In short Article

Drug interactions with CYP enzymes

Cytochrome P450 enzymes (CYP enzymes) are involved in the metabolism of many drugs. Since the activity of CYP enzymes can be inhibited or stimulated by other drugs, a large variety of interactions can occur. Whereas many of these interactions are not clinically relevant, some of them can have serious consequences. The information systems of prescribing doctors or pharmacists will show a message in case of interactions with CYP enzymes. But since these systems also generate other types of messages, it is sometimes unclear how these should be prioritized or dealt with. However, the CYP-enzyme interaction message is shown only if there is a risk of clinically relevant consequences for the patient. This means the interaction messages should be carefully evaluated, both when prescribing and when delivering and evaluating the drugs. 

  • The metabolism of a drug (and hence its effectiveness and toxicity) can be greatly influenced by changes in the activity of the liver enzymes that are involved in this metabolism, the cytochrome P450 enzymes.
  • Automated information systems used by doctors or pharmacists will only generate an interaction message if a potentially harmful or serious risk has been reported in the literature. The process of risk estimation is carried out by a multidisciplinary team and is based on scientific research (mostly observational studies).
  • If a message shows up when prescribing, extra care should be taken with drugs that are broken down by one enzyme, drugs with a narrow therapeutic window or agents which have a strong effect on liver enzymes.
  • In the early stages of the drug evaluation process, the presence of such inducing or inhibiting agents should be checked for, to ascertain whether interactions could potentially arise.

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  • Sanne van der Heijden, MSc, pharmacist Stichting Geneesmiddelenbulletin, Utrecht