Drugs may be administered by a variety of routes depending on the intended site of action, chemical properties of the medication, drug metabolism and ease of use. Drug absorption may occur through the gastrointestinal tract, skin, bloodstream, muscles or any of the moist body surfaces known as mucous membranes. These include the lining tissues of the nose, mouth, eyes, lungs, vagina and rectum. Drugs formulated for a specific route of administration should only be used as prescribed to ensure safe and efficient drug delivery.
Oral
Most medications are administered orally. Drugs taken by mouth and swallowed are absorbed by or act within the stomach and intestines. Antacids, for example, act locally within the stomach. Digestive enzymes taken by people with pancreatic insufficiency act within the small intestine. Medications such as nitroglycerin that are held under the tongue can be absorbed directly into the bloodstream, bypassing the stomach and intestines. The Merck Manual for Healthcare Professionals points out that swallowed medications intended for bloodstream absorption must be sufficiently stable to avoid inactivation by digestive fluids and enzymes. Protein-derived drugs such as monoclonal antibodies, immunoglobulins and antisera cannot be taken by mouth due to digestive deactivation. The presence of food in the stomach can increase or decrease the rate of absorption of certain oral medications.
Intravenous
Intravenous medications directly enter the bloodstream via a needle or catheter in a vein, notes The Merck Manual for Healthcare Professionals. This route of administration facilitates rapid action and distribution of the drug. It also allows for a controlled, continuous flow of medication if administered through an intravenous line run through a metered dosing machine. Drugs that would be broken down by the digestive system are often administered intravenously.
Transdermal
Transdermal drug administration occurs via absorption through the skin. A medication-infused patch is applied to the skin, where the drug is slowly absorbed through the pores over a specified period. Dr. Sharon Ternullo notes in an article published in the New York State Poison Centers' Toxicology Letter that advantages of transdermal administration include ease of use and continuous absorption of the medication. Continuous release reduces the variation in blood concentration that typically occurs with oral drug administration. Disadvantages of transdermal drug administration include skin sensitivity to the patch adhesive and slow onset of action when first beginning the medication. Examples of drugs that can be administered transdermally include birth control formulations, female hormone replacement, testosterone, fentanyl, lidocaine, nitroglycerine and nicotine. Only certain types of drugs can be absorbed through the skin, which limits the use of this route of administration.
References
- Merck Manual for Healthcare Professionals: Pharmacokinetics, Absorption
- Merck Manual, Home Edition: Drugs, Administration
- New York State Poison Centers Toxicology Letter: Transdermal Medication for Systemic Use
- "Pediatrics"; Alternative Routes of Drug Administration---Advantages and Disadvantages (Subject Review); American Academy of Pediatrics Committee on Drugs; July 1997
- Encyclopedia of Nursing and Allied Health: Administration of Medication
