At 24 hrs the plasma amounts of sildenafil ended up still approximately 200 ng/mL, in comparison with around 5 ng/mL when sildenafil was dosed on your own. This can be in keeping with ritonavir's marked effects on a wide selection of P450 substrates. VIAGRA had no impact on ritonavir pharmacokinetics [see DOSAGE AND ADMINISTRATION and DRUG INTERACT