Pharmacokinetic and pharmacodynamic interactions between dehydroepiandrosterone and prednisolone in the rat

The effects of multiple-dosing with dehydroepiandrosterone sulfate (DHEA-SO₄) on the pharmacokinetics and pharmacodynamics of prednisolone were examined. Prednisolone (25 mg/kg i.v.) was administered to male and female Sprague-Dawley rats (250-350 g) alone and following DHEA-SO₄ (4 mg/kg i.v., every 8 h for 4 days). Male control rats cleared prednisolone faster [3.68 ± 1.30 (males) vs 1.01 ± 0.7 l/h/kg; p<0.05] and had larger Vss (1.38 ± 0.459 vs 0.394 ± 0.500 l/kg; p<0.05) than females both due largely to lesser plasma protein binding. Prednisolone clearance and Vss were not altered by DHEA-SO₄ in males or females. The net effect of prednisolone on basophils and plasma corticosterone did not differ with gender. DHEA-SO₄ had no effect on plasma corticosterone and did not alter prednisolone action. DHEA-SO₄ inhibited basophil trafficking in males, but to a lesser extent than prednisolone, and antagonized the effect of prednisolone on basophil trafficking in both sexes. The steroid-sparing effect observed with DHEA clinically may not be due to an alteration of corticosteroid pharmacokinetics but partly to its ability to affect immune functions.