Katsuyoshi Uchino

Selective high-performance liquid chromatographic method for the determination of glycyrrhizin and glycyrrhetic acid-3-O-glucuronide in biological fluids: application of ion-pair extraction and fluorescence labelling agent.

A selective high-performance liquid chromatographic method has been developed for the simultaneous determination of glycyrrhizin and glycyrrhetic acid-3-O-glucuronide in biological fluids of the rat. The procedure is based on the ion-pair formation using tetra-n-amylammonium bromide, extraction with ethyl acetate-n-heptane from the salt-saturated aqueous phase, labelling with 4-bromomethyl-7-methoxycoumarin, followed by chromatographic separation with fluorescence detection. Glycyrrhizin in plasma, bile and urine could be precisely determined in concentrations as low as 1, 1 and 2.5 micrograms/ml, respectively, in a 0.1-ml sample. The equivalent values for the glucuronide were 1, 2.5 and 2.5 micrograms/ml, respectively. The method is applicable in pharmacokinetic studies of glycyrrhizin in small animals.

Estimation of plasma unbound phenobarbital concentration by using mixed saliva.

Summary: Relationships among plasma total (Ct), plasma protein unbound (Cf) and mixed salivary (Cs) concentrations of phenobarbital (PB) were studied in 29 epileptic patients. A highly significant correlation was observed between C, and Cf. Although a significant correlation was observed between Cf and Cs, Cs/Cf ratio was only 0.63. When Cs was corrected by using pKa (7.41) and pH of saliva to estimate free PB concentration (Cest f), a highly significant correlation was obtained between Cf and Cestf, and Cest f/Cf ratio was 0.96. The temporal course of Cest f obtained from Cs after an oral single dose of 50 mg PB in a healthy adult male volunteer was approximated as a triexponential equation. The peak time was 2 hr after ingestion and apparent half‐life was 66 hr. The prediction of minimum concentrations at steady state on the basis of these parameters corresponded well with actually obtained Cest f following repetitive administration of PB.

Quantitative determination of furosemide in plasma, plasma water, urine and ascites fluid by high-performance liquid chromatography

A high-performance liquid chromatographic method using spectrofluorometric detection is described for the determination of furosemide in plasma, plasma water, urine and ascites fluid. The extraction procedure decreases interference from endogenous substances. The detection limit of furosemide is 10 ng in 0.5 ml of biological sample. The method is sufficiently sensitive for pharmacokinetic study of furosemide with normal subjects and patients with liver cirrhosis and/or renal disease after oral administration of furosemide in a retard capsule, and for study of protein binding of furosemide in patients with various diseases.

Quantitative determination of propranolol in plasma and plasma water from normal subjects and patients with angina pectoris by high-performance liquid chromatography

A precise and sensitive high-performance liquid chromatographic method using a column packed with porous polystyrene gel is described for the determination of propranolol in plasma and plasma water from normal subjects and patients with angina pectoris. Propranolol in the samples was extracted with an n-heptane-isoamylalcohol (98.5:1.5) mixture after addition of penbutolol used as an internal standard. The extracts were chromatographed and detected with a spectrofluorophotometer. The quantitative limit of propranolol was 1 ng using 1 ml of plasma or 0.5 ml of plasma water. The present method should be useful for monitoring propranolol concentrations in plasma and plasma water during drug therapy and for pharmacokinetic study of propranolol.