Information about Tadalafil

Tadalafil is an orally adminstered 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 mre than once daily. Tadalafil is also currently undergoing Phase 3 clinical trials for the treatment of pulmonary arterial hypertension.

History

The history of Cialis cannot be discussed without mentioning Pfizer's drug, Viagra (sildenafil). The FDA's approval of Viagra on March 27, 1998, was a groundbreaking event for the treatment of erectile dysfunction and sales eventually reached over a billion dollars. The FDA subsequently approved Levitra (vardenafil) on August 19, 2003, and Cialis (tadalafil) on November 21, 2003.

In 1993, the Bothell, Washington-based biotechnology company Icos began studying IC351, which is a phosphodiesterase type 5 (PDE5) enzyme inhibitor. In 1994, Pfizer scientists discovered that sildenafil citrate, which also inhibits the PDE5 enzyme, caused patients that were participating in a clinical study of a heart medicine to have erections. Although the ICOS scientists were not testing the chemical compound IC351 for erectile dysfunction, it was recognized that the compound could have potential usefulness for the treatment of this disorder. Soon Icos received a patent in 1994 for IC351, which is structurally different from sildenafil (and vardenafil), and Phase 1 clinical trials began in 1995. In 1997, Phase 2 clinical studies were initiated in patients with erectile dysfunction and led to pivotal Phase 3 trials that supported approval.

In 1998, ICOS Corporation and Eli Lilly and Company formed a joint venture (Lilly ICOS LLC) to further develop and commercialize the drug for erectile dysfunction, and two years later they filed a New Drug Application with the U.S. Food and Drug Administration for IC351 (under the generic name tadalafil and the brand name Cialis). In May of 2002, Lilly ICOS reported to the American Urological Association that clinical trial testing in men with erectile dysfunction showed that tadalafil works for up to 36 hours, and one year later tadalafil was approved. One advantage that Cialis has over Viagra and Levitra is that tadalafil has a half-life of 17.5 hours^[1] (and thus Cialis is advertised to work for up to 36 hours, after which time there is still about one quarter of the absorbed dose in the body) as compared to 4 hours half-life for sildenafil (Viagra).^[2][3]

Eli Lilly purchased ICOS Corporation for $2.1 billion dollars in 2006.

Chemistry

The empirical formula for tadalafil is C₂₂H₁₉N₃O₄, and its official organic name is (6R,12aR)-6-(1,3-benzodioxol-5-yl)-2,3,6,7,12,12a- hexahydro-2-methyl-pyrazino[1 ,2 :1,6]pyrido[3,4-b]indole-1,4-dione. The molecular weight is 389.41. Tadalafil tablets are yellow, film-coated, and almond-shaped, and are produced in 5, 10, or 20 mg doses.

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 hyperension 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. A 20 mg dose of tadalafil is comparable to a 100 mg dose of sildenafil (Viagra). However, the recommended starting dose of Cialis in most patients is 10 mg, taken prior to anticipated sexual activity. The dose may be increased to 20 mg or decreased to 5 mg, based on individual efficacy and tolerability

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.

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 nitrates (such as the sex drug amyl nitrite) within this timeframe may increase the risk of life-threatening hypotension.

Since people who have taken tadalafil within the past 48 hours cannot take organic nitrates to relieve angina (such as glyceryl trinitrate spray), these patients should seek immediate medical attention if they experience anginal chest pain.^[4] In the event of a medical emergency, paramedics and medical personnel should be notified of any recent doses of tadalafil.

Marketing

In the United States, Eli Lilly has a multiyear agreement to promote tadalafil (Cialis) with professional golf's PGA Tour.

Cialis is one of the most frequent offerings of spam.

Trivia

Some individuals with the surname of "Cialis" objected to Lilly's naming of the drug, but the company insists that the drug's trade name has nothing to do with the surname.^[5]

References

External links

• Official site
• National Institutes of Health
• RxList - Tadalafil
• Medical safety data sheet

•  • [ e] Urologicals (G04)
Acidifiers	Ammonium chloride, Calcium chloride
Urinary antispasmodics (primarily antimuscarinics)	Darifenacin, Emepronium, Flavoxate, Meladrazine, Oxybutynin, Propiverine, Solifenacin, Terodiline, Tolterodine, Trospium
For erectile dysfunction	Alprostadil, Apomorphine, Moxisylyte, Papaverine, Phentolamine, Yohimbine, PDE5 inhibitors (Avanafil, Sildenafil, Tadalafil, Udenafil, Vardenafil)
Other urologicals	Acetohydroxamic acid, Collagen, Dimethyl sulfoxide, Magnesium hydroxide, Pentosan polysulfate, Phenazopyridine, Phenyl salicylate, Succinimide
For benign prostatic hypertrophy	5α-reductase inhibitors: Dutasteride, Finasteride Alpha blockers: Alfuzosin, Doxazosin, Tamsulosin, Terazosin Herbals: Pygeum africanum, Serenoa repens

•  • [ e] Selective Phosphodiesterase inhibitors (C01CE, G04BE)
PDE1	Vinpocetine
PDE2	EHNA
PDE3	Amrinone, Bucladesine, Enoximone, Milrinone
PDE4	Mesembrine, Rolipram
PDE5	Sildenafil, Tadalafil, Vardenafil

•  • [ e] Medications used in the management of pulmonary arterial hypertension (B01, C02)
Prostacyclin analogues	Beraprost, Epoprostenol, Iloprost, Treprostinil
Endothelin receptor antagonists	Ambrisentan, Bosentan, Sitaxsentan
PDE5 inhibitors	Sildenafil, Tadalafil
Adjunctive therapy	Calcium channel blockers, Diuretics, Digoxin, Oxygen therapy, Warfarin