Investigation of penbutolol-iron (III) complex and its spectrophotometric determination in tablets.

It has been established that penbutolol reacts with iron(III) chloride in the presence of ammonium thiocyanate to form a pink complex (2:1) that is soluble in chloroform with a maximum absorbance at 478 nm. By application of the methods of Sommer and Job involving non-equimolar solutions, the conditional stability constant (log k') of the complex at the optimum pH of 1.5 +/- 0.02 and an ionic strength of (mu) 0.14 M, was found to be 5.769. The molar absorptivity at 478 nm was 136 1 mol-1 cm-1 at pH 1.5 +/- 0.02. The validity of Beer's law has been tested in the concentration range 3-18 x 10(-4) M; the relative standard deviation (n = 8) was 1.52-3.21%. The proposed method was found to be suitable for the accurate, simple and rapid analysis of penbutolol in the bulk drug and in tablets.

Liquid-chromatographic determination of penbutolol and its principal metabolites in plasma and urine.

We describe a sensitive, specific liquid-chromatographic determination of penbutolol and its 4-hydroxy metabolite in plasma and urine. The method involves a simple organic extraction, evaporation of the solvent, reconstitution in methanol/water, and injection into the chromatograph. Penbutolol, its metabolites, and the internal standard, propranolol, are resolved on a CN reversed-phase column and detected fluorometrically. Conjugates of penbutolol and its 4-hydroxy metabolite may be determined after a 2-h enzymic hydrolysis. Detection limits are in the range of 3 to 12 micrograms/L of plasma. The assay is reproducible and nearly free of interferences. Representative concentrations in blood and urine of normal volunteers are reported.

Physico-chemical and anlytical studies of penbutolol.

In the present paper physico-chemical and analytical studies on penbutolol sulfate (Hoe 893d) are reported. In addition to an interpretation of ultraviolet and fluorometric spectra, data are given regarding the dissociation constant, solubility, distribution, and protein binding. The substance and its major metabolte, as well as their glucuronides, are detectable by means of a selective fluormetric method. Moreover, mention is made of the results of a human pharmacokinetic study.