Tadalafil

Tadalafil is a PDE5 inhibitor, currently marketed in pill form for treating erectile dysfunction (ED) under the name Cialis. It has also been recently been approved for the treatment of pulmonary arterial hypertension, and has also been used for other conditions. Cialis tablets, in 5 mg, 10 mg, and 20 mg doses , are yellow, film-coated, and almond-shaped. The approved dose for pulmonary arterial hypertension is 40 mg, and is marketed under the brand name Adcirca.
Cialis's 36-hour effectiveness earned it the nickname, "The Weekend Pill"; like sildenafil and vardenafil, tadalafil is recommended as an 'as needed' medication. Cialis is the only one of the three that is also offered as a once-daily medication.

Advantages Of Cialis Over Viagra

The advantage Cialis has over Viagra and Levitra is its 17.5-hour half-life. Cialis is advertised to work for up to 36 hours, after which time there remains approximately 25 percent of the absorbed dose in the body when compared to the four-hour half–life of Viagra.

Mechanism Of Action

Although sildenafil (Viagra), vardenafil (Levitra), and tadalafil (Cialis) all work by inhibiting PDE5, tadalafil's pharmacologic distinction is its longer half-life (17.50 hours) compared to Viagra (4.0–5.0 hours) and Levitra (4.0–5.0 hours) – resulting in longer duration of action, and so partly responsible for "The Weekend Pill" sobriquet.

Tadalafil 20 mg Tablet View Of Tadalafil 20 mg Tablet Photo Credit: Jean-Patrick Donzey

Penile erection during sexual stimulation is caused by increased penile blood flow resulting from the relaxation of penile arteries and the smooth muscle of the corpus cavernosum. 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 relaxes smooth muscle and increases blood flow to the corpus cavernosum.
The inhibition of phosphodiesterase type 5 (PDE5) enhances erectile function by increasing the amount of cGMP. Tadalafil (and sildenafil and vardenafil) inhibits PDE5, however, because sexual stimulation is required to initiate the local penile release of nitric oxide, tadalafil's inhibition of PDE5 will have no effect without direct sexual stimulation of the penis.

Tadalafil ( Cialis) Dosage

The recommended Cialis starting dose for most men is 10 mg. It is to be taken as needed before sexual activity but not more than once daily. The dose may be increased to 20 mg or decreased to 5mg as per its efficacy and the man's personal tolerance of the drug.
In June 2007, the European Commission approved low-dose (2.5 mg and 5 mg) Cialis to be used as single-daily Erectile Dsynfunction (ED) therapy.

Side Effects Of Tadalafil

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.
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.

Drug interactions

Since PDE5 inhibitors such as tadalafil may cause transiently low blood pressure (hypotension), organic nitrates should not be taken for at least 48 hours after taking the last dose of tadalafil. Using organic nitrites (such as the sex drug amyl nitrite) within this timeframe may increase the risk of life-threatening hypotension.
People who have taken tadalafil within the past 48 hours cannot take organic nitrates such as glyceryl trinitrate spray to relieve angina. These patients should seek immediate medical attention if they experience anginal chest pain. In the event of a medical emergency, paramedics and medical personnel should be notified of any recent doses of tadalafil.

More Information

Material Safety Data Sheet PDF file



Considerable portions of the text here is from http://en.wikipedia.org/wiki/Tadalafil and is reproduced here under the Creative Commons Attribution-ShareAlike License