Drug Interaction:
Sildenafil has no effect on bleeding time when taken alone or with aspirin Since metabolism of sidenafil is medicated by cytochrome P450, the cytocrome P450 inhibitors are likely to reduce sildenafil clearance.
Concomittant administration of sidenafil 100mg and amlodipine 5 or 10mg in hypertensive patients lead to a mean additional blood pressure reduction.
When taken with a high fat meal, the rate of sidenafil adsorption is reduced.
Adverse Reaction:
Headache, flushing, dyspepsia, nasal congestion, Uurinary tract infection, abnormal vision, Diarrhea, dizziness, Rash, Respiratory tract infection.
Contra-Indications:
Hypersensitivity Patients concurrently or intermittently using nitrates in any form.
Special precautions:
Sidenafil clearance reduced in severe renal impaired patients. Not indicated for use in women/newborns/children
Safety and efficacy of sidenafil with combinations not established Should not be used in men for whom sexual activity is inadvisable because of their underlying cardiovascular status.
Pharmacology/ Pharmacokinetics:
Ref - Drug Facts and Comparisons (2010)
Pharmacology:
Sidenafil induces erections in response to sexual stimulation by causing smooth muscle
relaxation in the corpus cavemosum through selective inhibition of phosphodiesterase type
5(PDE5). Since sidenafil only lowers the inactivation of cyclic guanosine monophosphate(cGMP) and does nor enhance its production, penile erection due to sodenafil is acheived only in response to sexual stimulation and not in absence of it.
Pharmocokinetics:
Sidenafil and its circulating N-desmethyl metabolite are approximately 96% bound to plasma proteins. Plasma protein binding is independent of total drug concentrations
Absorption and distribution-
Phosphodiesterase Type 5 Indicators Pharmacokinetics-
Parameters Sidenafil Todalafil Vardenafil
Bioavailability 40% Not determined ~15%
Tmax 0.5% to 2h 0.5% to 6h 0.5% to 2h
(median 1h) (median 2h) (median 1h)
Effect of food Cmax redu 29% No Cmax reduced
(High fat meal) Tmax incr 1h effect 18% to 50%
Onset of action ~30 min ~30min ~20min
Maximum effect no data no data 49 to 90min
Duration of >4h 36h <5h
action
vol of distribution 105L ~63L 208L
Protein binding ~96% ~94% ~95%
Metabolism CYP3A4(major) CYP3A4 CYP3A4(minor)
CYP2C9(minor) CYP3A5,CYP2C
isoforms(minor)
Active metabolite Yes No Yes
Terminal half-life ~4h 17.5h 4 to 5h
Excretion Feces(~80%) Feces(~61%) Feces(~91%to95%)
Urine(~13%) Urine(~36%) Urine(~2% to 6%)
Clearance no data 2.5L/h 56L/h
Manufacturer Details