![]() Rate of infusion = įinal answer: Supply 2 bottles of phenoxymethylpenicillin 250mg/5ml Dose by weight Our patient requires 1000 mg: 1000mg/50mg = 20 minutes Step 3: Calculate the infusion rate in ml/min Step 2: Calculate the total volume of infusion Volume (ml) of phenytoin = x volume of the original pack Step 1: Calculate the volume of phenytoin required Each 5 ml vial of phenytoin sodium contains 250 mg. The consultant has decided to commence intravenous phenytoin with a loading dose of 1000 mg, which is to be diluted in 100 ml of normal saline.Ĭalculate the infusion rate of phenytoin for this patient in ml/min. Whilst in ED, she develops prolonged seizures and status epilepticus. Each question is worth 2 marks.ĭrug calculation topics which may appear in the PSA includeĭuring your rotation in the emergency department, a 24-year-old woman who weighs 60 kg was brought in by ambulance following a seizure. There will be eight questions assessing drug calculation skills in the Prescribing Safety Assessment (PSA). In contrast, the paediatric population have under-developed organ systems, and medication doses are often based on the age, weight or body surface area of the child.Ĭommon drug calculation errors in clinical practice include miscalculating the concentration of medicine in solution, incorrect dose unit conversion and incorrect rate of administration for infusion. Medication doses may need to be adjusted, as the “safe” dose for a regular adult may no longer be appropriate for them. This is particularly important when prescribing for the elderly and paediatric populations, as they are more vulnerable to medication-related harm.įrailty and reduced renal function are commonly seen in the elderly population. ![]() There are seven drug dosage calculations to attempt you will be able to check your answers when you have completed all of the questions.Drug calculation skills are an important part of prescribing, as calculation errors may lead to significant patient harm. You can test what you have learnt with this drug calculations quiz. The available stock on the ward is 10mg/5ml (10mg in 5ml) elixir. Stock strength (what you’ve got): 100mgĪ patient requires dihydrocodeine 30mg.The strength required (what you want): 200mg.The available stock on the ward is 100mg/ml (100mg in 1ml) oral solution. How to calculate a liquid medication dosageĪ patient requires amisulpride 200mg. How many tablets should the nurse administer to patient X if the available stock strength on the ward is 2.5mg? The doctor prescribes bendroflumethiazide 7.5mg on patient X’s drug chart. Stock strength (what you’ve got): 10mg in one tablet.The strength required (what you want): 20mg.The available stock strength you have is 10mg. The Doctor prescribes promethazine hydrochloride 20mg for patient X. How to calculate the number of tablets required If you are unsure how to convert from one unit of measurement to another, take a look at the conversion table. ![]() Or another way this liquid dose formula can be expressed is: ( What you want / What you’ve got) × What it’s in = Volume dose required Worked examples with stepsīefore working through these worked example questions and attempting the drug calculations quiz in the next part, remember to make sure the strength required and stock strength is always in the same units of measure (ie., both ng, both mcg, both mg or both g). To calculate the volume dose for liquid medicine, use this formula: (Strength required / Stock strength) × Stock volume = Volume dose required Or another way this drug dosage formula can be expressed is: What you want / What you’ve got = Number of tablet(s) required To calculate the number of tablets, use the following formula: Strength required / Stock strength = Number of tablet(s) required Finally, in part 3, you can test what you have learnt by attempting the drug calculations quiz. ![]()
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