Routes of Medication Administration
Routes of Medication Administration
Why some medications are made to be administered certain way.
A majority of the drugs are administered orally as it is a convenient, safe and affordable route of administration. The effect of the drug in the body is dependent on its absorption in the digestive system. Absorption can begin in the mouth and stomach but is mostly completed in the small intestine. In order to reach the bloodstream, the drug needs to pass through the intestinal wall and liver which can chemically alter the drug. As a result, the amount of drug absorbed in the body is lower than the amount of drug administered initially.
Absorption of the drug is also affected by food and/or other oral drugs in the digestive tract. Specific instructions should be followed to maximize absorption. Some examples include taking the drug on an empty stomach, taking it with food and/or avoiding with other medications.
Alternate route should be utilized when oral route cannot be used:
- Patient cannot take anything by mouth
- Rapid administration or high doses of drugs are required
- Drug is poorly or erratically absorbed from the digestive tract
- Subcutaneous route: The drug is injected in the adipose (fat) tissues right beneath the skin. The drug enters the bloodstream through small blood vessels (capillaries) or the lymphatic vessels. Protein drugs (ex. Insulin) are administered subcutaneously because oral administration results in destruction of the protein in the digestive tract.
- Intramuscular route: The drug is injected into the muscles (upper arm, thigh or buttock) which lie below the skin and adipose (fat) tissues. It is usually used when larger volumes of drug products are needed. The absorption of the drug into blood depends on the blood supply to the muscle: higher the blood supply, quicker the absorption.
- Intravenous route: The drug is directly administered into a vein. It is absorbed completely, and is best way to deliver a precise dose quickly and in a well-controlled manner. It is also used for administering irritating solutions that could damage the tissue if administered subcutaneously or intramuscularly. The drug effects last for a shorter period of time and may require frequent or continuous administration.
- Intrathecal route: The drug is administered between two vertebrae in the lower spine and into the space around the spinal cord. The injection site is numbed using an anesthetic prior to drug administration. This route is used to produce rapid/local effects in the brain, spinal cord or meninges (layers of tissue that surrounds brain and spinal cord).
Sublingual and buccal routes:
The drug is placed under the tongue (sublingual) or between the gums and teeth (buccal). It dissolves and enters the bloodstream directly through the small blood vessels beneath the tongue. These drugs should not be swallowed, and require special formulation that enables its disintegration in the mouth.
The drug is administered in the rectum as a suppository. The drug is formulated with a waxy substance that dissolves or liquefies after it is inserted into the rectum. It is easily absorbed into the bloodstream through the rich blood supply present in the rectum wall. Most drugs that can be taken orally can also be administered rectally as a suppository.
The drug is administered vaginally as a solution, tablet, cream, gel, suppository or ring. It is absorbed through the vaginal wall. Vaginal symptoms such as dryness, soreness and redness during menopause can be relieved by applying estrogen through the vaginal route.
The drug is applied into the eye as liquid, gel or ointment. Liquid eye drops may have lower absorption as the drug may run off the eye quickly. Gel/ointment may have better absorption due to longer contact time with the eye surface, however they can cause blurred vision. It only produces local effect in the eyes and there is minimum systemic absorption.
The drug is administered in the outer ear canal as liquid drops. It is used to treat local infections/inflammation and there is minimum systemic absorption.
The drug is breathed in and absorbed through the thin mucous membranes that lines the nasal passage. Some drugs can irritate the nasal passage. Nicotine for smoking cessation, sumatriptan for migraine headaches and corticosteroid for allergies are some examples of drugs that can be used nasally.
The drug is inhaled through the mouth, passes through the trachea into the lungs. Size of the inhalation droplets determine how deep it penetrates in the lungs: smaller the size, deeper it goes and has higher absorption.
The drug is directly applied to the skin as cream, ointment, lotion, solution, powder or gel. It produces local effect and is used to treat superficial skin conditions such as eczema, infections or dry skin.
The drug is administered by applying a patch on the skin. The patch delivers the drug slowly and continuously for many hours or days. This results in constant drug levels throughout the day. Penetration of the drug in the body can be increased by mixing it with chemicals (such as alcohol). Only drugs that require small daily doses should administered using a patch. Some examples are fentanyl for pain relief, nicotine for smoking cessation and nitroglycerin for chest pain.
Some medications can only be administered via a specific route, some examples are listed below:
- Albuterol is only administered using the inhalation route. It is used for treating asthma/COPD and has the best effects when directly administered into the lungs.
- Insulin is only given via subcutaneous injection. It cannot be taken orally because the digestive tract destroys its structure and makes it inactive.
- Flu shot is administered as intramuscular injection. It cannot be given via subcutaneous or oral route due to slow absorption which can result in vaccine failure.
It is important to follow the directions provided by the health care provider on how to take the drug to ensure you receive maximum clinical benefit. Compounding of certain medications allows then to be administered in alternate route(s) that are not offered commercially. A compounding pharmacist can work with your doctor to see what options are available.
- Benet LZ. Effect of route of administration and distribution on drug action. J Pharmacokinet Biopharm. 1978;6(6):559-85.
- Merck Manual Consumer version. Retrieved February 13, 2019 from https://www.merckmanuals.com/home/drugs/administration-and-kinetics-of-drugs/drug-administration
- Through the skin [image]. Available at https://www.merckmanuals.com/home/drugs/administration-and-kinetics-of-drugs/drug-administration. Accessed February 13, 2019