Studying the Structural Stability of Leuprolide Acetate after Releasing from Lactide-co-Glycolide Copolymer by Different Spectroscopic Methods and HPTLC

Structural stability of the entrapped leuprolide acetate (LPA) in poly(DL-lactide-coglycolide) (PLGA) was studied after in-vitro release of the drug using UV-Vis, fluorescence , circular dichroism , 1HNMR spectroscopic and HPTLC techniques . To prepare the injectable implant, 3% (v/v) of LPA was dissolved in a mixture of 33% (v/v) of PLGA (intrinsic viscosity of 0.5 dUg) in N-methyl-2-pyrrolidone (NMP) as solvent. Upon introduction of 1 g of the above mixture (containing 30 mg of LPA) into 4 mL of aqueous carbonate buffer at pH 7.2, NMP diffuses out from the matrix causing the polymer to precipitate . Release of the drug into 4 mL of the fresh buffer solution at 37°C was measured every 24 h for one month. The UV-Vis and intrinsic fluorescence spectra of the solutions were recorded right after collection. Then, the release media were lyophilized and studied by 1H NMR spectroscopy. Although a clear interpretation of the CD spectra was faced to some ambiguities, the first derivative of the UV-Vis spectra and the results of fluorescence studies indicated that the tertiary structure of the peptide had suffered litlie destruction during its stay in PLGA. 1H NMR studies of the released medicine showed no change in the peptide primary structure . HPTLC analysis of the release medium showed one band with similar Rf to the original sample of LPA. The collected results indicate that the entrapped LPA suffers no structural changes during its stay in polymer formulation and remains stable during the first 24 h of release .