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Phosphodiesterase-5 (PDE5) Inhibitor Pregnancy: Avoid in PAH — PAH itself is life-threatening in pregnancy; specialist multidisciplinary decision required

Sildenafil (CTD-Associated PAH / Raynaud's)

Brand names: Revatio (PAH — 20 mg tablets), Viagra (erectile dysfunction — different indication)

Adult dose

Dose: 20 mg three times daily (PAH — Revatio); 25–100 mg once daily (Raynaud's — off-label)
Route: Oral
Frequency: Three times daily (PAH); once daily (Raynaud's)
Max: 20 mg TDS (PAH); 100 mg OD (Raynaud's off-label)
Revatio (20 mg, 3×/day) is the licensed preparation for PAH. Off-label in digital ulcers/Raynaud's associated with systemic sclerosis (SSc). Takes 4–6 hours for full effect on pulmonary vasculature. Avoid fatty meal before dose — delays absorption.

Paediatric dose

Route:
Paediatric PAH — 0.5–2 mg/kg three times daily; MHRA caution regarding use in children — seek specialist paediatric cardiology/rheumatology opinion

Dose adjustments

Renal

Reduce starting dose in severe renal impairment (eGFR <30 mL/min) — increased sildenafil exposure

Hepatic

Reduce starting dose in hepatic impairment — reduced hepatic clearance

Clinical pearls

  • SUPER-2 trial: sildenafil 20 mg TDS improved 6-minute walk distance by 50 m in WHO class II–III PAH — key rheumatology relevance is CTD-PAH (SSc, SLE, MCTD)
  • Systemic sclerosis: SSc-PAH is a major cause of death in SSc; early RHC recommended if echocardiographic PAP >40 mmHg or TAPSE reduction
  • Visual side effects: blue/violet tinge due to PDE6 inhibition in photoreceptors — warn patients before starting; NAION (rare, sudden unilateral visual loss) — stop immediately if occurs
  • Nitrate interaction is ABSOLUTE and FATAL — any patient on sildenafil presenting to ED must NOT receive GTN or nitrates without specialist guidance; time from last dose: 24 hours minimum
  • MHRA: Revatio (20 mg PAH) and Viagra (25/50/100 mg erectile dysfunction) contain same active ingredient — prescribe by brand to avoid confusion; different dosing regimens

Contraindications

  • Concurrent nitrates (GTN, isosorbide mononitrate) — ABSOLUTE CONTRAINDICATION; profound hypotension
  • Concurrent soluble guanylate cyclase stimulators (riociguat)
  • Severe left ventricular outflow obstruction
  • Hypersensitivity to sildenafil

Side effects

  • Headache — most common (25–30%); prostaglandin-mediated
  • Flushing
  • Dyspepsia
  • Visual disturbances — blue tinge (chromatopsia), blurred vision; due to PDE6 cross-inhibition in retina
  • Hypotension
  • Epistaxis
  • Non-arteritic ischaemic optic neuropathy (NAION) — rare; risk higher in pre-existing eye disease; sudden vision loss — stop immediately

Interactions

  • Nitrates — ABSOLUTE contraindication; additive hypotension; fatal hypotension reported
  • Alpha-blockers (doxazosin, tamsulosin) — enhanced hypotension
  • CYP3A4 inhibitors (ketoconazole, ritonavir, erythromycin) — increase sildenafil levels 2–10-fold; reduce dose
  • CYP3A4 inducers (rifampicin) — reduce sildenafil levels; efficacy loss

Monitoring

  • Blood pressure at baseline and periodically
  • 6-minute walk distance (PAH monitoring)
  • Pulmonary arterial pressures (RHC or echocardiography) at 3–6 months
  • Visual acuity — any new visual symptoms
  • Signs of worsening PAH or digital ischaemia

Reference: BNFc; BNF 90; SUPER-2 Trial (Circulation 2008); NICE TA311 (Sildenafil PAH); EULAR SSc Guidelines; SPC Revatio. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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