Sildenafil drug interactions

The most dramatic difference between the three agents is tadalahl s extended duration of action, earning it the nickname the weekender drug. While sildenafil and vardenafil have average half-lives of 3 to 4 hours, tadalafil s half life is approximately 18 hours.18 The extended half-life allows for more spontaneous sexual activity over a couple of days, but may increase the duration of adverse effects and liklihood of drug interactions or sildenafil. 

A drug-drug interaction is possible with sildenafil and which of the following agents ... 

Sildenafil has other minor adverse effects, such as headache, nasal congestion, and flushing. There are no clinically significant drug interactions between sildenafil and apomorphine. Apomorphine, like sildenafil, is orally active. However, unlike sildenafil, it exerts its action through the central nervous system. Apomorphine can produce dizziness, nausea, pallor, and hypotension, and in the presence of ethanol, it purportedly increases... 

Up to 2001, AERS indicated up to 39 case reports of possible drug interactions between St. John s wort and a prescription drug. In these case reports, the potential drug interactions occurred mostly with oral contraceptives, antidepressants, cyclosporine, and sildenafil. All cases were reported between 1997 and 2000. Most of the reported cases were in females (24),... 

Four cases of lack of effect or impotence were reported in patients using sildenafil while on St. John s wort and other concomitant drugs (what are they Are any of them significant from the standpoint of drug interaction ). The age range of the four male patients was between 55 to 73 years. Viagra... 

A physician reported that a 60-year-old male started sildenafil 50 mg while he was also taking 600 mg of St. John s wort daily for depression. When the patient increased the dose of St. John s wort to 1200 to 1800 mg daily for unknown reasons, the sildenafil was reported to be partially effective. Patient increased the dose of sildenafil to 100 mg but it was completely ineffective. The physician suspected that a drug interaction caused the adverse events. No other significant medical history was noted. 

Sildenafil, tadalafil and vardenafil have similar, although not identical, mechanisms of action and structural similarity, and are metabolized primarily by the CYP3A4 isoenzymes, Vardenafil is 32-fold more potent than sildenafil in inhibiting phosphodiesterase type 5. Tadalafil has a quicker onset of action and a longer duration of action - around 36 hours - hence the need to be aware of the potential for adverse drug interactions for nearly 2 days after the intake of a single tablet. 

Webb DJ, Freestone S, Allen MJ, Muirhead GJ. Sildenafil citrate and blood-pressure-lowering drugs results of drug interaction studies with an organic nitrate and a calcium antagonist. Am J Cardiol 1999 83(5A) C21-8. 

Drug interactions The concurrent use of sildenafil (used for erectile dysfunrtion) is contraindicated due to potentiation of hypotensive effects Of nitrates. Ergot alkaloids (used for migraine headaches) may cause increased blood pressure and decreased antianginai effects of nitrates—avoid concurrert use. 

Treiber, A., Schneiter, R., Hausler, S. and Stieger, B. (2007) Bosentan is a substrate of human OATP1B1 and OATP1B3 inhibition of hepatic uptake as the common mechanism of its interactions with cyclosporin A, rifampicin, and sildenafil. Drug Metabolism and Disposition The Biological Fate of Chemicals, 35, 1400-1407. 

Warrington, J.S., R.I. Shader, L.L. von Moltke, and D.J. Greenblatt (2000). In vitro biotransformation of sildenafil (Viagra) Identification of human cytochromes and potential drug interactions. Drug Metab. Dispos. 28, 392-397. 

Chung M, DiRico A, Calcagni A, Messig M, Scott R. Lack of a drug interaction between sildenafil and atorvastatin. J Clin Pharmacol (2000) 40, 1057. 

Unless otherwise stated, general information applies to the entire class of phosphodiesterase inhibitors. Sildenafil is highlighted because it was the first to be marketed and is the most thoroughly studied. The newer agents tadalafil and vardenafil have different pharmacokinetic profiles (Table 83-3), drug-food interactions, and adverse effects. 

Drugs that may interact with nitrates include alcohol, alteplase, aspirin, beta-blockers, calcium channel blockers, dihydroergotamine, heparin, nondepolarizing muscle relaxants, phenothiazines, phosphodiesterase inhibitors (eg, sildenafil, tadalafil, vardenafil), and vasodilators. 

Drug/Food interactions When taken with a high-fat meal, the rate of sildenafil absorption is reduced, with a mean delay in T ax minutes and a mean reduction in C ax 29%. High-fat meals caused a reduction in C ax vardenafil by 18% to 50%. 

Isosorbide Dinitrate Hydralazine (BiDil) [Antianginal, Antihypertensive/Vasodilator, Nitrate] Uses HF in African Amer-icans improve survival functional status, prolong time between hospitalizations Action Relaxes vascular smooth muscle peripheral vasodilator Dose Initially 1 tab tid PO (if not tol ated reduce to 1/2 tab tid), titrate >3-5 d as tolerated Max 2 tabs tid Caution [C, /-] recent MI, syncope, hypovolemia, hypotension, hep impair Contra For children, concomitant use w/ PDE5 inhibitors (sildenafil) Disp Tabs SE HA, dizziness, orthostatic hypotension, sinusitis, GI distress, tach, paresthesia, amblyopia Interactions t Risk of severe hypotension W/ antihypertensives, ASA, CCBs, MAOIs, phenothiazides, sildenafil, tadalafil, vardenafil, EtOH X pressor response Wf i -1- effects W7 NSAIDs EMS Use ASA, antihypertensives and CCBs w/ caution, may t hypotension concurrent Viagra-type drug use can lead to profound hypotension concurrent EtOH use can t effects OD May cause N/V, profound hypotension, skin flushing, HA from ICP, bradycardia, confusion, and circulatory collapse activated charcoal may be effective, epi use is contraindicated... 

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