Hypertension: In controlled trials, terazosin has been added to diuretics, and several beta-adrenergic blockers; no unexpected interactions were observed. Terazosin has also been used in patients on a variety of concomitant therapies; while these were not formal interaction studies, no interactions were observed. Terazosin has been used concomitantly in at least 50 patients on the following drugs or drug classes: analgesic/anti-inflammatory (e.g. paracetamol, aspirin, codeine, ibuprofen, indomethacin); antibiotics (e.g. erythromycin, trimethoprim, and sulfamethoxazole); anticholinergic/sympathomimetics (e.g., phenylephrine hydrochloride, phenylpropanolamine hydrochloride, pseudoephedrine hydrochloride); antigout (e.g. allopurinol); antihistamines (e.g. chlorpheniramine); cardiovascular agents (e.g. atenolol, hydrochlorothiazide, methyclothiazide, propranolol); corticosteroids; gastrointestinal agents (e.g., antacids); hypoglycemics; sedatives and tranquilizers (e.g., diazepam).
Caution should be observed when terazosin is administered concomitantly with other antihypertensive agents (eg. calcium antagonists) to avoid the possibility of significant hypotension. When adding a diuretic or other antihypertensive agent, dosage reduction and retitration may be necessary.
Benign Prostatic Hyperplasia (BPH): In BPH patients the adverse event profile of patients treated concurrently with other non-steroidal anti-inflammatory drugs (NSAID), theophylline, antianginal agents, oral hypoglycaemic agents, angiotensin converting enzyme (ACE) inhibitors or diuretics was compared against the profile in the general treated population. No clinically significant interactions have been observed except for ACE inhibitors and diuretics. In this small subset of patients, the percent reporting dizziness or other dizziness-related adverse events appears to be greater in those patients than in the total population of terazosin patients from double-blind, placebo-controlled studies.
PDE-5 Inhibitors: Hypotension has been reported when terazosin has been used with phosphodiesterase-5 (PDE-5) inhibitors (see PRECAUTIONS).