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
Isosorbide Mononitrate
Organic nitrate vasodilator · Antianginal
Also known as Isosorbide-5-mononitrate, ISMN
START
Check BP (ensure SBP >90). Verify no PDE5 inhibitor use in past 24-48h. Counsel on headache (common, usually resolves in 1 week).
TYPICAL MAX
240mg/day ER. Do not use TID/QID dosing (promotes tolerance). Maintain 10-12 hour nitrate-free interval daily.
STOP IF
SBP <90 mmHg, syncope, severe headache unresponsive to analgesia, methemoglobinemia (cyanosis, SpO2 discordance).
WATCH
Tolerance develops with continuous exposure—ensure 10-12 hour nitrate-free interval (asymmetric BID or morning-only ER). Headache is expected and usually transient. Hypotension risk increased with alcohol, other antihypertensives.
CDSCO approvedSchedule HJan AushadhiATC C01DA14
KDIGO 2024 + manufacturer label
- ONSET
- 1h · Onset 30-60 min (IR)
- PEAK
- 4h · Tmax ER 3.5-5 hours
- t½
- 5h · t½ ~5 hours
- DURATION
- 12h · 12-24 hours (ER)
EXCRETION
Renal as metabolites (~96%)
route + CYP
INTERACTIONS
11 major
incl. contraindicated
PREGNANCY
Limited data; use only if clearly needed. Animal studies at high doses show adverse effects.
FDA category + note
Top interactionssee all 12 →
- SildenafilContraindicatedTextbook-citedKDT 7e · p950
- TadalafilContraindicatedTextbook-citedKDT 7e · p950
- AvanafilContraindicatedDatabaseDDInter
- Pde5 InhibitorsContraindicatedDatabaseKimi deep-research + Cla
Available in India
116 branded formulations and 18 fixed-dose combinations. 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 → increased cGMP → dephosphorylation of myosin light chain → vasodilation. Preferentially dilates veins > arteries, reducing preload and myocardial oxygen demand.
Indications
Prevention of angina pectorisCongestive heart failure (adjunctive, with hydralazine—BiDil)
Dosing
- Adult
- Angina prophylaxis (IR): 20mg BID given 7 hours apart (asymmetric dosing to prevent tolerance). Angina prophylaxis (ER): 30-60mg daily in morning, may increase to 120mg daily; max 240mg/day (ER). Heart failure (BiDil): isosorbide dinitrate 20mg + hydralazine 37.5mg TID.
- Pediatric
- Not established in children.
- Renal adjustment
- No adjustment needed.
- Hepatic adjustment
- No adjustment needed; metabolized in liver but well-tolerated.
- Geriatric
- Start at 30mg ER daily; increased sensitivity to hypotension.
- Max dose
- 240mg/day (ER); 40mg/day (IR BID)
Pharmacokinetics
Onset
IR: 30-60 minutes; ER: 1-2 hours
Peak effect
IR: Tmax 0.5-1 hour; ER: Tmax 3.5-5 hours
Duration
IR: 6-8 hours; ER: 12-24 hours
Half-life
~5 hours (IR and ER)
Bioavailability
~100% (no first-pass metabolism, unlike ISDN)
Protein binding
~5%
Metabolism
Hepatic denitration to isosorbide and sorbitol; glucuronidation
Excretion
~96% in urine as metabolites; ~2% unchanged
Contraindications
- Hypersensitivity to nitrates
- Severe hypotension (SBP <90 mmHg)
- Cardiogenic shock
- Sildenafil, tadalafil, or vardenafil use within 24-48 hours (PDE5 inhibitors)
- Hypertrophic cardiomyopathy with outflow tract obstruction
- Closed-angle glaucoma (relative)
Side effects
Common
Headache (most common—dose-dependent, often transient)DizzinessHypotensionTachycardia (reflex)Flushing
Serious
- Severe hypotension / syncope
- Reflex tachycardia (may worsen angina)
- Methemoglobinemia (rare, high doses)
- Nitrate tolerance (with continuous exposure)
Pregnancy & lactation
Pregnancy
Limited data; use only if clearly needed. Animal studies at high doses show adverse effects.
Lactation
Excretion in breast milk unknown; use with caution. No adverse effects reported in nursing infants.
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
Avanafil
Contraindicated
Database
Profound and prolonged systemic hypotension, syncope, myocardial ischemia, and even death.
Concomitant use is absolutely contraindicated. A minimum of 12 hours should elapse between the last dose of avanafil and the administration of isosorbide mononitrate.
Source: DDInter
Pde5 Inhibitors
Contraindicated
Database
Potentiation of cGMP-mediated vasodilation → severe, potentially fatal hypotension.
Absolutely contraindicated. Sildenafil/vardenafil: avoid for 24h after nitrate. Tadalafil: avoid for 48h.
Source: Kimi deep-research + Cla
Riociguat
Contraindicated
Database
Riociguat (sGC stimulator) + nitrates → excessive hypotension.
Contraindicated. Use alternative antianginal if riociguat indicated.
Source: Kimi deep-research + Cla
Vardenafil
Contraindicated
Database
Profound and prolonged systemic hypotension, syncope, myocardial ischemia, and even death.
Concomitant use is absolutely contraindicated. A minimum of 24 hours should elapse between the last dose of vardenafil and the administration of isosorbide mononitrate.
Source: DDInter
Alpha Blockers (e.g., Prazosin, Doxazosin, Tamsulosin)
Severe
Database
Significant orthostatic hypotension, dizziness, syncope, and reflex tachycardia.
Use with extreme caution. Start with low doses of both drugs and titrate slowly. Monitor blood pressure closely, especially during initiation and dose adjustments. Advise patients about symptoms of hypotension and how to manage them (e.g., rise slowly).
Nicorandil
Severe
Database
Additive hypotensive effects, potentially leading to severe hypotension, dizziness, syncope, and reflex tachycardia.
Avoid concomitant use if possible. If co-administration is necessary, monitor blood pressure closely and consider reducing the dose of one or both agents. Educate the patient about symptoms of hypotension.
Nitrous Acid
Severe
Database
Clinical effect not specified
Source: DDInter
Prilocaine
Severe
Database
Clinical effect not specified
Source: DDInter
Tizanidine
Severe
Database
Clinical effect not specified
Source: DDInter
Alcohol
Moderate
Database
Additive vasodilation and hypotension; may precipitate syncope.
Advise patient to avoid or minimize alcohol while taking nitrates.
Source: Kimi deep-research + Cla
Related guidelines
Ask House about Isosorbide Mononitrate
Continue into a citation-backed clinical answer with the drug context already attached.
Sources: KD Tripathi 7e, Katzung, BNF·Verified: 2026-05-19 · House clinical team·Cockpit curated: 2026-05-19