Sildenafil
Contraindicated
Textbook-cited
Precipitous and potentially fatal fall in blood pressure; myocardial ischemia.
Concurrent use is absolutely contraindicated
Source: KDT 7e · p950
Drug reference
Nitroglycerin
Nitrate vasodilator / antianginal · Antianginal
Also known as Glyceryl Trinitrate, GTN
START
Acute: 0.3-0.4 mg SL at chest pain onset, sit down, repeat every 5 min x 3 if needed, call EMS if no relief after 3 doses. Prophylaxis: lowest effective dose with 10-12h nitrate-free interval to prevent tolerance
TYPICAL MAX
SL: 1.8 mg in 15 min (3 doses). IV: 200 mcg/min
STOP IF
SBP <90 mmHg, severe headache, syncope, methemoglobinemia (cyanosis, chocolate-colored blood)
WATCH
BP and HR (especially with first dose and dose increases), headache severity, signs of tolerance, ensure nitrate-free interval for long-acting forms
CDSCO approvedSchedule HJan AushadhiNPPA price-controlledATC C01DA02
KDIGO 2024 + manufacturer label
- ONSET
- 3min · SL: 1-3 minutes
- PEAK
- 6min · SL: 4-8 minutes
- t½
- 3min · 1-4 minutes (very short)
- DURATION
- 1h · SL: 30-60 minutes
EXCRETION
Renal (metabolites)
route + CYP
INTERACTIONS
9 major
incl. contraindicated
PREGNANCY
Use only if clearly needed; animal studies show adverse effects; nitrates used in pregnancy for hypertensive emergencies and uterine relaxation
FDA category + note
Top interactionssee all 11 →
- SildenafilContraindicatedTextbook-citedKDT 7e · p950
- TadalafilContraindicatedTextbook-citedKDT 7e · p950
- Pde5 InhibitorsContraindicatedDatabaseKimi deep-research + Cla
- AvanafilSevereDatabaseDDInter
Available in India
212 branded formulations. Look up specific brands in the Drugs workspace.
Jan Aushadhi — generic available at GoI pharmacies
Mechanism
Converted to nitric oxide (NO) in vascular smooth muscle, activating guanylate cyclase and increasing cGMP, leading to vasodilation. Predominantly venodilator at low doses (reduces preload) with arterial vasodilation at higher doses (reduces afterload). Also causes coronary vasodilation, improving myocardial oxygen supply.
Indications
Acute angina pectoris (sublingual, spray)Angina prophylaxis (long-acting oral, transdermal, ointment)Acute coronary syndrome (IV)Hypertensive emergency (IV)Acute pulmonary edema / heart failure (IV)Anal fissure (topical ointment - off-label)
Dosing
- Adult
- Acute angina: 0.3-0.6 mg SL (may repeat x3 at 5-min intervals). Prophylaxis: 2.5-9 mg PO TDS-QDS (sustained-release); 0.2-0.8 mg/hr patch (12-14h on, 10-12h off). IV: 5 mcg/min, titrate by 5 mcg/min every 3-5 min (max 200 mcg/min)
- Pediatric
- Not recommended for angina in children; IV use in pediatric cardiac surgery: specialized dosing
- Renal adjustment
- No adjustment needed
- Hepatic adjustment
- No adjustment needed; extensive first-pass metabolism actually reduced in hepatic impairment (monitor for increased effect)
- Geriatric
- Start low; increased sensitivity to hypotension and falls
- Max dose
- SL: 1.8 mg in 15 minutes (3 tablets). IV: 200 mcg/min. Oral SR: 26 mg QDS
Pharmacokinetics
Onset
SL: 1-3 minutes; Spray: 2 minutes; IV: immediate; Oral SR: 20-45 minutes; Patch: 30-60 minutes
Peak effect
SL: 4-8 minutes; IV: immediate
Duration
SL: 30-60 minutes; IV: 1-5 minutes after stopping; Patch: 18-24 hours (but tolerance develops >12-14h continuous)
Half-life
1-4 minutes (very short - parent compound)
Bioavailability
SL: ~40%; Oral: <1% (extensive first-pass); Transdermal: variable
Protein binding
60%
Metabolism
Hepatic rapid metabolism by organic nitrate reductases to 1,2-glyceryl dinitrate and 1,3-glyceryl dinitrate (active metabolites)
Excretion
Renal (primarily as metabolites)
Contraindications
- Hypersensitivity to nitrates
- Severe hypotension (SBP <90 mmHg)
- Cardiogenic shock
- Severe aortic stenosis
- Severe mitral stenosis
- Hypertrophic obstructive cardiomyopathy (HOCM)
- Constrictive pericarditis
- Cardiac tamponade
- Concurrent use with PDE5 inhibitors (sildenafil, tadalafil, vardenafil) - within 24-48h
- Increased intracranial pressure
- Severe anemia
Side effects
Common
Headache (most common - dose-related, usually improves with continued use)FlushingDizzinessHypotension / orthostatic hypotensionTachycardia (reflex)NauseaLightheadedness
Serious
- Severe hypotension / syncope
- Methemoglobinemia (rare, high doses)
- Reflex tachycardia (may worsen angina)
- Tolerance with continuous use (tachyphylaxis)
- Severe headache (intolerable)
Pregnancy & lactation
Pregnancy
Use only if clearly needed; animal studies show adverse effects; nitrates used in pregnancy for hypertensive emergencies and uterine relaxation
Lactation
Excretion in breast milk unknown; use with caution during breastfeeding
Drug interactions
Tadalafil
Contraindicated
Textbook-cited
Precipitous and potentially fatal fall in blood pressure; myocardial ischemia
Concurrent use is absolutely contraindicated
Source: KDT 7e · p950
Pde5 Inhibitors
Contraindicated
Database
Both increase cGMP; profound synergistic hypotension; risk of cardiovascular collapse and death
Absolute contraindication; do not use nitrates within 24h of sildenafil/vardenafil or 48h of tadalafil
Source: Kimi deep-research + Cla
Avanafil
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Nitrous Acid
Severe
Database
Clinical effect not specified
Source: DDInter
Prilocaine
Severe
Database
Clinical effect not specified
Source: DDInter
Riociguat
Severe
Database
severe hypotension and syncope
Concurrent use is contraindicated.
Source: DDInter
Tizanidine
Severe
Database
.
Source: DDInter
Vardenafil
Severe
Database
Co-administration can cause profound vasodilation and potentially catastrophic hypotension.
Avoid nitroglycerin if vardenafil has been used within 24 hours.
Source: DDInter
Alteplase
Moderate
Database
Increased hepatic alteplase clearance
Avoid concurrent IV nitroglycerin if possible
Source: Kimi deep-research + Cla
Amlodipine
Moderate
Database
Hypotension, dizziness.
Use with caution. Titrate carefully.
Source: DDInter
1 additional unreviewed or low-confidence interaction hidden because their provenance or source detail is insufficient.
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Ask House about Nitroglycerin
Continue into a citation-backed clinical answer with the drug context already attached.
Textbook-sourced·Sources: Goodman & Gilman 14e, Harrison 22e, Katzung, Nelson·Updated: 2026-05-19·Cockpit curated: 2026-05-19