Pharmacology - Writing a Prescription

Q1. What should be done before writing a prescription?

A: Before prescribing a medicine, review the patient’s current drug therapy carefully. This should also be done when rewriting an existing hospital drug chart.

Q2. What should you consider about the new medicine in relation to the patient’s existing treatment?

A: Ask how the new medicine will contribute to the current management of the disease. Consider whether it will:

• Improve or relieve symptoms.
• Modify the underlying pathophysiology of the disease.
• Prevent the disease or slow its progression.

Q3. Why should other medical conditions be considered before prescribing?

A: A medicine prescribed for one condition may worsen another disease.

For example:

• Diuretics used for heart failure may worsen gout.
• Beta-blockers may trigger or worsen asthma.

Q4. Why is it important to check for drug interactions?

A: A newly prescribed medicine may interact with other medicines the patient is already taking, which can reduce effectiveness or increase adverse effects.

Q5. Which medicines should be considered when checking for interactions?

A: Consider all medicines the patient uses, including:

• Medicines prescribed by other doctors, nurses, or pharmacists.
• Over-the-counter medicines.
• Herbal remedies.
• Other non-prescribed medicines or substances.

Practical Prescription Writing

Q6. Which drug names should generally be used when writing prescriptions?

A: Prescribers are encouraged to use the recommended International Non-proprietary Name (rINN) rather than brand or proprietary names, because brand names may cause confusion.

Q7. Should abbreviations or acronyms be used for drug names?

A: No. Drug names should be written clearly and in full whenever possible.

For example, write glyceryl trinitrate instead of using the abbreviation GTN.

Q8. How should the dose of a medicine be written?

A: The dose should be stated clearly using appropriate units. Commonly accepted units include:

• mg for milligrams.
• mL for millilitres.

Q9. How should microgram doses be written?

A: The word “micrograms” should be written in full.

The symbol μg should be avoided because it may be misread as mg, potentially causing a serious dosing error.

Q10. How should drug doses expressed in units be written?

A: Write the word “units” in full.

Avoid abbreviations or symbols such as U, because they may be misread as a zero and result in an incorrect dose.

Q11. Why should decimal points be avoided when writing doses?

A: Decimal points may be overlooked or misread, which can lead to significant dosing errors.

For example, .5 mL could mistakenly be read as 5 mL.

Q12. How should a decimal dose be written when it is necessary?

A: Always place a zero before the decimal point.

For example:

• Correct: 0.5 mL
• Incorrect: .5 mL

Route of Administration

Q13. What routes of administration should be stated on a prescription?

A: The route by which the medicine should be administered must be clearly documented.

Commonly recognised abbreviations include:

• po – by mouth.
• im – intramuscularly.
• iv – intravenously.
• sc – subcutaneously.

Frequency of Administration

Q14. What does “od” mean on a prescription?

A: od means the medicine should be taken once daily.

Q15. What does “bd” mean?

A: bd means the medicine should be taken twice daily.

Q16. What does “tds” mean?

A: tds means the medicine should be taken three times daily.

Q17. What does “qds” mean?

A: qds means the medicine should be taken four times daily.

Q18. What does “prn” mean?

A: prn means the medicine should be given or taken when required.

When prescribing a medicine on a PRN basis, the maximum permitted daily dose should also be stated.

Q19. What does “stat” mean?

A: stat means the medicine should be administered immediately.

Special Instructions

Q20. What special instructions may need to be included on a prescription?

A: Additional instructions may be required to ensure that the medicine is taken correctly.

Examples include:

• Dietary instructions, such as “take with food.”
• Timing instructions, such as “take at night.”

Q21. Why are special instructions important?

A: They help ensure safe and effective medicine use and may improve absorption, reduce adverse effects, or ensure that the medicine is taken at the most appropriate time.

Completing the Prescription

Q22. What must be done after completing a prescription?

A: The prescription should be:

• Signed by the prescriber.
• Dated clearly.

This confirms who prescribed the medicine and when it was prescribed.

Q23. Are there additional requirements for controlled drugs?

A: Yes. Prescriptions for controlled drugs are subject to additional legal and documentation requirements, so the relevant prescribing regulations must be followed carefully.