visual disturbance
Sildenafil (Viagra) Contraindications and Precautions
Sildenafil is contraindicated in patients with a known hypersensitivity to any component of the tablet. The safety and efficacy of combinations of sildenafil with other treatments for erectile dysfunction have not been studied. Therefore, the use of such combinations is not recommended.
Sildenafil is contraindicated in patients who are currently on nitrate/nitrite therapy (see Drug Interactions). Consistent with its known effects on the nitric oxide/cGMP pathway, sildenafil was shown to potentiate the hypotensive effects of organic nitrates and nitrites. Patients receiving nitrates in any form are not to receive sildenafil. This includes any patient who receives intermittent nitrate therapies. It is unknown if it is safe for patients to receive nitrates once sildenafil has been administered.
The following factors are associated with increased plasma concentrations of sildenafil: elderly (40% increase in sildenafil AUC), hepatic disease (e.g., cirrhosis, 80% increase), severe renal impairment (CrCl < 30 ml/min), concomitant use of potent cytochrome P450 3A4 inhibitors (erythromycin, itraconazole, ketoconazole, saquinavir). Because higher plasma concentrations may increase the incidence of adverse reactions, the sildenafil starting dose should be 25 mg in these patients. Additionally, ritonavir greatly increased the systemic concentrations of sildenafil in a study of healthy, non-HIV infected volunteers (11-fold increase in AUC). Based on these pharmacokinetic data, it is recommended not to exceed a maximum single dose of 25 mg sildenafil in a 48 hour period.
There is a degree of cardiac risk associated with sexual activity; therefore, prescribers should evaluate the cardiovascular status of their patients prior to initiating any treatment for erectile dysfunction. Over 75 deaths due to cardiovascular events have been reported in association with sildenafil use. In a study conducted at the Mayo Clinic, sildenafil was shown to have limited cardiovascular effects during exercise in men with known or probable coronary artery disease. The study reported that sildenafil had no effect on exercise capacity or the hemodynamic response to exercise. Systolic blood pressure was reduced an average of 7 mmHg compared to baseline. Another study showed that sildenafil inhibited ?-adrenergic-stimulated systolic function. Using dobutamine in healthy volunteers, investigators reported that sildenafil suppressed the cardiac response to dobutamine but had minimal effect under resting conditions. It was also reported that the effects of sildenafil were independent of cardiac afterload or preload changes. Health care professionals should consider whether the individual would be adversely affected by vasodilatory events. In particular, caution should be used if sildenafil is prescribed in the following patient groups: patients who have suffered a myocardial infarction, stroke, or life-threatening cardiac arrhythmias in the last 6 months; patients with resting hypotension (BP < 90/50) or resting hypertension (BP > 170/100); patients with cardiac disease, heart failure or coronary artery disease which causes unstable angina. The American College of Cardiology recommends that sildenafil be used with caution in the following: patients with active coronary ischemia who are not taking nitrates (e.g., positive exercise test for ischemia); patients with congestive heart failure and borderline low blood pressure and borderline low volume status; patients on a complicated, multidrug, antihypertensive program; and patients taking drugs that can prolong the half-life of sildenafil (see Drug Interactions). However, one study reported that sildenafil was effective and well tolerated in patients on multidrug antihypertensive regimens and was not associated with additional safety risks in these patients. Patients with left ventricular outflow obstruction (e.g., aortic stenosis, idiopathic hypertrophic subaortic stenosis) and those with severely impaired autonomic control of blood pressure can be particularly sensitive to the actions of sildenafil and other vasodilators. Doses of sildenafil above 25 mg should not be given within 4 hours of an alpha-blocker (e.g., doxazosin, see Drug Interactions).
Sildenafil and other agents for the treatment of erectile dysfunction should be used with caution in patients with penile structural abnormality (such as angulation, cavernosal fibrosis or Peyronie’s disease), or in patients who have conditions which may predispose them to priapism (such as such as sickle cell disease, leukemia, multiple myeloma, polycythemia, or a history of priapism). However, in one retrospective study, treatment with sildenafil did not cause any worsening deformity or progression of Peyronie’s disease.
Patients should be reminded that sildenafil offers no protection against sexually transmitted disease. Counseling of patients about protective measures, including the prevention of transmission of human immunodeficiency virus (HIV) infection, should be considered.
Sildenafil has no effect on bleeding time when taken alone or with aspirin. In vitro studies with human platelets indicate that sildenafil potentiates the antiaggregatory effect of sodium nitroprusside (a nitric oxide donor). There is no safety information on the administration of sildenafil to patients with a coagulopathy or active peptic ulcer disease. Therefore, sildenafil should be administered with caution to these patients.
Use sildenafil cautiously in patients with pre-existing visual disturbance. Post-marketing reports of sudden vision loss have occurred with phosphodiesterase inhibitors. Vision loss is attributed to a condition known as non-arteritic anterior ischemic optic neuropathy (NAION), where blood flow is blocked to the optic nerve. Also, there is no safety information on the administration of sildenafil to patients with known hereditary degenerative retinal disorders, including retinitis pigmentosa. A minority of patients with the inherited condition retinitis pigmentosa have genetic disorders of retinal phosphodiesterases. Therefore, it is recommended that sildenafil not be administered to these patients until further data are available.
Sildenafil is classified as FDA pregnancy risk category B. While animal studies have shown no evidence of teratogenicity of sildenafil during organogenesis, there is no information on the use of sildenafil in humans during pregnancy or during breast-feeding. Sildenafil is not indicated for use in pregnant or lactating women.
There is no known indication for the use of sildenafil in infants or children. Sildenafil should not be prescribed to these populations.
Sildenafil should be used cautiously in patients with gastroesophageal reflux disease (GERD) or hiatal hernia associated with reflux esophagitis. Sildenafil can decrease the tone of the lower esophageal sphincter and inhibit esophageal motility.
[ Last revised: 11/1/2005 7:09:00 PM ]
References
. Arruda-Olson AM, Mahoney DW, Nehra A, et al. Cardiovascular effects of sildenafil during exercise in men with known or probable coronary artery disease. JAMA 2002;287:719 - 25.
. Bortolotti M, Mari C, Giovannini M, et al. Effects of sildenafil on esophageal motility of normal subjects. Dig Dis Sci 2001;46:2301 - 6.
. Levine LA, Latchamsetty KC. Treatment of erectile dysfunction in patients with Peyronie’s disease using sildenafil citrate. Int J Impot Res 2002;14:478 - 82.
. Pickering TG, Shepherd AM, Puddey I, et al. Sildenafil citrate for erectile dysfunction in men receiving multiple antihypertensive agents: A randomized controlled trial. Am J Hypertens 2004;17:1135 - 42.
. Borlaug BA, Melenovsky V, Marhin T, et al. Sildenafil inhibits ?-adrenergic-stimulated cardiac contractility in humans. Circulation 2005;112:2642 - 49.
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