0.5 single IV dose 300 q12h, 3 days ↑ 86% ND 0.4 single oral 200 q12h, 13 days ↑ 22% ↔ dose This interaction may be due to modification of P-glycoprotein mediated digoxin efflux by ritonavir dosed as an antriretroviral agent or as a pharmacokinetic enhancer.