Which of the following is an advantage of the oral route of drug administration

Part one of this four-part series discusses the advantages and disadvantages of the oral route

Shepherd M (2011) Nursing Times; 107: 32/33, early online publication

• Figures and tables can be seen in the attached print-friendly PDF file of the complete article

5 key points

• The oral route is convenient and cost-effective 

• Children and older people may have problems swallowing tablets and capsules

• Modified-release formulations can delay, prolong or target drug delivery

• Modified-release tablets must not be crushed or broken

• Nurses should seek advice from a pharmacist or the prescribing doctor before crushing tablets

The way in which medicines are administered will to some extent influence their clinical benefit and whether patients experience any adverse effects. For example, if IV furosemide is administered too quickly, it can cause deafness, while oral penicillin V will not be well absorbed if given with food.

Two main factors determine whether a drug will reach its intended site of action in the body:

• Its bioavailability;
• How it is given (route of administration).

Bioavailability

Route of administration and formulation – tablet, capsule, liquid – can influence the bioavailability of a drug. Bioavailability is the proportion of a drug that reaches the systemic circulation and is therefore available for distribution to the intended site of action.

Drugs given by IV injection are said to have 100% bioavailability. Some drugs that are particularly well absorbed by the gastrointestinal mucosa may have bio-availability comparable with that of an IV dose, for example the antibiotic ciprofloxacin. However, most drugs do not have this level of availability by the oral route so the dose given orally is usually higher than that given parenterally. For example, the beta-blocker propranolol, when given orally, is administered in doses of 40mg and above. The equivalent IV dose is 1mg.

Routes of administration

There are various routes of administration (Box 1), each of which has advantages and disadvantages. These routes need to be understood in terms of their implications for the effectiveness of the drug therapy and the patient’s experience.

Box 1. Routes of administration

• Oral
• Sublingual
• Rectal
• Topical
• Parenteral – intravenous, intramuscular, subcutaneous

Oral route

This is the most frequently used route of drug administration and is the most convenient and cost-effective.

Although solid-dose forms such as tablets and capsules have a high degree of drug stability and provide accurate dosage, the oral route is problematic because of the unpredictable nature of gastrointestinal absorption. For example, food in the gastrointestinal tract may alter the gut pH, gastric motility and emptying time, as well as the rate and extent of drug absorption.

Patients’ tolerance of solid-dose forms also varies, particularly in very young
and older patients, for whom liquids or solutions may be preferable. However, many drugs are not stable in solution; in such cases, an alternative drug should be considered.

Modified-release preparations

Modified-release formulations can delay, prolong or target drug delivery. The aim is to maintain plasma drug concentrations for extended periods above the minimum effective concentration. Their main advantage for patients is that doses usually only need to be taken once or twice daily.

Modified-release tablets must not be crushed or broken. Damage to the release-controlling mechanism can result in the full dose of drug being released at once rather than over a number of hours. This may then be absorbed, leading to toxicity, or not be absorbed at all, leading to suboptimal treatment (Royal Pharmaceutical Society of Great Britain and British Medical Association, 2011).

Nurses should seek advice from a pharmacist or the prescribing doctor if they are uncertain about a formulation of solid-dose forms and whether they are suitable for crushing (Nursing and midwifery Council, 2008).  NT

Martin Shepherd is head of medicines management at Chesterfield Royal Hospital Foundation Trust

Other articles in this series

Part 2 – Alternatives to the oral route, 30 August

Part 3 – The parenteral route, 13 September

Part 4 – Patient self-administration, 20 September

Nursing and Midwifery Council (2008) Standards for Medicines Management. London: NMC. tinyurl.com/nmc-med-man

Royal Pharmaceutical Society of Great Britain and British Medical Association (2011) British National Formulary Number 61. www.bnf.org