Lipid microparticles as sustained release system for a GnRH antagonist (Antide).

Lipid microparticles (LMs) as a sustained release system for a gonadotropin release hormone (GnRH) antagonist (Antide) were prepared and evaluated. Antide loaded microparticles (Antide-LMs) were obtained by a cryogenic micronization process starting from two different monoglycerides (glyceryl monobehenate and glyceryl monostearate) and using two different incorporation methods (co-melting and solvent evaporation). Antide-LMs, 2% (w/w) loading, were characterized for drug incorporation by RP-HPLC, particle size by laser diffractometry and surface morphology by scanning electron microscopy. In vitro peptide release and in vitro biological activity were also studied. Serum Antide and testosterone levels, as pharmacodynamic marker, were assessed following subcutaneous administration in rats. Antide-LMs showed a mean diameter of approximately 30 micro m and variable Antide release depending on lipid matrix and incorporation method. In vivo experiments demonstrated that detectable Antide plasma levels were present, in the case of Antide-LMs based on Compritol E ATO obtained by co-melting procedure, for at least 30 days after dosing. Testosterone levels were consistent with prolonged pharmacokinetic profiles. In vitro release of Antide from LMs correlated well with the in vivo release. In conclusion, LMs can sustain the release of Antide for at least 1 month. The levels of the initial 'burst' and the extent of the pharmacodynamic effect can be influenced by the lipid characteristics and by process conditions.

Kinetics and mechanism of chlorine exchange between chloramine-T and secondary amines.

The kinetics and mechanisms of chlorine transfer from chloramine-T (CAT) to several amines are second order and independent of p-toluenesulfonamide concentration; thus, the reaction does not involve disproportionation of CAT to dichloramine-T. From the profile of pH versus rate, the following mechanisms were proposed: (1) reaction of the ionized species of CAT with the ionized amine (ionic mechanism) and (2) reaction of the un-ionized species of CAT with the un-ionized amine (nonionic mechanism). The second-order, pH-independent rate constants calculated for the ionic and nonionic mechanisms were 1.6 and 5 x 10(6) M-1 s-1, respectively. Although these two mechanisms are kinetically indistinguishable, the rate constant for the nonionic mechanism is of the same order of magnitude as those calculated for similar chlorination reactions involving nonionizable chloramines, such as N-chlorosuccinimide, N-chloroquinuclidine, and N-chloro-N-methylbenzenesulfonamide. The proposed mechanism for the chlorine exchange involves a molecule of water in a cyclic, six-membered transition state.

Structure-activity considerations in kinetics and mechanism of chlorine exchange between chloramine-T and secondary amines.

To study the mechanism of N-chlorination of secondary amines by chloramine-T, the kinetics of the reactions of some aromatic-substituted analogues of N-chlorobenzenesulfonamide with various secondary amines were determined. The importance of amine basicity and reactivity of the N-Cl bond of the N-chlorobenzenesulfonamide was also assessed. The results indicate that a mechanism involving the un-ionized species of both reactants (i.e., a molecular mechanism), rather than an ionic mechanism, is operating and that the reaction most likely proceeds via a six-membered-ring transition state that incorporates a water molecule.

S-acylation of cysteine by O-acetylsalicylic anhydride: a possible mechanism for aspirin hypersensitivity?

In order to elucidate the possible reaction pathways for the acylation of protein by O-acetylsalicylic anhydride, the mechanism of the reaction between L-cysteine and O-acetylsalicylic anhydride was studied. O-Acetylsalicylic anhydride reacts with L-cysteine via a consecutive kinetic pathway. The thiol anion first reacts with the anhydride to form an intermediate thiol ester which then undergoes an intramolecular rearrangement to form the stable N-(O-acetylsalicyloyl)-2-amino-3-thiopropionic acid, 5. The importance of the free amino group in the intramolecular reaction was established by the observed stability of the S-(O-acetylsalicyloyl) derivative of N-acetylcysteine under similar reaction conditions. The formation of the thiol ester was pH dependent, suggesting that the thiol anion was the attacking species. The acyl transfer to the adjacent amino group was catalyzed by both phosphate and acetate buffers. The results suggest that the reaction of O-acetylsalicylic anhydride with the thiol-containing amino acids of a protein molecule may proceed via formation of an initial thio ester, followed by an S to N intramolecular acyl transfer to form an immunogenic amide.