Sustained-release oral delivery of theophylline by use of polyvinyl alcohol and polyvinyl alcohol-methyl acrylate polymers.

Crystalline polyvinyl alcohol (PVA) polymer and low-crystallinity polyvinyl alcohol-methyl acrylate copolymer (PVA-MA) were examined as sustained-release tablet excipients with theophylline as a model drug. By blending of different proportions of the crystalline polymer and the low-crystallinity copolymer, it was possible to affect the release characteristics of the tablets. Tablets made with crystalline PVA provided instant release of theophylline in vitro. Tablets made with a larger proportion of PVA-MA relative to PVA provided a very prolonged release profile in vitro. A formulation containing PVA-MA:PVA:theophylline in a ratio of 1:9:10 provided sustained-release profiles in vitro and in vivo in dogs. The dissolution release profile of this PVA-blend tablet formulation in vitro agreed extremely well with the percentage of bioavailable dose absorbed over time in vivo. The formulation provided a plateau of levels in plasma over 16 h. The oral bioavailability of theophylline from this formulation in dogs was approximately 80% and was equivalent to that obtained after administration of Theo-Dur, a marketed extended-release theophylline tablet from Key Pharmaceuticals.

Parenteral formulation of the kappa agonist analgesic, DuP 747, via micellar solubilization.

The nonopioid kappa agonist analgesic amine, DuP 747, as a hydrochloride salt exhibited an aqueous solubility of 3 mg/ml. This solubility was insufficient to provide the desired dose in a solution formulation for intramuscular administration. Aqueous solutions of the hydrochloride salt exerted surface activity behavior; however, the critical micellar concentration (CMC) was not reached at the saturation solubility. Enhanced aqueous solubility required to reach the CMC could lead to micellization of the compound and a possible i.m. solution formula. The methanesulfonate salt was more water soluble than the hydrochloride salt and yielded a micellar solution with a concentration of 60 mg/ml.

Hollow fibers as an oral sustained-release delivery system using propranolol hydrochloride.

Fibers were spun by the downward configuration of the wet spinning technique. This configuration is capable of encapsulating nonspherical and/or coarse particles. We examined encapsulation of propranolol hydrochloride and the ability of the fibers to act as a sustained-release delivery system for propranolol hydrochloride as a model drug. The U.S.P. basket dissolution method was used to evaluate the in vitro drug release kinetics and the effect of the aspect ratio (length/diameter) on drug release. For in vivo evaluation, selected fibers were administered to dogs in gelatin capsules. The results of these in vitro and in vivo studies were compared to those obtained with a marketed sustained-release propranolol product (Inderal LA). The fiber delivery system provided a sustained-release profile of plasma propranolol concentrations similar to that observed with Inderal LA.

Polyvinyl alcohol-methyl acrylate copolymers as a sustained-release oral delivery system.

Low crystalline and crystalline polyvinyl alcohol-methyl acrylate (PVA-MA) copolymers were examined, because of their excellent flow and compressibility properties, as matrices for sustained-release tablets using phenylpropanolamine hydrochloride (PPA.HCl) as a model drug. Crystallinity of the copolymer affected the release characteristics from the tablet. Tablets made with low-crystalline PVA-MA provided sustained release of PPA, both in vitro and in vivo in dogs. PPA absorption from the low-crystalline PVA-MA tablet formulation was biphasic. An initial rapid phase was followed by a second, slower absorption phase which continued over 16 hr. Plasma PPA concentrations then declined with a half-life roughly parallel to the oral immediate-release half-lives. Oral bioavailability from the low-crystalline PVA-MA tablet formulation was 78.8 +/- 3.9%.

Enhancement of ampicillin partition behavior.

Several ion-pair or adduct forming additives tha" enhanced ampicillin partition behavior were identified and evaluated. At pH 3, picric acid and trichloroacetic acid increased the ampicillin aqueous-octanol partition coefficient 250 and 30 times, respectively. At pH 7, quaternary compounds gave the most significant increases in the partition coefficient. Values for an aqueous pH 7 chloroform system increased from zero in the absence of additives to 2.28, 1.86, 1.82, and 1.70 for equimolar amounts of benzalkonium, tetraheptylammonium, benzethonium, and cetalkonium chlorides, respectively. Extraction of ampicillin from aqueous pH 7 solution was possible by adding a quaternary agent in an equimolar amount. However, extraction of ampicillin from plasma required large molar excesses. Tetraheptylammonium chloride was added at a molar concentration 10(3) times greater than that of the ampicillin. Plasma samples spiked at the 3-microgram/ml level gave 93% recovery (CV 6.7%, n = 16) when extracted three times. The extracts were quantitated by TLC.

Determination of aqueous solubility and pKa values of estrogens.

Reported estrone pKa and solubility data show wide variation. Improved experimental procedures were designed and used to obtain reproducible results. The pKa values for several estrogens and related compounds also were determined to assess the effects of structural differences on ionization. No evidence was obtained for long-range D to A ring electronic transmission affecting pKa. Significant differences in pKa values resulted only when conjugated unsaturation was added into the B ring of estrone or estradiol. The aqueous solubilities of estrone and 17alpha-estradiol were 0.8 and 3.9 microgram/ml, respectively, at 25degrees.