Cialis Interactions with Other Drugs | My Canadian Pharmacy

Cialis interactions should be considered from two points of view: Its interactions with other drugs and how other drugs influence tadalafil. Let’s grapple with this question together.

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Influence of Other Drugs on Cialis

Tadalafil (Cialis main component) is mainly metabolized with the participation of isoenzyme CYP3A4. Selective inhibitor of isozyme CYP3A4:

ketoconazole (400 mg daily) increases exposure of tadalafil single dose (AUC) for 312% and Cmax by 22%;
ketoconazole (200 mg daily) increases exposure of tadalafil single dose (AUC) for 107% and Cmax by 15% relative to AUC and Cmax values for only one of tadalafil.
ritonavir (200 mg twice daily), an inhibitor of isoenzymes CYP3A4, 2S9, 2S19 and 2D6, increase exposure of tadalafil single dose (the AUC) by 124% without changing Cmax.

Despite the fact that specific interactions have not been studied, it is possible to assume that other HIV protease inhibitors such as saquinavir, as well as inhibitors isoenzyme CYP3A4, such as itraconazole, and erythromycin, increase tadalafil activity.

Isozyme selective inducer of CYP3A4, rifampicin (600 mg daily), reduces exposure of tadalafil single dose (AUC) by 88% and Cmax by 46%, relatively to AUC and Cmax values for tadalafil only. We can assume that simultaneous use of other inducers of CYP3A4 should also reduce tadalafil concentration in plasma.

Simultaneous treatment with antacid (hydroxide/magnesium aluminum hydroxide) reduces tadalafil absorption rate without altering area under the concentration-time curve for tadalafil.

Increasing pH of the stomach as a result of taking H2-histamine receptors blockers – nizatidine had no effect on tadalafil pharmacokinetics.

Cialis Effect on Other Drugs

It is known that tadalafil amplifies hypotensive nitrates effects. This is due to an additive effect of nitrates and tadalafil on the metabolism of nitric oxide II (NO) and cGMP. Therefore, Cialis use by patients taking nitrates is contraindicated.

Tadalafil has no clinically significant effect on drugs clearance, metabolism of which proceeds with the participation of cytochrome P450.

Studies have confirmed that tadalafil does not an inhibitor or induce such isozymes as:

CYP1A2;
CYP3A4;
CYP2C9;
CYP2C19;
CYP2D6;
CYP2E1.

Tadalafil has no clinically significant effect on the pharmacokinetics of S-warfarin or R-warfarin. Tadalafil did not affect the action of warfarin on prothrombin time.

Cialis does not increase bleeding duration caused by acetylsalicylic acid.

The drug has systemic vasodilating properties and may exacerbate effects of antihypertensive drugs aimed at lowering blood pressure.

Additionally, patients taking multiple antihypertensive agents whose hypertension is poorly controlled or who suffered from blood pressure reduction. The vast majority of patients do not associate this reduction with hypotensive symptoms. Patients applying treatment by means of antihypertensive drugs and taking tadalafil should get appropriate clinical advice.

There was no significant reduction in blood pressure when using Cialis with selective alfa1A-blocker – Tamsulosin.

Concomitant use of tadalafil with doxazosin is contraindicated. When using tadalafil in healthy volunteers who took doxazosin (4-8 mg per day), alpha 1-blocker were increased doxazosin hypotensive action. Some patients have experienced dizziness. Syncope was observed. The use of doxazosin in lower doses has not been studied.