Effect of Combination Therapy on Drug Potency.

Morphine and clonidine were administered in a dose-ratio of 1∶1 for spinal and 10∶1 for systemic administration; ∼ indicates that the ED50 value was determined by extrapolation (in cases where maximum efficacy was between 30 and 50%); γ = Interaction index (an index of 1 = no interaction, index >1 = potentiation, index 50 value of clonidine alone was not significantly different from that of clonidine in the presence of morphine; NA = not available (it is not possible to calculate these values).Effect of Combination Therapy on Drug Potency.