Stability of Cycloserine in Buffered Aqueous Solutions

Mycobacterium tuberculosis survival and biofilm formation studies: effect of D-amino acids, D-cycloserine and its components

D-amino acids play an important role in cell wall peptidoglycan biosynthesis. Mycobacterium tuberculosis D-amino acid oxidase deletion led to reduced biofilm-forming ability. Other recent studies also suggest that the accumulation of D-amino acids blocks biofilm formation and could also disperse pre-formed biofilm. Biofilms are communities of bacterial cells protected by extracellular matrix and harbor drug-tolerant as well as persistent bacteria. In Mycobacterium tuberculosis, biofilm formation or its inhibition by D-amino acids is yet to be tested. In the present study, we used selected D-amino acids to study their role in the prevention of biofilm formation and also if D-cycloserine's activity was due to presence of D-Serine as a metabolite. It was observed that D-serine limits biofilm formation in Mycobacterium tuberculosis H37Ra (Mtb-Ra), but it shows no effect on pre-formed biofilm. Also, D-cycloserine and its metabolic product, hydroxylamine, individually and in combination, with D-Serine, limit biofilm formation in Mtb-Ra and also disrupts existing biofilm. In summary, we demonstrated that D-alanine, D-valine, D-phenylalanine, D-serine, and D-threonine had no disruptive effect on pre-formed biofilm of Mtb-Ra, either individually or in combination, and D-cycloserine and its metabolite hydroxylamine have potent anti-biofilm activity.

Initial characterization of D-cycloserine for future formulation development for anxiety disorders

The purpose of this study is to characterize D-cycloserine (DCS) physicochemical properties to facilitate future formulation development of DCS for anxiety disorders. A stability-indicating HPLC assay method for the quantitation of DCS was developed and calibrated to be used for this study. The partition coefficient was determined and compared with the predicted value. The solution stability of DCS was studied under various pH (2.0-11.5) and ionic strengths of 10 and 20 mM at physiological temperature of 37°C. The 250 mg capsule was compounded to the nominal strength of 50 mg used for anxiety disorders. These capsules were then put under stability. The in vitro dissolution was also carried out at 37°C as per the United States Pharmacopeia (USP) guidelines. The partition coefficient value (Kp) determined for the DCS was log Kp = -2.89 ± 0.06 (n = 6). The pH-solution stability profile shows that DCS has maximum stability under alkaline conditions. The maximum rate of degradation was seen at pH of 4.7. The mean percent recovery of DCS from the capsules compounded to strength of 50 mg was 100.3 ± 1.4. The stability study of the reformulated capsules concluded that reformulated DCS is stable for at least one year at room temperature. The in vitro dissolution illustrates that all the DCS is released from the capsules in 10 min. The present characterization of DCS study will serve as guidance for the future directions regarding the reformulation of DCS in order to be used in anxiety disorders.

Solvent effects on chemical processes. 8. Demethylation kinetics of aspartame in binary aqueous-organic solvents

The kinetics of demethylation of aspartame were studied in binary aqueous-organic solvent mixtures at 25 degrees C under two solution conditions, namely 1.0 M HCl (pH 0.28 in water) and carbonate buffer (pH 10.1 in water). Under these conditions solvent effects on the acid dissociation constants of aspartame do not complicate the interpretation of the kinetics. The organic cosolvents were acetone, acetonitrile, dimethyl sulfoxide, dioxane, tetrahydrofuran, and methanol. The observed kinetic solvent effects were modest in magnitude, not exceeding a factor of 3 in rate constant, relative to the fully aqueous solution. The rate changes included both increases and decreases, and in some solvent mixtures extrema were observed. It is concluded that at least two contributory factors, identified as an electrostatic (dielectric constant) effect and a solvation effect, must be operating to produce the observed kinetic solvent effects.

Clinical pharmacokinetics of the antituberculosis drugs

The quantitative aspects of the disposition in man of 12 antituberculosis drugs [isoniazid, rifampicin, (rifampin), ethambutol, para-aminosalicylic acid, pyrazinamide, streptomycin, kanamycin, ethionamide, cycloserine, capreomycin, viomycin and thiacetazone] are reviewed. Isoniazid appears to be the only agent for which plasma concentrations and clearance are related to hereditary differences in acetylator status and for which there is an appreciable 'first-pass' effect. Recent data cast doubt on the suggestion that isoniazid may be more hepatotoxic for rapid as opposed to slow acetylators. Continuous administration of rifampicin leads to induction of enzymes in the liver with a concomitant decrease in maximum plasma concentrations, the time required to achieve this level, elimination half-life, and area under the plasma concentration-time curve (AUC). Coadministration of para-aminosalicylic acid leads to increases in the serum concentrations and elimination half-life of isoniazid. With a few exceptions, the metabolites of the antituberculosis drugs are devoid of antimicrobial activity; the exceptions are 25-desacetylrifampicin which accounts for approximately 80% of the drug's antimicrobial activity in human bile, the acetylated and glycylated metabolites of para-aminosalicylic acid, and the sulphoxide metabolites of ethionamide. The effect of renal impairment is relatively unimportant for the excretion of isoniazid, rifampicin and para-aminosalicylic acid, but the elimination half-life of streptomycin increases to 100 hours when the blood urea nitrogen level is greater than 100mg/100ml, and ototoxicity is strikingly more frequent. In states of malnutrition, such as kwashiorkor, the protein binding of para-aminosalicylic acid decreases from 15% to essentially zero and in the case of ethionamide and streptomycin binding decreases by 6% and 16% respectively. Of the data concerning age-related effects, most notable are the prolonged elimination half-life of isoniazid in neonates (up to 19.8 hours), and the lower peak serum concentrations of rifampicin in children of one-third to one-tenth those of adults following a similar dose on a weight basis. For kanamycin, the maximum plasma concentration varies inversely with age but is not influenced by birthweight; however, the clearance is directly dependent upon birthweight and postnatal age. For the elderly, age is an insignificant factor for the elimination of isoniazid when compared with young adults of similar acetylator status, and the metabolism of rifampicin may be considered globally unaltered in this age group.(ABSTRACT TRUNCATED AT 400 WORDS)