The stability of miconazole when mixed with peritoneal dialysis (PD) fluid and stored in plastic bags or glass ampuls was determined. Admixtures of miconazole and PD fluid were prepared in 2-L polyvinyl chloride (PVC) bags and in 1-mL glass ampuls to give a nominal initial concentration of 20 mg/mL. Duplicate samples of each solution were assayed in duplicate by high-performance liquid chromatography immediately after preparation and at various intervals up to nine days. All admixtures were stored in ambient light at 20 +/- 2 degrees C. A substantial loss of miconazole (greater than 10% of the initial concentration) occurred within four hours for admixtures stored in PVC bags, whereas similar solutions retained more than 90% of their initial miconazole concentration for at least three days when stored in glass ampuls under the same conditions. This suggests that the observed loss of miconazole from the PVC bags was largely due to an interaction with the container, rather than to chemical degradation in solution. About 28% of the miconazole lost from the solution during storage in PVC bags was recovered from the plastic by methanolic extraction. The rapid loss of miconazole when the drug was mixed with PD fluid and stored in PVC bags indicates that such admixtures should be prepared immediately before administration.