Drug delivery

Drug delivery involves various methods and technologies designed to transport pharmaceutical compounds to their target sites helping therapeutic effect.^[1][2] It involves principles related to drug preparation, route of administration, site-specific targeting, metabolism, and toxicity all aimed to optimize efficacy and safety, while improving patient convenience and compliance.^[3][4] A key goal of drug delivery is to modify a drug's pharmacokinetics and specificity by combining it with different excipients, drug carriers, and medical devices designed to control its distribution and activity in the body.^[3][5][6] Enhancing bioavailability and prolonging duration of action are essential strategies for improving therapeutic outcomes,^[7] particularly in chronic disease management. Additionally, some research emphasizes on improving safety for the individuals administering the medication. For example, microneedle patches have been developed for vaccines and drug delivery to minimize the risk of needlestick injuries.^[4][8]

Drug delivery is closely linked with dosage form and route of administration, the latter of which is sometimes considered to be part of the definition.^[9] Although the terms are often used interchangably, they represent distinct concepts. The route of administration refers specifically to the path by which a drug enters the body,^[10] such as oral, parenteral, or transdermal.^[11] In contrast, the dosage form refers to the physical form in which the drug is manufactured and delivered, such as tablets, capsules, patches, inhalers or injectable solutions. These are various dosage forms and technologies which include but not limited to nanoparticles, liposomes, microneedles, and hydrogels that can be used to enhance therapeutic efficacy and safety.^[12] The same route can accommodate multiple dosage forms; for example, the oral route may involve tablet, capsule, or liquid suspension. While the transdermal route may use a patch, gel, or cream.^[13] Drug delivery incorporates both of these concepts while encompassing a broader scope, including the design and engineering of systems that operate within or across these routes. Common routes of administration include oral, parenteral (injected), sublingual, topical, transdermal, nasal, ocular, rectal, and vaginal. However, modern drug delivery continue to expand the possibilities of these routes through novel and hybrid approaches.^[14]

Since the approval of the first controlled-release formulation in the 1950s, research into new delivery systems has been progressing, as opposed to new drug development which has been declining.^[15][16][17] Several factors may be contributing to this shift in focus. One of the driving factors is the high cost of developing new drugs. A 2013 review found the cost of developing a delivery system was only 10% of the cost of developing a new pharmaceutical.^[18] A more recent study found the median cost of bringing a new drug to market was $985 million in 2020, but did not look at the cost of developing drug delivery systems.^[19] Other factors that have potentially influenced the increase in drug delivery system development may include the increasing prevalence of both chronic and infectious diseases,^[17][20] as well as a general increased understanding of the pharmacology, pharmacokinetics, and pharmacodynamics of many drugs.^[3]