Route and rate of hydrallazine administration as determinants to its hypotensive effect in rabbits

1. The cardiovascular responses to varying doses of hydrallazine were studied in renal hypertensive rabbits. 2. The depressor effect of hydrallazine was independent of the rate of its i.v. administration (bolus v. a 15 min constant infusion). 3. Intraperitoneally administered hydrallazine was significantly less active than equimolar i.v. doses, and the relative potency (i.p. v. i.v.) did not increase with increasing doses. 4. In spite of inferential evidence to the contrary, we did not find any pharmacodynamic support for non-linear processes being involved in metabolism of hydrallazine.