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. Author manuscript; available in PMC: 2019 Apr 10.
Published in final edited form as: J Pain Symptom Manage. 2017 Nov 16;55(3):1047–1052. doi: 10.1016/j.jpainsymman.2017.11.005

Table 2:

Obesity Effect on Pharmacokinetic Properties

Pharmacokinetic Property Definition Obesity Effect on Pharmacokinetic Property
Absorption and Bioavailability Fraction of administered dose that reaches systemic circulation Not altered in oral drugs
Volume of distribution (Vd) Proportionality factor that relates the amount of drug in the body to the plasma concentration
Vd is based on physiochemical properties (e.g. lipophilicity, molecular size, degree of ionization, ability to cross biological membranes).
Principal parameter determining loading-dose		 Obesity will increase Vd, however weight-adjusted Vd will be smaller than that of normal weight patients for many drugs
Highly lipophilic drugs will have markedly increased Vd in obese patients
Drug clearance (CL) Relates the rate of elimination to the plasma concentration
Primary parameter determining maintenance dose		 CL increases somewhat proportionally with body weight
Obesity may decrease CYP3A4 activity, therefore CL may be decreased for drugs metabolized by CYP3A4 pathway
Elimination half-life (t½) Time required to reduce the plasma concentration of a drug by half Increases in Vd and/or decreases in CL can prolong t½.
Highly lipophilic drugs can accumulate in adipose tissue, leading to risk of side effects and possible toxicity