Viamax25 mg

Viamax 25 mg is a phosphodiesterase type 5 (PDE5) inhibitor primarily prescribed for two distinct clinical conditions:

• Erectile Dysfunction (ED): Sildenafil is indicated for the treatment of erectile dysfunction in men, a condition defined by the persistent inability to achieve or maintain a penile erection sufficient for satisfactory sexual performance. It is important to note that Sildenafil is not an aphrodisiac — sexual stimulation is required for the medication to produce its therapeutic effect. Without stimulation, Sildenafil does not induce an erection.
• Pulmonary Arterial Hypertension (PAH): Sildenafil is also indicated for the treatment of pulmonary arterial hypertension to improve exercise capacity and delay clinical worsening. In this indication, it works by relaxing the blood vessels in the lungs, thereby reducing pulmonary vascular resistance and easing the workload on the right side of the heart.

Sildenafil should only be used following a proper medical evaluation, as erectile dysfunction can sometimes be an early warning sign of an underlying cardiovascular condition.

Viamax 25 mg is a selective and reversible inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5), the enzyme responsible for the breakdown of cGMP in the smooth muscle of the corpus cavernosum. During sexual stimulation, nitric oxide is released locally, which triggers a chain of biochemical events that ultimately raises cGMP levels. By blocking PDE5, Sildenafil prevents the breakdown of cGMP, allowing it to accumulate and produce relaxation of the smooth muscle in the penile blood vessels. This relaxation increases blood flow into the penile tissue, resulting in an erection.

Sildenafil has no direct relaxant effect in the absence of sexual stimulation, which distinguishes it from older, non-selective erectile dysfunction treatments and helps preserve the natural, stimulation-driven nature of the response.

Drugs for Erectile Dysfunction (Phosphodiesterase Type 5 Inhibitors)

Mechanism of Action

Penile erection is a hemodynamic event that begins with the release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. Nitric oxide activates the enzyme guanylate cyclase, which increases levels of cyclic guanosine monophosphate (cGMP). Elevated cGMP produces smooth muscle relaxation, allowing increased blood inflow into the corpus cavernosum.

Sildenafil itself has no direct relaxant effect on isolated human corpus cavernosum tissue. Instead, it enhances the natural erectile response by selectively inhibiting PDE5, the enzyme responsible for degrading cGMP in this tissue. When sexual stimulation triggers local nitric oxide release, PDE5 inhibition by Sildenafil results in higher cGMP concentrations, producing smooth muscle relaxation and improved blood flow. At recommended doses, Sildenafil produces no effect without sexual stimulation, since PDE5 inhibition alone does not initiate the NO/cGMP cascade.

Pharmacokinetics and Metabolism

• Absorption: Sildenafil is rapidly absorbed after oral administration, reaching maximum plasma concentrations within 30–120 minutes (median 60 minutes) in the fasted state. The mean absolute bioavailability is approximately 41% (range 25–63%). Taking Sildenafil with a high-fat meal slows the rate of absorption.
• Distribution: Sildenafil is extensively bound to plasma proteins (approximately 96%).
• Metabolism: Sildenafil is eliminated predominantly via hepatic metabolism, chiefly by the cytochrome P450 3A4 (CYP3A4) enzyme pathway, with a minor contribution from CYP2C9. It is converted into an active N-desmethyl metabolite with a pharmacological profile similar to the parent compound. Both Sildenafil and its active metabolite have a terminal half-life of approximately 4 hours.
• Excretion: Following oral or intravenous administration, Sildenafil is excreted primarily as metabolites in the feces (approximately 80% of the administered oral dose) and, to a lesser extent, in the urine (approximately 13%).
• Elderly patients: Healthy elderly volunteers (65 years and older) show reduced clearance of Sildenafil, resulting in approximately 84–107% higher plasma drug exposure (AUC) compared to younger volunteers.

Sildenafil is metabolized principally by the cytochrome P450 isoenzyme 3A4 (major pathway) and 2C9 (minor pathway). Drugs that inhibit these enzymes can reduce Sildenafil clearance and raise its plasma concentration, while enzyme inducers can lower its plasma levels.

Other Notable Interactions

• Nitrates: Sildenafil significantly potentiates the hypotensive effect of nitrates. Concomitant use is strictly contraindicated.
• Alpha-blockers: Combined use can cause symptomatic hypotension; patients should be stable on alpha-blocker therapy before starting Sildenafil.
• Antacids: A single dose of magnesium hydroxide/aluminum hydroxide antacid does not affect Sildenafil bioavailability.
• No clinically significant effect was observed with CYP2C9 inhibitors (tolbutamide, warfarin), CYP2D6 inhibitors (SSRIs, tricyclic antidepressants), thiazide and related diuretics, ACE inhibitors, and calcium channel blockers.
• Loop and potassium-sparing diuretics increased the AUC of the active metabolite by 62%, and nonspecific beta-blockers by 102%; neither is considered clinically significant.

Sildenafil is generally well tolerated, but like all medications, it can cause side effects. These are organized below by body system.

Common Side Effects

• Headache, flushing, and dizziness
• Dyspepsia (indigestion) and dry mouth
• Nasal congestion and epistaxis (nosebleeds)
• Abnormal vision, including bluish tinge and light sensitivity

Cardiovascular

Angina pectoris, AV block, migraine, syncope, tachycardia, palpitation, hypotension, postural hypotension, myocardial ischemia, cerebral thrombosis, cardiac arrest, heart failure, abnormal ECG, and cardiomyopathy have been reported.

Digestive

Vomiting, glossitis, colitis, dysphagia, gastritis, gastroenteritis, esophagitis, stomatitis, dry mouth, abnormal liver function tests, rectal hemorrhage, and gingivitis.

Nervous System

Ataxia, hypertonia, neuralgia, neuropathy, paresthesia, tremor, vertigo, depression, insomnia, somnolence, abnormal dreams, decreased reflexes, and hyperesthesia.

Musculoskeletal

Arthritis, arthrosis, myalgia, tendon rupture, tenosynovitis, bone pain, myasthenia, and synovitis.

Skin

Urticaria, herpes simplex, pruritus, sweating, skin ulcer, contact dermatitis, and exfoliative dermatitis.

Special Senses

Sudden decrease or loss of hearing, mydriasis, conjunctivitis, photophobia, tinnitus, eye pain, ear pain, eye hemorrhage, cataract, and dry eyes. Post-marketing reports also include diplopia, temporary vision loss, ocular redness, ocular burning, increased intraocular pressure, retinal vascular disease or bleeding, and vitreous detachment.

Urogenital

Cystitis, nocturia, urinary frequency, breast enlargement, urinary incontinence, abnormal ejaculation, genital edema, and anorgasmia. Post-marketing reports include prolonged erection, priapism, and hematuria.

Serious Cardiovascular and Cerebrovascular Events

Post-marketing reports include myocardial infarction, sudden cardiac death, ventricular arrhythmia, cerebrovascular hemorrhage, transient ischemic attack, hypertension, subarachnoid and intracerebral hemorrhages, and pulmonary hemorrhage in temporal association with Sildenafil use. Most affected patients had pre-existing cardiovascular risk factors, and many events occurred during or shortly after sexual activity. A direct causal link to Sildenafil has not been established.

When to Seek Immediate Medical Attention

• An erection lasting longer than 4 hours (priapism)
• Sudden vision loss or decrease in one or both eyes
• Sudden hearing loss or ringing in the ears
• Chest pain during or after sexual activity

Viamax 25 mg is classified as Pregnancy Category B. There are no adequate and well-controlled studies of Sildenafil in pregnant women, and it is not indicated for use by women. Animal reproduction studies have shown no evidence of teratogenicity or embryotoxicity.

Since Sildenafil is not approved for use in women, no data are available regarding its excretion into breast milk or its effects during lactation.

A thorough medical evaluation to determine the underlying cause of erectile dysfunction should be performed before treatment begins.

Use with Alpha-Blockers

Both PDE5 inhibitors and alpha-adrenergic blockers are vasodilators. Combined use may cause an additive blood-pressure-lowering effect, leading to symptomatic hypotension (dizziness, lightheadedness, fainting). Key considerations include:

• Patients should be hemodynamically stable on alpha-blocker therapy before starting a PDE5 inhibitor.
• In patients stable on alpha-blockers, PDE5 inhibitors should be started at the lowest dose.
• In patients already on an optimized PDE5 inhibitor dose, alpha-blocker therapy should begin at the lowest dose.

Cardiovascular Risk

Sexual activity carries a degree of cardiac risk; therefore, Sildenafil should not generally be used in men for whom sexual activity is inadvisable due to underlying cardiovascular status. Sildenafil has mild systemic vasodilatory effects (mean maximum decrease of 8.4/5.5 mmHg in supine blood pressure in healthy volunteers). Physicians should carefully weigh this risk, particularly in combination with sexual activity.

Use with Caution In

• Patients with anatomical deformation of the penis (angulation, cavernosal fibrosis, or Peyronie's disease)
• Patients predisposed to priapism (e.g., sickle cell anemia, multiple myeloma, leukemia)
• Patients with bleeding disorders or active peptic ulceration
• Patients with left ventricular outflow obstruction (e.g., aortic stenosis)
• Patients with severely impaired autonomic control of blood pressure

No Controlled Data Available — Use With Caution

• Myocardial infarction, stroke, or life-threatening arrhythmia within the last 6 months
• Resting hypotension (BP <90/50) or hypertension (BP >170/110)
• Cardiac failure or unstable angina from coronary artery disease
• Retinitis pigmentosa
• Sickle cell anemia or related conditions

Priapism

Prolonged erection (greater than 4 hours) and priapism (painful erection greater than 6 hours) have been reported infrequently. Immediate medical attention is required for an erection lasting longer than 4 hours, as delayed treatment can result in permanent penile tissue damage and loss of potency.

Combination Therapy

The safety and efficacy of combining Sildenafil with other erectile dysfunction treatments has not been established, and such combinations are not recommended.

In studies involving healthy volunteers, single doses of up to 800 mg (16 times the maximum recommended dose) produced adverse events similar to those seen at lower doses, but with increased incidence and severity.

In cases of suspected overdose, standard supportive measures should be initiated as needed. Because Sildenafil is highly bound to plasma proteins and is not significantly eliminated in the urine, renal dialysis is not expected to accelerate its clearance.

• Store in a cool, dry place, protected from light and heat.
• Store at room temperature, ideally below 30°C.
• Keep out of the reach and sight of children.
• Do not use after the expiry date printed on the pack.

Elderly (65 years and older)

Clearance of Sildenafil is reduced in healthy elderly volunteers, resulting in 84–107% higher plasma exposure compared to younger adults. A starting dose of 25 mg should be considered.

Hepatic Impairment

Patients with hepatic impairment show reduced Sildenafil clearance and higher plasma levels. A starting dose of 25 mg is recommended.

Renal Impairment

In patients with severe renal impairment, plasma levels of Sildenafil are increased. A starting dose of 25 mg should be considered.

Pediatric Use

Sildenafil is not indicated for use in individuals under 18 years of age for erectile dysfunction. Its use in pediatric pulmonary arterial hypertension should only be under direct specialist supervision.

Women

Sildenafil is not indicated for use in women.