Cardiovascular effects of 0.5 milligrams per kilogram oral d-amphetamine and possible attenuation by haloperidol

In a series of earlier studies, an oral dose of 0.5 mg/kg d-amphetamine was administered to 81 patients with schizophrenia and eight normal control su bjects. Seven more subjects with schizophrenia received placebo. Blood pres sure and pulse rate were monitored before and 3 hours after drug administra tion. Blood pressure increased in both amphetamine groups, whereas placebo had no effect. However, pulse rate did not change in the schizophrenic grou p and only increased after 3 hours in normal control subjects as blood pres sure began to decrease. Significant negative correlations between systolic blood pressure and pulse rate occurred at 2 and 3 hours, suggesting that th e early cardiovascular response to amphetamine is an increase in blood pres sure that recruits reflex control of heart rate. Eighteen of these subjects had hypertensive responses. Six subjects received 5 mg haloperidol intramu scularly, and 12 others had their blood pressure monitored until normalizat ion. Haloperidol led to a more rapid decline of some but not all indices of blood pressure, suggesting that amphetamine-induced hypertension may have a dopaminergic component.