Doxazosin Interactions

7 DRUG INTERACTIONS Strong cytochrome P450 (CYP) 3A inhibitors may increase exposure to doxazosin and increased risk of hypotension. ( 7.1 ) Concomitant administration of doxazosin mesylate with a phosphodiesterase-5 (PDE-5) inhibitor can result in additive blood pressure lowering effects and symptomatic hypotension. ( 7.2 ) 7.1 CYP 3A Inhibitors In vitro studies suggest that doxazosin is a substrate of CYP 3A4.

Source: FDA drug label - doxazosin mesylate

Alpha-adrenergic blocking agents, such as prazosin, terazosin, and doxazosin, can antagonize the effects of midodrine.

Source: FDA drug label - midodrine hydrochloride

Central Alpha1-Blockers Doxazosin: Healthy volunteers participating in a multiple dose doxazosin-nifedipine interaction study received 2 mg doxazosin q.d. Co-administration of nifedipine resulted in a decrease in AUC and C max of doxazosin to 83% and 86% of the values in the absence of nifedipine, respectively. In the presence of doxazosin, AUC and C max of nifedipine were increased by factors of 1.13 and 1.23, respectively.

Source: FDA drug label - nifedipine

Postural hypotension has been reported in patients taking both beta-blockers and terazosin or doxazosin.

Source: FDA drug label - propranolol hydrochloride

In drug-drug interaction studies, sildenafil (25 mg, 50 mg, or 100 mg) and the alpha-blocker doxazosin (4 mg or 8 mg) were administered simultaneously to patients with benign prostatic hyperplasia (BPH) stabilized on doxazosin therapy.

Source: FDA drug label - sildenafil

Clinical pharmacology studies have been conducted with coadministration of tadalafil with doxazosin, tamsulosin or alfuzosin.

Source: FDA drug label - tadalafil