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PubMed2006

Topiramate and cortical excitability in humans: a study with repetitive transcranial magnetic stimulation.

Repetitive transcranial magnetic stimulation (rTMS) delivered at 5 Hz frequency and suprathreshold intensity progressively increases the size of muscle evoked potentials (MEPs) and the duration of the cortical silent period (CSP) in normal subjects. The aim of this study was to evaluate the effects of topiramate (TPM) at different doses on cortical excitability variables tested with rTMS. We tested the facilitation of the MEP size and CSP duration evoked by focal rTMS in eight patients before and after treatment with TPM at different doses for chronic neuropathic pain. In each patient, rTMS (5 Hz frequency-120% resting motor threshold) was applied at baseline and during the TPM induction phase (drug intake schedule: week I 25 mg/day, week II 50 mg/day, week III 75 mg/day, week IV 100 mg/day) and total TPM plasma concentrations were measured. The effects on the MEP size of 5 Hz-rTMS delivered over repeated sessions were tested in eight control subjects. TPM had no effect on the resting motor threshold. Antiepileptic treatment at increasing doses abolished the normal rTMS-induced MEP facilitation. ANOVA showed that this was a dose-related effect. Accordingly, in patients receiving TPM at higher doses (75 and 100 mg) rTMS failed to elicit the MEP facilitation. TPM left the progressive lengthening of the CSP during the rTMS train unchanged. In control subjects, rTMS applied over repeated sessions elicited a constant increase in MEP size. Our results suggest that TPM modulates the excitatory intracortical interneurons probably by altering rTMS-induced synaptic potentiation. These drug-induced effects are related to TPM doses and plasma concentrations. In conclusion, rTMS may be useful for quantifying the effectiveness of antiepileptic drugs and for assessing individual responses to different drugs but acting through similar mechanisms, thus combining functional neurophysiological information and laboratory data.

Adult↗

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Venlafaxine and bladder function.

BACKGROUND: Occasional case reports describe urinary incontinence in patients taking the selective serotonin and norepinephrine reuptake inhibitor antidepressant venlafaxine. OBJECTIVE: In this study the authors investigated the possible effect of venlafaxine on urinary function in a series of 9 patients with urinary retention resulting from spinal cord lesions. They primarily sought to understand whether the reported venlafaxine-induced urinary incontinence was a specific drug-induced effect and, if so, whether venlafaxine might be an effective treatment of urinary retention. METHODS: During a 1-week baseline period, patients measured postvoiding residual volume through a catheter and recorded the number of micturitions within 24 hours. At the end of the baseline period, venlafaxine 75 mg extended-release on a once-daily evening administration schedule was added to their therapy for 1 week. RESULTS: None of the patients reported severe/uncontrollable side effects while taking venlafaxine. Extended-release venlafaxine (75 mg/day) significantly reduced the postvoiding residual volume and increased the micturition rate; the volume diminished on the first day of treatment and remained stable over the ensuing days. CONCLUSION: These findings suggest that venlafaxine could be useful to improve voiding in patients with spinal cord disease.

Analysis of Variance↗