Simultaneous determination of acetaminophen, theophylline and salicylate in serum by high-performance liquid chromatography

High-pressure liquid chromatographic assay of theophylline in dog feces following oral administration of sustained-release products

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 beta-hydroxypropyl-theophylline as the internal standard. Separation and quantitation are achieved with a C18 analytical column. UV absorbance is monitored at 280 nm. Recovery of theophylline was > 50%. The assay is linear between 10 and 400 mg amounts of theophylline in 50 g 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 400 mg. By keeping the stool/solvent extraction ratio constant, the method is equally effective in extracting theophylline from different sizes of stool samples (50 versus 200 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.

A non-extraction HPLC method for the simultaneous determination of serum paracetamol and salicylate

A direct injection HPLC method for the sumultaneous measurement of serum paracetamol and salicylate is described using a Pinkerton internal surface reversed-phase column with benzoic acid as internal standard. The method is linear to at least 1000 mg/L for both drugs and shows good precision at levels of 62-500 mg/L. None of the drugs tested for interference affected the quantitation of either drug. In patient samples, the values obtained with this method correlated well with those from enzymatic paracetamol and Trinder salicylate methods.

Ion-pair high-performance liquid chromatographic procedure for the quantitative analysis of theophylline in serum samples

An ion-pair chromatographic system is described for the separation of theophylline and related xanthines from serum samples. The mobile phase consisted of 0.02 M tetrabutylammonium ion and 0.015 M Tris buffer in water-acetonitrile-methanol (93:3.5:3.5, v/v/v) at a precisely controlled pH (7.50 +/- 0.02, adjusted with hydrochloric acid). The flow-rate was 1.2 ml/min through a 15 cm X 4.6 mm I.D., 5-micron reversed-phase column (Ultrasphere C18 ion pair). Xanthines were extracted from serum (100 microliter) with 1 ml of acidified chloroform-isopropanol (95:5, v/v). After reconstitution in 200 microliter of mobile phase, the extracted xanthines, including theophylline, caffeine, theobromine and 1.7-dimethylxanthine, were baseline-resolved in less than 15 min. The method correlates well with a common clinical immunoassay for theophylline (EMIT Syva, r2 = 0.999) and yields excellent recovery and precision (98-101% and better than 2% at therapeutic levels, respectively). In addition, the use of the ion-pair chromatography mode eliminates many of the interferences noted in the published literature for the common reversed-phase separations of theophylline.

Two high-performance liquid chromatographic methods for quantitation of theophylline in plasma

Two high-performance liquid chromatographic methods are described for the assay of theophylline in plasma. Both allowed the separation of theophylline from the caffeine metabolites, theobromine and 1,7-dimethylxanthine. Method A, using 8-chlorotheophylline as internal standard, involved back extraction of theophylline from organic extract with 0.1 M sodium hydroxide. Method B used generally accepted solvent extraction followed by evaporation and beta-hydroxyethyltheophylline as internal standard. High-performance liquid chromatographic analyses were performed on reversed-phase phenyl columns (25 X 0.46 and 25 X 0.41 cm) using 20% methanol in 20 mM phosphate buffer at pH 5.6 for Method A and 2% acetonitrile and 8% methanol in 20 mM phosphate buffer for Method B. The column effluent was monitored at UV 273 nm. Standard curves for both Methods A and B were fitted by linear regression (r greater than 0.999) in the concentration range of 0.05-50 micrograms/ml. Either method was selective, accurate and reproducible over the concentration range 0.08-26 micrograms/ml. However, compared with Method B, Method A provided significant advantages in terms of simplicity, speed and efficiency.

Metabolic and drug profiling

Over recent years, advances in analytical technology have greatly improved our ability to study the metabolism of compounds from either endogenous or erogenous sources. The application of gas-liquid chromatography, mass spectrometry, high-performance liquid chromatography and immunological approaches are discussed in relation to the analysis of steroids, bile acids, organic acids, prostaglandins, porphyrins and bile pigments, amino acids, proteins, nucleotides, catecholamines, vitamins and drugs.