الفهرس 
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Abstract
Oral drug delivery is the most convenient route of drug administration. More efforts are
required to optimize this route to maximize its benefits. Biological factors in the GET have a
direct impact on bioavailability of the orally administered drugs and therefore design of any
orally administered dosage forms should address these factors. Different transporter proteins
are expressed in the OtT that affect the bioavailability of substrate drugs.
The aim of the present work was to evaluate the influence of different formulation designs and additives on the performance of some drugs known to be substrates to different influx and efflux intestinal transporter systems, namely, Valacyclovir (a substrate to the influx oligopeptide transporters) and Acyclovir (a substrate to the efflux transporter, P-gp).
This work was divided into two parts:
Part one: Formulation and Evaluation of
Multi-particulate Systems.
Different Valacyclovir mucoadhesive CR mini tablets were prepared by direct compression and evaluated for their physical properties, drug content, swelling profile, mucoadhesive properties and drug release profile. A selected formulation was subjected to a preliminary in
vivo bioavailability study. In addition to mini tablets, different microbeads formulations were prepared using sodium alginate by ionotropic gelation technique. The microbeads were evaluated for their shape, size, entrapment efficiency, swelling profile and drug release profile.
Results of this part inferred to
1. Absorption of the oligopeptide transporter substrate, Valacyclovir, was not optimum (54%) in relation to being a prodrug. This lower than expected bloavailability profile may be a result of saturation of absorption transporters and pre—absorption (not presystemic) metabolism to the active drug, Acyclovir, that has a poor absorption profile.
2. Using HPMC in absence or presence of Carbopol or Polycarbophil, the mini tablets prepared showed acceptable physical properties and drug content. Swelling of the prepared mucoadhesive mini tablets depend on the type and concentration of the
polymer(s) used.