sildenafil

CLINICAL USE

Treatment of erectile dysfunction (ED) To increase exercise ability in pulmonary arterial hypertension

DOSE IN NORMAL RENAL FUNCTION

ED: 25–100 mg 0.5–4 hours before sexual intercourse (ideally, about 1 hour); no more than 1 dose per dayPulmonary arterial hypertension: 20 mg 3 times daily

PHARMACOKINETICS

Molecular weight :666.7 (as citrate)

%Protein binding :96

%Excreted unchanged in urine : <2

Volume of distribution (L/kg) :1–2

half-life – normal/ESRD (hrs) :4/Increased

DOSE IN RENAL IMPAIRMENT

GFR (mL/MIN)

30–50 Dose as in normal renal function10–30 Dose as in normal renal function ED: Initial dose 25 mg and increase if required

<10 : Dose as in normal renal function ED: Initial dose 25 mg and increase if required

DOSE IN PATIENTS UNDERGOING RENAL REPLACEMENT THERAPIES

CAPD :Unlikely to be dialysed. Dose as in GFR <10 mL/min

HD :Unlikely to be dialysed. Dose as in GFR <10 mL/min

HDF/high flux :Not dialysed. Dose as in GFR <10 mL/min

CAV/VVHD :Unlikely to be dialysed. Dose as in GFR 10 to 20 mL/min

IMPORTANT DRUG INTERACTIONS

Potentially hazardous interactions with other drugsAlpha-blockers: enhanced hypotensive effect – avoid for 4 hours after sildenafil

Antivirals: ritonavir significantly increases sildenafil concentration – avoid concomitant use; concentration possibly increased by saquinavir, amprenavir, indinavir and nelfinavir – reduce dose of sildenafil; side effects possibly increased by atazanavirNicorandil: enhanced hypotensive effect – avoid concomitant use

Nitrates: enhanced hypotensive effect – absolutely contraindicated

ADMINISTRATION

Reconstition

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Route

Oral

Rate of Administration

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Comments

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OTHER INFORMATION

Dialysis is not expected to increase clearance as sildenafil is highly protein boundPatients should seek prompt medical advice if their erections last for more than 4 hoursRecommend use on non-dialysis days due to hypotension. In peritoneal dialysis, treatment with sildenafil is well toleratedAnecdotally it has been used at Guy’s hospital, London for diabetic gastroparesis at a dose of 25 mg 3 times a dayThe use of sildenafil is potentially hazardous in patients with active coronary ischaemia, those with congestive heart failure, and those with complicated multi-drug antihypertensive therapy regimensIn 9 patients on maintenance haemodialysis, sildenafil 50 mg appeared to produce firmer erections and greater sexual satisfaction, but the effects were prolonged for up to 48 hours after administration.

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