Ritonavir can cause marked rises in
serum sildenafil levels. A fatal heart attack occurred in a man taking
ritonavir and saquinavir when he also took
sildenafil.
If the decision is taken to use
sildenafil in a patient taking
ritonavir, the dose of
sildenafil should not exceed 25 mg in a 48-hour period, but note that the fatality
described above occurred despite the use of this dose. There appears to be no direct information about
ritonavir used as a pharmacokinetic enhancer, but given the magnitude of the effect with
ritonavir 400 mg (11-fold rise), it would seem prudent to take a cautious approach, and follow the advice for high-dose
ritonavir. Use of
ritonavir with
sildenafil used for the management of
pulmonary hypertension is contraindicated.