Isosorbide Dinitrate
Contraindicated
Textbook-cited
Precipitous and potentially fatal fall in blood pressure; myocardial ischemia.
Concurrent use is absolutely contraindicated
Source: KDT 7e · p950
Drug reference
Sildenafil
Phosphodiesterase-5 (PDE5) inhibitor · Antihypertensive (Pulmonary), Erectile Dysfunction Agent
Also known as Sildenafil citrate, Revatio, Granpidam, Mysildecard, Viagra, Vizarsin
START
ED: 50 mg PO ~1 h before activity; PAH: 20 mg PO three times daily
TYPICAL MAX
100 mg/day (ED); PAH titrate per response
STOP IF
Sudden vision/hearing loss, priapism, severe hypotension, or chest pain
WATCH
Visual / auditory symptoms, BP; absolutely no nitrate co-use
CDSCO approved,null,ATC G04BE03
KDIGO 2024 + manufacturer label
- ONSET
- 30min · absorption
- PEAK
- 1h · Tmax
- t½
- 4h · t½
- DURATION
- 4h · ED window
EXCRETION
Mainly faecal (~80%); ~13% renal
route + CYP
INTERACTIONS
12 major
incl. contraindicated
PREGNANCY
Use in PAH per benefit/risk; ED use not applicable.
FDA category + note
Top interactionssee all 12 →
- Isosorbide DinitrateContraindicatedTextbook-citedKDT 7e · p950
- Isosorbide MononitrateContraindicatedTextbook-citedKDT 7e · p950
- NitroglycerinContraindicatedTextbook-citedKDT 7e · p950
- Glyceryl TrinitrateContraindicatedTextbookKDT 7e · p542
Mechanism
Selective inhibitor of cGMP-specific PDE5 in vascular and corporal smooth muscle, prolonging cGMP-mediated vasodilation in response to nitric oxide; relaxes corpus cavernosum (erection) and pulmonary vasculature (PAH).
Indications
Erectile dysfunctionPulmonary arterial hypertension (Group 1 PAH)
Dosing
- Adult
- ED: 50 mg PO ~1 h before sexual activity (25–100 mg range). PAH: 20 mg PO three times daily (or 2.5–10 mg IV three times daily).
- Pediatric
- PAH ≥1 y (specialist; weight-based).
- Renal adjustment
- CrCl <30: start ED 25 mg; PAH dosing no fixed adjustment but monitor.
- Hepatic adjustment
- Mild–moderate: start 25 mg (ED); severe: avoid.
- Geriatric
- ≥65 y ED: start 25 mg.
- Max dose
- 100 mg/day (ED); 80 mg three times daily (PAH off-label / higher doses)
Pharmacokinetics
Onset
~30 min (Tmax fasting); delayed by high-fat meal
Peak effect
~1 h (Tmax)
Duration
~4 h (ED); ~8 h (PAH dosing interval)
Half-life
~4 h
Bioavailability
~40%; food delays onset
Protein binding
~96%
Metabolism
Hepatic CYP3A4 (major) and CYP2C9
Excretion
Mainly faecal (~80%); ~13% renal
Contraindications
- Concomitant nitrates / nitric-oxide donors (absolute)
- Concomitant guanylate cyclase stimulators (riociguat)
- Severe hypotension / unstable cardiovascular disease
- Recent stroke or MI (within ~6 weeks)
- Severe hepatic impairment
- Hereditary degenerative retinal disorders (retinitis pigmentosa) — caution
Side effects
Common
HeadacheFlushingDyspepsiaNasal congestionVisual disturbance (blue tint, photopsia)
Serious
- Severe hypotension (with nitrates)
- NAION (non-arteritic ischaemic optic neuropathy)
- Sudden hearing loss
- Priapism (>4 h erection)
- QT prolongation (high dose, susceptible)
Pregnancy & lactation
Pregnancy
Use in PAH per benefit/risk; ED use not applicable.
Lactation
Limited data; small milk transfer; weigh benefit.
Drug interactions
Isosorbide Mononitrate
Contraindicated
Textbook-cited
Precipitous and potentially fatal fall in blood pressure; myocardial ischemia
Concurrent use is absolutely contraindicated
Source: KDT 7e · p950
Nitroglycerin
Contraindicated
Textbook-cited
Precipitous and potentially fatal fall in blood pressure; myocardial ischemia.
Concurrent use is absolutely contraindicated
Source: KDT 7e · p950
Glyceryl Trinitrate
Contraindicated
Textbook
Severe hypotension, myocardial infarction, and deaths.
Glyceryl trinitrate should not be administered if the patient has taken sildenafil in the past 24 hours.
Source: KDT 7e · p542
Isosorbide Dinitrate Hydralazine
Contraindicated
Textbook
Severe hypotension.
Contraindicated.
Source: G&G 14e · p664
Isosorbide 5 Mononitrate
Contraindicated
Textbook
Extreme hypotension, potentially life-threatening.
PDE5 inhibitors should not be prescribed to patients receiving any form of nitrate. Patients should be warned not to use PDE5 inhibitors and nitrates concurrently. No PDE5 inhibitor should be used in the 24 hours prior to initiating nitrate therapy. If significant hypotension occurs, fluids and α adrenergic receptor agonists may be used for support.
Source: G&G 14e · p612
Molsidomine
Contraindicated
Textbook
Extreme hypotension, potentially life-threatening.
PDE5 inhibitors should not be prescribed to patients receiving any form of nitrate. Patients should be warned not to use PDE5 inhibitors and nitrates concurrently. No PDE5 inhibitor should be used in the 24 hours prior to initiating nitrate therapy. If significant hypotension occurs, fluids and α adrenergic receptor agonists may be used for support.
Source: G&G 14e · p612
Organic Nitrates
Contraindicated
Textbook
Dangerously low blood pressures.
The administration of PDE5 inhibitors to patients receiving organic nitrates is contraindicated. The patient’s underlying cardiovascular status and concurrent use of hypotensive agents (e.g., nitrates, α adrenergic antagonists) must be considered prior to use of this class of drugs.
Source: G&G 14e · p999
Tadalafil
Contraindicated
Textbook
Extreme hypotension, potentially life-threatening.
PDE5 inhibitors should not be prescribed to patients receiving any form of nitrate. Patients should be warned not to use PDE5 inhibitors and nitrates concurrently. A period longer than 24 hours (especially with tadalafil) may be needed following administration of a PDE5 inhibitor for safe use of nitrates. If significant hypotension occurs, fluids and α adrenergic receptor agonists may be used for support.
Source: G&G 14e · p612
Vardenafil
Contraindicated
Textbook
Extreme hypotension, potentially life-threatening.
PDE5 inhibitors should not be prescribed to patients receiving any form of nitrate. Patients should be warned not to use PDE5 inhibitors and nitrates concurrently. No PDE5 inhibitor should be used in the 24 hours prior to initiating nitrate therapy. If significant hypotension occurs, fluids and α adrenergic receptor agonists may be used for support.
Source: G&G 14e · p612
Isosorbide
Contraindicated
Database
Severe hypotension.
Absolute contraindication.
Source: DDInter
Nicorandil
Contraindicated
Database
Extreme hypotension, potentially life-threatening.
PDE5 inhibitors should not be prescribed to patients receiving any form of nitrate. Patients should be warned not to use PDE5 inhibitors and nitrates concurrently. No PDE5 inhibitor should be used in the 24 hours prior to initiating nitrate therapy. If significant hypotension occurs, fluids and α adrenergic receptor agonists may be used for support.
Related guidelines
Ask House about Sildenafil
Continue into a citation-backed clinical answer with the drug context already attached.
Sources: KD Tripathi 7e, Goodman & Gilman 14e, Harrison 22e, Katzung·Verified: 2026-05-20 · House clinical team·Cockpit curated: 2026-05-20