The effect of a polyvinyl chloride (PVC) i.v. administration system on the availability of quinidine gluconate was studied. Quinidine gluconate diluted in 5% dextrose injection was administered intravenously to five healthy volunteers via conventional PVC infusion sets, and the subjects received oral quinidine sulfate two days later. The mean +/- S.D. oral bioavailability of quinidine was, unexpectedly, greater than 100% (147 +/- 44%). To test the possibility that this occurred because of reduced delivery of i.v. quinidine, the percentage of drug delivered via two systems was evaluated in simulation studies, one involving a conventional PVC administration set and the other a glass syringe attached to shorter PVC tubing and a winged i.v. catheter. Spectrophotometric analysis revealed a 5-7% reduction in absorbance associated with loss of quinidine in the PVC infusion bag and a further 34-38% reduction in absorbance attributable to quinidine loss in the PVC tubing. However, with the winged i.v. catheter system the loss was reduced to less than 3%. More than 40% of a dose of quinidine gluconate was lost when the drug was administered with a conventional PVC i.v. administration set. Drug loss was reduced by using a winged i.v. catheter and shorter tubing.