Development and validation of a hydrophilic interaction liquid chromatography with tandem mass spectrometry method for the simultaneous detection and quantification of etilefrine and oxilofrine in equine blood plasma and urine.

A sensitive hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry method was developed and validated for the simultaneous detection and quantification of etilefrine and oxilofrine in equine blood plasma and urine. The method is highly sensitive and specific with good precision and accuracy. In plasma the limit of detection and limit of quantification are 0.03 and 0.1 ng/mL, respectively, for both analytes. In urine the limit of detection and limit of quantification are 0.3 and 1 ng/mL, respectively, for both analytes. The suitability of the method for doping control analysis in equine species is demonstrated by analyzing postadministration samples collected after a single intravenous administration of 50 mg etilefrine to a standardbred mare. Etilefrine was detected up to 120 h in urine and up to 48 h in plasma. Etilefrine is highly conjugated in equine urine whereas it exists in the free form in equine plasma. Therefore, enzyme hydrolysis prior to sample preparation is recommended for the detection and quantification of etilefrine and oxilofrine in equine urine.

Determination of phenolic sympathomimetic drugs in pharmaceutical samples and biological fluids by flow-injection chemiluminescence.

A rapid and highly sensitive flow-injection chemiluminometric method was developed for determination of 3 sympathomimetic drugs, namely, etilefrine hydrochloride, isoxsuprine hydrochloride, and prenalterol hydrochloride. The method is based on chemiluminescence induced by oxidation of drugs with acidified potassium permanganate in the presence of formic acid as a carrier. The calibration graphs were linear over the concentration ranges 0.2-9, 0.2-12.5, and 0.025-1.25 microg/mL for the 3 compounds, respectively. The method was applied successfully in determining the drugs in dosage forms and in biological fluids. A proposal for the reaction pathway is suggested.

Pharmacokinetic comparison of etilefrine to its prodrug, the stearic acid ester of etilefrine.

The relative bioavailability of a prodrug of etilefrine, its stearic acid ester, was determined by means of plasma levels and renal excretion. The comparison of the plasma levels and renal excretion was carried out in a cross-over design in six subjects. 3H-etilefrine (20 mg) and 3H-2-etylamino-1-(3-stearoylphenyl)ethanol hydrochloride (44.42 mg) were administered orally in equimolecular amounts. The stearic acid ester of etilefrine does not appear in the blood; the ester is split even during absorption. The relative bioavailability of the stearic acid ester of etilefrine, which was determined from the comparison of the areas under the plasma level and the renal excretion, amounts to 51% related to etilefrine. The investigation of the renal excretory products after administration of etilefrine and its prodrug showed the same metabolic pattern. The sulfuric acid ester of etilefrine is the main metabolite. In addition to etilefrine, two basic metabolites are excreted. According to mass- and NMR-spectrometric findings, these two metabolites are two isomeric tetrahydroisoquinolines which formally developed by condensation of etilefrine with formaldehyde. These tetrahydroisoquinolines are excreted free and conjugated with sulfuric acid.