No pharmaceutical opinion available for this interaction.
Atazanavir / ritonavir may possibly inhibit the metabolism (CYP 2D6 and 3A4) and consequently increase the concentration of Trazodone.
Possible additive effects for the prolongation of the QT interval .
3A4, P-gp/3A4 > 2D6, P-gp
Ritonavir: 1A2, 2C9, 2C19, UGT, 2B6, 3A4 (auto-induction)
3A4, UGT1A1, P-gp E et 2C8/3A4 > 2D6 > 2A6, 2E1, P-gp, MRP2
3A4 (major) 2D6 (minor)/ Metabolized into m-chlorophenylpiperazine.
Possible increase of adverse effects.
Increased risk of QT interval prolongation.
If antiretroviral therapy is going on, start with a small dose and gradually increase depending on efficacy and safety.
If patient already on trazodone and antiretroviral therapy is started, reduce the dose by 50% and gradually increase depending on efficacy and safety.
In patients already being treated with this combination and tolerating it, if deemed appropriate, keep actual treatment and exercise close monitoring of adverse effects.
Use with caution especially in patients with factors of prolongation of the QT interval.
Trazodone toxicity: dizziness, fatigue, sweating, orthostatic hypotension, syncope, priapism.
Anticholinergic adverse effects: xerostomia, constipation, urinary retention, sedation, drowsiness, blurred vision, akathisia, convulsions, tachycardia, hypotension, etc.
Ref #1515 : When co-administering a single dose of trazodone with ritonavir 200 mg BID an increase was observed in trazodone AUC and Cmax of 140% and 34%, respectively. Cases of patients showing symptoms as nausea, dizziness, fatigue, performance issues, hypotension and syncope have been reported.
Ref #1382 : Atazanavir product monograph recommends caution when it is prescribed in combination with drugs that may prolong the QT interval.