To determine the acute effects of intravenous (IV) cocaine on primarily digital skin blood flow and diffusion capacity for carbon monoxide (CO), and secondarily on subjective and cardiovascular measures.

A double-blind, Latinsquare, placebo-controlled, dose-response study was conducted in an inpatient general clinical research center and clinical pharmacology unit of a university teaching hospital. Twelve adult males with histories of illicit drug use including IV cocaine received 0, 25, and 50 mg of IV cocaine given as 1-minute infusions, on 3 consecutive test days. Digital cutaneous blood flow was determined via laser doppler flowmetry and skin temperature. Diffusing capacity for carbon monoxide (D_CO) was measured with standard techniques. Subjective responses were measured by oral report of a numerical ranking of strength of drug effect. Heart rate and blood pressure responses were measured by electronic syphygmomanometer.

A maximal decrease in skin blood flow occurred at 2 to 3 minutes after infusion, and was not distinguished among drug conditions. Blood flow returned to baseline more rapidly after placebo than after cocaine: 7 minutes (placebo), 35 minutes (25 mg cocaine), 50 minutes (50 mg cocaine). Skin temperature decreased by 1.25 °C after placebo and by 2.75 and 3.25 °C after 25 and 50 mg of cocaine, respectively. D_CO changed by −1.02 (mean) ± 0.25 (standard deviation), 0.16 ± 1.22, and 0.21 ± 1.63 ml/min/mm Hg following placebo, 25, and 50 mg of cocaine, respectively. Typical subjective, chronotropic, and pressor responses to cocaine were demonstrated, and these occurred in close temporal relationship to digital blood flow and skin temperature responses.

The digital cutaneous circulation is highly sensitive to vasoconstrictor effects of cocaine. Pulmonary blood volume tends to be preserved after IV cocaine. Subjective effects and cardiovascular responses occur in concert with peripheral blood flow changes. The peripheral vasoconstrictor effects have implications for cocaine users with concurrent vasospastic or vasculopathic disorders.