Predicting drug substances autoxidation.

PURPOSE: Chemical degradation and stability in formulation is a recurrent issue in pharmaceutical development of drugs. The objective of the present study was to develop an in silico risk assessment of active pharmaceutical ingredients (APIs) stability with respect to autoxidation. METHODS: The chemical degradation by autoxidation of a diverse series of APIs has been investigated with molecular modelling tools. A set of 45 organic compounds was used to test and validate the various computational settings. Aiming to devise a methodology that could reliably perform a risk assessment for potential sensibility to autoxidation, different types of APIs, known for their autoxidation history were inspected. To define the level of approximation needed, various density functional theory (DFT) functionals and settings were employed and their accuracy and speed were compared. RESULTS: The Local Density Approximation (LDA) gave the fastest results but with a substantial deviation (systematic over-estimation) to known experimental values. The Perdew-Burke-Ernzerhof (PBE) settings appeared to be a good compromise between speed and accuracy. CONCLUSIONS: The present methodology can now be confidently deployed in pharmaceutical development for systematic risk assessment of drug stability.

Functional identification of rat atypical beta-adrenoceptors by the first beta 3-selective antagonists, aryloxypropanolaminotetralins.

1. We have assessed the relative abilities of compounds belonging to the new aryloxypropanolaminotetralin (APAT) class and of the reference beta-adrenoceptor-blocking agent, alprenolol, to antagonize functional responses in vitro and in vivo involving atypical (beta 3) or conventional (beta 1 and beta 2) beta-adrenoceptors. 2. The range of pA2 values for three representative APATs against inhibition of spontaneous motility in the rat isolated colon by the selective beta 3-adrenoceptor agonist, SR 58611A (8.1-8.8), was well above similarly calculated values for non-competitive antagonism of guinea-pig trachea relaxation by salbutamol (beta 2, 6.5-6.9) and the atrial chronotropic response by isoprenaline (beta 1, 6.7-7.3). Alprenolol, however, was substantially more potent in antagonizing atrial (pA2, 8.2) and tracheal (pA2, 8.9) responses than SR 58611A mediated inhibition of colonic motility (pA2, 6.8). 3. Several APAT isomers with different configurations at the chiral carbons, when tested on isolated organs, presented stringent stereochemical requirements for beta 3-selectivity, including high antagonist potency-ratios between active and inactive enantiomers. 4. In vivo, the inhibition of colonic motility and the thermogenic response of brown adipose tissue elicited in rats by the selective beta 3-adrenoceptor agonists SR 58611A and BRL 37344 respectively were substantially diminished by the representative APAT, SR 59230A, at oral doses (< or = 5 mg kg-1) well below those half maximally effective (ID50) for preventing beta 1-(isoprenaline tachycardia > or = 80 mg kg-1) or beta 2-(salbutamol bronchodilatation, 44 mg kg-1) mediated responses. Alprenolol, as expected, was a less potent and nonselective antagonist of the putative beta 3-responses. 5. These findings support APATs as the first potent, orally effective selective antagonists at beta 3-adrenoceptors, and provide final unambiguous evidence that beta 3-adrenoceptors underlie inhibition of colonic motility and brown adipose tissue thermogenesis in rats.

Autoxidation of tetrazepam in tablets: prediction of degradation impurities from the oxidative behavior in solution.

The major route of degradation of tetrazepam (1) is oxidation to 7-chloro-5-(3-keto-cyclohexen-1-yl)-1,3-dihydro-1-methyl-2H-1, 4-benzodiazepin-2-one (3) via the stable 7-chloro-5-(3-hydroperoxy-cyclohexen-1-yl)-1,3-dihydro-1-methyl-2H -1, 4 benzodiazepin-2-one (2). Minor degradation products are 7-chloro-5-(1,2-epoxycyclohexan-1-yl)-1,3-dihydro-1-methyl-2H-1, 4-benzodiazepin-2-one (5) and 7-chloro-1,3-dihydro-1-methyl-2H-1, 4-benzodiazepin-2,5-dione (4), resulting from cleavage of the C-C bond between the cyclohexene ring and the benzodiazepine ring. After 48 h, AIBN (2,2'-azobis[2-methyl-propanenitrile]) in acetonitrile at 40 degrees C produced qualitatively the same impurities as those observed in the stability study of tablets of 1. Other stress tests (thermal stress at 80 degrees C, heavy metal oxidation, hydrogen peroxide, acid-catalyzed oxidation) caused qualitatively different profiles of degradation.

Reproducibility of 1H-NMR integrals: a collaborative study.

The quantitative use of NMR spectroscopy was investigated by a reproducibility study of 1H-NMR integrals involving five laboratories. A significant laboratory effect was found confirming the difficulty to obtain very precise data by integration of complex signals. The reproducibility of any NMR assay measurement, which requires a high precision should be validated by an interlaboratory study.

Autoxidation of drugs: prediction of degradation impurities from results of reaction with radical chain initiators.

In the study of the degradation of drug substances by molecular oxygen, their specific reaction mechanisms must be taken into account. The rate-determining step is usually the reaction of the substrate with a radical chain initiator, which is often an unknown impurity. The reactivity and selectivity of autoxidation can be controlled better by using a radical chain initiator, such as AIBN, than by changing the temperature or the oxygen pressure. In this paper the products profiles of four pharmaceutical substances in a simple oxidation test with AIBN are compared with the results of long term natural stability tests or with already established stabilities.