Biodegradable microspheres for the delivery of small molecules, proteins and macromolecules have been in application. These are prepared by water/oil/water emulsion–solvent evaporation method and have shown zero-order drug release over one to three months after intramuscular or subcutaneous injection.
Suspensions can be a potential parenteral sustained release system. When a drug is administered as an aqueous or oil suspension subcutaneously, it results in the formation of a depot at the site of injection. Typical examples are oleaginous suspension of micronized crystal of penicillin procaine in peanut or sesame oil gelled with 2% aluminum monostearate.
Implants administered parenterally are defined as viscous liquids or semisolid formulations, which are injected with a needle, and as liquids that gel following administration, impregnated with a drug substance. Implants are used in chronic treatment such as hormone replacement therapy and prostate cancer.
When a drug is esterified into a bioconvertible prodrug ester and then formulated into an injectable form, it gives rise to esterification type depot preparation. This chemical approach depends upon the number of enzymes (esterases) present at the injection site, and the formulation forms a drug reservoir at the site of injection. The absorption rate…
Encapsulating the drug within a permeation barrier or dispensing drug particles in a diffusion matrix is the formulation process involved in the encapsulation type depot preparation. The drug release is controlled by the permeation rate across the permeation barrier and the rate of biodegradation of the barrier macromolecules. Different biodegradable or bioabsorbable macromolecules such as…
The binding of drug molecules to adsorbents is the approach to depot preparation. The unbound drug from the preparation undergoes absorption and subsequently fractions of the bound drug molecules are released to maintain equilibrium condition. This type of formulation is used in vaccine preparations in which the antigens are bound to highly dispersed aluminum hydroxide gel…
The process of dissolution of drug particles from the formulation or the drug particles surrounded by tissue fluids is the rate limiting step. Based on this concept, the rate of drug absorption can be controlled by slow dissolution of drug particles. Drug dissolution rate under sink conditions is given as (Q/t)d = Sa Ds Cs/hd …
Learning Objective Based on the mechanism of drug release, depot formulations can be categorized into the following four types:
Learning Objective The administration of drugs via intravenous, subcutaneous or intramuscular injection leads to rapid drug absorption and rapid drug elimination from the body, hence the importance of sustained or controlled parenteral drug delivery system, which maintains an effective drug concentration in blood for a longer duration of time is needed. The effective systemic drug…