Employing atmospheric pressure photoionization in liquid chromatography/tandem mass spectrometry to minimize ion suppression and matrix effects for the quantification of venlafaxine and O-desmethylvenlafaxine

During the development of a method for quantitative determination of venlafaxine and its major metabolite O-desmethylvenlafaxine, elevated concentrations of the analyte as well as co-eluting matrix compounds caused ion suppression. This ion suppression was inconsistent and therefore influenced the reproducibility of detection. The use of atmospheric pressure photoionization (APPI) in the positive mode was investigated as a tool to circumvent this problem. Employing APPI resulted in negligible ion suppression and increased linearity of the concentration range. A selective, sensitive and rapid liquid chromatography/tandem mass spectrometry method for the determination of venlafaxine and its major metabolite O-desmethylvenlafaxine in human plasma was developed. The analyte was extracted from plasma into tert-butyl methyl ether followed by back extraction into 2% formic acid. An Agilent 1100 high-performance liquid chromatography (HPLC) system, employing reversed-phase chromatography on a cyano column, coupled to an Applied Biosystems API 3000 triple quadrupole mass spectrometer set to multiple reaction monitoring (MRM) mode, was used for separation and detection of the analytes. The method was validated between 2.36-605 ng per mL with a mean recovery of approximately 88% for both parent compound and metabolite analytes. APPI technology was employed to improve the reproducibility of detection enabling rapid, selective and sensitive quantification of venlafaxine and O-desmethylvenlafaxine in human plasma samples.

Effects of three cytochrome P450 inhibitors, ketoconazole, fluconazole, and paroxetine, on the pharmacokinetics of lasofoxifene

AIMS

Two studies were conduced to assess the effects of ketoconazole, a CYP3A4/5 inhibitor; fluconazole, a CYP2C9 inhibitor; and paroxetine, a CYP2D6 inhibitor, on lasofoxifene pharmacokinetics.

METHODS

The first parallel group study was conducted in 45 healthy postmenopausal women (15 per group) to compare the pharmacokinetics of a single dose of lasofoxifene (0.25 mg) administered alone and in combination with ketoconazole (400 mg daily x 20 days) or fluconazole (400 mg daily x 20 days). Lasofoxifene was administered on day 2 and blood samples were collected serially for up to 456 h postdose (20 days). The second study enrolled 20 healthy postmenopausal women (10 per group) to compare the pharmacokinetics of a single dose of lasofoxifene (0.25 mg) alone and in combination with paroxetine (30 mg qd x 21 days). Lasofoxifene was given on day 8 of paroxetine treatment and blood samples were collected serially for up to 336 h postdose.

RESULTS

All subjects completed the study and the treatments were well tolerated. Lasofoxifene C(max) and AUC ratios [90% confidence interval (CI)] with/without ketoconazole were 111% (98.4, 127) and 120% (105, 136), respectively, and were 91.3% (80.3, 104) and 104% (91.4, 118), respectively, with/without fluconazole. Lasofoxifene C(max) and AUC ratios (90% CI) with/without paroxetine were 118% (95.4, 146) and 135% (120, 152), respectively.

CONCLUSIONS

Coadministration of potent inhibitors of CYP3A4/5 and CYP2D6, but not CYP2C9, resulted in a moderate increase in lasofoxifene exposure. No dosage adjustment should be required when lasofoxifene is coadministered with ketoconazole, fluconazole, paroxetine or other agents that inhibit these CYP enzymes.

Ritonavir has minimal impact on the pharmacokinetic disposition of a single dose of bupropion administered to human volunteers

A drug-drug interaction study was conducted to determine whether ritonavir (200 mg; 4 doses over 2 days) alters the pharmacokinetic disposition of bupropion (75 mg; once) coadministered to 7 healthy volunteers in a placebo-controlled 2-way crossover study. Serum samples collected from 0 to 24 hours after bupropion administration were assayed for concentrations of bupropion and metabolites (hydroxybupropion, threohydrobupropion, and erythrohydrobupropion). Derived pharmacokinetic parameters were compared between placebo/bupropion and ritonavir/bupropion trials by paired t test. The effect of ritonavir on most pharmacokinetic parameters was minimal (<20% mean change). The only parameters that showed a statistically significant effect were threohydrobupropion area under the blood concentration curve (14% +/- 5% decrease, mean +/- SE; P = .04) and erythrohydrobupropion time-to-maximal serum concentration (161% +/- 92% increase, P = .03), suggesting that ritonavir may inhibit the carbonyl reductase enzyme responsible for formation of these metabolites. These findings indicate that short-term ritonavir dosing has only minimal impact on the pharmacokinetic disposition of a single dose of bupropion in healthy volunteers.

Steady-state clinical pharmacokinetics of bupropion extended-release in youths

OBJECTIVE

To examine in children and adolescents the 24-hour, steady-state clinical pharmacokinetics of an extended-release (XL) formulation of bupropion (Wellbutrin XL).

METHOD

Subjects were six male and four female patients (ages 11.5-16.2 years) prescribed bupropion XL in morning daily doses of either 150 mg (n = 5) or 300 mg (n = 5) for at least 14 days. During an overnight hospitalization, subjects had serial blood draws every 1.5 to 3 hours from an intravenous port to measure plasma levels of bupropion and its metabolites. Pharmacokinetic variables were determined by noncompartmental analysis for bupropion and exponential analyses for metabolites.

RESULTS

Bupropion and metabolites demonstrated linear pharmacokinetics. Bupropion's mean maximum concentration (Cmax) was lower (p = .021) and its mean time to Cmax longer (p = .057) in the current sample on bupropion XL relative to a previously studied sample of youths on bupropion sustained-release (Wellbutrin SR). Mean 24-hour area under the curve ratios of metabolites to bupropion ranged from 1.0 for erythrohydrobupropion to 16.4 for hydroxybupropion.

CONCLUSIONS

Once-daily dosing is justified in youths prescribed bupropion XL. The active metabolite hydroxybupropion probably has key pharmacodynamic effects, given its higher and more sustained levels relative to the other metabolites or to bupropion.

Terbinafine increases the plasma concentration of paroxetine after a single oral administration of paroxetine in healthy subjects

OBJECTIVE

Paroxetine is believed to be a substrate of CYP2D6. However, no information was available indicating drug interaction between paroxetine and inhibitors of CYP2D6. The aim of this study was to examine the effects of terbinafine, a potent inhibitor of CYP2D6, on pharmacokinetics of paroxetine.

METHODS

Two 6-day courses of either a daily 150-mg of terbinafine or a placebo, with at least a 4-week washout period, were conducted. Twelve volunteers took a single oral 20-mg dose of paroxetine on day 6 of both courses. Plasma concentrations of paroxetine were monitored up to 48 h after dosing.

RESULTS

Compared with the placebo, terbinafine treatment significantly increased the peak plasma concentration (C(max)) of paroxetine, by 1.9-fold (6.4 +/- 2.4 versus 12.1 +/- 2.9 ng/ml, p < 0.001), and the area under the plasma concentration-time curve from zero to 48 h [AUC (0-48)] of paroxetine by 2.5-fold (127 +/- 67 vs 318 +/- 102 ng/ml, p < 0.001). Elimination half-life differed significantly (15.3 +/- 2.4 vs 22.7 +/- 8.8 h, p < 0.05), although the magnitude of alteration (1.4-fold) was smaller than C(max )or AUC.

CONCLUSION

The present study demonstrated that the metabolism of paroxetine after a single oral dose was inhibited by terbinafine, suggesting that inhibition of CYP2D6 activity may lead to a change in the pharmacokinetics of paroxetine. However, further study is required to confirm this phenomenon at steady state.

Acute antidepressant response and plasma levels of bupropion and metabolites in a pediatric-aged sample: an exploratory study

Studies examining associations between antidepressant response and plasma levels of bupropion and its metabolites have yielded contradictory findings. There have been no such studies in youth. This study explored such associations in 8 boys and 8 girls, age 11 to 17 years, all prescribed bupropion sustained release (SR) for major depression (n = 6) or depressive disorder not otherwise specified (n = 10) as part of a pharmacokinetic (PK) study. All were started on morning doses of bupropion SR of 100 mg/day, and most eventually had doses increased to 200 mg/day because of inadequate clinical response. After taking prescribed dose of bupropion SR at least 14 days (median = 21 days), subjects had steady-state serial plasma levels of bupropion and its metabolites measured during a 24-hour period after morning doses. A total of 9 subjects underwent these PK assessments on doses of 100 mg/day, and 6 underwent these on doses of 200 mg/day, with 4 studied on both doses. In this 24-hour assessment, the treating psychiatrist rated subjects' antidepressant response using the Clinical Global Impression's Improvement scale (CGI-I), blind to plasma levels, but informed by child and parent rating scales of depressive symptoms and clinical interviews. Relative to 7 nonresponders, 9 responders (CGI-I < or = 2) had significantly higher mean areas under concentration curves for bupropion (P = 0.03), threohydrobupropion (P = 0.02), and erythrohydrobupropion (P = 0.02), and especially hyroxybupropion (P = 0.006). Plasma levels 7.5 hours after morning doses reaching the following cut points discriminated responders from nonresponders: bupropion > or = 37 ng/mL (P = 0.001), hydroxybupropion > or = 575 ng/mL (P = 0.003), threohydrobupropion > or = 240 ng/mL (P = 0.009), or erythrohydrobupropion > or = 45 ng/mL (P = 0.009). These preliminary findings suggest that plasma levels of bupropion and metabolites, particularly hydroxybupropion, may predict acute antidepressant response in depressed youths taking bupropion SR.

The population pharmacokinetics of citalopram after deliberate self-poisoning: a Bayesian approach

Defining the pharmacokinetics of drugs in overdose is complicated. Deliberate self-poisoning is generally impulsive and associated with poor accuracy in dose history. In addition, early blood samples are rarely collected to characterize the whole plasma-concentration time profile and the effect of decontamination on the pharmacokinetics is uncertain. The aim of this study was to explore a fully Bayesian methodology for population pharmacokinetic analysis of data that arose from deliberate self-poisoning with citalopram. Prior information on the pharmacokinetic parameters was elicited from 14 published studies on citalopram when taken in therapeutic doses. The data set included concentration-time data from 53 patients studied after 63 citalopram overdose events (dose range: 20-1700 mg). Activated charcoal was administered between 0.5 and 4 h after 17 overdose events. The clinical investigator graded the veracity of the patients' dosing history on a 5-point ordinal scale. Inclusion of informative priors stabilised the pharmacokinetic model and the population mean values could be estimated well. There were no indications of non-linear clearance after excessive doses. The final model included an estimated uncertainty of the dose amount which in a simulation study was shown to not affect the model's ability to characterise the effects of activated charcoal. The effect of activated charcoal on clearance and bioavailability was pronounced and resulted in a 72% increase and 22% decrease, respectively. These findings suggest charcoal administration is potentially beneficial after citalopram overdose. The methodology explored seems promising for exploring the dose-exposure relationship in the toxicological settings.

Effects of Caffeine on the Kinetics of Fluvoxamine and its Major Metabolite in Plasma After a Single Oral Dose of the Drug

The effects of caffeine on the kinetics of fluvoxamine (FLV) and its major metabolite fluvoxamino acid (FLA) in plasma, after a single oral dose of the drug, were studied in 12 healthy male volunteers. The subjects received caffeine 300 mg/d or placebo for 11 days in a double-blind randomized crossover manner, and on the eighth day they received a single oral 50-mg dose of FLV. Blood sampling and pharmacodynamic evaluation were conducted up to 72 hours after FLV dosing. Plasma concentrations of FLV and FLA were measured by high-performance liquid chromatography. Caffeine significantly decreased the plasma concentrations at 6 time points (P<0.05) and total area under the plasma concentration-time curve (156.5+/-51.7 vs. 118.9+/-38.2 ng/h/mL, P<0.01) of FLV. Plasma concentration and pharmacokinetic parameters of FLA were not affected by caffeine. Caffeine induced no significant change in the pharmacodynamic effects of FLV. The present study suggests that caffeine slightly induces the metabolism of FLV, probably mediated by CYP1A2.

Distribution of antidepressants between plasma and red blood cells

OBJECTIVE

The distribution of different antidepressants between plasma and red blood cells (RBCs) or between water and erythrocyte membranes (ghosts) has not been sufficiently compared so far.

MATERIALS AND METHODS

Distribution of seven antidepressants (amitriptyline, nortriptyline, imipramine, desipramine, didesmethylimipramine, dothiepin, and citalopram) was measured in vitro in small volumes of blood or erythrocyte membrane suspension using radiolabeled drugs. Blood samples were taken from healthy subjects.

RESULTS

The distribution of antidepressants between plasma and RBCs is strongly affected by temperature; however, it does not depend on the antidepressant concentration in the range of their therapeutic concentrations. The data analysis proved that the ratio of RBCs to plasma volume concentrations is the suitable parameter characterizing antidepressant distribution in whole blood. Significantly higher ratios of RBCs to plasma concentrations were found for demethylated metabolites of tricyclic antidepressants and in the case of citalopram. Citalopram showed the highest accumulation in intact RBCs and at the same time the lowest binding to isolated membranes. The binding of drugs to isolated erythrocyte membranes was much higher than in whole blood.

CONCLUSION

The concentration ratio of antidepressant in RBCs and in plasma is sensitive not only to the binding properties of plasma proteins and cell membranes, but also to changes in drug molecule, both in aminopropyl chain and in aromatic rings. This ratio is to a large extent characteristic of a particular antidepressant.

Multiple dose pharmacokinetics of paroxetine in children and adolescents with major depressive disorder or obsessive-compulsive disorder

The current study examined the pharmacokinetics (PK), safety, and tolerability of paroxetine after repeated multiple oral dosing in children and adolescents with major depressive or obsessive-compulsive disorder. In this 6-week, open-label, repeat dose, dose-rising study, 62 patients (27 children and 35 adolescents) were treated with paroxetine 10 mg/day for the first 2 weeks of the study, 20 mg/day for the next 2 weeks, and 30 mg/day for the final 2 weeks. Pharmacokinetic sampling and safety assessments occurred at baseline and subsequently on the final treatment day of each dosing level. Between-patient variability in PK was pronounced at the 10 mg dose level, but markedly reduced at higher doses. A supra-proportional increase in plasma concentrations with increasing dose was evident in both age groups. Data for C(max) and AUC(0-24) indicated that, at each dose level, paroxetine steady-state systemic exposure was higher in children than in adolescents. The differences between age groups, however, diminished with each increasing dose, and were virtually abolished when differences in weight among different age groups were considered. Stepwise regression analysis indicated that both oral clearance and volume of distribution were highly dependent on paroxetine dose, cytochrome P4502D6 genotype, and weight (p<0.0001), but not age or sex. Paroxetine was generally safe and well tolerated in both age groups, with the most frequently observed adverse events being largely consistent with those observed in prior paroxetine studies of adult psychiatric patients. Certain gastrointestinal and behavioral activation events (aggressive reaction and nervousness) were reported more frequently in the youngest age group.

Time course of in vivo 5-HTT transporter occupancy by fluvoxamine

The pharmacokinetics of drugs with specific binding sites in the brain needs to be evaluated at these sites. In this study, we measured the time course of the selective serotonin reuptake inhibitor fluvoxamine in the human brain based on serotonin transporter (5-HTT) occupancy by positron emission tomography. Consecutive positron emission tomography scans were performed using [11C]3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile before, 5 hours, 26 hours, and 53 hours after 50 mg of fluvoxamine administration in 6 healthy male volunteers (mean, 24.3 +/- 4.8 years). Quantification was performed using the multilinear reference tissue model 2. Mean 5-HTT occupancies were 72.9% +/- 4.9% at 5 hours, 50.3% +/- 11.0% at 26 hours, and 24.7% +/- 15.3% at 53 hours, and plasma concentrations were 13.9 +/- 5.5 ng/mL at 5 hours, 5.1 +/- 3.2 ng/mL at 26 hours, and 1.5 +/- 1.7 ng/mL at 53 hours. The relationship between the plasma concentration of fluvoxamine and 5-HTT occupancy at these different time points was fitted to the law of mass action.

A genetic algorithm-based, hybrid machine learning approach to model selection

We describe a general and robust method for identification of an optimal non-linear mixed effects model. This includes structural, inter-individual random effects, covariate effects and residual error models using machine learning. This method is based on combinatorial optimization using genetic algorithm.

The pharmacokinetics of escitalopram after oral and intravenous administration of single and multiple doses to healthy subjects

The pharmacokinetics of escitalopram (S-citalopram) and its principal metabolite, S-demethylcitalopram (S-DCT), were investigated after intravenous and oral administration to healthy subjects. After intravenous infusion of escitalopram, the mean systemic clearance and volume of distribution were 31 L/h and 1,100 L, respectively. After oral administration of single or multiple doses, the absorption was relatively fast, with the maximum observed plasma or serum concentration (C(max)) attained after 3 to 4 hours. The mean half-lives were 27 and 33 hours, respectively; steady state was attained within 10 days. The area under the plasma or serum concentration time curve from time zero to 24 hours and C(max) was both linear and proportional to the dose. The apparent volume of distribution was around 20 L/kg. Comparison of the systemic and oral clearance implied a high absolute bioavailability. There was no evidence of interconversion from S-citalopram to R-citalopram either in plasma or in urine. Concurrent intake of food had no effect on the pharmacokinetics of escitalopram or its metabolite. All treatments were well tolerated.

Case report of a fatal intoxication by citalopram

Citalopram is an antidepressant drug within the group of the selective serotonin reuptake inhibitors (SSRI). It is widely prescribed both in Europe and in United States, and it has always been considered a "safe" drug as pure intoxication with lethal outcome is rare, and most cases of overdose, even with high doses of citalopram ingested, are reported to have an uneventful course. We report the case of a young woman found dead at home. She had been prescribed citalopram by her family doctor 3 weeks before her death for a depressive syndrome. Police found in her house 3 empty blister packages of 28 citalopram tablets (20 mg) and 2 bottles of citalopram oral solution (4%, 15 mL each). The autopsy findings were unremarkable. Nasal swabs, blood from femoral vein, urine, bile and tissue samples were collected for toxicologic investigation. Citalopram separation was performed by solid/liquid method, using Bond-Elute columns. The extracts were analyzed by GLC and GC/MS methods. The toxicologic analysis showed high levels of citalopram in all the examined fluids and tissue samples (blood concentration: 11.60 mg/L). No other drugs and alcohol were detected. Our data confirm that if no other drug is involved, fatal complications occur only after ingestion of very high doses. However, there is no predefined "toxic dose," and the conditions under which the overdose occurs can be very important. We report the exact concentrations of the citalopram in the organs, and wethink that this can be useful in the cases where the blood samples were not available (ie, carbonized or decomposed body).

Enantiomeric screening of racemic citalopram and metabolites in human urine by entangled polymer solution capillary electrophoresis: An innovatory robustness/ruggedness study

Several CE methods have been developed to achieve the chiral separation of citalopram (CIT) and its metabolites demethylcitalopram (DCIT), didemethylcitalopram (DDCIT), and citalopram N-oxide (CIT-NO). All of these compounds were present as racemic mixtures. The best method, which led to the first ever chiral screening of CIT, DCIT, DDCIT, and CIT-NO, involved the use of carboxymethyl-gamma-CD (CM-gamma-CD) and the entangled polymer hydroxypropylmethylcellulose (HPMC) as chiral and selectivity additives, respectively, in the buffer system. In an effort to improve the selectivity and sensitivity of the method, the chemical and instrumental parameters were optimized. The best conditions were short-end anodic hydrodynamic injection (6 s, 0.7 psi); as BGE pH 5, 20 mM phosphate buffer, 0.2% w/v CM-gamma-CD, 0.05% w/v HPMC; voltage of 28 kV with a ramp applied (0.4 s); cartridge temperature of 20 degrees C; detection at 205 nm. In addition, a simple and rapid achiral CE method for the determination of citalopram propionic acid (CIT-PA, the only anionic metabolite of CIT) is also reported for the first time. Prior to the electrophoretic procedure it was necessary to apply an extraction and preconcentration step to obtain analytes from the human urine samples. This was achieved using an optimized SPE process. Moreover, an innovatory experimental and statistical design approach, which involves the simultaneous evaluation of the global robustness and ruggedness effects, was applied. Both of the proposed methods proved to be very useful in the chiral pharmacokinetic screening of CIT and related metabolites in clinical human urine samples.

Pharmacokinetics of Fluoxetine in Elderly Men and Women

Fluoxetine is widely prescribed as an antidepressant for geriatric patients. Despite a large scientific literature describing its efficacy and safety, there are few published data describing the pharmacokinetics of fluoxetine in the elderly. Given the common practice of polypharmacy in this population, additional pharmacokinetic information in elderly men and women is needed so that physicians can better assess potential drug-drug interactions. Twenty-five subjects, men and women between ages 65 and 83, received 20 mg of fluoxetine for 1 week followed by 40 mg for 5 weeks. Serum fluoxetine levels were measured during the period of drug administration and for 8 weeks after. The plasma concentration of fluoxetine and norfluoxetine in our subjects was higher than previously reported in the literature. Elderly women had a significantly higher serum level of norfluoxetine than men. The terminal half-life of norfluoxetine was longer in patients over age 75; elderly women had a significantly slower rate of norfluoxetine elimination than similarly aged men.

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

RATIONALE

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Pharmacokinetic interaction between fluoxetine and metoclopramide in healthy volunteers

The pharmacokinetic interaction of fluoxetine with metoclopramide in healthy volunteers was evaluated. A dose of 20 mg metoclopramide in combination with 60 mg fluoxetine was administered to 24 healthy male volunteers in a two treatment study design, separated by 8 days in which the fluoxetine alone was administered as a single p.o. dose daily. Plasma concentrations of metoclopramide were determined during a 24 h period following drug administration. Metoclopramide plasma concentrations were determined by a validated HPLC method. Pharmacokinetic parameters of metoclopramide were calculated using non-compartmental analysis. In the two periods of treatment, the mean peak plasma concentrations (Cmax) were 44.02 ng/ml (metoclopramide alone) and 62.72 ng/ml (metoclopramide after pre-treatment with fluoxetine). The times taken to reach Cmax and tmax, were 1.15 h and 1.06 h, respectively. The total areas under the curve (AUC(0-infinity)) were 312.61 ng.h/ml and 590.62 ng.h/ml, respectively. The half-life values (t1/2) were 5.52 h and 8.47 h. Statistically significant differences were observed for both AUC(0-infinity) and t1/2 of metoclopramide when administered alone or after 8 days treatment with fluoxetine. The experimental data demonstrate the pharmacokinetic interaction between fluoxetine and metoclopramide and suggest that the observed interaction may be clinically significant, but its relevance has to be confirmed.

A Mathematical Model for Paroxetine Antidepressant Effect Time Course and Its Interaction with Pindolol

Although selective 5-HT reuptake inhibitors (SSRIs) block monoamine uptake within hours of administration to patients, their full clinical effect does not appear until 2-4 weeks after treatment onset. Pindolol, a betablocker with weak partial 5-HT1A receptor agonist activity has been shown to produce a more rapid onset of antidepressant action of SSRIs. However, the optimal dosing schedule of pindolol remains controversial. Building on a set-point model described previously for the hypothermic effect of 5-HT agonists, we have developed a model based on the concept of homeostatic control mechanisms, in which SSRIs exert their antidepressant effect by increasing the transduction set-point of the postsynaptic 5-HT1A receptor, and pindolol exerts its effect by increasing the rate of feedback mechanisms. The predictive distribution of the proportion of responders at each day of measurement (based on population simulation from the model) was not significantly different from the proportions observed in two published clinical trials, one with fluoxetine, the other with paroxetine alone or combined with pindolol. The model was applied to the simulation of paroxetine response (clinical score) time course with or without pindolol, after administration of different doses of each drug. The simulated total scores on the MADR scale obtained after treatment with paroxetine alone (20 mg/day) or paroxetine (20 mg/day) with different doses of pindolol (1.5, 7.5 and 37.5 mg/day) support that the reason for inconstant pindolol efficacy is that the 7.5 mg dose is too low. The model might be useful as a basis for clinical trial simulation.

Bupropion for major depressive disorder: Pharmacokinetic and formulation considerations

BACKGROUND

Major depressive disorder (MDD) is a common psychiatric condition, with 6.6% of the adult population in the United States experiencing a major depressive episode during any given year. Depressed patients must receive adequate treatment to maximize the likelihood of clinical success. Bupropion hydrochloride, a noradrenergic/dopaminergic antidepressant, is available in 3 oral formulations: immediate release (IR) (given TID), sustained release (SR) (given BID), and extended release (XL) (given QD). Understanding the pharmacokinetic (PK) properties and formulations of bupropion can help optimize clinical use.

OBJECTIVES

: The aims of this article were to provide a review of the PK properties of bupropion and identify its various formulations and clinical applications to help optimize treatment of MDD.

METHODS

: In this review, data concerning PK trials/reports were collected from articles identified using a PubMed search. The search was conducted without date limitations and using the search terms bupropion, bupropion SR, bupropion XL, bupropion pharmacokinetics, bupropion metabolism, and bupropion drug interactions. Additional reports were selected from references that appeared in articles identified in the original search. In addition, data from studies summarized in product information and labeling were obtained. All available information, concentrating on studies in humans, pertinent to bupropion PK properties and/or formulations was included.

RESULTS

: Bupropion is extensively metabolized by the liver (t(1/2), approximately 21 hours). Hydroxybupropion, the primary active metabolite (t(1/2), approximately 20 hours), is formed by cytochrome P450 (CYP) 2B6. At steady state, C(max) of hydroxybupropion is 4- to 7-fold higher, and the AUC is approximately 10-fold greater, compared with those of the parent drug. Threohydrobupropion and erythrohydrobupropion (mean [SD] t(1/2) values, approximately 37 [13] and approximately 33 [10] hours, respectively), the other active metabolites of bupropion, are formed via nonmicrosomal pathways. Relative to bupropion, the C(max) values are approximately 5-fold greater for threohydrobupropion and similar for erythrohydrobupropion. Based on a mouse antitetrabenazine model, hydroxybupropion is approximately 50% as active as bupropion, and threohydrobupropion and erythrohydrobupropion are approximately 20% as active as bupropion. Bupropion lowers the seizure threshold and, therefore, concurrent administration with other agents that lower the seizure threshold should be undertaken cautiously. Potential interactions with other agents that are metabolized by CYP2B6 should be considered. In addition, bupropion inhibits CYP2D6 and may reduce clearance of agents metabolized by this enzyme. Absorption of the XL formulation is prolonged compared with the IR and SR formulations (T(max), approximately 5 hours vs approximately 1.5 and approximately 3 hours, respectively). Bupropion is dosed without regard to food.

CONCLUSIONS

: Understanding the PK profile and formulations of bupropion can help optimize clinical use. Bupropion is metabolized extensively, resulting in 3 active metabolites. This metabolic profile, various patient factors (eg, age, medical illnesses), and potential drug interactions should be considered when prescribing bupropion. The 3 formulations-bupropion, bupropion SR, and bupropion XL-are bioequivalent and offer options to optimize treatment for patients with MDD.

Risperidone Half-Life in a Patient Taking Paroxetine

This case report further establishes the inhibitory effects of paroxetine on risperidone (R) metabolism in a patient whose R was discontinued due to side effects. Baseline through levels in ng/ml were 33 for R, 9 for 9-hydroxyrisperidone (9-OHR) and 42 for the total moiety. The fourth morning after R discontinuation, levels were 4 for R, 1 for 9-OHR and 5 for the total moiety. The estimated half-lives were 23.8 hours for R, 22.8 hours for 9-OHR and 23.5 hours for the total moiety.

Chronopharmacological Study of Antidepressants in Forced Swimming Test of Mice

The influence of dosing time on the anti-immobility effect of antidepressants and mechanisms underlying this phenomenon were investigated in mice. In the forced swimming test (FST), the immobility time of mice treated with amitriptyline (15 mg/kg) and fluvoxamine (30 mg/kg) showed a significant 24-h rhythm. The anti-immobility effect of fluvoxamine in FST was potent at the early part of the dark phase without increasing locomotor activity. Concerning pharmacokinetics, although K(e) of fluvoxamine was approximately 1.3-fold higher in mice injected with fluvoxamine at 9:00 PM than at 9:00 AM, no dosing time dependence was demonstrated for either plasma or brain fluvoxamine concentration at 0.5 h after the drug injection. On the other hand, serotonin transporter (SERT) mRNA expression and 5-hydroxytryptamine (5-HT) uptake activity in the mouse midbrain showed significant time-dependent changes with higher levels during the dark phase and lower levels during the light phase. These results suggest that the reuptake of 5-HT might be more increased during the dark phase. Since the reuptake of 5-HT is inhibited almost completely by injection with 30 mg/kg fluvoxamine at any time, the extracellular 5-HT level may be more increased by the injection of fluvoxamine at the early part of the dark phase. The present results suggest that the anti-immobility effect of fluvoxamine in FST increases depending on dosing time. Furthermore, the time-dependent change of SERT mRNA expression and uptake activity in the midbrain is suggested to be the mechanism underlying the 24-h rhythm of anti-immobility effect of fluvoxamine.

Metabolic activation of the nontricyclic antidepressant trazodone to electrophilic quinone-imine and epoxide intermediates in human liver microsomes and recombinant P4503A4

Therapy with the antidepressant trazodone has been associated with several cases of idiosyncratic hepatotoxicity. While the mechanism of hepatotoxicity remains unknown, it is possible that reactive metabolites of trazodone play a causative role. Studies were initiated to determine whether trazodone undergoes bioactivation in human liver microsomes to electrophilic intermediates. LC/MS/MS analysis of incubations containing trazodone and NADPH-supplemented microsomes or recombinant P4503A4 in the presence of glutathione revealed the formation of conjugates derived from the addition of the sulfydryl nucleophile to mono-hydroxylated- and hydrated-trazodone metabolites. Product ion spectra suggested that mono-hydroxylation and sulfydryl conjugation occurred on the 3-chlorophenyl-ring, whereas hydration and subsequent sulfydryl conjugation had occurred on the triazolopyridinone ring system. These findings are consistent with bioactivation sequences involving: (1) aromatic hydroxylation of the 3-chlorophenyl-ring in trazodone followed by the two-electron oxidation of this metabolite to a reactive quinone-imine intermediate, which reacts with glutathione in a 1,4-Michael fashion and (2) oxidation of the pyridinone ring to an electrophilic epoxide, ring opening of which, by glutathione or water generates the corresponding hydrated-trazodone-thiol conjugate or the stable diol metabolite, respectively. The pathway involving trazodone bioactivation to the quinone-imine has also been observed with many para-hydroxyanilines including the structurally related antidepressant nefazodone. It is proposed that the quinone-imine and/or the epoxide intermediate(s) may represent a rate-limiting step in the initiation of trazodone-mediated hepatotoxicity.

Postmortem tissue distribution of olanzapine and citalopram in a drug intoxication

A 40-year-old white male was found dead in bed in a group home for mentally ill adults. The decedent had been diagnosed a paranoid schizophrenic. An autopsy was performed at the Office of the Cuyahoga County Coroner in Cleveland, Ohio. Toxicological testing detected olanzapine and citalopram in post mortem specimens. Multiple fluids and tissues were assayed by liquid-liquid extraction followed by gas chromatography with nitrogen phosphorus detection, and qualitative confirmation by electron impact gas chromatography/mass spectrometry. Drug concentrations [olanzapine: citalopram; mg/L or mg/Kg] determined in this case are the highest reported to date involving these drugs- 1.38:3.35 heart blood, 1.11:1.65 femoral blood, 60.24:32.43 urine, 6.47:10:71 liver, and 38.36:49.16 lung, respectively. Drug concentrations in tissues were found to be the highest in lung for both drugs and lowest in the heart. Citalopram but not olanzapine was detected in bone. The cause of death was ruled acute intoxication by the combined effects of olanzapine and citalopram and the manner, accident.

Steady-state pharmacokinetics of bupropion SR in juvenile patients

OBJECTIVE

To examine the steady-state pharmacokinetic properties of bupropion sustained release (SR) and their potential developmental differences in youths.

METHOD

Eleven boys and eight girls aged 11 to 17 years old were prescribed bupropion SR monotherapy for attention-deficit/hyperactivity disorder (n = 16) and/or depressive disorders (n = 16). Bupropion SR was given in morning doses of 100 mg/day (n = 11) or 200 mg/day (n = 8) for 14 days or less, with five subjects studied on both doses. All subjects had blood draws from an intravenous port every 1 to 3 hours for 24 hours after their usual morning doses. Pharmacokinetic variables were determined by noncompartmental and compartmental analyses for bupropion and metabolites, respectively.

RESULTS

Bupropion and its metabolites exhibited linear pharmacokinetics. Areas under the concentration curves for the hydroxybupropion, threohydrobupropion, and erythrohydrobupropion were 20, 12, and 2.7 times higher, respectively, than for bupropion. Relative to adults, the mean half-lives of bupropion (12.1 hours) and threohydrobupropion (26.3 hours) were significantly shorter, and areas under the concentration curve ratios of metabolites to bupropion were 19% to 80% higher.

CONCLUSIONS

Youths metabolize bupropion SR faster to hydroxybupropion and other active metabolites than adults. Until the clinical importance of bupropion's metabolites is clarified, bupropion SR should be given in divided doses to youths, as the manufacturer recommends for adults taking higher doses.

Bioavailability investigation of two different oral formulations of citalopram, a so-called 'second generation' antidepressant drug

Citalopram (CAS 59729-33-8) belongs to the so-called 'second generation' antidepressant drugs and is used for the treatment of patients with major depression or other depressive disorders. In the present study, two different oral citalopram formulations (Citalopram-ratiopharm film-coated tablets as test preparation and tablets of a reference preparation distributed in Germany) were investigated in 20 healthy volunteers in order to prove bioequivalence between both preparations. A single 40 mg oral dose was administered according to an open, randomised, two-period cross-over design in the fasted state. Blood samples for determination of citalopram plasma concentrations were collected at pre-defined time points up to 168 h following drug administration. A wash-out period of 21 days separated both treatment periods. Citalopram plasma concentrations were determined by means of a validated HPLC method with fluorescence detection. Maximum plasma concentrations (Cmax), of 34.77 ng/ml (test) and 34.42 ng/ml (reference) were achieved. Areas under the plasma concentration-time curve (AUC0-infinity) of 1,719.69 ng*h/ml (test) and 1,725.71 ng*h/ml (reference) were determined. The results showed nearly identical rate and extent of drug absorption. Also further pharmacokinetic parameters were well comparable with each other. Thus, tmax showed values of 3.29 h (test) and 3.77 h (reference). The plasma elimination half-life (t1/2) was 42.50 h (test) und 44.46 h (reference). Both primary target parameters Cmax and AUC0-infinity were tested parametrically by analysis of variance (ANOVA). Bioequivalence between test and reference preparation was demonstrated since for both parameters AUC and Cmax the 90 % confidence intervals of the T/R-ratios of logarithmically transformed data were in the generally accepted range of 80 %-125 %.

Combination therapy with venlafaxine and carbamazepine in depressive patients not responding to venlafaxine: pharmacokinetic and clinical aspects

The chiral antidepressant venlafaxine (VEN) is both a serotonin and a norepinephrine uptake inhibitor. CYP2D6 and CYP3A4 contribute to its metabolism, which has been shown to be stereoselective. Ten CYP2D6 genotyped and depressive (F32x and F33x, ICD-10) patients participated in an open study on the pharmacokinetic and pharmacodynamic consequences of a carbamazepine augmentation in VEN non-responders. After an initial 4-week treatment with VEN (195 +/- 52 mg/day), the only poor metabolizer out of 10 depressive patients had the highest plasma concentrations of S-VEN and R-VEN, respectively, whereas those of R-O-demethyl-VEN were lowest. Five non-responders completed the second 4-week study period, during which they were submitted to a combined VEN-carbamazepine treatment. In the only non-responder to this combined treatment, there was a dramatic decrease of both enantiomers of VEN, O-demethylvenlafaxine, N-desmethylvenlafaxine and N, O-didesmethylvenlafaxine in plasma, which suggests non-compliance, although metabolic induction by carbamazepine cannot entirely be excluded. The administration of carbamazepine [mean +/- SD, range: 360 +/- 89 (200-400) mg/day] over 4 weeks did not result in a significant modification of the plasma concentrations of the enantiomers of VEN and its O- and N-demethylated metabolites in the other patients. In conclusion, these preliminary observations suggest that the combination of VEN and carbamazepine represents an interesting augmentation strategy by its efficacy, tolerance and absence of pharmacokinetic modifications. However, these findings should be verified in a more comprehensive study.

Poststroke depression: psychopharmacological considerations

PSD is a common psychiatric complication of stroke. It is often underrecognized and untreated. Numerous studies show that untreated PSD impedes the rehabilitation and recovery process, jeopardizes quality of life, and increases mortality. Successful management of the PSD requires early recognition and initiation of appropriate treatment to facilitate an optimal level of functioning. As active members of the interdisciplinary treatment team, psychiatric consultative-liaison nurses play a pivotal role in facilitating positive treatment outcomes during both the acute and rehabilitation phases in the management of PSD.

A pilot study of newer antidepressant concentrations in cord and maternal serum and possible effects in the neonate

Antidepressants are often used antenatally, and placental transfer may lead to adverse effects (toxicity) in the neonate. Pregnant women taking fluoxetine (n=4), sertraline (n=4), paroxetine (n=2) or venlafaxine (n=1) in the last trimester were studied. Maternal and cord sera were collected at delivery and infant serum on day 5 after birth for measurement of antidepressant concentrations. Neonatal Abstinence Scores (NAS) were measured in the infants on days 13 after birth. In maternal serum, median drug concentrations were: fluoxetine (96 microg/l), norfluoxetine (110 microg/l), sertraline (11 microg/l), desmethylsertraline (38 microg/l), paroxetine (mean 12 microg/l), venlafaxine (220 microg/l), and O-desmethylvenlafaxine (392 microg/l). Corresponding median values in cord serum were: fluoxetine (65 microg/l), norfluoxetine (81 microg/l), sertraline (10 microg/l), desmethylsertraline (27 microg/l), paroxetine (mean 6 microg/l), venlafaxine (232 microg/l), and O-desmethylvenlafaxine (406 microg/l). Corresponding median cord:maternal concentration ratios were 0.67 for fluoxetine and 0.72 for norfluoxetine, 0.67 for sertraline and 0.63 for demethylsertraline, 0.52 (mean) for paroxetine, and 1.1 and 1.0 for venlafaxine and O-desmethylvenlafaxine respectively. The neonates of two patients taking fluoxetine had high NAS. Only fluoxetine and norfluoxetine were detected in infant serum. Our data show substantial placental transfer of antidepressants, but only fluoxetine persisted in the infants serum. Neonatal toxicity may be associated with serotonin uptake blockade, and also be influenced by neonatal clearance.

Paroxetine controlled release

A controlled-release (CR) formulation of the SSRI paroxetine has been developed. This CR formulation delays the release of paroxetine until the tablet has passed through the stomach; the drug is then released over 4-5 hours. In well designed placebo-controlled trials in patients with major depressive disorder (including a study in the elderly), social anxiety disorder or premenstrual dysphoric disorder (PMDD), paroxetine CR was consistently superior to placebo with regards to primary endpoints (i.e. mean Hamilton Rating Scale for Depression total score [major depressive disorder], Liebowitz social anxiety scale total score and Clinical Global Impressions-Global Improvement score [social anxiety disorder] and Visual Analogue Scale-Mood score [PMDD]). The duration of treatment was 12 weeks or, in PMDD, over three menstrual cycles (intermittent or continuous administration). Paroxetine CR also demonstrated efficacy in three well designed studies in patients with panic disorder with or without agoraphobia. Paroxetine CR was generally well tolerated in clinical trials, with an adverse-event profile typical of SSRIs, although recipients of paroxetine CR experienced significantly less nausea than recipients of immediate-release paroxetine in the first week of treatment.

Gender based response to fluoxetine hydrochloride medication in endogenous depression

OBJECTIVE

To determine the gender based response to fluoxetine HCl medication in relation to tryptophan metabolism in depressed patients.

DESIGN

A comparative, analytical study.

PLACE AND DURATION OF STUDY

Clinical Biochemistry and Psychopharmacology Research Unit, Department of Biochemistry, University of Karachi during the year 2002 to 2003.

SUBJECTS AND METHODS

Sixteen adults depressed patients who were not having any other major comorbidity were selected from the outpatients department of local psychiatric clinic for the study. They were subjected to a semi-structured interview for associated clinical characteristics and diagnosis of depression according to ICD-10 criteria. A control group of normal health male and female individuals was identified for comparison with the depressed group. All the depressed patients were treated with fluoxetine hydrochloride (Prozac 20 mg/day) for four weeks. Healthy individual's data was compared with the depressed group and evaluated for gender based response to fluoxetine HCl medication.

RESULTS

Significant decreases were found in total tryptophan concentrations (33 %, p<0.01,56%, p<0.01) in depressed male and female patients respectively, in contrast, serum cortisol levels were increased by 68% and 98% in male and female depressed patients respectively as compared to healthy controls. Significant increases (23%, p<0.05) in albumin levels were found in females only. Four weeks treatment of male and female depressed group by Fluoxetine HCL (Prozac) 20 mg/kg/day, increased serum total tryptophan concentrations significantly by 32% (p<0.05) in males and by 83% (p<0.01) in females. Serum-free tryptophan concentrations were increased by 22% (p<0.05) in males only. In contrast serum cortisol concentrations were decreased by 31% (p<0.01) and 45.35% (p<0.01) in males and females respectively.

CONCLUSION

Increases in tryptophan and decreases in cortisol concentrations were greater in females which may contribute to better response of the drug in females.

Long-term sequestration of fluorinated compounds in tissues after fluvoxamine or fluoxetine treatment: a fluorine magnetic resonance spectroscopy study in vivo

Fluorine magnetic resonance spectroscopy (19F MRS), spectroscopic imaging (MRSI) and proton anatomical magnetic resonance imaging (1H MRI) were performed on brains and lower extremities of six subjects in vivo concurrently with HPLC of serum to investigate tissue and plasma drug localization and withdrawal kinetics in humans treated with fluvoxamine or fluoxetine. 19F MRS signal was unexpectedly detected in the lower extremities months after complete disappearance of signal from plasma and brain. MRSI suggested that the lower extremity fluvoxamine signal originated mainly from bone marrow. Results suggest long-term sequestration of these drugs or their metabolites mainly in bone marrow and possibly in surrounding tissue and demonstrate the usefulness of MRS to reveal drug-trapping compartments in the body.

Pharmacogenetic determinants of interindividual variability in bupropion hydroxylation by cytochrome P450 2B6 in human liver microsomes

Bupropion is primarily metabolized in human liver by cytochrome P450 (CYP) 2B6, an isoform that shows high interindividual variability in expression and catalysis. The aim of this study was to identify mechanisms underlying this variability through comprehensive phenotype-genotype analysis of a well-characterized human liver bank (n = 54). There was substantial variability in microsomal bupropion hydroxylation activities (over 45-fold) and CYP2B6 protein content (over 288-fold), with excellent correlation between protein and activity values (rs = 0.88). CYP2B6 mRNA levels showed less variability (13-fold) and poorer correlation (rs = 0.44) to CYP2B6 protein resulting from 20-30% of livers that contained substantial CYP2B6 mRNA, but low CYP2B6 protein. Livers were genotyped for the common coding polymorphisms (Q172H, K262R and R487C) and 14 additional variations identified by sequencing of the gene promoter to -3000 bp. Of 14 haplotypes that were inferred, *1A (reference), *1H (-2320t>c; -750t>c) and *6B (-1456t>c; -750t>c; Q172H; K262R) were most common with frequencies of 0.28, 0.20 and 0.26, respectively. Alcohol use history (P = 0.011) and *6B haplotype (P = 0.011) were identified as significant predictors of bupropion hydroxylation. A consideration of the effects of these variables on CYP2B6 mRNA and protein levels suggests that alcohol use is associated with enhanced CYP2B6 gene transcription, but the presence of at least one *6B allele reduces this effect on bupropion hydroxylation at the post-transcriptional level. In conclusion, the results of this study indicate that interindividual variability in bupropion hydroxylation is a consequence of interactions between environmental and genetic influences on CYP2B6 gene function.

Efficacy and pharmacokinetics of fluvoxamine maleate in patients with mild depression undergoing hemodialysis

Seven Japanese patients on maintenance hemodialysis who were comorbid with mild depression were medicated with 50 mg/day fluvoxamine maleate for 28 days. Effectiveness was obtained in four out of seven patients (57%). The plasma fluvoxamine concentrations were examined in three patients. The plasma fuvoxamine concentration decreased by 22% by hemodialysis. There is a tendency for the dialyzed rate of fluvoxamine to become lower if the plasma albumin concentration is higher. The half-life of fluvoxamine was possibly shortened more in the patient with hypoalbuminaemia. The plasma fluvoxamine concentration reached a steady state 8 days after the start of medication and thereafter. The time required to reach steady state was lengthened when compared with the results in normal Japanese volunteers.

Subjective Effects of Slow-Release Bupropion versus Caffeine as Determined in a Quasi-Naturalistic Setting

Bupropion (BUP), which in its slow-release formulation (Zyban) is used as a smoking-cessation drug, increases dopamine overflow in the nucleus accumbens and serves as a reinforcer in animal experiments, both suggesting that BUP may possess some abuse liability. The present study examined if BUP produced subjective effects indicative of abuse liability in a quasi-naturalistic setting, with caffeine (CAF) serving as a positive control. In a randomized double-blind crossover design, male smokers (n = 50) ingested two doses (interdosing interval, 6 h) of placebo (PLC), 178 mg CAF, or 150 mg slow-release BUP in their normal mid-week work environment. They completed questionnaires administered by telephone at regular intervals. CAF significantly increased ratings of 'pleasant effects' (p = 0.008) and 'high' (p = 0.03), whereas BUP produced a 'high' of only very moderate size (p = 0.02). In 3 subjects each, BUP or CAF produced ratings of 'pleasant effects' that were >9-fold higher than those for PLC. Finally, BUP increased the number of cigarettes smoked by 29% (i.e., from 24 to 31 per day; p = 0.004) only in those subjects who were unable to report any effect of either BUP or CAF. CAF had no effect on cigarette consumption. These findings suggest that BUP, like CAF, might be of some abuse liability in a small subgroup of smokers (i.e., 6% each of the present sample), and it may transiently increase, rather than decrease, smoking during early phases of treatment in continuing smokers.

Metabolism of the newest antidepressants: comparisons with related predecessors

The need for better acute and long-term treatment for depressive disorders has led to the development of new agents, including escitalopram, duloxetine (Boehringer Ingelheim Corp/Eli Lilly & Co/Eli Lilly Japan KK/Shionogi & Co Ltd) and gepirone. These drugs undergo extensive biotransformation, with cytochrome P450 (CYP) isoforms playing a major role. Escitalopram is biotransformed by CYP2C19, CYP3A4 and CYP2D6; partly extrapolating from studies of citalopram, polymorphism at CYP2C19 and drug interactions at CYP2D6 may be clinically significant. Duloxetine is metabolized by CYP2D6 and CYP1A2, with moderate potential for interactions at CYP2D6. The metabolism of gepirone involves CYP3A4 and to a lesser extent CYP2D6.

Treatment of premenstrual dysphoric disorder with luteal phase dosing of sertraline

Sertraline (Zoloft, Pfizer Inc.) is a selective serotonin re-uptake inhibitor (SSRI) which has been approved by the US FDA for the treatment of premenstrual dysphoric disorder (PMDD). PMDD is a severe form of premenstrual syndrome (PMS) which affects at least 5 - 8% of women of reproductive age. It is characterised by cyclic appearance at the late luteal phase of the menstrual cycle, and disappearance following the beginning of menses, with no symptoms during at least 1 week of the cycle - usually during the mid-follicular phase. Due to the cyclic luteal occurrence of PMDD, luteal phase dosing of SSRIs has been suggested and proven effective for sertraline as well as several other SSRIs. The clinical response of sertraline is reported to be within several days following initiation of treatment. Despite repeated cyclic discontinuation, no significant discontinuation adverse effects have been reported. In addition to its proven clinical efficacy, luteal-phase dosing may offer the advantages of minimising adverse effects of SSRIs while reducing the personal and economic burden of taking a prescription medication continuously for long periods and thus increasing compliance.

The treatment of depression with different formulations of venlafaxine: a comparative analysis

Venlafaxine is the first of a group of antidepressants that show dual reuptake inhibition of serotonin and noradrenaline (SNRIs). Originally marketed in an immediate release (IR) formulation a microencapsulated, extended release (XR) formulation is now available. Significant differences exist between these two formulations with respect to pharmacokinetic parameters which have an impact on clinical use. The XR has lower maximum plasma concentrations (Cmax) and achieves these at a later time (higher Tmax). The longer apparent elimination half-life of the drug after single XR doses suggests that it is suitable for once daily dosing compared with the twice daily dosing regimen required by the IR formulation. With respect to antidepressant efficacy the XR formulation is equivalent to other marketed antidepressants and to the IR formulation. Consistent with its pharmacokinetic properties the use of the XR formulation is associated with less nausea and dizziness at the initiation of therapy. While in clinical usage XR might be expected to increase compliance with medication and to reduce discontinuation syndromes there are few comparative studies for which this has been evaluated. The XR formulation of venlafaxine is no worse than the IR form with respect to tolerability and offers some benefits to patients in terms of ease of use. On the other hand there does not appear to be any increase in the efficacy of the active agent.

Studies on Intestinal Absorption of Sulpiride (3): Intestinal Absorption of Sulpiride in Rats

The aim of this study was to investigate whether the concomitant administration of the substrates or inhibitors of PEPT1, OCTN1, OCTN2, and P-glycoprotein affects the intestinal absorption of sulpiride in rats. The absorption of sulpiride from rat intestine was decreased by the substrates or inhibitors of PEPT1, OCTN1, and OCTN2. On the other hand, the absorption was increased by the substrates of P-glycoprotein. The effects of these concomitantly administered drugs on the pharmacokinetic behavior of sulpiride after oral administration in rats were investigated. Peak concentration (C(max)) and area under the plasma concentration-time curve (AUC(0-8 h)) of sulpiride were decreased by the concomitant administration of the substrates or inhibitors of PEPT1, OCTN1, and OCTN2. However, the same parameters were significantly increased by the concomitant administration of the substrates of P-glycoprotein. The present results suggest the possibility of drug-drug interaction during the absorption process in the small intestine due to the coadministration of sulpiride and these agents. These findings provide important information for preventing adverse effects and for ensuring the effectiveness of sulpiride and concomitantly administered drugs.

Escitalopram

Escitalopram, a selective serotonin reuptake inhibitor (SSRI) was recently approved by the United States Food and Drug Administration (FDA) for the treatment of major depression. This chapter reviews preclinical and clinical studies with escitalopram, focusing on its therapeutic profile of action and tolerability. Escitalopram is the S-enantiomer of the racemic SSRI citalopram. It has been proposed that the S-enantiomer of citalopram is the isomer that holds antidepressant efficacy, and that the R-enantiomer is clinically inactive; preclinical and clinical data support this. Based on in vitro radioligand binding data, escitalopram is the most selective SSRI available. Hypotheses that escitalopram has a more rapid onset of action or fewer adverse effects than citalopram have not yet been fully documented in published studies, although its profile is at least comparable to citalopram. Escitalopram is more effective than placebo in the treatment of major depression and as effective as other SSRIs, including citalopram. Comparable to other SSRIs, it is well tolerated, safe in overdose and has a low incidence of adverse effects or drug interactions.

Time course of clinical response to venlafaxine: relevance of plasma level and chirality

OBJECTIVE

Early clinical response to antidepressant treatment is an important therapeutic goal, considering the psychological, social and economic consequences of depression. The aim of the present study was to investigate the relationship between the time course of response and the concentration of venlafaxine (V), its active metabolite O-desmethylvenlafaxine (ODV) and enantiomeric ratios V(+)/V(-) and ODV(+)/ODV(-).

METHODS

Depressed inpatients ( n=35) received V orally at a fixed 300 mg daily dose. Accepted comedication included clorazepate (maximum 60 mg/day), zopiclone (maximum 15 mg/day) and low-dose trazodone (maximum 200 mg/day). Severity of depression was assessed on days 0, 4, 7, 11, 14, 21 and 28 (Montgomery and Asberg Depression Rating Scale). Blood samples were taken on day 14 and day 28 and submitted to stereoselective determination. All measurements reflected trough steady-state values. First, pattern analysis was used to provide a categorical perspective of clinical response (50% improvement from baseline depression score). Patients displaying non-response, transient response, early persistent response and delayed persistent response were compared with respect to racemic concentrations and enantiomeric ratios. Second, in a dimensional perspective, mixed-effects modelling was used to analyse severity of depression versus time curves with respect to the possible influence of concentrations and enantiomeric ratios.

RESULTS

Comparison of patients with and without persistent response did not reveal any significant difference for V, ODV, V+ODV plasma levels or enantiomeric ratios. Persistent response was significantly associated with less frequent pre-study antidepressant medication and less frequent comedication with zopiclone (day 14) and clorazepate (day 28) during the study. Focus on patients with persistent response ( n=19, 54.3%) indicated that early response, first observed before day 14, was associated with significantly higher V+ODV concentration than delayed response (median 725 ng/ml versus 554 ng/ml, P=0.023). No difference was found for pre-study medication or comedication during the study. Shorter time to onset of response was significantly associated with lower V(+)/V(-) enantiomeric ratio (r(s)=0.48, P<0.05). Mixed-effects modelling of depression severity versus time curves in patients with persistent response confirmed that either higher V+ODV plasma level or lower V(+)/V(-) ratio were significantly associated with more rapid decrease of depression score (likelihood ratio tests, P=0.012 and P=0.046, respectively).

CONCLUSION

Considering its modest sample size, naturalistic design and limited observation period, the present study provided preliminary indication that earlier clinical response may occur with higher V+ODV plasma level, extending previous dose-response studies. The hypothesis was also raised that exposure to a more potent noradrenergic therapeutic moiety, as reflected by a lower V(+)/V(-) ratio, may be relevant to early improvement of depression.

Age-dependent antidepressant pharmacogenomics: polymorphisms of the serotonin transporter and G protein beta3 subunit as predictors of response to fluoxetine and nortriptyline

In 169 depressed patients randomized to treatment with either fluoxetine or nortriptyline, we examined whether polymorphisms of the serotonin transporter and the G protein beta3 subunit influenced response to these antidepressants. For depressed patients under the age of 25 yr the T allele of the G protein beta3 subunit was associated with a markedly poorer response to nortriptyline, while serotonin transporter polymorphisms did not predict antidepressant response. However, in patients 25 yr or older, the G protein beta3 polymorphisms did not predict antidepressant response, while the s,s genotype of the serotonin transporter was associated with a poorer response to both fluoxetine and nortriptyline. These differential pharmacogenetic predictors of antidepressant response by age, may provide clues to understanding the discontinuities in pharmacological responsiveness of child/adolescent and adult depressive disorders.

HPLC determination and pharmacokinetics of sustained-release bupropion tablets in dogs

The pharmacokinetics and bioequivalency of a newly developed sustained-release bupropion tablet was studied in six dogs after single oral administration and compared with a regular tablet (RT) in randomized two-period crossover design. A sensitive and rapid HPLC method was developed and validated for the quantitative determination of bupropion in dog plasma. The compound and the internal standard (I.S.) (hydroxyethylfludiazepam) were extracted from the plasma samples by liquid-liquid extraction. The extracts were analyzed by a reversed-phase HPLC with 50 mmol/l phosphate buffer (pH 5.5)-methanol (45:55, v/v) as the eluent. The assay was specific for bupropion. The calibration curves were linear in the range between 1 and 750 ng/ml. The validated lower limit of quantification was 1 ng/ml. The overall precision (expressed as R.S.D.) of quality controls were within 15%. The method was successfully applied to the bioequivalency study of bupropion in the two formulations. The Cmax of sustained-release tablet (ST) was significantly lower than that of the RT and the Tmax was significantly longer than that of the RT (P<0.05). The relative bioavailability of the ST was (99.1+/-1.51)%, the results of ANOVA and two one sided tests indicated that the new ST exhibited good sustained release properties and was bioequivalent to the RT.