Particular caution should be used when prescribing ritonavir in patients using trazodone. Coadministration of ritonavir (200 mg twice daily) and trazodone (50 mg single dose) increased trazodone AUC by 2.4-fold and increased Cmin by 34%. An increase in the incidence of trazodone-related adverse events (nausea, dizziness, hypotension and syncope) was noted when coadministered with ritonavir dosed as an antiretroviral agent or as a pharmacokinetic enhancer. If trazodone is co-administered with ritonavir, the combination should be used with caution, initiating trazodone at the lowest dosage and monitoring for clinical response and tolerability.
Norvir Summary of Product Characteristics, AbbVie Ltd, September 2016.

Concomitant use of trazodone and ritonavir increases plasma concentrations of trazodone. Coadministration of ritonavir (200 mg twice daily) and trazodone (50 mg single dose) to 10 subjects increased trazodone AUC by 2.4-fold and increased Cmin by 34%. Adverse events of nausea, dizziness, hypotension and syncope) have been observed following co-administered trazodone and ritonavir. A lower dose of trazodone should be considered.
Norvir Prescribing Information, AbbVie Inc, December 2016.