Effects of Midodrine on Chlorpromazine-Induced Orthostatic Hypotension in Rabbits : Comparison with Amezinium, Etilefrine and Droxidopa

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Orthostatic hypotension was produced in urethane-anesthetized rabbit by a combination of chlorpromazine (0.1 mg/kg, i.v.) and 45° head-up tilt. The effect of midodrine (1 and 3 mg/kg, i.d.) was investigated in comparison with amezinium (10 and 30 mg/kg, i.d.), etilefrine (10 and 30 mg/kg, i.d.) and droxidopa (30 and 100 mg/kg, i.d.). The higher doses of each drug significantly mitigated the chlorpromazine-induced orthostatic hypotension, while none of the lower doses caused a significant effect. The effect of midodrine developed most rapidly; a significant effect was observed 25 min after administration. The order of onset time was midodrine<etilefrine<amezinium<droxidopa. The effect of droxidopa was significant only at 130 to 160 min after administration. The amplitude of effect was in the following order; midodrine=droxidopa≧etilefrine>amezinium. Midodrine (3 mg/kg, i.d.)mitigated orthostatic hypotension induced by prazosin (0.1 mg/kg, i.v.), but not by pentolinium (0.6 mg/kg, i.v.). It is suggested that midodrine competes with chlorpromazine at α_1-adrenoceptors and subsequently recovers reflex vasconstriction. Midodrine may be useful to protect patients with impaired baroreflex activity from accidental orthostatic hypotension during treatment with neuroleptics.
公益社団法人日本薬学会の論文
2000-12-01