Seizures associated with therapeutic doses of venlafaxine and trimipramine

Cytochrome P450-mediated inhibition of venlafaxine metabolism by trimipramine

OBJECTIVE

The aim of this study was to ensure patients' safety and to enhance treatment efficacy, knowledge about pharmacokinetic interactions even in complex clinical situations of polypharmacy is invaluable. This study is to uncover the potential of pharmacokinetic interactions between venlafaxine and trimipramine in a naturalistic sample.

METHODS

Out of a therapeutic drug monitoring database with plasma concentrations of venlafaxine (VEN) and O-desmethylvenlafaxine (ODV), we considered two groups of patients receiving venlafaxine without known cytochrome P450 confounding medications, taking solely venlafaxine: V0 (n = 905), and a group of patients co-medicated with trimipramine, VTRIM (n = 33). For VEN, ODV and active moiety (sum of VEN + ODV) plasma concentrations and dose-adjusted concentrations as well as ODV/VEN ratios were compared between groups using the Mann-Whitney U test with a significance level of 0.05.

RESULTS

Patients co-medicated with trimipramine had higher plasma concentrations of VEN (183.0 vs. 72.0, +154%, P = 0.002) and AM (324.0 vs. 267.5, +21%, P = 0.005) and higher dose adjusted plasma concentrations than patients in the control group (P = 0.001 and P = 0.003). No differences were found for ODV and C/D ODV (P < 0.05 for both comparisons). The metabolite to parent ratio, ODV/VEN, was significantly lower in the VTRIM group (1.15 vs. 2.37, P = 0.012).

CONCLUSION

Findings suggest inhibitory effects of trimipramine on venlafaxine pharmacokinetics most likely via an inhibition of CYP 2D6 or by saturated enzyme capacity. The lack of in vitro data hampers the understanding of the exact mechanisms. Clinicians should be aware of drug-drug interactions when combining these agents. Therapeutic drug monitoring helps to ensure treatment efficacy and patients' safety.

Seizure Induced by a Therapeutic Dose of Venlafaxine ER: A Case Report

Venlafaxine is a selective serotonin and norepinephrine reuptake inhibitor commonly used for the treatment of depression. Although listed as an adverse reaction, seizure activity associated with a therapeutic dose of venlafaxine has rarely been documented. A review of the literature reveals only 2 cases of venlafaxine-induced seizures, both of which were generalized tonic-clonic seizures in patients on doses at the higher end of the therapeutic range. We report the case of a 44-year-old woman undergoing antituberculosis therapy who suffered complex partial seizures after ingestion of a low therapeutic dose of venlafaxine extended release (ER). Her first seizure was observed soon after venlafaxine ER was titrated from 37.5 to 75 mg daily, with a total of 9 witnessed complex partial seizures. After titrating the dose of the venlafaxine ER back down to 37.5 mg daily and beginning lamotrigine anticonvulsant therapy, the patient exhibited no further seizures. The development of seizure activity under therapeutic dosing of venlafaxine should be brought to the attention of the health care prescriber. The potential for drug-drug interactions involving venlafazine, particularly in combination with multiple drugs, such as isoniazid and levofloxacin, needs to be recognized.

Review of Duloxetine and Venlafaxine in Depression

Objectives:

To compare the efficacy and pharmacologic, pharmacokinetic, drug interaction and adverse effect profiles of duloxetine and venlafaxine.

Methods:

A systematic review of the literature pertaining to duloxetine and venlafaxine was conducted using a computer-aided search of MEDLINE and EMBASE for the period January 1988 to May 2008 with the following search terms: venlafaxine and duloxetine and depression, clinical studies, pharmacology, drug interactions, pharmacokinetics, adverse effects, safety, case reports and review articles.

Results:

Duloxetine and venlafaxine have comparable efficacy and share similar pharmacologic profiles but differ somewhat in their pharmacokinetic profiles, drug interactions and adverse effects. Both agents block the reuptake of serotonin and norepinephrine and both are substrates for the cytochrome P450 2D6 isoenzyme; however, duloxetine inhibits these enzymes to a moderate extent, whereas venlafaxine is only a weak inhibitor. Furthermore, duloxetine is more extensively bound to protein than venlafaxine. Venlafaxine is more likely to elevate blood pressure in a dose-related manner. Both duloxetine and venlafaxine have the potential to cause hepatic injury.

Conclusions:

Although venlafaxine and duloxetine have similar efficacy in the treatment of depression, differences in their adverse effects and pharmacokinetic profiles suggest that one agent may be preferred over the other in certain patient groups.

Multimodality imaging in a depressed patient with violent behavior and temporal lobe seizures

Patients suffering from epilepsy commonly experience behavioral symptoms. Behavioral manifestations are especially prevalent in patients with seizures originating in the limbic system. This case report illustrates how an objective, multimodality work-up can guide the clinician in the diagnosis and the treatment of a patient with a complex presentation. After the discontinuation of some medications, the patient underwent a multimodality work-up that consisted of MRI, SPECT, and conventional and quantitative EEG (LORETA). In this case, the functional imaging studies showed a convergence of findings across the three modalities: MRI, SPECT and qEEG. Because of these findings, we supported more aggressive treatment of the seizure disorder. Ultimately this treatment resulted in resolution of the aggression and the depression. In summary, when applied routinely, a comprehensive, systematic, diagnostic approach will minimize treatment false starts and failures, may reduce costs, and also, potentially decrease the severity and the duration of symptoms.

Proconvulsant effects of high doses of venlafaxine in pentylenetetrazole-convulsive rats

Venlafaxine, an atypical antidepressant drug, has been used to treat several neurological disorders, presenting excellent efficacy and tolerability. Clinical seizures after venlafaxine treatment have occasionally been reported when the drug was used at very high doses or in combination with other medications. The aim of the present study was to investigate the convulsant effects of venlafaxine in rats under controlled laboratory conditions. Adult male Wistar rats (8 per group) receiving venlafaxine or saline at the doses of 25-150 mg/kg were subjected 30 min later to injections of pentylenetetrazole at the dose of 60 mg/kg. The animals receiving 75, 100 and 150 mg/kg venlafaxine presented increased severity of convulsion when compared to controls (P = 0.02, P = 0.04, and P = 0.0004, respectively). Indeed, an increased percentage of death was observed in these groups (50, 38, and 88%, respectively) when compared to the percentage of death in the controls (0%). The group receiving 150 mg/kg showed an reduction in death latency (999 +/- 146 s) compared to controls (1800 +/- 0 s; cut-off time). Indeed, in this group, all animals developed seizures prior to pentylenetetrazole administration. Surprisingly, the groups receiving venlafaxine at the doses of 25 and 50 mg/kg showed a tendency towards an increase in the latency to the first convulsion. These findings suggest that venlafaxine at doses of 25 and 50 mg/kg has some tendency to an anticonvulsant effect in the rat, whereas doses of 75, 100 and 150 mg/kg presented clear proconvulsant effects in rats submitted to the pentylenetetrazole injection. These findings are the first report in the literature concerning the role of venlafaxine in seizure genesis in the rat under controlled conditions.