Extractionless method for the simultaneous high-performance liquid chromatographic determination of urinary caffeine metabolites for N-acetyltransferase 2, cytochrome P450 1A2 and xanthine oxidase activity assessment.

Urinary metabolic ratios of caffeine are used in humans to assess the enzymatic activities of cytochrome P450 isoenzyme 1A2 (CYP1A2), xanthine oxidase (XO) and for phenotyping individuals for the bimodal N-acetyltransferase 2 (NAT2), all of them involved in the activation or detoxification of various xenobiotic compounds. Most reported analytical procedures for the measurement of the urinary metabolites of caffeine include a liquid-liquid extraction of urine samples prior to their analysis by reversed-phase HPLC. At neutral to basic pH however, 5-acetylamino-6-formylamino-3-methyluracil (AFMU), a metabolite of caffeine, spontaneously decomposes to 5-acetylamino-6-amino-3-methyluracil (AAMU).

Validation of an HPLC method for the determination of urinary and plasma levels of N1-methylnicotinamide, an endogenous marker of renal cationic transport and plasma flow.

N1-Methylnicotinamide (NMN) is an endogenous cationic metabolite of nicotinamide (niacine, vitamine PP) whose renal clearance reflects both the capacity of the renal tubular transport system to secrete organic cations and renal plasma flow. NMN is present in human plasma and urine at the 1-117-ng ml(-1) and 0.5-25-microg ml(-1) concentration range, respectively, and its level depends notably on pathophysiological (age, renal or hepatic diseases) conditions.

The mobile order solubility equation applied to polyfunctional molecules: The non-hydroxysteroids in aqueous and non aqueous solvents.

The solubility equation for real solutions derived from the thermodynamics of mobile order in liquids is used to predict the solubility of non-hydroxysteroids in water and in common polar and nonpolar organic solvents. Strictly obtained on a thermodynamic basis, the model allows not only correct predictions of the solubilities from the knowledge of a limited number of characteristics of solutes and solvents, but also enables a better understanding of the solution process and of the factors that determine solubility. Some practical rules are derived which might help to orient the choice of a solvent for liquid pharmaceutical forms.