New product formulations, pharmacokinetics and bioavailability of dyphylline Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rb68xg13s

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  • Product formulation and in vitro dissolution characteristics of sustained-release chewable tablet dosage forms are presented in chapter one of this thesis. In vivo single dose and multiple dose studies of two sustained-release formulations as well as one conventional dyphylline formulation are described in chapter two. The pharmacokinetics of dyphylline following inhalation is shown in chapter three. Phase-separation coacervation microencapsulation and polymer matrix methods with five variables (ratio of drug to polymer material, wall sealants, tabletting pressure, particle size and elasticizing agent) have been investigated for making new dyphylline dosage forms. There is 307 in vitro dyphylline released within the first hour from microencapsulated formulation and 507 in vitro dyphylline released within the first hour from a polymer matrix formulation. The remaining dyphylline in both formulations was released very slowly over 24 hours. This release pattern may be clinically useful. These formulations were chosen along with the conventional dyphylline tablet for determining in vivo relative bioavailability of these sustained-release dyphylline chewable tablet dosage forms in swine. The sustained-release microencapsulated formulation is a good formulation since it has a slow rate of absorption and has an equal extent of bioavailability with the commercial product. The steady-state concentrations following multiple-dosing studies for the microencapsulated product were maintained at about 7-8 ug/ml for one pig and above 10 ug/ml for two other pigs. Linear correlations were found between the time for 50% dyphylline release in vitro and the in vivo parameters Cmax, Tp, and MAT for formulations A, B, and C. Dyphylline may be effective when given by the inhalation route since it is highly water-soluble and non-irritating, has a low toxicity and has a direct effect on the bronchioles. Four New Zealand white rabbits were anesthetized with sodium pentobarbital and four ml (1000 mg) of dyphylline intramuscular solution was administered into the trachea of rabbits with a plastic nebulizer connected to a breathing air tank. Blood dyphylline concentrations were quite high. The pharmacokinetics was best described as a two-compartment open model with constant rate inhalation.
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