Cytochrome P450 enzyme system drugs affecting

The cytochrome P450 system is actually a family of related liver enzymes. Each specific enzyme within this family is called an isoenzyme. New isoenzymes within the cytochrome P450 system are constantly being discovered. The 1A2, 2C9/2C19, 2D6, and 3A4 isoenzymes are the best understood. Table 3.10 shows the impact of the newer antidepressants on particular cytochrome P450 isoenzymes and the drugs that may be affected. 

Memantine is not a major substrate for hepatic cytochrome P450 isoenzymes and has not been shown to significantly inhibit or induce these enzymes. However, memantine is partially excreted by renal tubular secretion. Thus, concomitant use of other medications that use the same renal system (i.e., triampterene, hydrochlorothiazide, digoxin, cimetidine, ranitidine, metformin, and quinidine) may affect plasma levels of both drugs (Namenda 2005). Memantine should not be used in combination with other NMDA receptor antagonists, such as amantadine or dextromethorphan, because these combinations have not been formally studied. The clearance of memantine can be reduced when the urine is alkalinized, such as with the concomitant use of sodium bicarbonate or carbonic anhy-... 

All azole drugs affect the mammalian cytochrome P450 system of enzymes to some extent, and consequently they are prone to drug... 

Drug Interactions. Zonisamide does not inhibit or induce the cytochrome P450 system. Enzyme inducers and CYP3A4 inhibitors can affect the concentration of zonisamide. Treatment with enzyme inducers can reduce zonisamide half-life to 27 to 36 hours. ... 

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