Effects of peripheral and central catechol-O-methyltransferase inhibition on striatal extracellular levels of dopamine: a microdialysis study in freely moving rats.

Tolcapone is a mixed (peripheral and central) catechol-O-methyltransferase (COMT) inhibitor, whereas entacapone is a preferential peripheral COMT inhibitor. Both drugs are able to decrease the peripheral conversion of L-DOPA into 3-O-methyl-DOPA and thereby increase plasma and cerebral levels of L-DOPA, the precursor of dopamine (DA). Tolcapone may also impair the extraneuronal catabolism of DA by inhibiting COMT activity in the brain. To evaluate the role played by peripheral and central COMT inhibition, we compared the effects of tolcapone and entacapone on COMT activity in peripheral tissues, and on striatal extracellular levels of L-DOPA and DA in rats. Tolcapone and entacapone, at the dose of 15 mg/kg p.o., were almost equally effective in inhibiting COMT activity in duodenum and liver. Tolcapone decreased striatal extracellular levels of homovanillic acid (HVA), thus confirming its central COMT inhibitory effect, whereas entacapone did not alter HVA efflux. Following L-DOPA/benserazide administration (50/15 mg/kg p.o.), both COMT inhibitors significantly increased striatal levels of L-DOPA and DA compared with saline. The levels of L-DOPA were similar after treatment with either COMT inhibitors, whereas the increase in DA output was significantly greater in rats given tolcapone compared to those given entacapone. We conclude that the blockade of central DA catabolism by tolcapone contributes to the greater increase in striatal DA levels achieved with this drug.

Treatment of patients with tardive dystonia with olanzapine.

Tardive dystonia represents a complication of long-term use of neuroleptics and its treatment is often unsatisfactory. Atypical neuroleptics appear to improve tardive dystonia, and cases of tardive dystonia successfully managed with clozapine have been reported. The aim of this open-label video-blinded study was to evaluate the antidystonic efficacy of olanzapine, a new atypical neuroleptic with a low risk of agranulocytosis, in a group of four patients (one man and three women) with tardive cervical dystonia. They developed severe dystonia after several years of neuroleptic treatment. Extensive laboratory evaluations, as well as neurophysiologic and neuroradiologic investigations, were negative. Olanzapine was started at a dose of 5 mg/d and increased up to 7.5 mg/d. All patients were evaluated at baseline and after 2, 4, 8, and 12 weeks of treatment, using the Toronto Western Spasmodic Torticollis Rating Scale, and videotaped. At the end of the trial, the videotapes were reviewed and scored by a blind observer. A self-rating visual analog scale completed the disability evaluation.A moderate to marked improvement in dystonia was observed in all patients, and significant differences were observed in Toronto Western Spasmodic Torticollis Rating Scale scores and videotape ratings after 8 and 12 weeks of treatment compared with the basal values (p < 0.05). The average percentage of improvement in Toronto Western Spasmodic Torticollis Rating Scale score and visual analog scale was 26.4% and 42.6%, respectively. No serious side effects were reported at the maximum dosage reached (7.5 mg/d). This study warrants a larger controlled study to conclusively demonstrate the efficacy of olanzapine in tardive dystonia.