Spectrophotometric Determination and Thermodynamic Parameters of Charge Transfer Complexation Between Stavudine and Chloranilic Acid

Purpose: The official assay methods for most antiretroviral drugs are limited by cost and unavailability of good test equipment in several developing countries. Therefore, this study investigates the use of charge transfer complexation in the spectrophotometric assay of stavudine as an alternative method to conventional methods.Methods: Charge transfer complex formation between stavudine (n-donor) and chloranilic acid (Π-acceptor) in 1,4-dioxan using a spectrophotometer was employed. Thermodynamic parameters of the complex formed were determined. The proposed method was employed in the analysis of commercially available stavudine dosage form.Results: The wavelength of maximum absorption (λmax) of the complex was at 526 nm compared to 457 nm for p-acceptor alone. Beer’s law was obeyed in the range of 5 - 40 mg % while the stoichiometry of the complex was found to be 2:1. The complex formed was still stable 24 h later. Its formation was spontaneous with a ΔHo of -3.78×103 J/mol. The standard entropy change was from 12.18 ± 0.78 to 11.08 ± 1.23 cal/deg/mol over the temperature range of 30 - 60 oC while molar absorptivity decreased from 2.45×105 to 1.2×105 over the same temperature range. The assay result of the standard stavudine solution was of high accuracy with a recovery value of 99.85 ± 1.95 %.Conclusion: The proposed method is reliable and reproducible and should be suitable for the quality control of stavudine in bulk and dosage forms.Keywords: Assay, Charge transfer, Stavudine, Spectrophotometric analysis, Chloranilic acid, Thermodynamic

Hypoglycemic Activity of the Extract and Fractions of Anthocleista vogelii (Planch) Stem Bark

Purpose: To investigate the hypoglycemic effect of the methanol extract and fractions of Anthocleista vogelii stem bark.Methods: The methanol extract of A. vogelii stem bark (ME) was subjected to gradient chromatographic separation using four solvents - chloroform, ethyl acetate, acetone and water - to afford the respective fractions - CF, EF, AF and WF. ME was administered orally to normoglycemic rats at 200 and 400 mg/kg and fasting blood glucose (FBG) monitored for 6 h. Alloxan-induced diabetic rats were also treated orally with ME and the various fractions (each at 200 mg/kg and 400 mg/kg), with glibenclamide(0.2 mg/kg) and normal saline (2 ml/kg) serving as standard and control, respectively. ME and the fractions were also subjected to phytochemical analysis following standard procedures.Results: The extract possessed comparable hypoglycemic effect to glibenclamide in healthy rats. The extract and its fractions also exhibited significant (p < 0.05) antidiabetic effect. ME, CF, EF, AF and WF each at 400 mg/kg, produced maximum reduction (64.10, 38.53, 36.50, 60.77 and 12.79 %, respectively) in FBG of the animals after 6 h, compared to 53.77 % for glibenclamide. Presence of alkaloids, carbohydrates, reducing sugars, saponins, flavonoids, glycosides, steroids, terpenoids, tannins, proteins, fats and oils were observed in ME, EF and AF. Alkaloids,  flavonoids, steroids, terpenoids, fats and oil were also detected in CF while WF showed the presence of carbohydrates, glycosides, saponins and proteins.Conclusion: This study establishes the antidiabetic activity of the stem bark of A. vogelii. The acetone fraction is the most active antidiabetic fraction.Keywords: Anthocleista vogelii, Antidiabetic, Hyperglycemia, Hypoglycemia, Phytochemical analysi

Stability studies and degradation kinetics of some commercially available metronidazole suspensions in Nigeria

The present study was undertaken to investigate the effect of temperature on the degradation of metronidazole suspensions commercially available in Nigeria. Six different brands of metronidazole suspension, coded as MTZ A to MTZ F, were evaluated for their active contents using microbiological assay method. They were stored at three different elevated temperatures of 30 °C, 37 °C and 45 °C and at each temperature, the degradation rate constant was determined from a plot of logarithm of concentration versus time. The shelf-life of the various brands of the drug was predicted from Arrhenius equation and compared with their manufacturers’ label claim. Results confirmed that increase in temperature led to increase in the degradation rate constants for the various brands of the drug. The shelf-life ranged from 35.0 to 80.8 weeks for all the brands studied while the percentage of the calculated shelf -life in comparison with the label claim ranged from 29.3 % to 67.3 % of the manufacturers’ stated shelf-life. This study has shown that increase in temperature causes increased degradation of metronidazole suspensions. It may be concluded that some of the metronidazole suspensions commercially available in Nigeria may have expired long before the actual date stated on the product labels

Comparative Analysis of Imipramine Hydrochloride by UV-Spectrophotometry and Charge-Transfer Complexation

A comparative evaluation of two spectrophotometric methods for the assay of imipramine is described. The first method, based on UV spectrophotometry was compared with a second method which is based on the molecular interaction between imipramine and chloranilic acid, to form charge-transfer complexes in which the drug acts as n-donor and chloranilic acid as a π acceptor. A complete, detailed investigation of the complex formed was made with respect to its thermodynamic parameters. Good quantitative recoveries were achieved at 255 nm via UV spectrophotometry with Beer’s law being obeyed over the concentration range of 0.98-7.85 mg % for imipramine. Meanwhile, chloranilic acid was found to form a charge-transfer complex in a 1:1 stoichiometry with maximum absorption band at 526 nm. Conformity with Beer’s law was also evident over the concentration range of 1.96-19.63 mg %. Results from the evaluated thermodynamic parameters showed that the complex was more stable at lower temperatures and possessed an enthalpy change (ΔHo) of -2.902 Kcal. The method based on charge-transfer complexation has been successfully applied to the analysis of commercially available imipramine tablets without interference from the excipients. Both spectrophotometric methods proved adequate in the quantitative assay of the drug but charge-transfer complex formation via chloranilic acid gave better recoveries with higher reproducibility and precision, hence proved a superior method for routine laboratory assay of the drug