Parenteral Drug Delivery for Older Patients

Abstract

Parenteral drug delivery is widely used for older adults to achieve and maintain therapeutic concentration of drugs that have a narrow therapeutic index or have poor oral bioavailability. Parenteral products are usually available in solution, suspension or emulsion form; liposome, microsphere and implants are available as well. Intravenous, subcutaneous, intramuscular, intradermal, and epidural deliveries are mostly used for parenteral administration of drugs to older patients. Other routes of parenteral drug delivery include: intraarterial, intraventricular, intrathecal, intracisternal, intraarticular, intraocular, intracardiac, and intraperitoneal. Continuous intravenous infusion is administered to maintain a constant and sustained drug level within a therapeutic concentration range for effective treatment in aging adults, especially for drugs with very short biologic half-lives. The intramuscular route is beneficial for larger injection volumes and also for oil-based formulations, where the subcutaneous route is used for chronic diseases and vaccines, among many others. The intradermal route is useful for allergy testing, antigens and vaccines. Epidural administration of analgesics are very beneficial for older adults during surgeries. The progress in targeted or controlled release drug delivery—such as, the application of microspheres, liposomes, gels, suspensions, in situ forming implants, lipophilic solutions, solid lipid nanoparticles (SLN), and drug eluting stents—have reduced the dosing frequency in seniors, which may provide improved patient compliance. Parenteral delivery is also beneficial for delivering total parenteral nutrition to older adults.