CHARACTERISTICS OF XENOBIOTICS APPROPRIATE FOR EXTRACORPOREAL THERAPY

The appropriateness of any modality for increasing the elimination of a given xenobiotic depends on various properties of the molecules in question. Effective removal is limited by a large volume of distribution (Vd). A drug with a relatively small Vd, considered amenable to extracorporeal elimination, distributes in an apparent volume not much larger than total body water. Total body water is approximately 60% of total body weight, so that a Vd equal to total body water is approximately 0.6 L/kg body weight. Additionally, high protein binding may interfere with many of the techniques used to enhance elimination. Finally, when assessing the efficacy of any technique of enhanced elimination, a generally accepted principle is that the intervention is worthwhile only if the total body clearance of the xenobiotic is increased by at least 30%. This substantial increase is easier to achieve when the compound has a low endogenous clearance.

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