Oral administration of drugs is the most common and acceptable route for drug administration, especially for out-patients. When possible, oral route usually abbreviated as p.o. or PO (Latin per os, meaning through the mouth) is the first choice for the administration of drugs since it is both convenient and economical.
Drugs administered orally (e.g., tablets, capsules, syrup, solutions, suspensions, powders, emulsions, etc.) are placed in the mouth and swallowed. Although a few drugs taken orally are intended to be dissolved in the mouth, nearly all drugs taken orally are swallowed. Of these, most are taken for the systemic drug effects that result after absorption from the various surfaces along the gastrointestinal tract. A few drugs, such as antacids, are swallowed for their local action in the gastrointestinal tract.
Orally administered drugs usually pass through the gut wall and liver, which contain several inactivating enzymes. This process is called “pre-systemic” or “first-pass” metabolism. This indicates that only a fraction of the administered drug actually reaches the systemic circulation (this fraction is referred to as the oral “bioavailability” of a drug).
Advantages of oral route of drug administration
1. It is the simplest, most convenient, and safest means of drug administration.
2. It is convenient for repeated and prolonged use.
3. It can be self-administered and pain-free.
4. It is economical since it does not involve the patient in extra cost. Where the drug is a solid e.g., tablet and capsule, the patient needs just one or two cups of water, which in most cases is freely available. If the drug is in liquid form, nothing is needed except a measuring tool that comes with the drug in most cases.
5. No sterile precautions needed.
6. Danger of acute drug reaction is minimal.
7. Neither special knowledge nor special supplies (syringes, needles) is required for its use.
Disadvantages of oral route of drug administration
1. It is not suitable for emergency as onset of action of orally administered drugs is relatively slow.
2. It can only be used in conscious patients and those patients who can swallow.
3. It requires patient’s cooperation or compliance, especially outpatients.
4. It is not suitable for:
- unpalatable and highly irritant drugs
- drugs that are destroyed by gastric acid and digestive juices (e.g., insulin)
- drugs with extensive first-pass metabolism (e.g. lignocaine, imipramine)
- patients with severe vomiting and diarrhea.
5. Oral route of drug administration is sometimes inefficient as absorption is in most cases irregular and incomplete.
6. Changes in drug solubility can result from reactions with other materials present in the gastrointestinal tract e.g., the interference of absorption of tetracyclines through the formation of insoluble complexes with calcium, which can be available from dairy products or formulation additives.
- Talevi, A. and Quiroga, P. (2018). ADME Processes in Pharmaceutical Sciences: Dosage, Design, and Pharmacotherapy Success. Switzerland AG: Springer.
- Raj, G. and Raveendran, R. (2019). Introduction to Basics of Pharmacology and Toxicology Volume 1: General and Molecular Pharmacology: Principles of Drug Action. Springer Nature Singapore Pte Ltd.