Critical
Quetiapine × ritonavir
Atypical antipsychotics×HIV protease inhibitor / pharmacokinetic booster
Mechanism
Quetiapine is cleared via hepatic CYP3A4. Ritonavir is the strongest available CYP3A4 inhibitor. Quetiapine plasma levels rise 6- to 10-fold.
Symptoms
Marked sedation, orthostatic hypotension with syncope, tachycardia, QT prolongation on ECG. Hyperglycaemia and metabolic disturbance worsen. Older patients face higher fall and fracture risk.
Management
The combination is not prescribed. Alternative antipsychotics on ritonavir: paliperidone (minimal CYP3A4 metabolism) or aripiprazole with caution and a 50% dose cut.