https://interactions.guidetherapeutiquevih.com/en/interaction-details?id=19730

Atazanavir / cobicistat

Doxazosin

Dosage adjustment may be necessary.

No pharmaceutical opinion available for this interaction.

Mechanism

Atazanavir / cobicistat can inhibit the metabolism (CYP 3A4) and increase the plasma concentration of Doxazosin.

Atazanavir / cobicistat

Pharmacodynamic effects

–

Recommendations

–

Alternative solution(s)

–

Doxazosin

Pharmacodynamic effects

Possible increase of adverse effects.

Recommendations

Use this combination with caution.

Start with a lower dose and adjust the dosage as a function of efficacy and the occurence of adverse effects.

Monitor closely for adverse 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.

A decrease in dosage may be necessary.

Alternative solution(s)

–

Monitor

Side effects of doxazosin: dizziness, orthostactic hypotension, vertigo and headaches.

Tests

–

Pharmacokinetic parameters

–

Comment

Little has been written about doxazosin and its interactions. However, a case report of priapism has been reported with the combination of boceprevir (CYP3A4 inhibitor) and doxazosin (ref #2956).

As doxazosin is administrated at different dosages (1 to 16 mg), it would be better to start with a smaller dosage and to adjust the dosage as a function of tolerance and efficacy, particularly when it is prescribed with a powerful inhibitor of CYP3A4.

Comment
Reference
  • 2557
    Doxazosine (Cardura), Pfizer, Québec, Canada, 4 avril 2017.
  • 2956
    Hammond KP, Nielsen C, Linnebur SA, Langness JA, Ray G et al. Priapism Induced by Boceprevir-CYP3A4 Inhibition and α-Adrenergic Blockade: Case Report. Clinical Infectious Diseases, 2014; 58(1): e35-38.