Tadalafil Tablets (Cialis)
By William T. Elliott, MD, FACP, and James Chan, PharmD, PhD
The FDA has approved tadalafil, the third phosphodiesterase type 5 inhibitor (PDE5) for the treatment of erectile dysfunction. The approval of tadalafil occurred just 3 months after the approval of vardenafil (Levitra), which, along with sildenafil (Viagra) represent the 2 previously approved drugs for this indication. Tadalafil has a duration of action of up to 36 hours (hence the nickname the "weekend drug") and will be marketed by Lilly as "Cialis."
Indications
Tadalafil is indicated for the treatment of erectile dysfunction.1
Dosage
The recommended dose is 10 mg taken prior to sexual activity. The dose range is 5 mg to 20 mg depending on effectiveness and side effects. It may be taken without regard to meals. In patients with moderate renal dysfunction, the dose should not exceed 5-mg once daily and 10-mg every 48 hours. In patients with mild or moderate hepatic dysfunction, the dose should not exceed 10-mg once daily. In patients taking concomitant drugs that are potent CYP3A4 inhibitors (eg, ritonavir, ketoconazole), the dose of taladafil should not exceed 10 mg every 72 hours.1
Tadalafil is available as 5-mg, 10-mg, and 20-mg tablets.
Potential Advantages
Tadalafil has a mean elimination half-life of 17.5 hours compared to 4-5 hours for sildenafil and vardenafil.1-3 A single 10-mg or 20-mg dose has been reported to improve the likelihood of successful intercourse up to 36 hours.1,4
Potential Disadvantages
Similar to other PDE5 inhibitors, tadalafil is metabolized by CYP3A4. Potent inhibitors of this isoform are expected to increase the level of these drugs and 3A4 inducers (eg, rifampin) may decrease drug levels. Side effects are also similar among PDE5 inhibitors. The most common are headache (11-15% vs 5% for placebo) and dyspepsia (4-10% vs 1%).1,5
Comments
Similar to other PDE5 inhibitors, tadalafil improves erectile function in men with erectile dysfunction. Tadalafil has demonstrated efficacy in 2 US studies (n = 402) and 5 studies outside the United States (n = 1112) in men with general erectile dysfunction.1 Efficacy was assessed primarily by the Erectile Function domain score of the International Index of Erectile Function and 2 questions on penetration and successful intercourse. Specifically efficacy has also been demonstrated in patients with diabetes mellitus and in patients following radical prostatectomy.1,6 In contrast to sildenafil and vardenafil, tadalafil has shown efficacy up to 36 hours. In a randomized, placebo-controlled study (n = 348), after a 20-mg dose of tadalafil, 59.2% of intercourse attempts were successful 33-39 hours after dosing compared to 28.3% in the placebo group.1,4 In a second study (n = 483), the percent successful intercourse at 36 hours post-dose were 33%, 56%, and 67% for placebo, 10 mg, and 20 mg dose, respectively.1 Successful erection (1 in 4 attempts) within 30 minutes was more likely to be achieved with the 20-mg dose compared to the 10-mg or placebo, 52%, 38%, and 35%, respectively. Similar to other PDE5 inhibitors, tadalafil is well tolerated but has potential drug interactions including potent inhibitors of CYP3A4 isoform, nitrates, and alpha-blockers (except tamsulosin). A small decrease in blood pressure (eg, 4-6 mm Hg systolic and 1-4 mm Hg diastolic) may occur when tadalafil is used with other antihypertensive drugs such as diuretics, ACE inhibitors, or beta blockers.1 As with other PDE5 inhibitors the wholesale cost for all the strengths are priced the same. Tadalafil and sildenafil are priced at $8.10 per tablet and vardenafil is priced at $6.93 per tablet.
Clinical Implications
Tadalafil offers another option to sildenafil and vardenafil with a longer duration of action that may be attractive. No comparative studies among PDE5 inhibitors have been published.
Dr. Elliott is Chair, Formulary Committee, Northern California Kaiser Permanente, and Assistant Clinical Professor of Medicine, University of California-San Francisco. Dr. Chan is Pharmacy Quality and Outcomes Manager, Kaiser Permanente, Oakland, CA. Both are associate editors of Internal Medicine Alert.
References
1. Cialis Product Information. Eli Lilly and Company. November 2003.
2. Viagra Product Information. Pfizer Laboratories. November 1998.
3. Levitra Product Information. Bayer Pharmaceuticals Corporation. August 2003.
4. Porst H, et al. Urology. 2003;62(1):121-125.
5. Curran MP, Keating GM. Drugs. 2003;63(20):2203-2212.
6. Sanez de Tejada I, et al. Diabetes Care. 2002;25:2159-2164.
The FDA has approved tadalafil, the third phosphodiesterase type 5 inhibitor (PDE5) for the treatment of erectile dysfunction.
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