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Viagra Drug Interactions

by on July 16, 2012

People taking Viagra (Sildenafil) should be aware of the drugs that can potentially interact with it. There are certain medications that can cause moderate to severe drug interactions when used together with Viagra.

Significant Drug Interactions

Some of the medications that can cause significant drug interaction with Viagra include the following:

CYP3A4 inhibitors – Viagra is metabolized in the body with the help of an enzyme known as CYP3A4. However, there are certain medications that can interfere with the body’s CYP3A4 production potentially leading to reduced clearance of Viagra. Combining Viagra with these medications can increase the blood levels of Viagra. This also increases the risk of side effects particularly low blood pressure. As much as possible, such drug combination should be avoided.

  • Ketoconazole (Nizoral)
  • Ritonavir (Norvir)
  • Saquinavir (Invirase)
  • Erythromycin (E-mycin)
  • Itraconazole (Sporanox)
  • Cimetidine (Tagamet)
  • Other HIV protease inhibitors

CY3A4 inducers – These medications increase the breakdown and excretion of Viagra from the body, as a result, the blood levels of Viagra drops potentially making it less effective. Dose adjustments may be necessary when combining Viagra with CY3AP inducers.

  • Rifampin (Rifadin)
  • Carbamazepine (Tegretol)
  • Phenytoin (Dilantin)
  • Phenobarbital (Donnatal)
  • Bosentan (Tracleer)

Alpha adrenergic blockers – These medications are usually prescribed for patients with high blood pressure and benign prostatic hyperplasia. Combining these medications with Viagra can potentiate its blood pressure lowering effects thereby causing very low blood pressure. Caution should be taken when using these drugs together. Also, patients should have a stable blood pressure and should be started at the lowest possible dose.

  • Alfuzosin (Uroxatral)
  • Doxazosin (Cardura)
  • Phenoxybenzamine (Dibenzyline)
  • Phentolamine (Regitine)
  • Prazosin (Minipress)
  • Silodosin (Rapaflo)
  • Tamsulosin (Flomax)
  • Terazosin (Hytrin)

Antihypertensives – Viagra causes vasodilation (widening of blood vessels) which can potentially cause law blood pressure. Combining antihypertensive drugs with Viagra can lead to a sudden drop in blood pressure. Caution should be taken if using antihypertensives with Viagra.

Nitrates - Combining Viagra with nitrate-containing medications can enhance the blood pressure lowering effects of nitrates which can lead potentially life threatening adverse effects. It is recommended that people with chest pain (angina), especially those who are taking nitrates, should avoid taking Viagra.

  • Nitroglycerin tablets, spray or patches
  • Isosorbide dinitrate (Isordil)
  • Isosorbide mononitrate (Imdur)
  • Amyl nitrite “poppers”

Erectile dysfunction medications/PDE5 inhibitors – Viagra should not be used together with other PDE5 inhibitors, even if they are used for other medical purposes.

  • Tadalafil (Cialis)
  • Vardenafil (Levitra)

This medication guide does not discuss all the drugs that can potentially interact with Viagra. Be sure to discuss with your healthcare provider all drugs you normally to take to avoid possible drug interactions.

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