The objective of this study was to develop long-acting injectable dosage forms of Orntide, a peptide GnRH antagonist, to provide tailored release for 6-month duration. Using a polylactide homopolymer and the solvent extraction/evaporation method, three microsphere formulations (Formulations A, B, and C) were prepared at various drug loadings (11.85–15.79%). The microspheres were characterized for particle size by laser diffractometry, surface morphology by scanning electron microscopy (SEM), and bulk density by tapping, as well as long-term in vitro drug release, mass loss and hydration at 37°C, and short-term in vitro drug release at elevated temperatures (51–59°C). Experiments at 37°C revealed that drug release was triphasic and occurred due to slow degradation of the polylactide polymer. Short-term in vitro release results indicated that drug release was diffusional. Application of the Higuchi equation to short-term release confirmed the temperature dependency of the diffusional rate constant. Using the rate constant and the Arrhenius equation, an Ea value of 45 kcal/mol (Formulation A) and approximately 25 kcal/mol (Formulations B and C) was obtained for diffusional release. Study results suggest that by selection of an appropriate biodegradable polymer, injectable dosing forms that release drug for 6 months or longer can be developed.

01 Mar 2004·AAPS PharmSci

Assessment of fertility in male rats after extended chemical castration with a GnRH antagonist

Article

Author: Susan S. D'Souza ; Santos B Murty ; Wei Qiu ; Patrick P DeLuca ; Francesca Selmin ; BC Thanoo

The purpose of this study was to assess whether male rats whose testosterone levels were suppressed to castration levels (<0.5 ng/mL) for a 1-year period by the sustained delivery of orntide acetate, a GnRH antagonist, would return to fertility (ie, produce offspring) after serum testosterone returned to control levels. Male rats comprising a treatment group (orntide microspheres, dose = 27 mg/kg/y), a vehicle control group, and a control group of proven male breeders were used. For the treatment and vehicle control groups, serum orntide and testosterone levels were monitored at periodic intervals for 14 months from the initiation of treatment. After serum testosterone levels returned to vehicle control levels and orntide serum levels were no longer discernible for the treated group, each of the animals was housed with 2 drug-naive, female, proven breeders. All the breeder females produced offspring with the exception of 1 female housed with a male rat from the treatment group and the 2 females housed with a single male rat from the vehicle control group. The mean size and weight of the litters from each group were not statistically different. Further, fertility of the offspring from each group was assessed. The male and female offspring studied were all shown to be fertile. The results suggest that lack of fertility due to testosterone suppression in male rats is reversible after cessation of treatment with the GnRH analog, orntide.

01 Nov 2002·Journal of Pharmacy and PharmacologyQ3 · MEDICINE

Poly(L-lysine) as a model drug macromolecule with which to investigate secondary structure and microporous membrane transport, part 2: diffusion studies

Q3 · MEDICINE

Article

Author: Velde, David G Vander ; Mitra, Ashim K ; Salamat-Miller, Nazila ; Alur, Hemant H ; Chittchang, Montakarn ; Johnston, Thomas P

AbstractPeptide drugs are hydrophilic in nature and so their preferred pathway of membrane transport is by the paracellular route, which primarily involves passive diffusion across intercellular pores. The objective of the present study was to investigate the effect of secondary structure on the aqueous diffusion of a model polypeptide, poly(l-lysine), through a microporous membrane. The primary aim was to systematically evaluate the variables (e.g. viscosity and/or hydrodynamic radius) that may contribute to the difference, if any, in the calculated values of the aqueous diffusion coefficient (Daq) for each conformer of poly(l-lysine). Variations in pH and temperature of the medium were used to induce secondary structural changes in poly(l-lysine). Transport studies were conducted for 3 h at 25 or 37°C using side-by-side diffusion cells. Hydrophilic microporous polyester membranes with a 1-μm pore diameter were used to measure the free diffusion of each conformer. The values for the apparent permeability (Papp) and Daq were calculated using standard equations. The viscosity of each conformer solution was determined and the hydrodynamic radius of each conformer was then estimated. At 25°C, both Papp and Daq of the α-helix conformer were approximately the same as those of the random coil conformer. In contrast, at 37°C, the Papp and the Daq of the β-sheet conformer were significantly (P < 0.05) less than those of the random coil conformer. At 25°C, the solutions containing primarily either the random coil or the α-helix conformers had approximately the same viscosity. On the other hand, at 37°C, the solutions containing the β-sheet conformer had a significantly (P < 0.05) higher viscosity than when this conformer was absent. The random coil and the α-helix conformers appeared to have comparable sizes, whereas the hydrodynamic radius estimated for the β-sheet conformer was significantly (P < 0.05) larger than those for the other two conformers. In summary, changing the secondary structure of poly(l-lysine) from the random coil to the α-helix did not affect its Papp and intrinsic Daq. On the other hand, appearance of the β-sheet conformer significantly decreased the values of Papp and Daq. The differences appeared to result from the significantly higher solution viscosity as well as the extended structure associated with the β-sheet conformer of poly(l-lysine). This strategy may represent a potential mechanism to sustain the delivery of therapeutic peptide drugs from a controlled drug delivery device.

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