Pharmaceutics & Novel Drug Delivery Systems

Vaccine Drug Delivery Systems

Vaccine is a material that induces an immunologically mediated resistance to a disease but not necessarily an infection. Vaccines are generally composed of killed or attenuated organisms or subunits of organisms or DNA encoding antigenic proteins of pathogens. Sub-unit vaccines though exceptionally selective and specific in reacting with antibodies often fail to show such reactions in circumstances such as shifts in epitopic identification center of antibody and are poorly immunogenic. Delivery of antigens from oil-based adjuvants such as Freunds adjuvant lead to a reduction in the number of doses of vaccine to be administered but due to toxicity concerns like inductions of granulomas at the injection site, such adjuvants are not widely used. FDA approved adjuvants for human uses are aluminium hydroxide and aluminium phosphate in the form of alum. Hence, search for safer and potent adjuvants resulted in the formulations of antigen into delivery systems that administer antigen in particulate form rather than solution form.

Other reasons driving the development of vaccines as controlled drug delivery systems are as follows:

• Immunization failure with conventional immunization regimen involving prime doses and booster doses, as patients neglect the latter. Vaccines delivery systems on the other hand:
• Allow for the incorporation of doses of antigens so that booster doses are no longer necessary as antigens are released slowly in a controlled manner.
• Control the spatial and temporal presentation of antigens to the immune system there by promoting their targeting straight to the immune cells.