Drug Delivery Systems and Routes of Administration
Drug delivery systems and routes of administration concern how a medicine is presented to the body and how it reaches the site where it is intended to act. A drug delivery system is the formulation or device that carries an active substance, while the route of administration is the path by which that system enters the body, such as oral, parenteral, transdermal, pulmonary, or specialized routes. Together they determine how much drug becomes available, how fast, and for how long.
Definition
Drug delivery is the set of formulation, carrier, and device strategies, together with the chosen anatomical route of administration, that govern how an active pharmaceutical ingredient is released, absorbed, distributed, and made available at its site of action.
Scope
This area orients the reader to the major routes of administration and the formulation and device technologies that serve them. It groups the field into oral absorption, parenteral injection, transdermal and topical application, inhaled and pulmonary delivery, and specialized routes such as nasal, rectal, and ocular delivery. It treats delivery as a pharmaceutical and biopharmaceutical topic and not as clinical prescribing guidance.
Sub-topics
Core questions
- Which route of administration matches a drug's physicochemical and biopharmaceutical properties?
- How does the delivery system control the rate and extent of drug release and absorption?
- What barriers (epithelial, enzymatic, first-pass) does each route impose, and how are they overcome?
- How do carrier technologies such as nanoparticles and liposomes change a drug's distribution?
Key concepts
- Route of administration
- Bioavailability
- First-pass metabolism
- Biopharmaceutics Classification System (BCS)
- Controlled and sustained release
- Targeted delivery
- Absorption barriers
- Carrier systems (liposomes, nanoparticles)
Mechanisms
The performance of a delivery system reflects the interaction between the drug's properties (solubility, permeability, stability) and the barriers of the chosen route. The Biopharmaceutics Classification System organizes oral drugs by solubility and permeability, the two properties that most constrain absorption (Amidon et al., 1995). Parenteral routes bypass absorption barriers entirely, while oral, transdermal, pulmonary, and mucosal routes must cross an epithelium and may face enzymatic or first-pass loss. Carrier technologies such as liposomes and engineered nanoparticles alter where and how fast a drug distributes, enabling sustained release and, in some cases, more selective accumulation (Torchilin, 2005; Mitchell et al., 2021; Allen & Cullis, 2004).
Clinical relevance
The route of administration and the delivery system shape a medicine's onset, duration, and tolerability, and understanding them supports appraisal of why a given product is formulated as it is. This entry describes the principles by which formulations are designed and is a reference resource, not a basis for selecting or adjusting therapy for an individual.
Evidence & guidelines
Foundational frameworks include the Biopharmaceutics Classification System, which underpins regulatory thinking on oral bioavailability and biowaivers (Amidon et al., 1995), and standard pharmaceutics references that codify formulation principles across routes (Aulton & Taylor, 2018). Reviews of carrier-based delivery summarize the state of liposomal and nanoparticle technologies (Torchilin, 2005; Mitchell et al., 2021).
History
Systematic drug delivery developed alongside twentieth-century formulation science, moving from simple immediate-release dosage forms toward controlled-release systems and, from the 1970s onward, carrier-based and targeted approaches. The Biopharmaceutics Classification System (1995) gave the field a unifying way to relate molecular properties to absorption, and liposomal and nanoparticle carriers brought engineered delivery into mainstream therapeutics (Allen & Cullis, 2004; Torchilin, 2005).
Key figures
- Robert Langer
- Nicholas Peppas
- Vladimir Torchilin
- Gordon Amidon
Related topics
Seminal works
- amidon-1995
- torchilin-2005
- mitchell-2021
Frequently asked questions
- What is the difference between a route of administration and a drug delivery system?
- The route of administration is the anatomical path a drug takes into the body (for example oral or intravenous), whereas the drug delivery system is the formulation or device that carries the drug and controls how it is released along that route.
- Why does the same drug come in different formulations?
- A drug's solubility, permeability, and stability, together with the desired onset and duration of effect, determine which route and delivery system are feasible, so one active substance may be presented in several forms to suit different clinical situations.