Tadalafil is an orally administered drug used to treat male erectile dysfunction (impotence). It was initially developed by the biotechnology firm ICOS and subsequently developed and marketed worldwide by a joint venture of ICOS Corporation and Eli Lilly and Company (Lilly ICOS LLC) under the brand name Cialis.In the United States, tadalafil has Food and Drug Administration approval and became available in December, 2003 as the third impotence pill after sildenafil (Viagra) and vardenafil (Levitra). Due to its 36-hour effect it is also known as the weekend pill. As with sildenafil and vardenafil, it is recommended that tadalafil be used no more than once daily. Tadalafil is also currently undergoing Phase 3 clinical trials for the treatment of pulmonary arterial hypertension.
What is Cialis?

Cialis relaxes muscles and increases blood flow to particular areas of the body.

Cialis is used to treat erectile dysfunction (impotence).

Cialis may also be used for purposes other than those listed in this medication guide.

Important information about Cialis
Do not take Cialis if you are also using a nitrate drug for chest pain or heart problems. This includes nitroglycerin (Nitrostat, Nitrolingual, Nitro-Dur, Nitro-Bid, and others), isosorbide dinitrate (Dilatrate-SR, Isordil, Sorbitrate), and isosorbide mononitrate (Imdur, ISMO, Monoket). Nitrates are also found in some recreational drugs such as amyl nitrate or nitrite (”poppers”). Taking Cialis with a nitrate medicine can cause a serious decrease in blood pressure, leading to fainting, stroke, or heart attack. During sexual activity, if you become dizzy or nauseated, or have pain, numbness, or tingling in your chest, arms, neck, or jaw, stop and call your doctor right away. You could be having a serious side effect of Cialis Do not take this medication more than once a day. Allow 24 hours to pass between doses. Contact your doctor or seek emergency medical attention if your erection is painful or lasts longer than 4 hours. A prolonged erection (priapism) can damage the penis.

Cialis can decrease blood flow to the optic nerve of the eye, causing sudden vision loss. This has occurred in a small number of people taking Cialis, most of whom also had heart disease, diabetes, high blood pressure, high cholesterol, or certain pre-existing eye problems, and in those who smoke or are over 50 years old. It is not clear whether this medication is the actual cause of vision loss.
Stop using Cialis and get emergency medical help if you have sudden vision loss.

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How Cialis Works
Cialis works by increasing the flow of blood to the penis during sexual stimulation. It allows most men to get and keep an erection long enough to complete sexual relations. When sex is over, the erection dissipates normally.

Advantage of Cialis
The effectiveness of most other ED tablets is just a few hours but Cialis works for up to 36 hours. This gives couples the freedom to relax and let the moment happen naturally. Cialis begins to work as quickly as half an hour after taking it, so it’s also possible to be more spontaneous.

Cialis works for mild, moderate or severe ED in most men. And because you can take Cialis with or without food, it’s easy to fit dosing into your schedule

How should I take Cialis? Take Cialis exactly as it was prescribed for you. Do not take it in larger doses or for longer than recommended by your doctor. Follow the directions on your prescription label.
Take this medication with a full glass of water.

Cialis can be taken with or without food.

Cialis is usually taken only when needed, just before sexual activity. The medication can help achieve an erection when sexual stimulation occurs. An erection will not occur just by taking a pill. Follow your doctor’s instructions.
Do not take Cialis more than once a day. Allow 24 hours to pass between doses. Contact your doctor or seek emergency medical attention if your erection is painful or lasts longer than 4 hours. A prolonged erection (priapism) can damage the penis. Store this medication at room temperature away from moisture and heat.
What happens if I miss a dose?

Since Cialis is used as needed, you are not likely to be on a dosing schedule.
What happens if I overdose?
Seek emergency medical attention if you think you have used too much of this medicine.

Overdose symptoms may include chest pain, nausea, irregular heartbeat, and feeling light-headed or fainting.

Mechanism of action
Although Viagra, Levitra, and Cialis all work by inhibition of PDE5, tadalafil’s distinguishing pharmacologic feature is its longer half-life (17.5 hours) compared with Viagra and Levitra (4-5 hours). This longer half-life results in a longer duration of action and is, in part, responsible for the Cialis nickname of the “weekend pill.” This longer half-life also is the basis of current investigation for tadalafil’s use in pulmonary arterial hypertension as a once-daily therapy. At present, sildenafil (trade name Revatio) is approved in various regions worldwide as a 3-times daily therapy for pulmonary arterial hypertension.

Penile erection during sexual stimulation is caused by increased penile blood flow resulting from the relaxation of penile arteries and corpus cavernosal smooth muscle. This response is mediated by the release of nitric oxide (NO) from nerve terminals and endothelial cells, which stimulates the synthesis of cGMP in smooth muscle cells. Cyclic GMP causes smooth muscle relaxation and increased blood flow into the corpus cavernosum. The inhibition of phosphodiesterase type 5 (PDE5) enhances erectile function by increasing the amount of cGMP.Tadalafil (as well as sildenafil and vardenafil) inhibits PDE5. Because sexual stimulation is required to initiate the local release of nitric oxide, the inhibition of PDE5 by tadalafil has no effect in the absence of sexual stimulation. The recommended starting dose of Cialis in most patients is 10 mg, taken as needed before anticipated sexual activity (but no more than once daily). The dose may be increased to 20 mg or decreased to 5 mg, based on individual efficacy and tolerability. To avoid the inconvience of men with erectile dysfunction needing to plan use of Cialis around anticipated sexual activity, Lilly ICOS embarked upon a clinical development program to evaluate the benefits and risks of chronic (once-a-day) use. In June 2007, the European Commission approved low-dose (2.5 mg and 5 mg) Cialis to be used as a once-a-day therapy for men with erectile dysfunction.

Tadalafil is currently undergoing clinical trials for the treatment of pulmonary arterial hypertension. In patients with pulmonary arterial hypertension, it is believed that there is an imablance of the PDE5/NO system in the pulmonary vasculature that favors selective vasoconstriction of the pulmonary artery. Investigation of tadalafil in this disease assumes that PDE5 inhibition will result in pulmonary artery vasodilation, thus lowering pulmonary artery pressure and pulmonary vascular resistance. These physiologic changes may then reduce the workload of the right ventricle of the heart. Right heart failure is the main consequence of pulmonary arterial hypertension.
Side effects

Tadalafil has been used in approximately 15,000 men participating in clinical trials, and over 8 million men wordwide (primarily in the post-approval/post-marketing setting). The most common side effects when using tadalafil are headache, indigestion, back pain, muscle aches, flushing, and stuffy or runny nose. These side effects reflect the ability of PDE5 inhibition to vasodilate (cause blood vessels to widen) and usually go away after a few hours. Back pain and muscle aches can occur 12 to 24 hours after taking the drug, and the symptom usually disappears after 48 hours.

In May 2005, the U.S. Food and Drug Administration found that tadalafil (along with other PDE5 inhibitors) was associated with vision impairment related to NAION (non-arteritic anterior ischemic optic neuropathy) in certain patients taking these drugs in the post-marketing (outside of clinical trials) setting. Most, but not all, of these patients had underlying anatomic or vascular risk factors for development of NAION unrelated to PDE5 use, including: low cup to disc ratio (“crowded disc”), age over 50, diabetes, hypertension, coronary artery disease, hyperlipidemia and smoking. Given the small number of NAION events with PDE5 use (less than 1 in 1 million), the large number of users of PDE5 inhibitors (millions) and the fact that this event occurs in a similar population to those who do not take these medicines, the FDA concluded that they were not able to draw a cause and effect relationship, given these patients underlying vascular risk factors or anatomical defects. However, the label of all three PDE5 inhibitors was changed to highlight clinicians to a possible association.

In October 2007, the FDA announced that the labeling for all PDE5 inhibitors, including tadalafil, requires a more prominent warning of the potential risk of sudden hearing loss as the result of postmarketing reports of deafness associated with use of PDE5 inhibitors.