Jeffrey Paul

Cytochrome P450 2D6 phenotype predicts antidepressant efficacy of venlafaxine: a secondary analysis of 4 studies in major depressive disorder.

INTRODUCTION Venlafaxine, a serotonin-norepinephrine reuptake inhibitor antidepressant, is metabolized primarily by the cytochrome P450 2D6 enzyme into O-desmethylvenlafaxine (ODV). The ODV/venlafaxine ratio can be used to distinguish between extensive metabolizers (EMs) and poor metabolizers (PMs). OBJECTIVES To determine the relative efficacy and tolerability of venlafaxine in EM vs PM patients with major depressive disorder (MDD). METHOD Data from 4 double-blind, placebo-controlled studies of patients with MDD were pooled. Blood samples were analyzed for plasma concentrations of venlafaxine, ODV, total venlafaxine + ODV, and ODV/venlafaxine ratio. Patients were classified as EMs or PMs on the basis of ODV/venlafaxine ratios. Changes from baseline in depression scale scores were compared between EMs and PMs using t tests. Rates of response, remission, discontinuation, and adverse events (AEs) were compared for EMs and PMs using Fisher exact tests. RESULTS Compared with PMs, EMs had significantly greater mean changes from baseline on 4 of 5 depression rating scales (all 4 comparisons, P ≤ .020). A significantly greater percentage of EMs achieved response or remission by most measures compared with PMs (4 of 5 comparisons, P ≤ .015). Rates of discontinuation and AEs did not differ significantly between EMs and PMs. Since there were no substantial differences between EMs and PMs in terms of venlafaxine dose or tolerability, these factors are not likely to account for the efficacy findings. CONCLUSIONS Venlafaxine treatment in EMs was associated with greater efficacy in MDD on virtually all measures compared with PMs, with no important tolerability differences.

Comparison of the Pharmacokinetics of Venlafaxine Extended Release and Desvenlafaxine in Extensive and Poor Cytochrome P450 2D6 Metabolizers

Background: The goal of this study was to evaluate the impact of cytochrome P450 2D6 extensive metabolizer (EM) or poor metabolizer (PM) status on the pharmacokinetics of single doses of venlafaxine extended release (ER) and desvenlafaxine (administered as desvenlafaxine succinate) in healthy adults. Methods: In an open-label, crossover study, 14 healthy volunteers (aged 18-55 years; 7 EMs and 7 PMs) received, in randomized sequence, single doses of venlafaxine ER 75 mg/d or desvenlafaxine 100 mg/d. Cytochrome P450 2D6 genotyping was performed, and plasma drug levels were measured. The arithmetic means and standard deviation (SD) for area under the plasma concentration-versus-time curve (AUC) and peak plasma concentration (Cmax) were calculated. Comparisons of AUC and Cmax between cytochrome P450 2D6 EMs and PMs were calculated using a Wilcoxon exact test. Results: After administration of venlafaxine ER, mean Cmax and AUC of venlafaxine were significantly greater in PMs compared with EMs, whereas mean Cmax and AUC of its metabolite, desvenlafaxine, were significantly lower for PMs than for EMs (P = 0.001, all comparisons). In contrast, mean Cmax and AUC of desvenlafaxine after administration of desvenlafaxine were comparable between EMs and PMs. Conclusions: Cytochrome P450 2D6 genetic polymorphisms had no discernible impact on exposure to desvenlafaxine after desvenlafaxine administration; in contrast, compared with an EM phenotype, a PM phenotype had a significant effect on venlafaxine and desvenlafaxine plasma concentrations after venlafaxine ER administration. This reduced pharmacokinetic variability of desvenlafaxine may translate into better uniformity of response for patients receiving desvenlafaxine versus venlafaxine, but additional studies are required to test this hypothesis.

An Assessment of Drug-Drug Interactions: The Effect of Desvenlafaxine and Duloxetine on the Pharmacokinetics of the CYP2D6 Probe Desipramine in Healthy Subjects

A number of antidepressants inhibit the activity of the cytochrome P450 2D6 enzyme system, which can lead to drug-drug interactions. Based on its metabolic profile, desvenlafaxine, administered as desvenlafaxine succinate, a new serotonin-norepinephrine reuptake inhibitor, is not expected to have an impact on activity of CYP2D6. This single-center, randomized, open-label, four-period, crossover study was undertaken to evaluate the effect of multiple doses of desvenlafaxine (100 mg/day, twice the recommended therapeutic dose for major depressive disorder in the United States) and duloxetine (30 mg b.i.d.) on the pharmacokinetics (PK) of a single dose of desipramine (50 mg). A single dose of desipramine was given first to assess its PK. Desvenlafaxine or duloxetine was then administered, in a crossover design, so that steady-state levels were achieved; a single dose of desipramine was then coadministered. The geometric least-square mean ratios (coadministration versus desipramine alone) for area under the plasma concentration versus time curve (AUC) and peak plasma concentrations (Cmax) of desipramine and 2-hydroxydesipramine were compared using analysis of variance. Relative to desipramine alone, increases in AUC and Cmax of desipramine associated with duloxetine administration (122 and 63%, respectively) were significantly greater than those associated with desvenlafaxine (22 and 19%, respectively; P < 0.001). Duloxetine coadministered with desipramine was also associated with a decrease in 2-hydroxydesipramine Cmax that was significant compared with the small increase seen with desvenlafaxine and desipramine (-24 versus 9%; P < 0.001); the difference between changes in 2-hydroxydesipramine AUC did not reach statistical significance (P = 0.054). Overall, desvenlafaxine had a minimal impact on the PK of desipramine compared with duloxetine, suggesting a lower risk for CYP2D6-mediated drug interactions.

The Effects of Desvenlafaxine and Paroxetine on the Pharmacokinetics of the Cytochrome P450 2D6 Substrate Desipramine in Healthy Adults

The potential for cytochrome P450 (CYP) 2D6 substrates to interact with desvenlafaxine (administered as desvenlafaxine succinate) and paroxetine was evaluated. In an open‐label, crossover study, 20 healthy volunteers (aged 21–50) were randomized to 2 series of 9 days each of desvenlafaxine (100 mg/d) or paroxetine (20 mg/d), separated by a 5‐day washout. The CYP2D6 substrate desipramine (50 mg) was administered alone on day 1 and coadministered on day 6 of dosing with either desvenlafaxine or paroxetine. CYP2D6 genotype was determined at baseline. Based on least squares geometric mean ratios between reference (desipramine alone) and test treatments, desvenlafaxine produced minor increases in desipramine area under the plasma concentration versus time curve (AUC; 36%) and peak plasma concentration (Cmax; 30%) (vs paroxetine: 419%, 90%, respectively; both P < .001). Desvenlafaxine produced little change in 2‐hydroxydesipramine AUC (16% increase) and Cmax (0%) versus paroxetine (18% and 82% decreases, respectively; P = .008, P < .001, respectively), indicating that desvenlafaxine, especially at the recommended therapeutic dose of 50 mg/d for major depressive disorder in the United States, has little potential to interact with CYP2D6 substrates.

Effect of desvenlafaxine on the cytochrome P450 2D6 enzyme system.

Background The cytochrome P450 2D6 (CYP2D6) enzyme is responsible for metabolizing approximately 25% of pharmaceutical agents. Individuals with impaired CYP2D6 metabolism and those concomitantly receiving agents that inhibit CYP2D6 can have variations in concentrations of such medications and their metabolites. Methods Five studies assessing the interaction between desvenlafaxine and CYP2D6 are reviewed. Study 1 compared desvenlafaxine area under the plasma concentration-versus-time curve (AUC) in CYP2D6 extensive metabolizers (EMs) and poor metabolizers (PMs) after administration of 100 mg of desvenlafaxine or 75 mg of venlafaxine extended release (ER). Studies 2 to 5 assessed the effect of concomitant administration of desvenlafaxine 100 mg (studies 2, 4, and 5) or 400 mg (study 3), paroxetine (20 mg, study 4), and duloxetine (30 mg twice daily; study 5) on the CYP2D6 probe desipramine. Results In study 1, there was no significant difference in mean desvenlafaxine AUC between the CYP2D6 EMs and PMs (−11%; P=0.641) who were administered desvenlafaxine. However, PMs receiving venlafaxine ER had significantly higher venlafaxine and lower desvenlafaxine AUCs compared with EMs (+350% and −74%, respectively; P<0.001 for each). In studies 2, 4, and 5, the mean increases in desipramine AUC with concomitant administration of desvenlafaxine 100 mg ranged from 17% to 36%; the increase with concomitant administration of desvenlafaxine 400 mg (study 3) was 90%. Paroxetine and duloxetine produced increases in mean desipramine AUC of 419% and 122%, respectively, which were significantly greater than the increases seen with desvenlafaxine 100 mg (P<0.001 for each comparison). Conclusions Based on the findings presented here, desvenlafaxine is expected to have a low risk for variability in efficacy and safety/tolerability resulting from CYP2D6 polymorphisms or drug-drug interactions when coadministered with CYP2D6 substrates or inhibitors.

P4-366: GSI-953, a potent and selective gamma-secretase inhibitor: Modulation of beta-amyloid peptides and plasma and cerebrospinal fluid pharmacokinetic/pharmacodynamic relationships in humans

change). The maximal score of SIB-L is 41 points, and the measurement error is 3.7 points, and therefore patients with a SIB-L score 37.3 were excluded from the analysis. In order to take symptom severity into account, patients with a SIB-L score 30 (median), and 23 (25% quartile) at baseline, were also analysed separately. Results: After 24 weeks, memantine-treated patients had significantly less mean change from baseline in SIB-L score than placebo-treated patients (p 0.0452). This indicates a beneficial effect of memantine on language performance. The percentage of SIB-L patient responders was also significantly superior in the memantine group as compared with the placebo group (18.7% vs 6.5%; p 0.011), after 24 weeks. In addition, in the subgroup of patients with SIB-L 30, responder rates for memantine-treated patients were significant versus placebo (25.0% vs 7.1%; p 0.008), as were responder rates in the SIB-L 23 group (30.6% vs 11.4%; p 0.036). Conclusions: Memantine treatment benefits language problems in patients with AD, as shown by a significantly higher responder rate, and less change from baseline, versus placebo. This marked effect indicates that memantine could be considered as an option for AD patients with language difficulties, regardless of their symptom severity on the MMSE.

Desvenlafaxine for major depressive disorder: incremental clinical benefits from a second-generation serotonin-norepinephrine reuptake inhibitor.

Importance of the field: Genetic and pharmacologically-driven variations in common mechanisms involved in the disposition of antidepressant medications may contribute to variable interpatient response. This review describes the pharmacological properties underlying the safety and efficacy of desvenlafaxine, a second-generation serotonin–norepinephrine reuptake inhibitor (SNRI). Areas covered in this review: Literature published between January 2006 and September 2010 evaluating desvenlafaxine was reviewed. What will the reader gain: Desvenlafaxine therapy is initiated at the therapeutic dose (50 mg/day) without a need for dose titration. Desvenlafaxine metabolism and distribution are not appreciably affected by altered function of cytochrome P450 (CYP) enzymes or permeability glycoprotein (P-gp). Desvenlafaxine has clinically insignificant effects on the activity of CYP and P-gp. The efficacy of desvenlafaxine in treating major depressive disorder has been established. Adverse events are characteristic of the SNRI class. Notably, the rate of discontinuation due to adverse events with the 50 mg/day recommended therapeutic dose is comparable to that seen with placebo. Take home message: Incremental benefits with desvenlafaxine, derived from straight-forward dosing, a simple metabolic profile and lack of interaction with active transporter P-gp and CYP enzymes may contribute to more consistent response, good tolerability and lower incidence of drug–drug interactions with concomitant medications.

Effects of desvenlafaxine on the pharmacokinetics of desipramine in healthy adults.

The results of two single-center, two-period, open-label trials that evaluated the effects of multiple doses of desvenlafaxine on the pharmacokinetics of desipramine, a cytochrome P450 (CYP) 2D6 enzyme substrate, are presented. Healthy individuals aged 18–45 years were administered a single oral dose of 50 mg desipramine with and without 100 mg daily (n=34) or 400 mg daily (n=23) desvenlafaxine for 5 days. After coadministration of 100 mg desvenlafaxine, desipramine exposure, measured by peak plasma concentration (C max) and total area under the plasma concentration-versus-time curve (AUC), showed minimal increases of 25 and 17%, respectively; coadministration of 400 mg desvenlafaxine resulted in a 52% increase in desipramine C max and a 90% increase in AUC. For the 100 mg dose, the geometric least squares mean ratios and 90% confidence intervals (CIs) for desipramine AUC (117%; 90% CI 110–125%), 2-hydroxydesipramine AUC (114%; 90% CI 110–119%), and C max (110%; 90% CI 104–116%) were all within the 80–125% interval, showing the bioequivalence for AUC between desipramine administered alone and in combination with 100 mg desvenlafaxine. These results indicate that desvenlafaxine is a relatively weak inhibitor of CYP2D6 and that desvenlafaxine 100 mg, twice the recommended therapeutic dose of 50 mg, is unlikely to cause drug–drug interactions with CYP2D6 substrates.