CYP3A substrates such as terfenadine or loratadine may result in increased exposure to these drugs. A potential pharmacodynamic consequence is electrocardiographic QTc prolongation, which has been associated with torsade de pointes cardiac arrhythmia. Therefore a clinical pharmacokinetic-pharmacodynamic evaluation of this potential interaction was conducted.

METHODS

A randomized, double-blind, double-dummy, parallel group, multiple-dose design was used. Healthy men and women who were given doses of 60 mg of terfenadine every 12 hours, 20 mg of loratadine once daily, and 300 mg of nefazodone every 12 hours were studied. Descriptive pharmacokinetics (time to maximum concentration, maximum concentration, and area under the plasma concentration-time curve) were used for the examination of interactions among the respective parent drugs and metabolites. QTc prolongation (mean value over the dosing interval) was the pharmacodynamic parameter measured. Kinetic and dynamic analysis was used for the examination of pooled concentration and QTc data with the use of a linear model.

RESULTS

Concomitant nefazodone treatment markedly increased the dose interval area under the plasma concentration-time curve of both terfenadine (mean value, 17.3 +/- 8.5 ng. mL/h versus 97.4 +/- 48.9 ng. mL/h; P <.001) and carboxyterfenadine (mean value, 1.69 +/- 0.48 microg. h/mL versus 2.88 +/- 0.53 microg. h/mL; P <.001) and moderately increased the dose interval area under the plasma concentration-time curve of both loratadine (mean value, 31.5 +/- 27.9 ng. h/mL versus 43.7 +/- 25.9 ng. h/mL; P <.014) and descarboethoxyloratadine (mean value, 73.4 +/- 54.9 ng. h/mL versus 81.9 +/- 26.2 ng. h/mL; P <.002). The mean QTc was unchanged with terfenadine alone; however, it was markedly prolonged with concomitant nefazodone and terfenadine (mean [90% confidence interval] prolongation 42.4 ms [34.2, 50.6 ms]; P <.05). Similarly, the mean QTc was unchanged with loratadine alone; however, it was prolonged with concomitant nefazodone and loratadine (21.6 ms [13.7, 29.4 ms]; P <.05). Nefazodone alone did not change mean QTc. QTc was positively correlated with terfenadine plasma concentration (r (2) = 0.21; P =.0001). Similarly, QTc was positively correlated with loratadine plasma concentration (r (2) = 0.056; P =.0008) but with a flatter slope. There was no relationship between QTc and nefazodone plasma concentration during treatment with nefazodone alone (r (2) = 0.002, not significant).

CONCLUSIONS

In healthy men and women, concomitant nefazodone treatment at a therapeutic dose increases exposure to both terfenadine and carboxyterfenadine. This increased exposure is associated with marked QTc prolongation, which is correlated with terfenadine plasma concentration. A similar interaction occurs with loratadine, although it is of lesser magnitude. Concomitant administration of nefazodone with terfenadine may have predisposed individuals to the arrhythmia associated with QTc prolongation, torsade de pointes, when terfenadine was available for clinical use. However, a new finding is that in the context of higher than clinically recommended daily doses (20 mg) of loratadine concomitant administration with a metabolic inhibitor such as nefazodone can also result in QTc prolongation.

Influence of coadministration of fluoxetine on cisapride pharmacokinetics and QTc intervals in healthy volunteers

STUDY OBJECTIVE

To evaluate the effect of fluoxetine on the pharmacokinetics and cardiovascular safety of cisapride at steady state in healthy men.

DESIGN

Open-label, three-phase, sequential study.

SETTING

Clinical research center.

SUBJECTS

Twelve healthy male volunteers.

INTERVENTIONS

Each subject was treated according to the following sequence: baseline; phase 1 (days 1-6): cisapride 10 mg 4 times/day; washout (days 7-13); phase 2 (days 14-44): fluoxetine 20 mg/day; and phase 3 (days 45-52): cisapride 10 mg 4 times/day (days 45-51) plus fluoxetine 20 mg/day (days 45-52).

MEASUREMENTS AND MAIN RESULTS

Blood samples were drawn and 12-lead electrocardiograms performed at specified time points after the last morning dose of cisapride in phases 1 and 3. Blood samples also were taken before morning doses on the 3rd, 4th, and 5th days of phases 1 and 3. Electrocardiograms were done at baseline and on the last day of the washout period and phase 2. Coadministration of fluoxetine significantly decreased cisapride plasma concentrations. There were no clinically significant changes in corrected QT intervals during administration of cisapride alone or with fluoxetine. Cisapride was well tolerated when administered alone or with fluoxetine.

CONCLUSION

Cisapride can be administered safely to patients receiving low therapeutic dosages of fluoxetine.

Bioanalysis of racemic reboxetine and its desethylated metabolite in a therapeutic drug monitoring setting using solid phase extraction and HPLC

Reboxetine is a new antidepressant drug acting as a potent and selective noradrenaline reuptake inhibitor on the noradrenergic neuronal system. Because of an expected interindividual variability in drug metabolism in the clinical practice the need for therapeutic drug monitoring routines in psychiatry is always a prominent feature. In this application, the preferred bioanalytic methodology was solid phase extraction combined with reversed-phase high-performance liquid chromatography and ultraviolet detection at 210 nm. The technique proved reliable, with interday and intraday variation of less than 5% and a quantification limit for reboxetine and one of its main metabolites O-desethylreboxetine (O-reboxetine) at 5 and 30 nmol/L, respectively. The method was applied on serum samples from 38 patients treated chronically with reboxetine. These samples were drawn as trough levels in steady state with a dosage range of 2-16 mg/day. They evidenced a mean reboxetine concentration that was fairly linear and dose proportional, although the variance in concentration was large between patients, even those taking the same dosage. O-reboxetine was detected in quantifiable amounts in only 1 of the 38 patients (<3%). In conclusion, these results suggest that a routine reboxetine therapeutic drug monitoring service that is robust enough to produce reliable and reproducible results may be introduced into everyday clinical practice.

The selective serotonin reuptake inhibitor sertraline: its profile and use in psychiatric disorders

The naphthylamine derivative sertraline is a potent and selective inhibitor of serotonin reuptake into presynaptic terminals. Sertraline has a linear pharmacokinetic profile and a half-life of about 26 h. Its major metabolite, desmethylsertraline does not appear to inhibit serotonin reuptake. Sertraline mildly inhibits the CYP2D6 isoform of the cytochrome P450 system but has little effect on CYP1A2, CYP3A3/4, CYP2C9, or CYP2C19. It is, however, highly protein bound and may alter blood levels of other highly protein bound agents. Sertraline is a widely used serotonin reuptake inhibitor that has been shown to have both antidepressant and antianxiety effects. Many clinical trials have demonstrated its efficacy in depression compared with both placebo and other antidepressant drugs. Its efficacy has also been demonstrated in randomized, controlled trials of patients with obsessive-compulsive disorder, panic disorder, social phobia, and premenstrual dysphoric disorder. In short-term, open-label studies it has appeared efficacious and tolerable in children and adolescents and in the elderly, and data are positive for its use in pregnant or lactating women. Typical side effects include gastrointestinal and central nervous system effects as well as treatment-emergent sexual dysfunction; withdrawal reactions may be associated with abrupt discontinuation of the agent. The safety profile of sertraline in overdose is very favorable. Sertraline's efficacy for both mood and anxiety disorders, relatively weak effect on the cytochrome P450 system, and tolerability profile and safety in overdose are factors that contribute to make it a first-line agent for treatment in both primary and tertiary care settings.

Drug-drug interaction studies with mirtazapine and carbamazepine in healthy male subjects

In two studies, the effects of the potentially interacting drugs mirtazapine and carbamazepine on their pharmacokinetics have been investigated. Subjects were treated with carbamazepine combined with placebo for 21 days and subsequently with carbamazepine combined with mirtazapine for another 7 days (Study A) or with mirtazapine combined with placebo for 7 days and subsequently mirtazapine combined with carbamazepine for another 21 days (Study B). Pharmacokinetic results indicate that carbamazepine decreased significantly AUC and Cmax values for mirtazapine and increased values for demethyl-mirtazapine Cmax. Mirtazapine had no effect on carbamazepine pharmacokinetic parameters, but did lower carbamazepine-10,11-epoxide levels. Mirtazapine did not affect the single dose kinetics or the enzyme inducing properties of carbamazepine. VAMRS alertness scores reflected the somnolence-inducing effects of carbamazepine and mirtazapine and psychometric test results revealed impairment of specific tasks. The combination was safe and routine laboratory testing did not reveal clinically relevant abnormalities. The dose of mirtazapine in patients on carbamazepine may have to be increased for optimal antidepressant efficacy.

Pharmacological treatment of depression: the role of paroxetine

Depression is reaching epidemic proportions in the western world. With each successive generation more people are becoming more severely depressed at a younger age.

Pharmacokinetic comparison of oral solution and tablet formulations of citalopram: a single-dose, randomized, crossover study

BACKGROUND

Citalopram tablets fulfill most dosing needs in the treatment of depression, but some patients may have difficulty swallowing tablets and thus may be less likely to comply with their medication regimen. A liquid formulation of citalopram could be beneficial for such patients.

OBJECTIVE

This study was undertaken to compare the pharmacokinetic profiles of oral solution and tablet formulations of citalopram in healthy volunteers.

METHODS

In this open-label, single-dose, randomized, crossover, bioequivalence study, healthy volunteers alternately received one 60-mg dose of citalopram as an oral solution (10 mg/5 mL) and one 60-mg dose as a tablet. Doses were separated by a 14-day interval.

RESULTS

Of 24 subjects enrolled (mean age 27 years), 24 (16 men and 8 women) received the citalopram oral solution and 23 (15 men and 8 women) received the tablet; 1 subject discontinued before receiving the tablet. Citalopram was rapidly absorbed, with peak plasma concentrations occurring at approximately 4 hours with both formulations. The rate and extent of absorption were similar between the 2 formulations, and no statistically significant differences were observed in half-life or oral clearance between formulations. Similarly, the pharmacokinetic profile for demethylcitalopram (the major metabolite of citalopram) did not differ between the 2 formulations. Both formulations were well tolerated, with no serious adverse events reported.

CONCLUSION

The oral solution and tablet formulations of citalopram 60 mg were determined to be bioequivalent in this population.

Steady-state pharmacokinetics of citalopram in young and elderly subjects

STUDY OBJECTIVES

To compare the steady-state pharmacokinetics of citalopram after multiple-dose administration in elderly and young subjects, and to correlate pharmacokinetic measurements with tolerability.

DESIGN

Single-blind, multiple-dose, dose-escalating, randomized, placebo-controlled trial.

SETTING

The Orlando Clinical Research Center, Orlando, Florida.

SUBJECTS

Twenty-four healthy elderly and eight healthy young men and women.

INTERVENTIONS

Subjects randomized to citalopram received 10 mg once/day for the first week, 20 mg once/day for the second week, and 40 mg once/day for the remaining 3 weeks.

MEASUREMENTS AND MAIN RESULTS

Blood samples were collected weekly to determine steady-state pharmacokinetics of citalopram and its primary metabolites. During dose escalation, samples were collected just before dose increase. After the final dose, blood samples were collected periodically over 480 hours to characterize the terminal elimination phase. In elderly subjects, maximum concentration, time associated with the maximum concentration, area under the concentration versus time curve from 0-24 hours, half-life, and volume of distribution were all slightly increased; oral clearance was slightly decreased. However, only half-life was statistically different between the groups, 30% longer in the elderly. In addition, the frequency and severity of adverse events were comparable between the two age groups and did not appear to be dose related.

CONCLUSIONS

The pharmacokinetics and tolerability of citalopram in elderly subjects are similar to those observed in younger subjects. The slight differences observed in the elderly likely reflect declining liver and kidney function.

Birth outcomes following prenatal exposure to fluoxetine

BACKGROUND

Although pregnancy has frequently been described as a time of emotional well-being, some women experience significant antenatal depression that may require treatment with antidepressants. The purpose of this investigation was to examine the relative effects of early and late trimester exposure to fluoxetine and perinatal outcome.

METHODS

Obstetric and neonatal records were reviewed for 64 mother-infant pairs where there was documented use of fluoxetine at some point during pregnancy. Differences in several measures of obstetrical outcome and neonatal well-being were examined in early trimester- and late trimester-exposed infants.

RESULTS

No differences in birth weight and acute neonatal outcome were evident across the two groups, though there was a higher frequency of special care nursery admissions for infants with exposure to fluoxetine late in pregnancy. Special care nursery admissions could not be attributed to any specific factor.

CONCLUSIONS

Given the growing numbers of women who are treated with antidepressants, including fluoxetine, during pregnancy, and the strong association between depression during pregnancy and risk for postpartum depression, patients may be best advised to continue treatment with antidepressants through labor and delivery versus making any change in intensity of treatment during the acute peripartum period.

Amniotic fluid and umbilical cord blood concentrations of antidepressants in three women

BACKGROUND

Pregnancy and the postpartum period are a time of increased risk for women to develop mood disorders. As such, the reproductive safety data on antidepressant use during pregnancy have rapidly expanded over the last decade; however, there is relatively sparse information on maternal/fetal exchange of these medications and no data reporting their concentrations in amniotic fluid.

METHODS

We report on three women treated during pregnancy with fluvoxamine, sertraline, and venlafaxine, respectively. Amniotic fluid at amniocentesis and umbilical cord blood and maternal blood at delivery were collected and analyzed for antidepressant concentrations using high performance liquid chromatography with UV detection.

RESULTS

Antidepressant and metabolite concentrations were detectable in all amniotic fluid samples, though parent compound concentrations were less than maternal serum and umbilical cord blood concentrations. No adverse effects of the medication were reported.

CONCLUSIONS

The presence of these antidepressants in amniotic fluid suggests that fetal exposure to these medications is continual and may occur through a variety of paths, thus accounting for increased fetal exposure. These paths include circulatory via placental passage, gastrointestinal via fetal swallowing, and respiratory secondary to fetal lung absorption.

CYP2B6 mediates the in vitro hydroxylation of bupropion: potential drug interactions with other antidepressants

The in vitro biotransformation of bupropion to hydroxybupropion was studied in human liver microsomes and microsomes containing heterologously expressed human cytochromes P450 (CYP). The mean (+/-S.E.) K(m) in four human liver microsomes was 89 (+/-14) microM. In microsomes containing cDNA-expressed CYPs, hydroxybupropion formation was mediated only by CYP2B6 at 50 microM bupropion (K(m) 85 microM). A CYP2B6 inhibitory antibody produced more than 95% inhibition of bupropion hydroxylation in four human livers. Bupropion hydroxylation activity at 250 microM was highly correlated with S-mephenytoin N-demethylation activity (yielding nirvanol), another CYP2B6-mediated reaction, in a panel of 32 human livers (r = 0.94). The CYP2B6 content of 12 human livers highly correlated with bupropion hydroxylation activity (r = 0.96). Thus bupropion hydroxylation is mediated almost exclusively by CYP2B6 and can serve as an index reaction reflecting activity of this isoform. IC(50) values for inhibition of a CYP2D6 index reaction (dextromethorphan O-demethylation) by bupropion and hydroxybupropion were 58 and 74 microM, respectively. This suggests a low inhibitory potency versus CYP2D6, the clinical importance of which is not established. Since bupropion is frequently coadministered with other antidepressants, IC(50) values (microM) for inhibition of bupropion hydroxylation were determined as follows: paroxetine (1.6), fluvoxamine (6.1), sertraline (3.2), desmethylsertraline (19.9), fluoxetine (59.5), norfluoxetine (4.2), and nefazodone (25.4). Bupropion hydroxylation was only weakly inhibited by venlafaxine, O-desmethylvenlafaxine, citalopram, and desmethylcitalopram. The inhibition of bupropion hydroxylation in vitro by a number of newer antidepressants suggests the potential for clinical drug interactions.

An unusual multiple drug intoxication case involving citalopram

A 47-year-old male with a history of drug abuse and suicide attempts was found dead at home. The death scene investigation showed evidence of cocaine abuse and multiple drug ingestion. Citralopram, a new selective serotonin reuptake inhibitor, cocaine, oxycodone, promethazine, propoxyphene, and norpropoxyphene were identified and quantitated in the postmortem samples by gas chromatography-mass spectrometry. The concentration of citalopram in the femoral blood was 0.88 mg/L. The heart blood concentration was 1.16 mg/L. Femoral blood concentrations of the other drugs were as follows: cocaine, 0.03 mg/L; oxycodone, 0.06 mg/L; promethazine, 0.02 mg/L; propoxyphene, 0.02 mg/L; and norpropoxyphene, 0.07 mg/L. Other tissue samples were also analyzed. The concentrations of cocaine, oxycodone, promethazine, and propoxyphene in the blood, liver, brain, and gastric contents did not suggest an intentional overdose. However, the possibility of multiple drug interactions including citalopram was evident. In this case, the citalopram concentrations were consistent with those reported in fatal cases involving multiple drug use. Citalopram was present in urine at a concentration of 0.9 mg/L.

Lithium augmentation of venlafaxine: an open-label trial

The authors conducted an open-label study of the efficacy and tolerability of venlafaxine and of lithium augmentation in outpatients with depression who were not responding to venlafaxine. Outpatients aged 18 to 70 years were eligible if they had a minimum baseline score of 16 on the 17-item Hamilton Rating Scale for Depression (HAM-D). Patients were started on venlafaxine 37.5 mg twice daily for 1 week. For weeks 2 through 4, the dose of venlafaxine was increased to 75 mg twice daily, and for weeks 5 through 7, the dose was further increased to 75 mg three times daily. At the end of the 7-week treatment period, patients with a <50% decrease in their HAM-D scores from baseline were given lithium carbonate 600 mg once daily. The dose of lithium carbonate was adjusted to maintain plasma levels in the range of 0.6 to 1.0 mmol/mL. Efficacy was assessed with the 17-item HAM-D, Montgomery-Asberg Depression Rating Scale, and the Clinical Global Impressions Scale. Data were analyzed on an intent-to-treat basis. At the end of the 7-week treatment period, 35% of patients showed a > or = 50% decrease in their HAM-D scores from baseline. Lithium augmentation was initiated in 23 patients. The results showed that the addition of lithium was well-tolerated and led to a further decrease in the HAM-D scores, with eight patients responding and two of them presenting a remission. The addition of lithium to venlafaxine was found to be a well-tolerated strategy in treatment-resistant patients.

The decreased in vivo clearance of CYP2D6 substrates by CYP2D6*10 might be caused not only by the low-expression but also by low affinity of CYP2D6

CYP2D6 exhibits genetic polymorphism with interindividual differences in metabolic activity. We have found a significant influence on the pharmacokinetics of venlafaxine by the CYP2D6*10 allele in a Japanese population. CYP2D6.10, which is translated from CYP2D6*10, has two amino acid substitutions: Pro34 --> Ser and Ser486 --> Thr. In this study, CYP2D6.10 was expressed in Saccharomyces cerevisiae and its catalytic activity for CYP2D6 substrates was investigated. The CYP2D6*10B- and *10C-associated cDNA were isolated from human lymphocyte genotyped as CYP2D6*10. In addition, three forms of CYP2D6, Pro34/Thr486 (PT), Ser34/Ser486 (SS), and Pro34/Ser486 (wild type, CYP2D6.1), were constructed by PCR-site mutagenesis to clarify the effects of the two amino-acid substitutions. The expression of CYP2D6 protein was confirmed by immunoblotting using CYP2D antibody. The absorbance at 450 nm was measured by CO-reduced difference spectra from five all microsome preparations. The CYP2D6 forms with Pro34 --> Ser amino acid substitution were at a lower expression than CYP2D6.1 from the findings of immunoblotting and spectral analysis. The apparent K(m) values of CYP2D6.1, CYP2D6.10A, and CYP2D6.10C were 1.7, 8.5, and 49.7 microM, respectively, for bufuralol 1'-hydroxylation, and 9.0, 51.9, and 117.4 microM, respectively, for venlafaxine O-demethylation, respectively. The V(max) values were not significantly different among the three variants. These findings suggest that the decreased in vivo clearance by CYP2D6*10 was caused not only by low expression of but also the increased K(m) value of CYP2D6.

The Antidepressant Nefazodone: A Review of its Pharmacology, Clinical Efficacy, Adverse Effects, Dosage, and Administation

Nefazodone is an antidepressant medication which received approval from the Food and Drug Administration for treatment of major depressive disorder in 1994. This article summarizes the pharmacodynamics, pharmacokinetics, adverse effects, and drug interactions of nefazodone as well as its administration and dosing schedule. The potential efficacy of nefazodone in treating anxiety, premenstrual syndrome, chronic pain conditions, and sleep disturbances also is summarized. Nefazodone has a favorable side effects profile which makes it an attractive alternative option for patients who withdraw from treatment when they develop adverse effects to other available antidepressants.

Nefazodone pharmacokinetics in depressed children and adolescents

OBJECTIVE

To describe the pharmacokinetics and safety of nefazodone (NFZ) in depressed children and adolescents.

METHOD

Depressed youths aged 7 to 17 years were eligible to participate. Intensive sampling for pharmacokinetic analyses of NFZ and 3 of its active metabolites was performed after single and multiple dose administration. Treatment was continued for 6 more weeks and titrated to maximize clinical response.

RESULTS

Twenty-eight patients were enrolled. Systemic exposure to NFZ and 3 metabolites was generally higher in children than adolescents. NFZ and metabolite disposition profiles showed high intra- and interpatient variability. Compared to published data in adults, the half-life of NFZ and 2 of its metabolites appears shorter in children and adolescents. Meta-chlorphenylpiperazine pharmacokinetic parameters were different in 5 patients determined to be poor metabolizers of cytochrome P450 2D6 (CYP2D6). NFZ was well tolerated, and administration was associated with significant reductions (p < .001) in depressive symptoms.

CONCLUSIONS

The pharmacokinetics of NFZ in pediatric patients is highly variable. NFZ appears to be safe in this small, short-term study. Pediatric patients who are poor metabolizers of CYP2D6 do not appear to be at increased risk for NFZ-associated adverse events. Open-label treatment of NFZ is associated with reductions in depressive symptoms.

[Pharmacokinetics of second generation antidepressants]

This paper presents the pharmacokinetic properties of newer second generation antidepressants, with an emphasis on the main metabolic pathways of drugs and metabolites as well as their effects on the cytochrome P450 enzymes. Except for Milnacipran all newer antidepressants are biotransformed in the presence of at least one cytochrome P450 izoenzyme. Drugs and their metabolites may be the substrates or inhibitors of cytochromes P450. The knowledge of drugs' metabolic pathways as well as the knowledge of substrates and inhibitors of izoenzymes assists in choice of a proper drug and its dose. It is particularly important in case of polypharmacotherapy when there is a high risk of adverse events. It is also important to remember about genetic polymorphism of some cytochrome P450 izoenzymes (CYP2D6, CYP2C19) that underlies the marked inpatient variability in drug metabolism.

The impact of the CYP2D6 and CYP2C19 genotypes on venlafaxine pharmacokinetics in a Japanese population

OBJECTIVE

The cytochrome P450 isozymes CYP2D6 and CYP2C19 exhibit genetic polymorphism in human, including a marked interethnic difference. As the functional status of the isozymes CYP2D6 and CYP2C19 have an impact on the pharmacokinetics of some antidepressants, we investigated whether the disposition of venlafaxine was affected by the CYP2D6 and CYP2C19 genotypes.

METHODS

Twenty-eight adult Japanese men in good health participated in this study. Genomic DNA was isolated from peripheral lymphocytes, and the CYP2D6 genotype was determined using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis and XbaI-RFLP analysis. Subjects were categorized into the following four groups: group 1 CYP2D6*10/*10; group 2 CYP2D6*1/*10 and *2/*10; group 3 CYP2D6*1/*1, *1/*2 and *2/*2; and group 4 the other genotypes. Two defective CYP2C19 alleles (CYP2C19*2 and CYP2C19*3) were identified by means of PCR-RFLP analysis. Venlafaxine was administered orally following an overnight fast. Plasma concentrations of venlafaxine and O-desmethylvenlafaxine were monitored using high-performance liquid chromatography up to 24 h.

RESULTS

The peak plasma concentration and values of area under the concentration-time curve up to 24 h for venlafaxine were 298% and 453% higher for group 1 than group 3, and 91% and 120% higher for group 2 than for group 3, respectively. The homozygote for two defective alleles of CYP2C19 showed a higher concentration of venlafaxine within group 1 and group 2.

CONCLUSION

The CYP2D6*10 allele and two CYP2C19 defective alleles, common in an Asian population, are the most likely genetic factors to use in determining interindividual differences in the pharmacokinetics of venlafaxine, although the results with respect to CYP2C19 are preliminary because of the few subjects used.

Marked increase of venlafaxine enantiomer concentrations as a consequence of metabolic interactions: a case report

On three occasions, unusually high trough plasma concentrations of venlafaxine were measured in a patient phenotyped and genotyped as being an extensive CYP2D6 metabolizer and receiving 450 mg/day of venlafaxine and multiple comedications. Values of 1.54 and of 0.60 mg/l of venlafaxine and O-desmethylvenlafaxine, respectively, were determined in the first blood sample, giving an unusually high venlafaxine to O-desmethylvenlafaxine ratio. This suggests an impaired metabolism of venlafaxine to O-desmethylvenlafaxine, and is most likely due to metabolic interactions with mianserin (240 mg/day) and propranolol (40 mg/day). Concentration of (S)-venlafaxine measured in this blood sample was almost twice as high as (R)-venlafaxine ((S)/(R) ratio: 1.94). At the second blood sampling, after addition of thioridazine (260 mg/day), which is a strong CYP2D6 inhibitor, concentrations of venlafaxine were further increased (2.76 mg/l), and concentrations of O-desmethylvenlafaxine decreased (0.22 mg/l). A decrease of the (S)/(R)-venlafaxine ratio (-20%) suggests a possible stereoselectivity towards the (R)-enantiomer of the enzyme(s) involved in venlafaxine O-demethylation at these high venlafaxine concentrations. At the third blood sampling, after interruption of thioridazine, concentrations of venlafaxine and O-desmethylvenlafaxine were similar to those measured in the first blood sample. This case report shows the importance of performing studies on the effects of either genetically determined or acquired deficiency of metabolism on the kinetics of venlafaxine.

Evidence of the dual mechanisms of action of venlafaxine

BACKGROUND

Indirect evidence suggests that the antidepressant venlafaxine hydrochloride selectively inhibits serotonin (5-HT) uptake at low doses, whereas at high doses, it inhibits both 5-HT and norepinephrine (NE) uptake. We hypothesized that, in vivo, both high and low doses would inhibit the 5-HT uptake of platelets but that the higher dose would differentially blunt the pressor response to tyramine, a marker for NE uptake.

METHODS

Healthy male volunteers aged 18 to 45 years received either 75 mg or 375 mg of venlafaxine hydrochloride per day, the 5-HT uptake inhibitor sertraline hydrochloride (50 mg/d), or the NE uptake inhibitor maprotiline hydrochloride (150 mg/d) (n = 8 for each of 4 treatment groups). Changes in platelet 5-HT uptake and the pressor response to intravenous tyramine were assessed following the initial dose and after 1 and 2 weeks of drug administration.

RESULTS

Platelet 5-HT uptake was inhibited by venlafaxine across the dose range and by sertraline but not maprotiline. Inhibition was competitive, related to increases in affinity and not related to capacity. Steady-state drug levels were associated with a 5-HT uptake inhibition of 87% or more in subjects taking venlafaxine or sertraline. The pressor response to tyramine differentially distinguished maprotiline from sertraline and the low dose of venlafaxine but not from the high dose of venlafaxine.

CONCLUSION

This study provides the first in vivo evidence in healthy humans that both 5-HT uptake and NE uptake inhibition are mechanisms of action sequentially engaged by venlafaxine over its clinically relevant dose range.

Penetration of amitriptyline, but not of fluoxetine, into brain is enhanced in mice with blood-brain barrier deficiency due to mdr1a P-glycoprotein gene disruption

Mice with a genetic disruption (knockout) of the multiple drug resistance (Mdr1a) gene were used to examine the effect of the absence of the drug-transporting P-glycoprotein at the blood-brain barrier on the uptake of amitriptyline (AMI) and fluoxetine (FLU) and their metabolites into the brain. One hour after intraperitoneal injection of AMI or FLU, knockout (-/-) and wild-type (+/+) mice were sacrificed and drug concentrations of brain, kidney, liver, testis, and plasma were measured. The plasma concentrations of the AMI metabolites and the brain:spleen ratios of AMI, nortriptyline (NOR), 10-OH-AMI and 10-OH-NOR were significantly higher in the -/- mice, demonstrating that AMI and its metabolites are substrates of the P-glycoprotein and that mdr1a activity at the level of the blood-brain barrier reduces the penetration of these substances into the brain. In contrast, tissue distributions of FLU and its metabolites among the various tissues tested were indistinguishable between groups. The herein reported differences in brain penetration of antidepressant drugs depending on the presence of the mdr1a gene may offer an explanation for differences in the treatment response at a given plasma concentration. Moreover, individual differences in mdr1 gene activity may account for variable response patterns at different episodes and development of therapy resistance.

Dose-response evaluation of the interaction between sertraline and alprazolam in vivo

In vitro data show the inhibition of alprazolam metabolism by sertraline via CYP3A4; therefore, using a randomized, double-blind, placebo-controlled design, the authors conducted this study to assess the potential for similar in vivo inhibition in humans. Ten healthy volunteers participated in two test sessions (placebo/alprazolam 1 mg orally) before the initiation of sertraline treatment. Blood samples were obtained over a 32-hour period and pharmacodynamic measures (sedation, psychomotor performance, memory function) were obtained over an 8-hour period. After a minimum of 2 weeks of daily sertraline self-administration (50, 100, or 150 mg/day), test sessions were repeated. Alprazolam concentrations (N = 6, 4, and 6 at sertraline doses of 50, 100, and 150 mg/day, respectively) showed no significant changes based on peak concentration (Cmax), time to maximum concentration (Tmax), elimination half-life (t1/2[beta]), and area under the concentration-time curve (AUC(0-8)), with the exception of a reduced Cmax in the 50 mg/day group. Similarly, dynamic data showed no significant variations based on peak effect, Tmax, and AUC(0-infinity), with the exception of increased peak impairment in one measure of psychomotor performance. No differences were detected between placebo alone and placebo plus sertraline. These findings suggest that sertraline (50-150 mg/day) does not alter the single-dose kinetics or dynamics of alprazolam; therefore, the combination may be prescribed without an increased risk of alprazolam toxicity.

Pharmacokinetics and pharmacodynamics of antidepressant medications. Based on a presentation by C. Lindsay DeVane, PharmD

Antidepressants can be categorized by their pharmacodynamic and pharmacokinetic properties. Of the various types of antidepressants, selective serotonin reuptake inhibitors (SSRIs) have become the most often prescribed. Some major pharmacokinetic and pharmacodynamic differences among the SSRIs include half-life, ease of discontinuation of therapy, and the potential for involvement in metabolic drug-drug interactions. Antidepressants are also compared with respect to efficacy, although little difference is thought to exist in the efficacy of different SSRIs. Thus, managed care providers must consider the more subtle differences among the effects of SSRIs in order to rank-order the preferences for selecting a specific drug for a particular patient.

Carbamazepine-nefazodone interaction in healthy subjects

The pharmacokinetic interaction between nefazodone and carbamazepine was investigated in 12 healthy male volunteers. Subjects received nefazodone 200 mg twice daily for 5 days, and blood sample collection was performed on day 5 for 0- to 48-hour pharmacokinetic analysis. A 4-day wash-out phase then followed from days 6 to 9. Carbamazepine 200 mg was administered once daily from days 10 to 12, and then 200 mg was given twice daily from days 13 to 44. A 0- to 48-hour pharmacokinetic analysis was performed on day 38. Nefazodone 200 mg twice daily was added to the dosing regimen from days 40 to 44, and a subsequent 0- to 48-hour pharmacokinetic analysis was performed on day 44. Coadministration of nefazodone increased steady-state plasma area under the concentration-time curve (AUC) of carbamazepine from 60.77 (+/-8.44) to 74.98 (+/-12.88) microg x hr/mL (p < 0.001) and decreased the active carbamazepine-10,11-epoxide metabolite AUC concentration from 7.10 (+/-1.16) to 5.71 (+/-0.52) microg x hr/mL (p < 0.005). During the combination, the steady-state AUC of nefazodone decreased from 7,326 (+/-3,768) to 542 (+/-191) ng x hr/mL, and the AUCs of its metabolites (hydroxynefazodone, meta-chlorophenylpiperazine, and triazoledione) decreased significantly as well (p < 0.001). Coadministration of nefazodone 200 mg twice daily and carbamazepine 200 mg twice daily was found to be safe and well tolerated; however, the increased plasma exposure to carbamazepine may warrant monitoring of plasma carbamazepine concentrations with the combination. However, higher doses (>400 mg/day) of carbamazepine could yield more extensive induction, affecting tolerability of the combination. No change in the initial nefazodone dose is necessary, and subsequent dose adjustments should be made on the basis of clinical effects; however, the repercussion of carbamazepine induction of nefazodone metabolism on the antidepressant efficacy has yet to be studied.

Comparative bioavailability of a new formulation of fluoxetine drops

Fluoxetine drops and marketed fluoxetine capsules had quite the same Cmax (50.25 +/- 4.43 vs 47.55 +/- 5.29 ng/ml), but significantly different AUC0-t (717.27 +/- 71.29 vs 644.91 +/- 78.91 ng/ml/h). Furthermore the drops were characterised by a very early Tmax (4.61 +/- 0.85 hours) with a highly significant difference in comparison to the capsules reference compound (6.72 +/- 1.23 hours). After log transformation 90% C.I. for Cmax, AUC 0-t and AUC0-. were 1.05, 1.11, 0.82 respectively. The two products, therefore, cannot be considered bioequivalent. Our results demonstrate that fluoxetine drops and capsules significantly differ for their pharmacokinetics, with an earlier Tmax and a higher AUC0-t after the administration of the drops preparation.

Pharmacokinetic and pharmacodynamic responses to chronic administration of the selective serotonin reuptake inhibitor citalopram in rats

The number of drugs used to treat affective disorders such as depression is rapidly increasing. Citalopram (CIT), an antidepressant, is a selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitor (SSRI). In the present study, rats were treated with 10 mg/kg/d racemic CIT for two weeks with use of osmotic pumps, and the following were monitored: open-field behavior, racemic and enantioselective concentrations of CIT and metabolites in blood, brain parenchyma, and extracellular space, and the brain extracellular monoamine levels. The racemic CIT concentration in serum was estimated about tenfold lower than in brain parenchyma but much higher than in brain extracellular fluid. The major CIT metabolites, demethylcitalopram (DCIT) and didemethylcitalopram (DDCIT) were 20% and 30%, respectively, of the amounts of CIT in serum and even lower in the brain parenchyma. The S-enantiomer/R-enantiomer ratios for CIT and DCIT were about 1.01 and 0.31, respectively, in blood and brain. There was a clear correlation between the different drug components within and between blood and brain compartments. Citalopram had no measured effect on open-field behavior, but it elevated extracellular 5-HT and decreased 5-HIAA levels. No correlations between any of the drug components and the brain monoamines were found. In summary, the drug components after chronic dosing correlated well between the periphery and the brain, but not with the brain monoamine concentrations. Further studies investigating the combined pharmacokinetic/dynamic effects could take advantage of blood drug monitoring for the commonly used novel antidepressant drugs.

Lack of effect of cimetidine on the pharmacokinetics of sustained-release bupropion

The objective of this study was to assess whether cimetidine affects the pharmacokinetics of sustained-release (SR) bupropion hydrochloride and the active metabolite, hydroxybupropion. This randomized, open-label, two-period crossover study was conducted in 24 healthy volunteers 18 to 45 years of age. ANOVA showed that administration of two 150 mg bupropion SR tablets with one 800 mg cimetidine tablet following an overnight fast did not change values for AUC infinity, Cmax, tmax, t1/2, and CL/F (CL/F calculated for bupropion only) for either bupropion or hydroxybupropion as compared with two 150 mg bupropion SR tablets alone. In this study, it appears that there is no effect of cimetidine on the pharmacokinetics of bupropion SR.

Pharmacokinetic considerations of antidepressant use in the elderly

The elderly can be more difficult to treat with antidepressants than are young adults. Older patients take more medications, which increases the potential for drug interactions. Their altered physiology results in widely variable plasma drug concentrations from standard doses. Pharmacokinetic and pharmacodynamic changes in this population may predispose patients to experience an increased number of adverse events. The newer antidepressants have been studied for pharmacokinetic changes in the elderly compared with younger volunteers. Most antidepressants show some changes, including slower metabolic clearance and an extended elimination half-life, although the changes described are not uniform between drugs. Recommended initial doses are lower for the elderly for all antidepressants, although optimal doses may not differ from those for younger patients once dosing is individualized.

Human cytochromes and some newer antidepressants: kinetics, metabolism, and drug interactions

The appearance of selective serotonin reuptake inhibitor antidepressants in the mid-1980s caused the discipline of clinical psychopharmacology to refocus attention to the topics of drug metabolism and drug interactions. This article reviews the metabolic profiles of some newer antidepressants, the clinical implications of metabolic properties, and research methodology that can be applied in determining which specific human cytochromes P450 (CYP) mediate metabolic pathways. Also reviewed are the relative activities of various new antidepressants as inhibitors of CYPs, and the benefits and drawbacks of in vivo and in vitro methodologies for identification and quantitation of drug interactions.

Influence of CYP2D6 activity on the disposition and cardiovascular toxicity of the antidepressant agent venlafaxine in humans

According to in-vitro studies with microsomes from human livers and from yeast expression systems with high CYP2D6 activity, the major oxidation pathway of venlafaxine is catalysed by CYP2D6. In this study, we investigated the role of the CYP2D6 polymorphism and the effects of low-dose quinidine, a selective inhibitor of, CYP2D6, on the disposition of venlafaxine. Fourteen healthy men, eight with the extensive metabolizer and six with the poor metabolizer phenotype were administered venlafaxine hydrochloride 18.75 mg orally every 12 h for 48 h on two occasions (1 week apart); once alone and once during the concomitant administration of quinidine sulfate 100 mg every 12 h. Blood and urine samples were collected under steady-state conditions over one dosing interval (12 h). When venlafaxine was administered alone, the oral clearance of venlafaxine was more than fourfold less in poor metabolizers compared to extensive metabolizers (P < 0.05). This was mainly due to a decreased capability of poor metabolizers to form O-desmethylated metabolites at the position 4 of the aromatic moiety. In extensive metabolizers, quinidine decreased venlafaxine oral clearance from 100 +/- 62 l/h to 17 +/- 5 l/h (mean +/- SD; P < 0.05) without any effects on renal clearance (4 +/- 1 l/h during venlafaxine alone and 4 +/- 1 l/h during venlafaxine plus quinidine). In these individuals, the sequential metabolism of venlafaxine to O-desmethylvenlafaxine and to N,O-didesmethylvenlafaxine was inhibited by quinidine coadministration so that metabolic clearances to O-desmethylated metabolites decreased from 43 +/- 32 l/h to 2 +/- 1 l/h (P < 0.05). In poor metabolizers, coadministration of quinidine did not cause significant changes in oral clearance and partial metabolic clearances of venlafaxine to its various metabolites. Decreased CYP2D6 activity could also be associated with cardiovascular toxicity as observed in four patients during treatment with the drug. Thus, genetically determined or pharmacologically altered CYP2D6 activity represents a major determinant of venlafaxine disposition in humans.

Paroxetine in human milk

AIMS

The primary aims of the study were to estimate the exposure of infants to paroxetine via breast milk and to determine the maternal milk:plasma ratio (M/P) of paroxetine. Secondary aims were to compare single point and area under the curve (AUC) estimates of M/P, to assess variability of M/P in fore and hind milk, and to compare the observed M/P with that predicted by a model.

METHODS

Two studies were performed. In one study, six nursing mothers who were being treated with paroxetine were studied over a 24 h dose interval at steady-state. The total amount of paroxetine in the milk was measured, which represented the 'dose' to the infant. The M/PAUC was calculated and compared with a predicted value. In the second study, four nursing mothers who were being treated with paroxetine, were studied at steady-state, around a normal infant feeding time. A single plasma sample and a prefeed milk sample were taken approximately 3 h after the morning dose of paroxetine, and a postfeed milk sample taken around 1 h later. The dose received by the infant was estimated from the average milk concentrations of the pre and postfeed samples using standard assumptions, and M/P calculated directly. Plasma concentrations of paroxetine were measured in 8 of the 10 infants in the two studies.

RESULTS

The mean dose of paroxetine received by the infants in the first study was 1.13% (range 0.5-1.7) of the weight adjusted maternal dose. The mean M/PAUC was 0.39 (range 0.32-0.51). The predicted M/P was 0.22. The mean dose of paroxetine received by the infants in the second study was 1.25% (range 0.38-2.24) of the weight adjusted maternal dose. The mean M/P was 0.96 (range 0.31-3.33) and did not differ between fore and hind milk. The drug was not detected in the plasma of seven of the infants studied and was detected but not quantifiable (<4 microg l-1 ) in one infant. No adverse effects were observed in any of the infants.

CONCLUSIONS

Measured M/P and estimated infant dose were similar in the two studies, although the range was wider for the single point study. Paroxetine can be considered 'safe' during breast feeding because the dose transferred to the infant is well below the recommended safety limit of 10% of the weight adjusted maternal dose, concentrations in the infants were generally undetectable, and no adverse effects were reported.