Robustness of barrier membrane coated metoprolol tartrate matrix tablets: Drug release evaluation under physiologically relevant in vitro conditions

Robust in vitro drug release behavior is an important feature of extended release (ER) hydrophilic matrix formulations for accurate prediction of in vivo drug release. In this study, ER hydrophilic matrix tablets of metoprolol tartrate were formulated using a high viscosity grade of hypromellose as a rate-limiting polymer. Expectedly, this formulation showed an undesirable initial burst release followed by controlled drug release. Application of a barrier membrane (BM) coating of ethylcellulose with a pore former (hypromellose) resulted in the elimination of the burst effect. The aim of this study was to investigate the robustness of in vitro metoprolol release from BM-coated hydrophilic matrix tablets by simulating the physicochemical properties of gastrointestinal fluids and mechanical stress in the fasted- and fed state human gastrointestinal (GI) tract. Uncoated and BM-coated matrices were subjected to various dissolution studies simulating the varying pH conditions and additional physicochemical parameters, and the mechanical stress that can be caused by GI motility during both fasted and fed state GI passage. The BM-coated formulation showed robust drug release without an initial burst in all test scenarios. BM-coated matrix formulations thus represent a very promising approach for obtaining a highly controlled and robust drug release from oral ER formulations.

Effect of oxovanadium(IV) complexes on nondiabetic and streptozotocin-diabetic rats

The effects of vanadium complexes with organic ligands, [VO(phen)2]SO4.3H2O, [VO(bpy)2]SO4.2H2O, and [VOCl2(Hmcp)2H2O], on blood glucose and plasma lipid levels were studied in nondiabetic and streptozotocin-diabetic rats and compared to that of [VO(mal)2] (the reference compound). The present results provide evidence that the compounds examined possess lower toxicity than [VO(mal)2]. One of the compounds examined, viz. [VO(bpy)2]SO4.2H2O, decreases, statistically significantly, the glucose level and a second one, viz. [VOCl2(Hmcp)2H2O], decreases, also significantly, the total cholesterol level.

Insulin-like effects on liver Golgi membrane preparations of bis(oxalato)oxovanadate(IV) complex ion, a new vanadate compound

Recent studies have shown the insulin-like effect of vanadyl sulphate or sodium ortho (or meta-)vanadate administered orally to rats. Toxicity of these drugs and reluctance by the animals to drink the solutions and take food, concerning the amelioration of some diabetes syndrome discussed in 1994 by Domingo et al. (1), McNeill et al. (2) and Wiliams and Malabu (3), prompted us to investigate a new vanadate complex: disodium bis(oxalato)oxovanadate (IV), Na2[VO(OX)2]H2O. The main object of the experiment was to study whether this complex administered as 3 mmol/l solution in 0.5% NaCl during 7 days could act on the subcellular level and influence the activity of liver Golgi membrane galactosyltransferase activity. Free blood sugar level was lowered (but was still higher than in the control group) in diabetic rats after seven days of vanadate action and was accompanied by lowered, however not statistically significant, serum triglyceride levels. The yields of isolated Golgi-rich membrane fractions were about half of the level in diabetic groups (untreated and treated with vanadium) compared with the control groups. Purity of these membrane fractions, expressed as nmol Gal transferred per mg of proteins and per h, was the same in four groups investigated and showed the possibility to compare them. Activity of galactosyltransferase calculated in nmol Gal transferred per 1 g of liver and per 1 h or per whole liver in the same time (as a possibility of glycosylation of the secretory and membrane glycoproteins) was lower in both diabetic groups. However, after vanadium treatment (D+V group), the activity was higher than in untreated diabetic rats (D group) in three of five investigated animals. Vanadyl-oxalate complex did not normalize in a statistically significant manner the enzyme activity which was significantly lower in diabetes than in control. This is similar to insulin influence on the galactosyltransferase activity reported previously by Kaczmarski et al. in 1981 (4) and Kordowiak et al. in 1981 (5).