ABSTRACT
Development of injectable formulations typically requires specific considerations on the type and quality of excipients used. The criteria for excipient selection depend on a number of factors, including the type of drugs and route of injection. Excipient considerations for biopharmaceutical drugs (proteins and vaccines) have been addressed in separate chapters, hence, this chapter will focus on formulation development only for small molecules (molecular weight <1000). The site of injection could be intravenous (into a vein), subcutaneous (SC) (into adipose tissue), intramuscular (IM) (into deep muscle), and, in rare occasions, intradermal (within the skin), intraocular (in the eye), intrathecal (in the spinal fluid), or intratumoral (in the tumor). Injections can be made in a bolus fashion (rapid) or infused over a longer period of time. A number of devices can be used to inject drugs, from conventional needle and syringe to needle-free injectors. The container-closure system may vary from a lyophilized vial to a prefilled syringe or a flexible plastic bag. The drug itself can be formulated as a lyophilized cake, a solution, or a dispersed system (liposomes and suspensions). All these factors play a vital role in selection of the excipients for injectable formulations. Whereas some specific systems, such as liposomes, have specific requirements, the concepts of parenteral science and excipient selection discussed in this chapter are valid for all injectable systems.
