Viagra 20 mg/tab (UP)

1. Description — Clinical summary

Viagra (active ingredient: sildenafil citrate) is an orally administered phosphodiesterase type 5 (PDE5) inhibitor primarily indicated for the treatment of erectile dysfunction (ED) in adult males. It increases the ability to achieve and maintain an erection sufficient for sexual activity in the presence of sexual stimulation. Sildenafil is also available under other brand names and at different doses for pulmonary arterial hypertension (PAH), but dosing and indications differ.

Typical formulation: film‑coated tablets (commonly 25 mg, 50 mg, 100 mg). Onset of effect usually begins within 30–60 minutes; efficacy can persist up to about 4 hours in many patients. Oral bioavailability is ~40%; elimination half‑life ~3–5 hours.

Note: This guide is educational and not a substitute for individualized medical advice. Prescribe or use sildenafil only under the guidance of a qualified healthcare professional.

2. How does Viagra work? — Mechanism of action

• Sexual stimulation causes release of nitric oxide (NO) in the corpus cavernosum. NO activates guanylate cyclase, increasing cyclic guanosine monophosphate (cGMP).
• cGMP causes smooth muscle relaxation in the penile vasculature and corpus cavernosum, allowing increased blood flow and producing an erection.
• PDE5 is the enzyme that breaks down cGMP. Sildenafil selectively inhibits PDE5, reducing cGMP breakdown, thereby enhancing and prolonging smooth muscle relaxation and penile erection in response to sexual stimulation.
• Sildenafil has little intrinsic effect in the absence of sexual stimulation because it amplifies the natural NO–cGMP pathway rather than directly causing erection.

3. Dosage — medical and usage guidelines

General principles

• Sildenafil for ED is taken orally as needed. Sexual stimulation is required for effect.
• Dosage should be individualized based on efficacy and tolerability. Maximum recommended frequency: once every 24 hours (do not take more than once daily for ED).
• Time to onset: commonly 30–60 minutes; can be affected by food. A high‑fat meal can delay absorption and onset.

Typical starting and adjustment doses (adults with ED)

• Typical starting dose: 50 mg taken about 30–60 minutes before sexual activity.
• Dose may be adjusted:
  • Decrease to 25 mg if adverse effects occur or if the patient has factors that increase sildenafil exposure.
  • Increase to 100 mg if 50 mg is well tolerated but response is inadequate.
• Maximum single dose: 100 mg; do not exceed 100 mg per 24 hours.

Special populations and considerations

• Older adults (≥65 years): consider starting at 25 mg or 50 mg depending on comorbidities and concomitant medications; many clinicians use 25–50 mg as a cautious initial dose because of higher drug exposure and increased sensitivity to adverse effects.
• Hepatic impairment: in moderate to severe hepatic impairment (e.g., cirrhosis), start with lower dose (commonly 25 mg) and adjust carefully because sildenafil exposure is increased.
• Renal impairment:
  • Mild–moderate renal impairment: usual dosing may be acceptable, but monitor.
  • Severe renal impairment (including dialysis): consider starting at 25 mg; adjust based on response and tolerability.
• Concomitant potent CYP3A4 inhibitors (e.g., ritonavir, cobicistat, ketoconazole, itraconazole): sildenafil exposure can be substantially increased. Use reduced starting dose (25 mg) and exercise caution; dosing frequency may need restriction (follow specialist or product labeling).
• Concomitant moderate CYP3A4 inhibitors (e.g., erythromycin): consider dose reduction and closer monitoring.

Other indications (example)

• Pulmonary arterial hypertension (PAH): sildenafil dosing and schedules differ (e.g., Revatio is a branded sildenafil formulation for PAH; typical adult dosing is 20 mg three times daily). Do not substitute dosing across indications without clinician guidance.

Contraindications to dosing

• Do NOT administer sildenafil to patients using any form of nitrates (organic nitrates or nitric oxide donors) or who have recently used them, because the combination can produce severe, potentially life‑threatening hypotension.
• Concomitant use with riociguat (a soluble guanylate cyclase stimulator) is contraindicated.

Emergency situations

• Priapism (erection lasting >4 hours) requires urgent medical attention to prevent permanent injury; immediate consultation with emergency services/urology is necessary.

4. Side effects — common and rare adverse effects

Common (frequency varies by trial; typical):

• Headache
• Flushing (face)
• Dyspepsia (indigestion)
• Nasal congestion
• Dizziness
• Visual disturbances (blurred vision, altered color perception such as a blue tint — transient)
• Myalgia, back pain (more commonly after higher doses or formulations used for PAH)

Less common / potentially serious (rare but important)

• Sudden decrease or loss of vision in one or both eyes (non‑arteritic anterior ischemic optic neuropathy, NAION). This is rare but potentially permanent — seek immediate medical attention.
• Sudden decrease or loss of hearing, sometimes with tinnitus and dizziness. Rare but reported.
• Prolonged erection / priapism: an erection lasting >4 hours is a medical emergency that can cause permanent tissue damage and requires immediate treatment.
• Hypotension (especially if combined with nitrates or substantial alpha‑blocker therapy) — can be severe.
• Cardiac events: myocardial infarction, ventricular arrhythmias, stroke — reported rarely; many events occurred in patients with preexisting cardiovascular disease and may be related to sexual activity as well as drug effects.
• Allergic reactions: rare hypersensitivity/anaphylaxis.

Drug–drug interaction adverse outcomes

• Combining sildenafil with nitrates → severe, refractory hypotension.
• Concomitant alpha‑blockers (e.g., tamsulosin, doxazosin): can cause symptomatic hypotension; if combination is necessary, initiate sildenafil at a low dose and titrate carefully with monitoring.
• Potent CYP3A4 inhibitors increase sildenafil plasma concentrations and risk of adverse effects.
• Use with other PDE5 inhibitors or with soluble guanylate cyclase stimulators (riociguat) is not recommended/contraindicated.

Monitoring and precautions

• Evaluate cardiovascular status before prescribing sildenafil for patients with significant cardiovascular disease; sexual activity itself poses a cardiac risk in persons with unstable heart disease.
• Use caution in patients with bleeding disorders, active peptic ulcer disease, severe hepatic or renal impairment, or anatomical deformation of the penis (e.g., Peyronie’s disease).
• Inform patients to stop the drug and seek urgent care for sudden visual or hearing loss or for an erection lasting longer than 4 hours.

5. Storage — how to store it

• Store at controlled room temperature, typically 20–25°C (68–77°F). Short excursions usually permitted (e.g., 15–30°C) — follow the product labeling for exact storage range.
• Keep tablets in the original packaging (blister pack or bottle) until use to protect from moisture and light.
• Protect from excessive heat and humidity (do not store in bathrooms).
• Keep out of reach and sight of children and pets.
• Do not use beyond the printed expiration date.
• Disposal: follow local regulations for medication disposal. Many communities have drug take‑back programs. If no take‑back option is available, mix unused tablets with an undesirable substance (e.g., coffee grounds or kitty litter), place in a sealed container, and discard in household trash, after removing personal information from prescription labels.

Final notes

• Sildenafil is a prescription medication. A healthcare professional should assess suitability (cardiovascular risk, concomitant medications, comorbid conditions) before initiating therapy.
• If you experience severe or unexpected adverse effects, or if you are taking nitrates, contact your healthcare provider or emergency services immediately.

1. Description — Clinical summary

Viagra is the brand name for the oral medication whose active ingredient is sildenafil citrate (commonly referred to as sildenafil). It is primarily indicated for the treatment of erectile dysfunction (ED) in adult men. Sildenafil is also available and used under other brand names/dosing regimens for pulmonary arterial hypertension (PAH) but that indication and dosing differ from the ED formulation.

Key clinical points

• Therapeutic goal: facilitate erection adequate for sexual activity in men with ED when sexual stimulation is present. It does not increase libido and is not an aphrodisiac.
• Onset/duration: onset commonly 30–60 minutes (sometimes as early as 15–20 minutes); typical effective window up to ~4 hours, though variability exists between individuals.
• Formulations: film‑coated tablets (commonly 25 mg, 50 mg, 100 mg for ED). Other formulations/dosing regimens for PAH exist (e.g., 20 mg three times daily for sildenafil marketed as Revatio).

2. How does Viagra work? — Mechanism of action

Sildenafil is a selective inhibitor of phosphodiesterase type 5 (PDE5). The mechanism in ED:

• Sexual stimulation releases nitric oxide (NO) in the corpus cavernosum.
• NO activates guanylate cyclase, increasing cyclic guanosine monophosphate (cGMP).
• cGMP causes smooth muscle relaxation in penile vasculature, allowing increased blood inflow and erection.
• PDE5 breaks down cGMP; sildenafil inhibits PDE5, increasing cGMP levels and enhancing the erectile response to sexual stimulation.

Note: sildenafil does not cause erection in the absence of sexual stimulation and acts systemically — PDE5 is present in other tissues (lungs, vascular beds, retina), explaining some extra‑genital effects and adverse events.

3. Dosage — Medical and varying usage guidelines

General principles: choose the lowest effective dose, adjust based on efficacy and tolerability, and observe contraindications and interacting medications.

A. Erectile dysfunction (typical adult dosing)

• Usual starting dose: 50 mg taken as needed about 1 hour before anticipated sexual activity.
• Dose range: 25 mg to 100 mg.
  • If 50 mg provides inadequate response and side effects are tolerable, increase to 100 mg.
  • If side effects are problematic or patient is elderly/has certain comorbidities, reduce to 25 mg.
• Maximum: do not exceed 100 mg per dose and do not take more than once every 24 hours.

Administration notes

• Take on an empty stomach for more rapid absorption; a high‑fat meal may delay onset and reduce peak concentration.
• Sexual stimulation is required for efficacy.

B. Special populations and adjustments

• Elderly (≥65 years): often start with 25 mg due to increased susceptibility to side effects and decreased clearance.
• Hepatic impairment: start at a lower dose (typically 25 mg) because hepatic dysfunction increases sildenafil exposure.
• Renal impairment: moderate renal impairment — dosing adjustments may not be necessary for mild–moderate disease; severe renal impairment may warrant dose reduction.
• Concomitant potent CYP3A4 inhibitors (e.g., ritonavir, some azole antifungals, certain macrolides): these increase sildenafil levels — reduce starting dose (commonly to 25 mg) and increase monitoring. Avoid taking higher doses and avoid dosing more frequently than recommended (with some potent inhibitors clinicians advise spacing doses further; consult product labeling or an experienced clinician).
• Concomitant alpha‑blockers: start at a low sildenafil dose (25 mg) and ensure patient is hemodynamically stable on their alpha‑blocker; monitor for symptomatic hypotension.

C. Pulmonary arterial hypertension (PAH)

• Sildenafil is also used at different dosing when indicated for PAH (usually 20 mg three times daily in the sildenafil PAH formulation). This is a different indication and regimen — do not interchange without medical guidance.

D. Pediatric use

• Sildenafil for ED is not approved in pediatric patients. Separate pediatric dosing and indications may exist for PAH and require specialist oversight.

E. Missed dose / Overdose

• For on‑demand ED use, missed doses are simply taken when needed (one dose per 24 hours max). Overdose (taking more than recommended) increases risk of adverse events — seek medical care if overdose occurs.

Always individualize dose adjustments based on response, tolerability, and interacting medications; follow local prescribing information and specialist advice for complex cases.

4. Side effects — Common and rare adverse effects

Common (generally mild to moderate, often transient)

• Headache
• Flushing
• Dyspepsia (indigestion)
• Nasal congestion
• Myalgia/back pain (usually later onset, transient)
• Dizziness
• Visual disturbances: alterations in color perception (blue/green tinge), increased light sensitivity

Less common but serious (require immediate medical attention)

• Priapism: prolonged erection >4 hours — medical emergency to prevent permanent penile damage.
• Sudden hearing loss: sometimes accompanied by tinnitus and dizziness; prompt medical evaluation recommended.
• Nonarteritic anterior ischemic optic neuropathy (NAION): sudden loss of vision in one or both eyes reported rarely; risk may be higher in patients with predisposing vascular risk factors.
• Significant hypotension: particularly when combined with nitrates or certain other vasodilators; can cause syncope, myocardial ischemia.
• Cardiovascular events: myocardial infarction, arrhythmias, stroke have been reported post‑marketing in temporal association with sexual activity and/or sildenafil use; causal relationship often unclear — caution in patients with severe cardiovascular disease.

Contraindicated combinations that increase adverse effect risk

• Nitrates (e.g., nitroglycerin, isosorbide dinitrate/mononitrate): co‑administration can produce life‑threatening hypotension — absolute contraindication.
• Riociguat: combined use is contraindicated due to symptomatic hypotension.
• Potent CYP3A4 inhibitors: increase sildenafil concentrations and risk of adverse effects; adjust dose and monitoring.

Other precautions

• Evaluate cardiovascular status before initiating sildenafil in patients with significant cardiac disease (unstable angina, recent myocardial infarction or stroke, uncontrolled arrhythmias, severe heart failure).
• Use with caution in patients with conditions that predispose to priapism (sickle cell disease, multiple myeloma, leukemia).

If any severe adverse effect occurs (loss of vision/hearing, chest pain, prolonged erection), seek immediate medical help.

5. Storage — How to store it

• Store tablets at room temperature, typically between 15–30°C (59–86°F) unless manufacturer directions indicate otherwise. Avoid extreme heat.
• Keep in original packaging (blister pack or bottle) to protect from moisture and light.
• Do not store in the bathroom or other damp areas.
• Keep out of reach of children and pets.
• Dispose of expired or unused tablets according to local regulations; do not flush medications down the toilet unless instructed.

Patient counseling points (brief)

• Take sildenafil about 1 hour before sexual activity; allow for variability (15 min–4 hrs).
• Sexual stimulation is required; sildenafil will not cause an erection without it.
• Avoid nitrates and inform all healthcare providers you are taking sildenafil.
• If erection lasts >4 hours, sudden vision or hearing loss, or chest pain occurs — seek emergency care.
• Discuss all medications and supplements you take with your clinician to check for interactions (particularly nitrates, riociguat, alpha‑blockers, and strong CYP3A4 inhibitors).

This guide summarizes common clinical information about sildenafil (Viagra) but does not replace professional medical advice. For individualized dosing and decisions, consult a prescriber or pharmacist and refer to the product’s official prescribing information.