Drug dosing and monitoring in obese patients undergoing allogenic stem cell transplantation.

BACKGROUND: The effects of physiological changes in patients with obesity on pharmacokinetic parameters and the time course of drug response, especially in the field of haematology/oncology, are poorly understood. For some antimicrobial drugs, dosing considerations exist, while for cytostatic drugs, dose modifications for obese patients are not consistently recommended. Glomerular filtration rate and renal perfusion appear to be similar in obese and normal weight individuals, thus elimination of hydrophilic and extensively renally cleared drugs mainly depends upon creatinine clearance. AIM OF THE REVIEW: To provide information about drug dosing in morbidly obese patients undergoing allogenic haematopoietic stem cell transplantation and to develop dosing recommendations for those patients, based on literature data, pharmacokinetic properties and own experiences.
METHOD: A review on the literature on drug dosing in obese patients as well as on the pharmacokinetic properties of drugs which are supposed to be used in the field of stem cell transplantation was combined with own data on drug dosing and pharmacokinetic drug monitoring in a morbidly obese patient undergoing matched-unrelated allogenic peripheral blood stem cell transplantation.
RESULTS: For hydrophilic and extensively renally cleared drugs (e.g. piperacillin/sulbactam, cotrimoxazole, fludarabine) standard dosages for adult patients or dosing based on ideal body weight (IBW) (e.g. aciclovir, methotrexate) can be used. For ciclosporin and digitoxin we could show that high initial doses are needed to achieve sufficient plasma concentrations. After steady state distribution was completed, maintenance doses comparable to normal weight patients are sufficient. Likewise, distribution of enoxaparin and phenytoin seems to take longer in obese patients. Dosing recommendations of 25 drugs that can be used in morbidly obese patients undergoing allogenic stem cell transplantation are given.
CONCLUSIONS: Pharmacotherapy in morbidly obese patients undergoing allogenic stem cell transplantation is possible, if pharmacokinetic properties of the drugs are considered and close monitoring of plasma concentrations is performed.