Dihydroergotamine: pharmacokinetics and usefulness in spinal anaesthesia

In a double-blind study, 0.5 mg of dihydroergotamine or the same volume of placebo was used to prevent hypotension caused by spinal anaesthesia. The plasma concentrations of dihydroergotamine were determined by a new radioimmunoassay developed for ergot alkaloids, and pharmacokinetic calculations were based on the equation of a two-compartment open model. No significant changes were observed in the heart rates of the two patient groups. In Group I, which received dihydroergotamine, significant increased in both systolic and diastolic blood pressures were measured after drug administration, and, compared to the base-line measurements before spinal anaesthesia, no significant decreases in systolic or diastolic blood pressures were recorded. In contrast to Group I, there was a significant decrease in both systolic and diastolic blood pressures in the placebo Group II during spinal anaesthesia. There were no significant differences, however, in the temperature of the great toe between Groups I and II. Dihydroergotamine disappeared quickly from plasma, with a mean alpha-phase half-life of 1.35 min, which explained its rapid effect on blood pressure. Beta-phase half-life (mean 23.20 min), the volume of distribution at beta-phase (mean 0.25 I/kg), and the total plasma clearance (mean 1562.8 ml/min) indicate rapid elimination of the drug from the body.