Effect of venlafaxine and desvenlafaxine on drug efflux protein expression and biodistribution in vivo.

Venlafaxine, and to a lesser extent desvenlafaxine, has previously been shown to induce the expression of the drug efflux transporters P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in whole cells and alter the cellular permeability of a known drug efflux probe (rhodamine 123). To validate these in vitro findings, wild-type mice were treated for 4 days with 10 mg/kg venlafaxine or desvenlafaxine, and drug efflux transporter expression was examined in the brain, liver, and intestine. P-gp and BCRP expression was significantly upregulated in the intestine, following a treatment with venlafaxine (2.6- and 6.7-fold, respectively) or desvenlafaxine (2.3- and 4.8-fold, respectively). In addition, venlafaxine increased the BCRP expression in the brain (40%) and liver (60%), whereas desvenlafaxine had no effect on drug efflux transporter levels in these tissues. Using the same treatment paradigm, we observed a minimal impact of either drug on the brain disposition of the known drug efflux probe, topotecan. However, in the periphery, venlafaxine treatment significantly reduced the topotecan oral bioavailability by nearly 40%, whereas the impact of desvenlafaxine on topotecan plasma levels was more modest (23%). These studies demonstrate an effect of venlafaxine on the drug efflux transport activity and the potential for clinical drug-drug interactions.

Induction of drug efflux protein expression by venlafaxine but not desvenlafaxine.

Venlafaxine and its metabolite desvenlafaxine are serotonin-norepinephrine reuptake inhibitors currently prescribed for the treatment of depression. Previously, it was reported that venlafaxine is an inducer of MDR1, the gene responsible for P-glycoprotein (P-gp). The present study expanded upon these findings by examining the effect of venlafaxine and desvenlafaxine on the expression of both P-gp and the breast cancer resistance protein (BCRP) in human brain endothelial cells (HBMEC), an in vitro model of the blood-brain barrier (BBB). The HBMEC were treated for 1 h with various concentrations (500 nM to 50 µM) of venlafaxine and desvenlafaxine. Western blot analysis revealed treatment with venlafaxine significantly induced the expression of P-gp (2-fold) and BCRP (1.75-fold) in a dose-dependent manner, while treatment with desvenlafaxine had no effect on drug efflux transporter expression. To determine the functional significance of this effect, the permeability of a known drug efflux probe, rhodamine 123, across the BBB model and Caco-2 cells, a model of intestinal absorption, were examined. Treatment with venlafaxine (1-50 µM) for 1 h significantly reduced the apical-to-basolateral permeability of R123 across the BBB model (30%) and Caco-2 cell monolayers (25%), indicative of increased drug efflux transporter expression at the apical membrane. Conversely, desvenlafaxine had no effect on R123 permeability in either cellular model. These studies indicate that venlafaxine, but not desvenlafaxine is an inducer of drug efflux transporter expression, which consequently increases the potential for clinical drug-drug interactions. Therefore, based on these preliminary results, caution should be taken when prescribing venlafaxine with other P-gp substrates.

Assessment of human serotonin 1A receptor polymorphisms and SSRI responsiveness.

BACKGROUND: Depression is thought to involve, in part, dysregulation of serotonergic neurotransmission. In depressed individuals, the number of serotonin receptors, including the 5-hydroxytryptamine (serotonin)-1A (5-HT(1A)) autoreceptors, are increased. Clinical improvement with selective serotonin reuptake inhibitors (SSRIs) is not usually observed until several weeks after treatment initiation. This delay may be due to the time it takes for the autoreceptors to downregulate. Roughly one-third of patients with depression do not respond to an initial trial of antidepressant medication treatment, possibly as a result of structural variations in the 5-HT(1A) receptor. AIMS: This study was designed to determine the allelic frequency of seven 5-HT(1A) receptor polymorphisms in a depressed versus a nondepressed population, and in SSRI responders versus nonresponders. All the polymorphisms studied are single nucleotide polymorphisms (SNPs) in the HTR1A gene, which encodes 5-HT(1A). Seven prevalent SNPs were included in the analysis. RESULTS: The study showed no relationship between any of the HTR1A polymorphisms and SSRI responders versus nonresponders. CONCLUSION: While the study has several limitations, the results are consistent with a growing body of literature that suggests that the pharmacogenetics of depression (an inherently complex disorder) may turn out to be multifactorial, and may include the HTR1A gene in concert with other serotonin-related genes.

Long-term use of atypical antipsychotics in bipolar disorder.

Bipolar disorder is a chronic disease that may require lifetime treatment. The maintenance therapy of bipolar disorder can be challenging for the treating clinician. Currently, according to the American Psychiatric Association (APA) guidelines, lithium, valproic acid, lamotrigine, carbamazepine, oxcarbazepine, and the antipsychotics are recommended for the maintenance treatment of bipolar disorder. The antipsychotics are recommended to be continued only if the clinician decides that they are necessary for the control of persistent psychosis or for prophylaxis against recurrence. Although the APA guidelines provide sufficient evidence for the use of these mood stabilizers, newer drugs such as the atypical antipsychotics are being investigated for use in the maintenance phase of treatment of bipolar disorder.

Aripiprazole: a new atypical antipsychotic drug.

OBJECTIVE: To review the pharmacology, pharmacokinetics, clinical efficacy, and safety profile of aripiprazole for the treatment of schizophrenia. DATA SOURCES: Information was selected from MEDLINE (1995-August 2002). Abstracts, scientific posters, and presentations were also used. STUDY SELECTION/DATA EXTRACTION: All published information regarding the pharmacokinetic, pharmacodynamic, and clinical characteristics of aripiprazole was considered. Studies providing a comprehensive description of aripiprazole were selected. DATA SYNTHESIS: Aripiprazole is a dopamine partial agonist and a serotonin-2A antagonist; it is dosed 10-30 mg/d, with no initial titration necessary. Short-term clinical trials demonstrated efficacy in acute exacerbations, and long-term studies showed that aripiprazole can maintain remission of schizophrenia. Most adverse events were mild. The incidence of extrapyramidal symptoms was low, with akathisia being the most common. CONCLUSIONS: Aripiprazole currently demonstrates comparable efficacy and safety for use in schizophrenia.