No pharmaceutical opinion available for this interaction.
Atazanavir / ritonavir can inhibit the CYP 3A4 and P-gp and increase the plasma concentration of Silodosin.
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), UGT2B7 (active metabolite KMD-3213G, with long T1/2 life and AUC 4 fold silodosine). Dehydrogenase adehyde (inactive metabolite).Transporter:P-gp
Increased risk of orthostatic hypotension.
If the association can not be avoided, use the smallest possible dose (4 mg per day) and monitor closely side effects.
In patients already being treated with this combination and tolerating it, if deemed appropriate, keep actual treatment and exercise close monitoring of adverse effects.
* Terazosin, doxazosin and prazosin to start in small dose and close monitoring. These alpha-blockers are not uroselective and may not be suitable for some patients.
Side effects of silodosin: retrograde ejaculation, dizziness, orthostactic hypotension, vertigo and headaches.
* Alternatives: These choices are more secure because of the flexibility of the dosage with these agents and their metabolic pathways.
Ref #3105 : In a pharmacokinetic study with diltiazem, a moderate inhibitor of CYP 3A4, the AUC of silodosine increased by 30%. In another study with ketoconazole, a strong inhibitor of CYP 3A4 and P-gp, the AUC of silodosine increased by 3.7 fold.
Silodosin monograph contraindicates combining this product with a strong CYP3A4 or P-gp inhibitor such as ritonavir.
If an anticholinergic medication is used as an adjunct in order to decrease symptoms of enlarged prostate, the clinician must be careful because interactions between protease inhibitors and these agents are noted.