High-Pressure Liquid Chromatographic Assay of Theophylline in Dog Feces following Oral Administration of Sustained-Release Products

Abstract

A solid-phase-extraction reversed-phase HPLC assay is described for the determination of theophylline embedded in dog feces as powder, sustained-release tablets, or capsules. The feces is extracted with 5% isopropyl alcohol in chloroform in the presence of β-hydroxypropyl-theophylline as the internal standard. Separation and quantitation are achieved with a C18 analytical column. UV absorbance is monitored at 280nm. Recovery of theophylline was >50%. The assay is linear between 10 and 400mg amounts of theophylline in 50g of feces. Inter- and intraday coefficients of variation of the chromatographic assay were <3%, and the extraction procedure was highly reproducible with coefficients of variation of <10% at amounts of drug from 10 to 400mg. By keeping the stool/solvent extraction ratio constant, the method is equally effective in extracting theophylline from different sizes of stool samples (50 versus g of stool). The assay was applied to evaluate the theophylline content in feces following oral administration of the drug to dogs as tablet (Theo-Dur) and capsule (Slo-Bid) dosage forms. The resulting fecal recovery values of each product were inversely related to the corresponding bioavailability values obtained from the literature.