The influence of drug sorption on pharmacokinetic studies of chlormethiazole and lignocaine.

The influence of drug sorption on the measurement of dose and blood concentrations during pharmacokinetic studies of chlormethiazole and lignocaine in a chronically catheterized sheep preparation has been examined. There was no sorption to soda glass tubes, borosilicate glass volumetric flasks or soda glass microlitre syringes but minor sorption to polypropylene syringes, polypropylene pipette tips and rubber bottle stoppers after 240 min contact. During infusions through administration sets including either polyvinyl chloride or polyethylene catheters, no significant loss of lignocaine occurred, but only 41.7-63.9% of the chlormethiazole dose was delivered. No significant decreases in either drug occurred from blood sampled through an intravascular catheter and stopcock system. There was negligible degradation of the samples over 4 h. Sorption of chlormethiazole or lignocaine to the laboratory equipment used was not a significant source of error but polyvinyl chloride infusion catheters could result in significant reductions in chlormethiazole dose.