Bioelectrical impedance analysis measurements for drug pharmacokinetics.

I review the rationale, methods, and existing data for using bioelectrical impedance to determine drug pharmacokinetics. Because drugs distribute into body compartments after absorption, it is expected that bioelectrical impedance measurements may correlate with drug pharmacokinetics (absorption, distribution, metabolism, and excretion). Authors have examined correlations between total body water, extracellular fluid, and body cell mass and the drug volume of distribution or clearance and the elimination rate constant. Multiple-regression models with the all-subsets technique provided the most accurate equations with the lowest prediction errors and the highest correlation coefficients. Application of bioelectrical impedance-derived equations to a different set of patients allows prediction of pharmacokinetics. However, bioelectrical impedance equations do not yield more accurate dosing estimates than do standard dosing methods, and large dosing errors are possible in patients with aberrant physiology. Therefore, until multicenter trials in large subject populations can provide stable, accurate equations applicable to a wide variety of patient populations, bioelectrical impedance offers no advantage over standard pharmacokinetic dosing methods for the drugs studied.