Introduction
Cialis is FDA-approved for treatment of erectile dysfunction--a condition that involves the inability to achieve or maintain adequate penile erection for sexual intercourse. It is also known as tadalafil (generic name). It is an oral tablet, usually taken once a day.
Following an oral dose of the drug, it is extensively distributed in the body tissues. The portion in the blood stream is bound to proteins. These attributes account for its longevity in the body and the rationale for once daily dosing.
How Cialis is Broken Down
According to information available on the FDA website, Cialis is initially inactivated by a multistep process in the liver involving an enzyme system called the Cytochrome P450, specifically the CYP3A4 fraction of it. It takes almost 18 hours to break down half of the amount in the blood at any time. The initial byproduct undergoes further processing and appears as an inactive complex compound in the blood, called a glucoronide.
The inactive complex is principally eliminated in feces. This route accounts for 61 percent of the oral dose. A smaller percentage, about 36 percent, is excreted in the urine.
Clinical Correlates of Cialis Metabolism
Certain drugs actually block the action of the enzyme system that breaks down Cialis in the blood. This block can lead to extended action of the drug in the body beyond the desirable time period. The prescribing physician ought to know any other medication being taken by the patient, in order to prevent these kinds of adverse effects. Sometimes, dose reduction or spacing out of doses can address problems.
There are also precautions involving the use of Cialis in patients with liver disease, as this may limit the liver's ability to perform its usual task of inactivating the drug. Other precautions involve its use in kidney disease, though dosage adjustments are not prescribed.
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