Interaction between Prazosin and Tadalafil
Moderate
Synergy
| ID | DDInter1511 and DDInter1736 |
| Interaction | Tadalafil may potentiate the hypotensive effect of alpha blockers, resulting in symptomatic hypotension in some patients. Tadalafil inhibits phosphodiesterase-5-mediated degradation of cyclic guanosine monophosphate (cGMP), which in vascular smooth muscles can cause peripheral vasodilation that may be additive with that induced by alpha blockers. |
| Management | Caution is advised if tadalafil is used in combination with alpha blockers. Patients who demonstrate hemodynamic instability on alpha blocker therapy alone are at increased risk of symptomatic hypotension with concomitant use of tadalafil. Therefore, patients should be stable on alpha blocker therapy prior to initiating tadalafil, and tadalafil should be initiated at the lowest recommended dosage. In those patients already on an optimized dosage of tadalafil, alpha blocker therapy should be initiated at the lowest dosage. Clinicians should bear in mind that the safety of tadalafil in combination with alpha blockers may also be affected by other variables such as intravascular volume depletion and use of other antihypertensive medications. The combination of tadalafil and alpha blockers is not recommended for the treatment of benign prostatic hyperplasia (BPH) due to the lack of safety and efficacy data. Patients on alpha blocker therapy for BPH should discontinue the alpha blocker at least one day prior to starting tadalafil for once-daily use in the treatment of BPH. |
| References | |
| Alternative for Prazosin | - |
| Alternative for Tadalafil |
G04B
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Potential Metabolism Interactions
Substrate-Substrate Interaction：If more than one drug is metabolized by the same CYP, it is possible that its metabolism is inhibited because of the competition between the drugs. That means, it can be useful to lower the dosage of the drugs in the drug-cocktail because they remain longer in the organism than in monotherapy.
Inhibitor-Inhibitor Interaction：Combining two or more inhibitors of one CYP, should be compensated by lowering the dosage of these drugs because the metabolism is reduced and the drugs remain longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.
Inhibitor-Substrate Interaction：Combining drugs that have inhibitory effect and are substrates of one particular CYP, should be compensated by lowering the dosage. They rest longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.