Within the Consultation Domain of the Royal Pharmaceutical Society (2016) A competency framework for all prescribers, indicator 4.6, states that the prescriber ‘accurately completes and routinely checks calculations relevant to prescribing and practical dosing’. Recently updated regulatory standards for prescribing dictate that numeracy and drug calculations continue to be an essential core element of non-medical prescribing programmes. These require students to enhance their existing skills and expertise in respect of the medicines they aim to prescribe, within their sphere of practice (Nursing & Midwifery Council, 2018; General Pharmaceutical Council, 2019; Health & Care Professions Council, 2019). The following questions aim to assist both qualified prescribers and those in training to attain and maintain an aptitude for safe drug calculations by revisiting the basic principles of numeracy.
QUESTION 1
Mrs Smith is awaiting discharge following an uneventful appendectomy two days ago. You are writing a discharge prescription for analgesia. You prescribe co-codamol 30/500 mg tablets, 1-2 tablets every 4-6 hourly as required. You advise Mrs Smith that no more than eight tablets should be taken in any 24-hour period.
- How many tablets will you prescribe for 7 days' total treatment?
- Calculate the number of tablets Mrs. Smith requires if she takes half the maximum permissible dose for four days.
- Mrs Smith decides to use the remaining tablets by taking two tablets at bedtime. How many days will these last for?
QUESTION 2
You are asked to check the dose of a patient's antihypertensive treatment. The evidence base stipulates that for your patient type, the drug should be given at 25% less than the standard starting dose of 10 mg daily. The drug is available in strengths of 2.5 mg, 5 mg, 10 mg and 20 mg tablets.
- What is the daily dose that this patient should receive?
- What should this patient be prescribed on a daily basis?
- How many tablets in total will the patient take over a 30 day period?
QUESTION 3
Janet has been admitted to hospital for intravenous antibiotics for 14 days' duration. The antibiotic is mixed in 100 ml saline, infused over 30 minutes and is administered in six hourly doses.
- How many mls of saline will be infused over a 24-hour period?
- How many hours of Janet's stay in hospital will she be having her IV drug?
- Janet is discharged with oral antibiotics to be taken every 8 hours for 28 days. How many should be prescribed and dispensed for this period?
QUESTION 4
Your patient, aged six years, is experiencing an acute asthma attack and requires emergency nebulisers. The dose of drug is 2.5-5 mg, repeated every 20-30 minutes.
- Using the above guidance, what is the maximum amount of drug in mg that the child can receive over a two-hour period?
- After two hours, the child receives 2.5 mg nebulisers every four hours for 24 hours. How many mg of drug does the child receive in this 24-hour period?
- Over this period of time, how many nebulisers in total did the child require?
QUESTION 5
Your adult patient has a new diagnosis of moderate depression and you prescribe a Selective Serotonin Re-uptake Inhibitor (SSRI) tablet starting at a dose of 20 mg daily. You aim to review your patient after three weeks.
- How many 20mg tablets will you prescribe for three weeks?
- The British Medical Association (BMA) and Royal Pharmaceutical Society (RPS) (2019) advice states to increase the dose of this drug by 20 mg every 3-4 weeks as required up to a maximum of 40 mg daily. How many up-titrations of this drug will therefore be permissible?
- After six months of treatment on 40 mg daily, how many tablets will the patient have consumed in total, assuming the correct daily dose is adhered to and a month being 30 days?
QUESTION 6
You prescribe drug P for your patient. It is available in 250 mg/5 ml strength. Your patient needs 3g of drug P per day in 2 x divided doses.
- How many mg per day will the patient take?
- How many mls will the patient take at each dose?
- For 10 days supply, how many ml will you prescribe?