What is the role of the cytochrome P450 (CYP) system in drug metabolism in pediatric HIV infection?

Updated: Mar 05, 2020
  • Author: Delia M Rivera, MD; Chief Editor: Russell W Steele, MD  more...
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The CYP system is classified into families, 3 of which are important in humans: CYP1, CYP2, and CYP3. Further delineation into subfamilies is denoted with a capital letter (eg, CYP3A). The nomenclature is completed with the description of individual proteins called isoenzymes, which are delineated with a second number (eg, CYP3A4).

Drugs may be substrates, inhibitors, and/or inducers of particular isoenzymes. Substrates are metabolized by means of the CYP system. They may also be classified as inhibitors (ie, those with reversible and competitive action that decreases metabolism) and/or inducers (ie, those with reversible and competitive action that increases metabolism). Inhibitors decrease hepatic metabolism of isoenzyme substrates (ie, increase serum concentrations), whereas inducers increase this metabolism (ie, decrease serum levels).

All currently approved protease inhibitors and NNRTIs are metabolized in the CYP system, principally by the 3A4 isoenzyme. Some also induce or inhibit CYP3A4, respectively decreasing or increasing serum levels of the 3A4 substrate. Strong inhibitors (eg, ritonavir) have been used in small doses to increase drug levels (eg, of the lopinavir-ritonavir combination), enhancing the efficacy of those drugs with a low enough dose to limit the risk of adverse effects.

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