Critical
Methadone × ritonavir
Synthetic opioid, full mu-receptor agonist×HIV protease inhibitor / pharmacokinetic booster
Mechanism
Ritonavir has dual action: inhibits CYP3A4 (raises methadone) and induces CYP2B6 (lowers methadone). Net effect – unpredictable level swings plus additive QT prolongation.
Symptoms
Opioid withdrawal or overdose symptoms within 3-7 days. QT prolongation.
Management
For OST in HIV patient – ECG before and after ARV start, daily clinical monitoring for withdrawal/overdose signs first week. Alternative opioid – buprenorphine.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.