Obesity-associated changes in drug pharmacokinetics

Pharmacokinetics of drugs in obese patients can be affected by changes in drug distribution and/or changes in elimination functions. Drug dosing based on patients weight or body surface area may not be satisfactory in terms of safety or efficacy, especially for patients with a higher degree of obesity. However, current knowledge about most drugs does not provide sufficient guidance for dose adjustment in this group of patients. This article provides an overview of factors influencing changes in pharmacokinetics of drugs in obese, including some examples (eg. analgesics, antibiotics, anticoagulants and others). Due to different changes in pharmacokinetics, which cannot always be estimated from the physical and chemical properties of drug molecular structure, it is important to assess pharmacokinetic properties of a particular drug rather than looking for general rules for the most appropriate dosing. In case of drugs with a narrow therapeutic index (aminoglycoside antibiotics and vancomycin, anticonvulsants, immunosuppressants, lithium, digoxin and theophylline), it is always advisable to measure drug plasma levels and use therapeutic drug monitoring.