Sildenafil citrate full drug file

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Here is a comprehensive drug file for Sildenafil Citrate, synthesized from multiple authoritative sources.

💊 Sildenafil Citrate — Complete Drug File

1. DRUG IDENTITY

Property	Details
Generic Name	Sildenafil citrate
Brand Names	Viagra (ED), Revatio (PAH), and generics
Drug Class	Phosphodiesterase type-5 (PDE5) inhibitor
Chemical Nature	Pyrimidinone derivative; structurally mimics the purine ring of cGMP
Route	Oral (tablet, oral suspension), Intravenous

2. AVAILABLE FORMULATIONS

Formulation	Strengths
Tablets (Revatio / generics)	20 mg
Tablets (Viagra / generics)	25 mg, 50 mg, 100 mg
Oral suspension (Revatio)	10 mg/mL (112 mL); may contain sodium benzoate
Oral suspension (generics)	2.5 mg/mL
Injection (Revatio / generics)	0.8 mg/mL (12.5 mL)

3. MECHANISM OF ACTION

Sexual stimulation triggers the release of nitric oxide (NO) from penile nerve endings and vascular endothelial cells. NO diffuses into vascular and cavernous smooth muscle cells of the corpus cavernosum, stimulating guanylyl cyclase to produce cyclic GMP (cGMP). cGMP lowers cytoplasmic calcium → smooth muscle relaxation → penile erection.

PDE5 normally hydrolyzes cGMP, terminating this signal. Sildenafil is a competitive and selective inhibitor of PDE5, with >1000-fold selectivity for PDE5 over other phosphodiesterases. By blocking cGMP hydrolysis, sildenafil augments and prolongs the cGMP-PKG pathway, enhancing smooth muscle relaxation.

Critically: sildenafil does not create an erection on its own. Sexual arousal and NO release must precede its action.

In the pulmonary vasculature, PDE5 is abundant in pulmonary arterial smooth muscle cells (PASMCs). Sildenafil's inhibition of cGMP hydrolysis here produces selective pulmonary vasodilation, reducing pulmonary vascular resistance. It also has antifibrotic activity relevant to lung disease.

— Goodman & Gilman's Pharmacological Basis of Therapeutics, p. 719 | Smith and Tanagho's General Urology, 19th Ed., p. 631

4. PHARMACOKINETICS (ADME)

Parameter	Details
Absorption	Rapidly absorbed; peak plasma concentration ~1 hour after oral dosing
Effect of food	High-fat meals delay absorption (clinically relevant); this does not apply to tadalafil
Protein binding	96% (parent drug and active metabolite)
Metabolism	Hepatic: CYP3A4 (major route), CYP2C9/2C8 (minor route)
Active metabolite	N-desmethyl sildenafil — retains activity
Half-life	~4 hours (parent + metabolite); in PAH patients, t½ extends to ~4–7 h (up to 12 h)
Elimination	Feces 73–88% (predominantly); urine (minor); unmetabolized drug not detected in urine or feces
Special populations	Clearance reduced in elderly (>65 yr) — increased AUC; dose reduction required in severe hepatic/renal impairment

— Goodman & Gilman's, p. 719 | Harriet Lane Handbook, 23rd Ed., p. 1345

5. THERAPEUTIC INDICATIONS

A. Erectile Dysfunction (ED)

First-line therapy for ED across all etiologies: organic, psychogenic, and mixed
Effective regardless of baseline severity, age, or race
Efficacy rates: 56–84% of men on 25–100 mg vs. 25% placebo
Specific efficacy: 70% in hypertensives, 57% in diabetics, 43% post-radical prostatectomy, 80% in spinal cord injury
Also effective in men with coronary artery disease, depression, post-TURP, spina bifida, and those on antidepressants/antipsychotics/antihypertensives
Off-label (women): Some evidence for SSRI-induced anorgasmia and sexual inhibition

B. Pulmonary Arterial Hypertension (PAH) — FDA approved

Improves exercise capacity, functional class (WHO), and hemodynamics
Sildenafil 20 mg TID (adult) is the approved PAH dose
Combined with long-term epoprostenol therapy → delays clinical worsening of PAH
Controlled trial data supports its use in idiopathic PAH

C. Other / Investigational Uses

COPD with mild pulmonary hypertension — studied for acute hemodynamic effects
Pulmonary fibrosis / interstitial lung disease — antifibrotic properties under investigation
Facilitating weaning from inhaled nitric oxide (neonates and infants — limited data)
Portal hypertension — anecdotal/case reports

— Smith and Tanagho's Urology, p. 631 | Murray & Nadel's Respiratory Medicine, block 20 | Textbook of Family Medicine, 9th Ed.

6. DOSAGE AND ADMINISTRATION

Erectile Dysfunction (Adult)

Dose	Notes
Starting dose: 50 mg PO	Taken ~1 hour before intercourse (effect within 30 min)
Range: 25–100 mg	Adjust based on efficacy and tolerability
Frequency: Max once daily	Duration of action: usually 4 h; up to 8–12 h in young healthy men
25 mg starting dose in elderly (>65 yr), cirrhosis, severe renal impairment, or concurrent CYP3A4 inhibitors

Pulmonary Arterial Hypertension (Adult)

Oral: 20 mg TID (at least 4–6 hours apart)
IV: 10 mg TID
Can be titrated to 40–80 mg TID in combination with epoprostenol

Pediatric (PAH) — Limited data; use with caution

Age/Weight	Dose
Neonate (limited data)	0.5–3 mg/kg/dose Q6–12 hr PO; IV: 0.4 mg/kg over 3 hr, then 1.6 mg/kg/24 hr infusion
Infant/child	Start 0.25 mg/kg/dose Q6 hr or 0.5 mg/kg/dose Q8 hr; titrate to 1–2 mg/kg/dose Q6–8 hr
Child 1–17 yr, 8–20 kg	10 mg TID
Child 1–17 yr, 20–45 kg	20 mg TID
Child 1–17 yr, >45 kg	40 mg TID

⚠️ Pediatric mortality warning: Long-term use (≥2 yr) in children 1–17 years has been associated with increased mortality risk; hazard ratio 3.95 for high vs. low dose. Use is not recommended chronically in children.

— Harriet Lane Handbook, 23rd Ed., pp. 1345–1346 | Goodman & Gilman's, p. 720

7. ADVERSE EFFECTS

Common (dose-dependent)

Adverse Effect	Frequency
Headache	~16%
Flushing	~10%
Rhinitis / nasal congestion	5–10%
Dyspepsia / GI upset	Common
Diarrhea	Common
Dizziness	Less common

Visual Effects

Transient blue-green tinting of vision (cyanopsia) — due to inhibition of retinal PDE6 (involved in phototransduction); mild and transient
Increased light sensitivity, blurred vision
Non-arteritic anterior ischemic optic neuropathy (NAION) — rare but serious; sudden vision loss; shared risk factors with ED (age, DM, HTN, dyslipidemia); causal link not established. Advise patients to stop sildenafil and seek urgent care if sudden vision loss occurs.
Risk of severe retinopathy of prematurity in neonates (due to color discrimination impairment)

Serious / Rare

Priapism (prolonged painful erection — urologic emergency)
Sudden hearing loss / sensorimpairment — temporal association reported; FDA mandated label update 2007
Severe hypotension — when combined with nitrates (can be fatal)
Myocardial infarction — not directly caused by sildenafil per FDA analysis, but sexual activity increases cardiac O₂ demand

— Goodman & Gilman's, p. 720 | Smith and Tanagho's Urology, p. 632 | Kaplan & Sadock's Synopsis of Psychiatry

8. CONTRAINDICATIONS

Contraindication	Rationale
Concurrent organic nitrates (any form) — nitroglycerin, isosorbide, amyl nitrate ("poppers")	Combined action → precipitous, potentially fatal hypotension; no pharmacologic antidote
Concurrent riociguat (guanylate cyclase stimulator)	Severe hypotension
Hypersensitivity to sildenafil	—
Unstable angina, recent MI, uncontrolled arrhythmia	Unsafe cardiovascular risk with sexual activity
Resting BP <90/50 or >170/100–110 mmHg	Hemodynamic instability
Children (chronic PAH dosing)	Increased mortality risk
PH secondary to sickle cell disease	Risk of serious vaso-occlusive crises

Timing rule: Nitroglycerin must not be given within 24 hours of sildenafil use.

9. DRUG INTERACTIONS

Pharmacokinetic (CYP3A4/2C9-based)

Interaction Type	Drug	Effect
CYP3A4 inhibitors ↑ sildenafil levels	Ketoconazole, itraconazole, erythromycin (+182%), clarithromycin, protease inhibitors (HIV), cimetidine (+56%), verapamil, ciprofloxacin, grapefruit juice, nicardipine, propofol	Increased plasma sildenafil → increased adverse effects
CYP3A4 inducers ↓ sildenafil levels	Rifampicin/rifampin, bosentan, carbamazepine, phenobarbital, phenytoin, efavirenz, St. John's wort	Decreased efficacy

Pharmacodynamic

Drug	Effect
Organic nitrates (nitroglycerin, isosorbide)	Severe hypotension — CONTRAINDICATED
α-blockers (e.g., tamsulosin, doxazosin)	Additive vasodilation → symptomatic hypotension; use with caution
Antihypertensives / other vasodilators	Additive BP lowering
Epoprostenol (prostacyclin)	Sildenafil bioavailability reduced ~28% — not considered clinically significant

No significant laboratory interferences reported.

— Kaplan & Sadock's Synopsis of Psychiatry, p. 2131 | Harriet Lane Handbook, p. 1346 | Goodman & Gilman's, p. 720

10. SPECIAL POPULATIONS

Population	Recommendation
Elderly (>65 yr)	Reduce starting dose to 25 mg (ED); increased AUC due to reduced clearance
Hepatic impairment (severe)	Reduce dose; clearance significantly reduced
Renal impairment (severe, CrCl <30 mL/min)	Reduce starting dose to 25 mg; dose adjustment generally not required for mild-moderate impairment
Pregnancy	Not indicated in women for ED; use for PAH in pregnancy requires risk-benefit assessment
Breastfeeding	Limited data; use with caution
Pediatric	Restricted use; significant mortality risk with chronic high-dose therapy

11. CARDIOVASCULAR SAFETY CONSIDERATIONS

FDA concluded that sildenafil does not independently increase MI or death risk when used per approved labeling
Sexual intercourse itself increases cardiac O₂ demand — cardiovascular evaluation (including exercise tolerance assessment and nitrate use review) is recommended before prescribing in men with:
- Prior MI, stroke, or renal failure
- Hypertension or diabetes
- Age >70 years
No pharmacologic antidote exists for the PDE5 inhibitor–nitrate interaction

12. COMPARISON WITH OTHER PDE5 INHIBITORS

Parameter	Sildenafil	Vardenafil	Tadalafil	Avanafil
Starting dose (ED)	50 mg	10 mg	10 mg	50 mg
Max dose	100 mg	20 mg	20 mg	200 mg
Onset	~14–30 min	~10 min	~16 min	~15 min
Half-life	~4 h	~4 h	~17.5 h (18 h)	~5 h
Duration	4–8 h	4–6 h	Up to 36 h	4–6 h
Food interaction	Yes (fatty meal delays)	Yes	No	Yes
Unique side effects	Blue-green vision (PDE6)	QTc prolongation risk	Back pain/myalgia	—
Nitrate washout	24 h	24 h	48 h	12 h
PAH-approved (FDA)	Yes	No	Yes	No

13. STORAGE AND STABILITY

Store at room temperature, protected from moisture and light
Oral suspension (Revatio): discard unused portion per label instructions; contains sodium benzoate

Sources:

Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th Ed. — PDE5 Inhibitors section
The Harriet Lane Handbook, 23rd Ed. (Johns Hopkins) — Formulary, pp. 1345–1346
Smith and Tanagho's General Urology, 19th Ed. — pp. 631–632
Kaplan & Sadock's Synopsis of Psychiatry — pp. 2129–2133
Murray & Nadel's Textbook of Respiratory Medicine
Goldman-Cecil Medicine, International Ed.

Prevalance of ED in Africa

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erectile dysfunction prevalence Nigeria OR Ghana OR Kenya OR Uganda OR Tanzania

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Prevalence of Erectile Dysfunction (ED) in Africa

Overview

ED in Africa is highly prevalent but significantly underreported and understudied, driven by cultural stigma, limited healthcare-seeking behavior, and a low research output relative to the burden of disease. Across studies on the continent, prevalence rates range broadly from ~30% to over 70% depending on the population studied, the measurement tool used (predominantly IIEF-5), and the presence of comorbidities.

1. General Population Estimates

Population-level epidemiological data from Africa remain sparse. Based on available cross-sectional and clinic-based studies:

Country / Region	Setting	Prevalence	Notes
Nigeria (North-West, Kano)	Primary care clinic	52.3%	36% mild, 14.3% mild-moderate, 1.5% moderate, 0.5% severe. IIEF-5 used. Mean age 45 yr. [PMID: 38223611]
Nigeria (Bida, North-Central)	General outpatient clinic	56.4%	29.4% mild, 24.2% mild-moderate, 2.8% moderate. 66.4% had used performance-enhancing drugs. Only 5.6% ever reported ED to a doctor. [PMID: 38787782]
Egypt (Upper Egypt)	Case-control	High burden	658 men with ED studied; hypertension, DM, smoking identified as dominant risk factors [PMID: 20795441]
Ethiopia (diabetic patients)	Systematic review & meta-analysis	54.3% (95% CI: 28.2–80.5)	Among diabetic men; 1 in 2 diabetic Ethiopian men had ED [PMID: 33583238]
South Africa	Systematic review	High prevalence noted	Ejaculatory and erectile dysfunctions among the most prevalent sexual disorders; very limited SA-specific research published [PMID: 26301289]

The wide CIs in meta-analyses reflect significant heterogeneity in study designs, populations, and ED assessment tools across African settings.

2. ED in Diabetic Men — Particularly High Burden

Diabetes is a major driver of ED across Africa:

Ethiopia (meta-analysis, 2021): Pooled prevalence of ED in diabetic men = 54.3%. Older age (OR 4.42) and longer DM duration (OR 3.2) were the strongest independent predictors. [PMID: 33583238]
Nigeria (2025 study): Among Nigerian type-2 diabetic men, independent predictors of ED included:
- Age >60 years (OR 4.9)
- Serum testosterone <270 ng/mL (OR 3.8)
- LDL >160 mg/dL (OR 6.3) — strongest predictor
- Hypertension (OR 2.93)
- FBS >125 mg/dL (OR 2.6)
- Triglycerides >150 mg/dL (OR 2.9) [PMID: 40618378]
Global meta-analysis (2017, 145 studies): ED prevalence in all diabetic men worldwide was ~52%; Africa-specific subgroup data not separately reported but consistent with global trend [PMID: 28722225]

3. Risk Factors Identified Across African Studies

Risk Factor	Evidence
Age	Consistent and strongest predictor; prevalence rises sharply after 50 years. In Nigerian studies, ED was 100% among men aged 70–79 yr vs. 30.9% in men aged 20–29 yr
Diabetes mellitus	OR ~5.4 (Egypt); pooled prevalence ~54% in Ethiopian diabetics
Hypertension	OR 5.4 (Egypt); OR 2.93 (Nigeria/DM study)
Cigarette smoking	OR 3.1 (Egypt)
Obesity / overweight	OR 1.81 (Nigeria primary care study); significant in multiple studies
Low testosterone	OR 3.8 in Nigerian diabetic men
Dyslipidaemia (high LDL, high triglycerides)	OR 6.3 and 2.9 respectively in Nigerian DM study
Depression / psychological factors	Noted in SA systematic review; limited African-specific data
Antihypertensive drug use	Associated with ED in Nigerian primary care study
Duration of DM	OR 3.2 in Ethiopian meta-analysis

4. Healthcare-Seeking Behavior and Underreporting

A striking finding across African studies is the massive gap between prevalence and medical consultation:

In the Nigerian (Bida) study, 66.4% of men with ED had used performance-enhancing drugs — predominantly traditional and OTC remedies — yet only 5.6% had ever formally reported ED to a healthcare provider [PMID: 38787782]
A 2025 systematic review on African medicinal plants for ED [PMID: 42008323] confirms that traditional medicine use is widespread across the continent, driven by stigma, cost barriers, and cultural norms
The South African systematic review found only 5 published articles on male sexual dysfunction in South Africa since 1970 — illustrating the research gap [PMID: 26301289]

5. Research Gaps and Limitations

No continent-wide prevalence study exists for Africa; available data are fragmented by country, setting (hospital vs. community), and methodology
Most African studies are hospital/clinic-based, likely overrepresenting men with comorbidities → true community prevalence may differ
The IIEF-5 is the dominant tool used but not validated for all African language/cultural contexts
North Africa (Egypt, Tunisia) and West/East Africa (Nigeria, Ethiopia) are better represented; Central Africa and francophone Sub-Saharan Africa have minimal data
Underreporting due to stigma means all published figures likely underestimate the true burden

6. Comparison with Global Estimates

Region	Approximate ED Prevalence (general population)
Africa (clinic-based studies)	50–57%
Global (general population, all ages)	~30–40%
Diabetic men globally	~52%
Men >40 yr globally	~40–52%

African clinic-based figures appear higher than global averages, likely reflecting the high burden of comorbidities (DM, HTN) in the study populations rather than an inherently higher biological susceptibility.

Summary

ED is a common, underdiagnosed, and undertreated condition in Africa, with prevalence in clinic-based studies consistently exceeding 50%. The burden is driven primarily by age, diabetes, hypertension, dyslipidaemia, and obesity — all of which are rapidly increasing across the continent due to epidemiological transition. Cultural stigma leads to heavy reliance on traditional medicine and near-complete avoidance of formal medical consultation. A significant gap exists in population-representative, community-based epidemiological data for most African sub-regions.

Key References:

Prevalence of ED in North-West Nigeria, 2023 — PMID 38223611
Prevalence of ED in Bida, Nigeria, 2024 — PMID 38787782
ED in Ethiopian diabetics — meta-analysis, 2021 — PMID 33583238
ED predictors in Nigerian T2DM men, 2025 — PMID 40618378
ED risk factors in Upper Egypt, 2010 — PMID 20795441
Sexual dysfunction in South Africa — systematic review, 2014 — PMID 26301289
Traditional approaches to ED in Africa, 2025 — PMID 42008323

can you give a summary of age based ED % in these studies

Based on the data already retrieved from those studies, here is the age-based breakdown:

Age-Based ED Prevalence — African Studies

Nigeria (Bida, Federal Medical Centre) — PMID 38787782

n = 360 sexually active men, age range 22–75 yr, mean age 42 yr

Age Group	ED Prevalence
20–29 years	30.9%
70–79 years	100%
Overall	56.4%

Age-stratified data for intermediate decades (30s, 40s, 50s, 60s) were not broken out in the abstract — only the youngest and oldest extremes were reported.

Nigeria (Kano, Primary Care Clinic) — PMID 38223611

n = 392 men, mean age 45 ± 14 yr, range 26–86 yr

Age Threshold	Finding
Age ≥50 years	OR = 1.91 (95% CI: 1.28–2.85, p = 0.001) for ED vs. younger men
Overall prevalence	52.3%

This study did not publish a full age-stratified table in the abstract — it reported age ≥50 as a significant cut-off predictor rather than decade-by-decade rates.

Nigeria (Type 2 Diabetic Men) — PMID 40618378

Hospital-based, n = 102

Age Group	Finding
>60 years (diabetic)	OR = 4.9 for ED vs. younger diabetic men
Majority in both groups	>55 years

Again, no decade-by-decade prevalence table — age >60 yr reported as the key threshold.

Ethiopia (Diabetic Men, Meta-Analysis) — PMID 33583238

Pooled from multiple Ethiopian studies

Predictor	Finding
Older age	OR = 4.42 (95% CI: 2.83–6.00) for ED
Pooled overall (diabetic men)	54.3%

No age-decade breakdown — older age was treated as a continuous/categorical predictor.

Egypt (Upper Egypt, Risk Factor Study) — PMID 20795441

n = 658 men with ED vs. 821 age-matched controls

Detail	Finding
Age range	Adults to aged 80+ (wide range)
Age reported	Matched case-control design; no decade-by-decade prevalence published in abstract

Key Takeaway

Study	Youngest Group	Oldest Group	Direction
Nigeria – Bida	30.9% (age 20–29)	100% (age 70–79)	Sharp rise with age
Nigeria – Kano	Lower in <50 yr	OR 1.91 if ≥50 yr	Significant step-up at 50
Nigeria – DM cohort	Lower in <60 yr	OR 4.9 if >60 yr	Steep rise after 60 in diabetics
Ethiopia – DM meta-analysis	—	OR 4.42 for "older age"	Consistent age effect

The consistent pattern across all African studies mirrors global data: ED prevalence rises steeply with age, roughly doubling per decade after 40, and approaching near-universality in men over 70. The Bida (Nigeria) study is the only one in this set that directly reports decade-stratified percentages (30.9% → 100%), while the others quantify age as an odds ratio predictor rather than providing a full age-stratified table.

For decade-by-decade African prevalence data, a dedicated community-based study with full age-stratified reporting would be needed — a significant gap in the current literature.

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