Viagra

Viagra Medication Overview

Sildenafil citrate, marketed as Viagra, is a prescription medication used to treat erectile dysfunction (ED) in adult men. It functions by increasing blood flow to the penis to help achieve and maintain an erection when sexually stimulated. Viagra is a phosphodiesterase-5 (PDE5) inhibitor and is available in tablet form.

Dosage Forms and Strengths

Viagra comes in three dosage strengths: 25 mg, 50 mg, and 100 mg. Each tablet is film-coated with a blue, rounded-diamond shape. The strength of the medication is inscribed on one side of the tablet, while “Pfizer” is inscribed on the other.

Indications for Use

Viagra is indicated for the treatment of erectile dysfunction (ED). Patients are advised to take Viagra only upon a doctor’s prescription and ensure it is suitable for their condition and does not interact with other medications they might be taking.

Administration Guidelines

Viagra should be taken orally, approximately 30 minutes to 1 hour before sexual activity. However, it can be taken anywhere from 30 minutes to 4 hours before engaging in sexual intercourse. The medication should not be taken more than once per day. For best results, Viagra should not be taken with a high-fat meal, as this can delay the effectiveness of the drug.

Starting Dosage Recommendation

The recommended starting dose for Viagra when used as needed for ED is 50 mg, but a doctor may adjust the dosage based on effectiveness and toleration. Modifications could involve a reduction to 25 mg or an increase to the maximum recommended dose of 100 mg.

Dosage Adjustments in Special Populations

For patients aged 65 years or older, or those with hepatic impairment or severe renal impairment, the recommended starting dose of Viagra is 25 mg. Caution should be exercised when prescribing Viagra in these populations.

Medication Mechanism of Action

As a PDE5 inhibitor, Viagra works by blocking the enzyme PDE5, which is responsible for degrading cGMP in the corpus cavernosum. When sexual stimulation occurs, the increased levels of cGMP lead to smooth muscle relaxation and inflow of blood to the penis, facilitating an erection.

Pharmacokinetics

Viagra is rapidly absorbed after oral administration, with peak plasma concentrations reached within 30 to 120 minutes. Its bioavailability is about 40%. The medication is metabolized primarily by the cytochrome P450 (CYP) isoforms 3A4 (major route) and 2C9 (minor route) and has a terminal half-life of approximately 4 hours.

Contraindications and Precautions

Viagra is contraindicated in patients with a known hypersensitivity to sildenafil or any other component of the tablet. It should not be used in conjunction with nitrate medications or guanylate cyclase stimulators, as the combination can lead to a dangerous drop in blood pressure.

Drug Interactions

Caution is advised when Viagra is co-administered with alpha-blockers or anti-hypertensives. Drugs that inhibit CYP3A4 such as ketoconazole, itraconazole, and erythromycin can increase sildenafil levels in the blood, hence dose adjustments may be necessary. Similarly, CYP3A4 inducers like rifampin may decrease plasma levels of sildenafil.

Adverse Reactions

Common side effects of Viagra include headache, flushing, dyspepsia, abnormal vision, nasal congestion, back pain, myalgia, nausea, dizziness, and rash. Non-arteritic anterior ischemic optic neuropathy (NAION), a cause of decreased vision including permanent loss of vision, has been reported rarely post-marketing in temporal association with the use of PDE5 inhibitors, including Viagra.

Special Handling and Storage Conditions

Viagra should be stored at controlled room temperature between 20° to 25°C (68° to 77°F), with excursions permitted to 15°–30°C (59°–86°F). Tablets should be kept in their original package to protect from moisture, and they should be kept out of the reach of children.

Overdosage Information

In cases of overdose, standard supportive measures should be adopted as required. Renal dialysis is not expected to accelerate clearance as sildenafil is highly bound to plasma proteins and it is not eliminated in the urine.

Reporting of Side Effects

If the patient experiences any side effects that are persistent or worsen, they should contact their healthcare provider. Side effects can also be reported to the FDA through the MedWatch program or by calling 1-800-FDA-1088.

Patient Counseling Information

Patients should be informed about the potential for interactions with other medications, the importance of taking the drug on an as-needed basis prior to sexual activity, and the possibility of side effects which may require medical attention. They should also be counseled on the potential risk of priapism, and to seek immediate medical assistance if an erection persists longer than 4 hours.