Sildenafil

Sildenafil

[1 vial $14.87]

ADMINISTRATION ROUTES:

  • PO, NG

ALTERNATIVE NAMES:

  • Viagra

ICU INDICATIONS:

  1. Patients undergoing cardiac surgery who are at risk of, or who suffer from, peri-operative right ventricular (RV) failure due to raised pulmonary vascular resistance or exacerbation of pre-existing pulmonary hypertension

PRESENTATION AND ADMINISTRATION:

  • Tablets:
    Viagra 25mg (blue) and 50mg (blue)

DOSAGE:

  • PO:
    The typical dose is 50mg 3-4 times daily.
    In small or very sick patients an initial dose of 25mg would be appropriate. For most patients a duration of 3-5 days only is appropriate.

DOSAGE IN RENAL FAILURE AND RENAL REPLACEMENT THERAPY:

  • Dose in renal impairment [GFR (ml/min)]:
    <10: initially 25mg doses
    10-30: initially 25mg doses
    >30-50: initially 25mg doses
  • Dose in renal replacement therapy:
    CAPD: initially 25mg doses
    HD: initially 25mg doses
    CVVHDF: dose as in normal renal function

DOSAGE IN PAEDIATRICS:

  • PO:
    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 obstructon, hypovolaemia) may be at increased risk of hypotension with sildenafil. There are no reports in the literature of use in such patients.

PRECAUTIONS

  • General:
    May cause significant hypotension
  • Laboratory Tests: No tests are indicated in addition to routine ICU
  • Drug/Laboratory Test Interactions: None known

IMPORTANT DRUG INTERACTIONS FOR THE 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% in the sildenafil group. In the peri-operative environment with intensive monitoring instituted it is appropriate to use nitrates if indicated.
  • Nitric oxide 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 System: flushing, hypotension
  • Nervous System: headache, anterior ischemic optic neuropathy (causing sudden loss of vision)
  • Skin: rash
  • Digestive System: Diarrhoea, dyspepsia

Critical Care Drug Manual

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