Tadalafil

Tadalafil is a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5). The physiologic mechanism of erection of the penis involves release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. Nitric oxide then activates the enzyme guanylate cyclase, which results in increased levels of cGMP. Cyclic guanosine monophosphate causes smooth muscle relaxation in the corpus cavernosum thereby allowing inflow of blood; the exact mechanism by which cGMP stimulates relaxation of smooth muscles has not been determined. Phosphodiesterase type 5 is responsible for degradation of cGMP in the corpus cavernosum. Tadalafil enhances the effect of NO by inhibiting PDE5 thereby raising concentrations of cGMP in the corpus cavernosum. Tadalafil has no direct relaxant effect on isolated human corpus cavernosum and, at recommended doses, has no effect in the absence of sexual stimulation. In vitro studies show that tadalafil is selective for PDE5 and is 10,000-fold more potent for PDE5 than for PDE1, PDE2, PDE4, and PDE7, which are found in the heart, brain, blood vessels, liver, leukocytes, skeletal muscle, and other organs. Tadalafil is 10,000 fold more potent for PDE5 than for PDE3 found in the heart and blood vessels. Also, tadalafil has 700-fold greater selectivity for PDE5 versus PDE6, an enzyme found in the retina and involved in phototransduction. Compare this selectivity to the selectivity of sildenafil which has only a 10-fold selectivity for PDE5 versus PDE6. This lower selectivity of sildenafil for PDE5 vs PDE6 is thought to be the basis for abnormalities related to color vision observed with higher doses or plasma concentrations of sildenafil. Further, tadalafil is 9000-fold more potent for PDE5 than for PDE8, PDE9, and PDE10. Tadalafil is 14-fold more potent for PDE5 than for PDE11A1 and 40-fold more potent for PDE5 than for PDE11A4. PDE11 is an enzyme found in human skeletal muscle, prostate, testes, and in other tissues. Inhibition of human recombinant PDE11A1, and to a lesser extent, PDE11A4 activities occur at tadalafil concentrations within the therapeutic range. The physiological role and clinical effects of PDE11 inhibition in humans have not been elucidated.

Your health care provider needs to know if you have any of these conditions: bleeding disorders; eye or vision problems, including retinitis pigmentosa; Peyronie’s disease, or history of priapism (painful and prolonged erection); heart disease, angina, a history of heart attack, irregular heart beats; high or low blood pressure; history of blood diseases; history of stomach bleeding; kidney disease; liver disease; stroke; an unusual or allergic reaction to tadalafil. If you notice any changes in your vision while taking this drug, call your doctor or health care professional as soon as possible. Stop using this medicine and call your healthcare provider right away if you have a loss of sight in one or both eyes. Contact your healthcare provider right away if the erection lasts longer than 4 hours or if it becomes painful. If you experience symptoms of nausea, dizziness, chest pain or arm pain upon initiation of sexual activity after taking this medicine, you should refrain from further activity and call your healthcare provider immediately. Do not drink alcohol when taking this medicine as alcohol can increase your chances of getting a headache or getting dizzy, increasing your heart rate or lowering your blood pressure. Using this medicine does not protect you or your partner against HIV infection or other sexually transmitted infections.

Please discuss with your healthcare provider.

Back pain; dizziness; flushing; headache; indigestion; muscle aches; nausea; stuffy or runny nose. This list may not describe all possible side effects. Call your healthcare provider immediate if you experience signs of an allergic reaction like skin rash, itching or hives, swelling of the face, lips, or tongue; breathing problems; changes in hearing; changes in vision; chest pain; erection lasting more than 4 hours; fast, irregular heartbeat; seizures.

Store this medication at 68°F to 77°F (20°C to 25°C) and away from heat, moisture and light. Keep all medicine out of the reach of children. Throw away any unused medicine after the beyond use date. Do not flush unused medications or pour down a sink or drain.