Applications of high-voltage paper electrophoresis for the characterization of drug metabolites

Analysis of salbutamol enantiomers in human urine by chiral high-performance liquid chromatography and preliminary studies related to the stereoselective disposition kinetics in man

Enantiomers of salbutamol, extracted from human urine, were successfully separated and quantitated by high-performance liquid chromatography with electrochemical detection. This direct resolution was accomplished using a chiral alpha 1-acid glycoprotein column (EnantioPac) maintained at 0 degrees C and a mobile phase consisting of a 0.1% (v/v) triethylamine in 5.3 mM citrate buffer, pH 7.2. An amperometric detector incorporating a glassy carbon electrode was employed for detection. The between-day coefficients of variation for the determination of R(-)- and S(+)-salbutamol in human urine were 4.1 and 4.7%, respectively, at a drug level of 1.0 microgram/ml. The urinary excretion ratio of the biologically active (-)-isomer to (+)-isomer in one healthy subject who received an intravenous dose of racemic salbutamol (1.0 mg) decreased continuously over a 12-h period. A similar excretion pattern exhibiting a far more extensive distortion in the enantiomeric ratio was found in three subjects dosed with a single 4-mg tablet of racemic salbutamol.

Drug level monitoring of antiasthmatic drugs

In general assays pertaining to drug level monitoring (DLM) of antiasthmatic agents (except theophylline), published during the period 1978-1983, used mostly high-performance liquid chromatographic (HPLC) methodology (approximately 45%) with mass spectrometric (MS) based assays in second place (approximately 30%) followed by immunochemical techniques (approximately 25%). Whenever nanogram or subnanogram antiasthmatic drug concentrations had to be measured such as for the adrenergic stimulants or for the prophylactic agents, then both HPLC-and MS-based methodologies were employed with about equal frequency. The trend in DLM for the phosphodiesterase inhibitor class (theophyllines) seemed to be shifting towards the HPLC methodologies. In part, this was justified by the need for improved selectivity. This criterion appears to have been better satisfied by HPLC, but for all practical purposes the immunochemical methods are and will probably continue to prevail in the clinical laboratory setting until HPLC procedures become truly automated. In the case of DLM of corticosteroids used for the asthmatic, the situation is in our opinion still unclear. This is caused by the presence of endogenous corticosteroids and metabolites, the levels of which in man are known to vary. The current immunochemical procedures offer a facile but less selective option. The future for selective routine corticosteroid assays may well be in HPLC or gas chromatography coupled with MS.

Ranitidine hydrochloride

Ranitidine is a selective, competitive histamine H2-receptor antagonist recently approved by the Food and Drug Administration for use in the short-term treatment of active duodenal ulcers and gastric hypersecretory conditions. Ranitidine is four to ten times more potent than cimetidine on a molar basis in inhibiting stimulated gastric acid secretion. Clinical studies have demonstrated that ranitidine is as effective as cimetidine and is similarly well tolerated. Based on available literature (approximately 700 publications), this article reviews the pharmacology, safety profile, and clinical efficacy of ranitidine in duodenal ulcers and gastric hypersecretory conditions.