Erectile dysfunction

Sildenafil (Viagra ®)	tadalafil (Cialis ®)
vardenafil (Levitra ®)

Sildenafil (Viagra ®)

Phosphodiesterase-5 Enzyme Inhibitor.
INDICATIONS: Psychotropic-induced sexual dysfunction; primary pulmonary hypertension

Mechanism of Action
Does not directly cause penile erections, but affects the response to sexual stimulation. The physiologic mechanism of erection of the penis involves release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. NO then activates the enzyme guanylate cyclase, which results in increased levels of cyclic guanosine monophosphate (cGMP), producing smooth muscle relaxation and inflow of blood to the corpus cavernosum. Sildenafil enhances the effect of NO by inhibiting phosphodiesterase type 5 (PDE-5), which is responsible for degradation of cGMP in the corpus cavernosum; when sexual stimulation causes local release of NO, inhibition of PDE-5 by sildenafil causes increased levels of cGMP in the corpus cavernosum, resulting in smooth muscle relaxation and inflow of blood to the corpus cavernosum; at recommended doses, it has no effect in the absence of sexual stimulation.

Dosing (Adults): Oral:
Erectile dysfunction: For most patients, the recommended dose is 50 mg taken as needed, approximately 1 hour before sexual activity. However, sildenafil may be taken anywhere from 30 minutes to 4 hours before sexual activity. Based on effectiveness and tolerance, the dose may be increased to a maximum recommended dose of 100 mg or decreased to 25 mg. The maximum recommended dosing frequency is once daily.

Primary pulmonary hypertension (unlabeled use): 25 mg twice daily, titrated based on response. Dosages up to 100 mg 5 times/day have been used (limited data).

Dosage adjustment for patients >65 years of age, hepatic impairment (cirrhosis), severe renal impairment (creatinine clearance <30 mL/minute), or concomitant use of potent cytochrome P450 3A4 inhibitors (erythromycin, ketoconazole, itraconazole, ritonavir, amprenavir): Higher plasma levels have been associated which may result in increase in efficacy and adverse effects and a starting dose of 25 mg should be considered

Administration
Administer orally ~1 hour before sexual activity (may be used anytime from 4 hours to 30 minutes before).

Supplied: Viagra®: 25 mg, 50 mg, 100 mg tablet.

tadalafil (Cialis ®)

PDE-5 enzyme inhibitor.

Dosing (Adults): Erectile dysfunction: 10 mg orally prior to anticipated sexual activity (dosing range: 5-20 mg) - to be given as a single dose and not given more than once daily (Erectile function may be improved for up to 36 hours following a single dose).

Drug interactions: Alpha blockers: If stabilized on either alpha blockers or tadalafil therapy, initiate new therapy with the other agent at the lowest possible dose. CYP3A4 inhibitors: Dose reduction of tadalafil is recommended with strong CYP3A4 inhibitors. The dose of tadalafil should not exceed 10 mg, and tadalafil should not be taken more frequently than once every 72 hours. Some examples include: (azole antifungals, clarithromycin, doxycycline, erythromycin, grapefruit juice, imatinib, isoniazid, nefazodone, protease inhibitors, others...)

Renal Dosing:
Crcl 31-50 ml/min: Initial dose 5 mg once daily - maximum dose 10 mg not to be given more frequently than every 48 hours.
Crcl <30 ml/min or hemodialysis: Maximum dose 5 mg.

Hepatic impairment:
Mild-to-moderate hepatic impairment (Child-Pugh class A or B): Do not exceed 10 mg once daily.
Severe hepatic impairment: Use is not recommended.

Supplied: 5 mg, 10 mg, 20 mg tablet.

vardenafil (Levitra ®)

PDE-5 enzyme inhibitor.

Dosing (Adults): Erectile dysfunction: 10 mg orally 1 hour prior to sexual activity. Dosing range: 5-20 mg (given as one single dose and not given more than once daily). Patients >/= 65 yrs old: Initial: 5 mg 1 hr prior to sexual activity- to be given as one single dose and not given more than once daily.

Drug interactions: Alpha blocker (dose should be stable at time of vardenafil initiation): Initial vardenafil dose: 5 mg/24 hrs. If an alpha blocker is added to vardenafil therapy, it should be initiated at the smallest possible dose, and titrated carefully. Other: Erythromycin: Max vardenafil dose: 5 mg/24 hrs. Indinavir: Max dose: 2.5 mg/24 hrs. Itraconazole: 200 mg/day: Max dose: 5 mg/24 hours. 400 mg/day: Max dose: 2.5 mg/24 hrs. Ketoconazole: 200 mg/day: Max dose: 5 mg/24 hrs. 400 mg/day: Max dose: 2.5 mg/24 hrs. Ritonavir: Max dose: 2.5 mg/72 hrs.

Hepatic impairment: Child-Pugh class B: Initial: 5 mg 1 hr prior to sexual activity (max dose: 10 mg)- to be given as one single dose and not given more than once daily.

Supplied:: 2.5 mg, 5 mg, 10 mg, 20 mg tablet.

Disclaimer

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David F. McAuley, Pharm.D., R.Ph. GlobalRPh Inc.

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