Compounding a spironolactone suspension for a 12 kg child when the prescription and the ward notes disagree
A paediatric ward of a government general hospital asks its pharmacy to compound an oral liquid for a 3-year-old girl weighing 12 kg who has heart failure. The cardiologist's handwritten prescription reads: 'Spiromide 25 mg tablets - prepare 60 mL of a 5 mg/mL suspension; give 2.4 mL twice daily. Continue enalapril 2.5 mg twice daily and furosemide 10 mg once daily.' The pharmacy stocks only 25 mg spironolactone tablets, a preserved methylcellulose-based suspending vehicle (contains sodium benzoate; the label states 'store below 25 degrees C, do not refrigerate after preparation'), a glass mortar and pestle and a Class A measuring cylinder. No commercial spironolactone suspension is available anywhere in the hospital. Checking the ward notes, the pharmacist finds the dose recorded as 'spironolactone 12 mg/kg/day in two divided doses'. The nurse is waiting and says the child's morning dose is already two hours late.
1. Is the order as written clinically safe? Show the arithmetic for both versions of the dose and state what you would do before dispensing.
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The prescription volume is right and the ward note is wrong by a factor of six - but nothing should be dispensed until the prescriber confirms in writing.
Arithmetic:
- Prescription version: 2.4 mL of 5 mg/mL = 12 mg per dose, i.e. 24 mg/day. For 12 kg that is 2 mg/kg/day, squarely within the usual paediatric range of 1 to 3 mg/kg/day for heart failure.
- Ward-note version: 12 mg/kg/day x 12 kg = 144 mg/day, i.e. 72 mg per dose. That is six times the intended dose and far above the maximum.
So the two documents contradict each other and the discrepancy must be resolved by the prescriber, not by the pharmacist silently choosing the 'nicer' number. Make the call, record the name of the doctor, the time, and the confirmed instruction in the prescription.
There is a second safety issue independent of the arithmetic: the child is on enalapril plus spironolactone, a combination that causes hyperkalaemia, and on furosemide. Before the first dose, confirm today's serum potassium and creatinine. If potassium is already above 5.5 mmol/L, the prescriber must be told before any spironolactone is given.
2. How would you prepare the 60 mL batch, and what beyond-use date and labelling would you assign? Show the tablet count.
Read the worked answer
Quantity required: 60 mL x 5 mg/mL = 300 mg = 12 tablets of 25 mg.
Method (record it in the extemporaneous compounding log):
- Count and weigh 12 tablets; triturate to a fine, uniform powder in the glass mortar.
- Levigate with a small volume of vehicle to a smooth paste, then add vehicle in small geometric portions, scraping down the walls.
- Transfer to the measuring cylinder, rinse the mortar with vehicle, and make up to 60 mL. Mix gently to avoid frothing; transfer to an amber bottle.
Beyond-use date: the preserved aqueous oral liquid would normally attract a 35-day refrigerated limit, but this vehicle's label forbids refrigeration, so assign the conservative 14 days at controlled room temperature, label it clearly, and note the source of the limit in the compounding record. Do not exceed the manufacturer's own limit if it is shorter.
Labelling must carry: patient name and weight, 'spironolactone 5 mg/mL suspension, 60 mL', 'shake well before use', dose '2.4 mL twice daily', the preparation and expiry dates, storage instruction, and 'for oral use only'. Supply a 5 mL oral syringe with 0.2 mL graduations - the 0.4 mL increments on a 2.4 mL dose are not measurable with a household spoon.
3. What counselling points and monitoring would you give the nurse and the parents?
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Counselling should be practical and tied to the risks of this specific combination:
- Shake the bottle each time - it is a suspension, and an unshaken dose delivers either too little or too much drug.
- Measure 2.4 mL with the oral syringe, never a teaspoon; rinse the syringe after use. Give at roughly 12-hour intervals, and if the dose is given with food, keep it consistent.
- Do not add salt substitutes or potassium-rich supplements, and avoid giving the child any over-the-counter painkiller without asking - NSAIDs plus an ACE inhibitor plus a diuretic plus spironolactone is a recognised route to acute kidney injury.
- Report vomiting, diarrhoea, poor feeding, unusual drowsiness or muscle weakness - these signal dehydration and hyperkalaemia in a child on an ACE inhibitor and a potassium-sparing diuretic.
- Keep the bottle out of the child's reach, and discard the remainder after 14 days.
Monitoring: serum potassium and creatinine at baseline and within 3 to 5 days of starting or changing the dose, daily weight and fluid balance, and blood pressure before each dose while the child is an inpatient. The pharmacist should also record in the notes that the ward's reference to 12 mg/kg/day was corrected, so that the error does not propagate to the discharge summary.