Therapeutic Drug Monitoring of Antimetabolic Cytotoxic Drugs

Br J Clin Pharmacol. 1999 Feb;47(2):131-43. doi: 10.1046/j.1365-2125.1999.00884.x.


Therapeutic drug monitoring is not routinely used for cytotoxic agents. There are several reasons, but one major drawback is the lack of established therapeutic concentration ranges. Combination chemotherapy makes the establishment of therapeutic ranges for individual drugs difficult, the concentration-effect relationship for a single drug may not be the same as that when the drug is used in a drug combination. Pharmacokinetic optimization protocols for many classes of cytotoxic compounds exist in specialized centres, and some of these protocols are now part of large multicentre trials. Nonetheless, methotrexate is the only agent which is routinely monitored in most treatment centres. An additional factor, especially in antimetabolite therapy, is the existence of pharmacogenetic enzymes which play a major role in drug metabolism. Monitoring of therapy could include assay of phenotypic enzyme activities or genotype in addition to, or instead of, the more traditional measurement of parent drug or drug metabolites. The cytotoxic activities of mercaptopurine and fluorouracil are regulated by thiopurine methyltransferase (TPMT) and dihydropyrimidine dehydrogenase (DPD), respectively. Lack of TPMT functional activity produces life-threatening mercaptopurine myelotoxicity. Very low DPD activity reduces fluorouracil breakdown producing severe cytotoxicity. These pharmacogenetic enzymes can influence the bioavailability, pharmacokinetics, toxicity and efficacy of their substrate drugs.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Antimetabolites, Antineoplastic / therapeutic use*
  • Cytarabine / therapeutic use
  • Drug Monitoring / methods*
  • Fluorouracil / therapeutic use
  • Humans
  • Mercaptopurine / therapeutic use
  • Methotrexate / therapeutic use
  • Neoplasms / drug therapy*


  • Antimetabolites, Antineoplastic
  • Cytarabine
  • Mercaptopurine
  • Fluorouracil
  • Methotrexate