ADMINISTRATION ROUTES:
PO, NG
ALTERNATIVE NAMES:
Viagra
ICU INDICATIONS:
- Right ventricular dysfunction from raised pulmonary vascular resistance
- Exacerbation of pre-existing pulmonary hypertension
PRESENTATION AND ADMINISTRATION:
Tablets
Viagra 25mg (blue) and 50 mg (blue)
DOSAGE:
PO/NG:
50 mg TDS or QID for 3 - 5 days
Initial dose 25 mg for small or very sick patients
DOSAGE IN RENAL FAILURE AND RENAL REPLACEMENT THERAPY:
Dose in renal impairment
| GFR (ml/min) | DOSE |
|---|---|
| <10 | 25 mg dosing initially |
| 10-30 | 25 mg dosing initially |
| >30 | dose as in normal renal function |
Dose in renal replacement therapy
| MODALITY | DOSE |
|---|---|
| CAPD | 25 mg dosing initially |
| HD | 25 mg dosing initially |
| CVVHDF | 25 mg dosing initially |
DOSAGE IN PAEDIATRICS:
Not applicable
CLINICAL PHARMACOLOGY:
Sildenafil is a potent, selective inhibitor of cGMP-specific phosphodiesterase-5 (PDE-5). It has an established therapeutic role as a selective pulmonary vasodilator in patients with pulmonary hypertension in the non-operative setting. Recent limited data suggests it may have a similar role in the peri-operative setting in cardiothoracic surgical patients. However, evidence is very limited.
CONTRAINDICATIONS:
See ## WARNINGS
WARNINGS:
Patients with increased susceptibility to vasodilators (e.g. severe aortic stenosis, left ventricular outflow tract obstruction, hypovolaemia) may be at increased risk of hypotension with sildenafil.
PRECAUTIONS:
General:
May cause significant hypotension
Laboratory Tests:
No additionanl tests are indicated
Drug/Laboratory Test Interactions:
None known
IMPORTANT DRUG INTERACTIONS IN ICU:
Sildenafil potentiates the hypotensive effects of nitrates. The data sheet states that the combination of nitrates (nitric oxide donors including GTN, isosorbide salts, sodium nitroprusside, organic nitrates or organic nitrites) and sildenafil is contraindicated. However, in a recent double-blind placebo-controlled randomised trial of males with coronary artery disease the combination of sildenafil or placebo and IV GTN up to a dose of 80 mcg/min was tolerated without significant hypotension by 70% of the sildenafil group. In the peri-operative environment with intensive monitoring instituted it is appropriate to use nitrates if indicated. Nitric oxide (NO) co-administration is safe and potentiates the pulmonary vasodilator effects of sildenafil without any adverse effects. Sildenafil has been used to facilitate weaning of NO.
The combination of sildenafil with potent CYP3A4 inhibitors (e.g. ketoconazole, itraconazole, ritonavir) is contraindicated.
ADVERSE REACTIONS:
Cardiovascular:
Flushing, hypotension
Neurological:
Headache, anterior ischaemic optic neuropathy (causing sudden loss of vision)
Dermatological:
Rash
Gastrointestinal:
Diarrhoea, dyspepsia