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Tadalafil
Tadalafil is a phosphodiesterase 5 (PDE5) inhibitor1, used to treat erectile dysfunction2, benign prostatic hyperplasia2, and pulmonary arterial hypertension.1 Its effects can last up to 36 hours, longer than those of sildenafil.3 Combining it with other blood-pressure-lowering drugs, particularly nitroglycerin, can cause a serious drop in blood pressure. Rare but serious adverse effects include prolonged erections that can damage the penis, vision problems, and hearing loss.
Dosage & Duration
Dosage
Doses are population estimates that vary widely between individuals.
Threshold~2.5 mg
Light2.5-5 mg
Moderate5-10 mg
Strong10-20 mg
Heavy20+ mg
Duration
Total4-6 hours
Subjective Effects
Subjective Effects not written up yet
Pharmacology
Pharmacodynamics
Tadalafil selectively inhibits phosphodiesterase-5 (PDE5),4 slowing cGMP breakdown and strengthening nitric oxide-dependent signaling that relaxes smooth muscle.1 In the penis, this supports increased blood flow and erection in response to sexual stimulation;5 in pulmonary blood vessels, it promotes dilation and lowers pulmonary arterial pressure.4 Its benefit in benign prostatic hyperplasia may involve improved tissue oxygenation, reduced inflammation and tissue remodeling, and inhibition of cell proliferation through cGMP signaling. Tadalafil also inhibits PDE11A, PDE6, and PDE1, although the physiological significance of PDE11 inhibition is unknown.1
Pharmacokinetics
Tadalafil is metabolized primarily in the liver by CYP3A4, followed by methylation and glucuronidation; the principal circulating metabolite is inactive, as are the other known metabolites. Peak blood concentrations occur after 0.5-6 hours (median 2 hours) in healthy adults and 2-8 hours (median 4 hours) in adults with pulmonary arterial hypertension. Food does not significantly affect absorption.5 Plasma protein binding is 94%,1 and the mean apparent volume of distribution is 63 L in healthy adults and 77 L in adults with pulmonary arterial hypertension. Mean elimination half-life is 15-17.5 hours in healthy adults and 35 hours in adults with pulmonary arterial hypertension. Mean apparent oral clearance is 2.5-3.4 L/hour and 3.5 L/hour in these groups, respectively. Metabolites are excreted mainly in feces (61%) and urine (36%); hemodialysis is not expected to substantially increase clearance.4 Approximately 25% of the absorbed dose remains in the body after 36 hours.
Interactions
Interactions not written up yet
An unlisted combination is an unknown one, not a safe one. Check a dedicated combination chart before mixing.
Tolerance
Tolerance not written up yet
Harm Potential
Toxicity
Tadalafil can rarely cause a prolonged erection that may damage penile tissue.
Tadalafil use has been associated with vision impairment involving non-arteritic anterior ischemic optic neuropathy (NAION), but a causal relationship has not been established.
Sudden hearing loss is a rare but serious potential adverse effect of tadalafil.6
History & Culture
Discovery and clinical development
Tadalafil was discovered by Glaxo Wellcome through a drug-development partnership with ICOS that began in August 1991. In 1993, ICOS, based in Bothell, Washington, began investigating the compound IC351. Its researchers initially studied the compound for purposes other than erectile dysfunction,…
Legality
By Country
Prescription2
United StatesPrescription onlyFederal Food, Drug, and Cosmetic Act § 503(b) (21 U.S.C. § 353(b)); NDA 021368, NDA 022332, and current FDA tadalafil prescribing information52425126
Current FDA records classify oral tadalafil tablets under NDA 021368 (Cialis) and NDA 022332 (Adcirca) as prescription products, and current human tadalafil tablet labeling bears "Rx only" and reports no DEA schedule. NDA 021368 was initially approved on 21 November 2003, and NDA 022332 was approved for a new indication on 22 May 2009; current prescribing information identifies the latter product for pulmonary arterial hypertension. Under § 503(b) of the Federal Food, Drug, and Cosmetic Act, a human drug limited by its approved application to professional supervision may be dispensed only by prescription and must bear "Rx only." This federal classification concerns FDA-approved human tadalafil products and does not determine rules for bulk ingredient supply, pharmacy compounding, veterinary products, or additional state, district, territorial, tribal, or local requirements.
CanadaPrescription onlyFood and Drugs Act, R.S.C. 1985, c. F-27, s. 29.1; Prescription Drug List: Human Use; Food and Drug Regulations, C.R.C., c. 870, ss. A.01.010 and C.01.0411617181920212223
Canada's federal Prescription Drug List for human use lists tadalafil or its salts as a prescription drug, with an effective date of 19 December 2013. Under section C.01.041 of the Food and Drug Regulations, a prescription drug may be sold only by a person authorized under provincial law to dispense it, pursuant to a received verbal or written prescription, or under the exception in section C.01.043. These federal provisions regulate sale and dispensing and do not create a general prohibition on ordinary possession; provincial law determines who may dispense prescription drugs. Health Canada's Drug Product Database classifies marketed human tadalafil tablets, including CIALIS and AG-TADALAFIL, as PRESCRIPTION.
References
Citations
Article Status
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