Metabolic inactivation conjugation

Biotransformation or metabolic inactivation of drugs occurs mainly in the liver and, to a lesser extent, in the plasma, kidney, and other tissues, depending on the enzyme system involved. In the liver, microsomal enzymes catalyze many of the metabolic processes involved in the biotransformation of drugs. These metabolic processes may involve nonsynthetic reactions such as oxidation, reduction, or hydrolysis, or synthetic reactions, including conjugation, whereby the drug is coupled with an endogenous substrate (53). 

Metabolic inactivation of mephenytoin and its demethyl celalxilitc is by p-hydroxylation and then conjugation of the... 

As shown in Fig. 3, 2,3-DHBA and 2,5-DHBA may derive from SA as the products of metabolic inactivation which arises from additional hydroxylation of the aromatic ring. The rapid conjugation of SA with glucose to form P-D-o-glucosylsalicylic acid is the main metabolic inactivation mechanism in tobacco [37,38]. The glucose ester of SA was detected in soybean cell cultures fed with [ C]-labelled SA [39] and a small amount of these compound is also detected in tobacco [38]. 

Elimination of heroin (diacetylmorphine) is 80% renal. Metabolic inactivation mainly gives morphine-3-glucuronide together with a few percent of the metabolites 6-monoacetylmorphine, non-conjugated morphine and normorphine. Unchanged diacetylmorphine can be detected only in trace amounts if at all. The hydrolysis of heroin via 3-acetylmorphine takes place to a small extent only [44],... 

The acidic group also serves as a major site of metabolism by conjugation. Thus, a major pathway of clearance for many NSAIDs is glucuronidation (and inactivation) followed by renal elimination. 

The steroid hormones are mainly inactivated in the liver, where they are either reduced or further hydroxylated and then conjugated with glucuronic acid or sulfate for excretion (see p. 316). The reduction reactions attack 0X0 groups and the double bond in ring A. A combination of several inactivation reactions gives rise to many different steroid metabolites that have lost most of their hormonal activity. Finally, they are excreted with the urine and also partly via the bile. Evidence of steroids and steroid metabolites in the urine is used to investigate the hormone metabolism. 

Metabolism/Excretion-There are considerable variations in the reported half-life of testosterone, ranging from 10 to 100 minutes. The half-life of testosterone cypionate IM is approximately 8 days for oral fluoxymesterone, it is approximately 9.2 hours and for methyltestosterone it is 2.5 to 3 hours. Inactivation of testosterone occurs primarily in the liver. About 90% of a testosterone dose is excreted in the urine as conjugates of testosterone and its metabolites about 6% of a dose is excreted in the feces. 

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