Learning Objective

• Need for the parenteral controlled drug delivery
• Various approaches to control drug release in parenteral formulations

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 concentration can be achieved by two strategies:

1. Controlling the rate of drug absorption
2. Controlling the rate of drug excretion

Controlling the absorption rate of a drug (modifying dosage forms) is much easier than controlling the excretion rate (modifying physiology of body) of a drug. Continuous intravenous infusion is used to maintain a constant drug level within a therapeutic concentration range for effective treatment.

Approaches for the Development of Parenteral Controlled Drug Delivery

Pharmaceutical approaches to develop a parenteral controlled drug delivery system include the following:

1. Preparation of water-insoluble drug derivatives such as complexes and esters
2. Use of water-miscible, viscous vehicles such as aqueous solution of PVP (polyvinylpyrrolidone) or gelatin
3. Utilization of water-immiscible vehicles such as vegetable oils and water-repelling agents such as aluminum monostearte
4. Coadministration of vasoconstrictors
5. Formulation of thioxtropic suspensions
6. Dispersion in polymeric microspheres or microcapsules such as lactide–glycolide homopolymers or copolymers