OPRA Calculations, Screening, Primary Care and Safe Use of Medicines

Weight and time budget

The APC lists screening, dose calculations, primary health care, safe and effective use of medicines in populations needing extended consideration, safe and effective use of medicines, harm minimisation, health promotion and disease prevention, and confidentiality under therapeutics and patient care. We group these as one study block of about 18 questions. How many are calculations is not published. The APC sample content includes a dopamine infusion rate calculation and a lithium millimole calculation, so expect arithmetic to be present, and expect it to take longer than 75 seconds per item.

What is tested

• Dose calculations. Weight-based dosing, body surface area dosing and infusion rates.
• Concentration and dilution. Percentage strengths, mg per mL, dilution of stock solutions, and millimole calculations from mass.
• Paediatric dosing. Weight-based checks and the safety limits that go with them.
• Older people. Dosing, polypharmacy and the burden of medicines.
• Pregnancy and breastfeeding. Which medicines to avoid, which are acceptable, and the reasons.
• Renal and hepatic impairment. Adjusting doses and avoiding hazardous drugs.
• Primary health care. Minor ailments, over-the-counter and complementary medicines, and when to refer.
• Screening and point-of-care testing.
• Health promotion and prevention. Smoking cessation, vaccination, nutrition and physical activity, and public health principles.
• Harm minimisation. Needle exchange, naloxone and substance misuse.
• Medication management. Reconciliation, adherence and counselling.
• Medication safety. Look-alike names, high-risk medicines and abbreviations.
• Confidentiality and privacy. General principles of patient information.
• Contraception and sexual health.

Local guideline points

• Medication safety conventions: write "units", not "U". Write microgram in full. Avoid trailing zeros and use a leading zero. These match the ACSQHC approach the APC cites.
• Immunisation: the Australian Immunisation Handbook and the National Immunisation Program schedule are the references. Principles matter more than a memorised schedule.
• Pharmacist-only and pharmacy medicines: scheduling terms such as S2 and S3 may appear as context for primary health care. The APC says legislation is not tested, so reasoning about when to refer is the point.
• PBS: subsidy details are background. As an example of the kind of fact that changes, the general patient co-payment was listed by the PBS at up to AUD 25.00 from 1 January 2026. Do not spend revision time on subsidy numbers for OPRA.
• Confidentiality: the exam covers the principle. Australian privacy law is not tested.
• Harm minimisation: naloxone, needle exchange and opioid substitution are part of Australian practice. Know the clinical rationale.

Calculation types to practise

Three typical traps

1. Unit slips. Microgram versus milligram and minutes versus hours cause most calculation errors. Write units on every line of working.
2. The wrong weight or the wrong salt. A stem may give actual weight, ideal weight or surface area, and a drug may be given as a salt. Read the question for which to use.
3. Answering the calculation but missing the safety check. Some stems test whether you notice that the calculated dose exceeds a maximum or that the drug is unsuitable for the patient. Ask whether the answer is reasonable, not only whether it is arithmetically right.

Self-check before you move on

You are ready to leave this block when you can do each of the following without notes. If you cannot, return to that point before taking more mixed blocks.

• Convert between g, mg and microgram, and between L and mL, without hesitation.
• Set up an infusion rate from a per-kilogram dose and a bag concentration.
• Calculate millimoles from a mass, using the formula weight of the salt.
• Dilute a stock solution to a target concentration using C1V1 equals C2V2.
• Name five medicines to avoid or adjust in pregnancy, older age and renal impairment.
• List red-flag symptoms that require referral for three common minor ailments.
• Explain look-alike, sound-alike risks and give two examples of high-risk medicines.
• State the purpose of medication reconciliation and where it fits at transfers of care.

If any calculation in this list takes more than two minutes, return to the table above and drill that type again.

How to revise this block

1. Do five calculations a day by hand, every day. Rotate the types in the table. Time yourself against two minutes each.
2. Keep a log of unit errors. Most candidates repeat the same two or three mistakes.
3. Memorise the conversions. 1 g is 1000 mg; 1 mg is 1000 microgram; 1 L is 1000 mL; a w/v percentage is grams per 100 mL.
4. Study special populations by risk. For pregnancy, children, older people and organ impairment, list the drugs to avoid and why.
5. Rehearse primary care as referral logic. For each minor ailment, list the red flags that require referral, the safe over-the-counter option and the counselling point.
6. Read the calculation conventions in the exam. The APC guide does not publish a calculator rule, so see the exam day guide and confirm before you sit.

For the supporting science, see pharmacokinetics and pharmacodynamics. For the other therapeutics blocks, see body systems. The full picture is on the OPRA hub.