Compounding a Pediatric Sildenafil Suspension from Tablets
A 16 kg, 4-year-old child with pulmonary arterial hypertension is prescribed sildenafil 10 mg by mouth three times daily. The pharmacy stocks only sildenafil 20 mg film-coated tablets and a preserved oral suspending vehicle (Ora-Plus and Ora-Sweet combined 1:1, containing methylparaben and potassium sorbate). The prescriber wants a 10 mg/mL suspension and the caregiver is to receive 60 mL. Doses are given at 0700, 1500, and 2300; the child attends daycare during the day and the mother works night shifts.
1. Calculate how many tablets and how much vehicle are needed to prepare a batch that includes a practical overage for transfer loss, then state the final concentration and the volume of each dose.
Read the worked answer
Required drug mass: 10 mg/mL x 60 mL = 600 mg = 600 / 20 = 30 tablets as an absolute minimum.
Practical batch with overage: transfer and rinsing losses on a mortar-and-pestle or ointment-slab preparation are typically 5-10%, and 30 tablets does not allow a clean rinse. Prepare 80 mL:
- 10 mg/mL x 80 mL = 800 mg = 40 tablets of 20 mg
- Dispense 60 mL; the remaining ~20 mL absorbs the loss on the mortar, pestle, and graduate.
Method: levigate the crushed tablets (verify the tablets may be crushed and that the child has no excipient allergy) with a small portion of the 1:1 vehicle to a smooth paste, geometrically dilute, transfer to a calibrated graduate with rinses, and qs to 80 mL with the same 1:1 vehicle. Label 10 mg/mL.
Dose volume: 10 mg / 10 mg/mL = 1 mL per dose, three times daily (3 mL/day; 60 mL = a 20-day supply at the prescribed schedule).
2. Assign a beyond-use date and storage conditions for this preparation and justify them. What would change if the vehicle were unpreserved?
Read the worked answer
Default beyond-use date: 35 days, refrigerated (USP <795> default for a water-containing oral preparation made from a nonsterile commercial product with a preservative present). Refrigeration is chosen over room temperature for palatability and to slow microbial growth, and the bottle must be labeled with the date prepared and the calculated BUD.
Key qualifier: use the earlier of the default BUD and any product-specific stability data available for this drug, vehicle, and concentration. If published stability data support fewer than 35 days for this combination, that shorter date governs; document the source in the compounding record.
If the vehicle were unpreserved: the default for an aqueous, unpreserved oral liquid is 14 days, refrigerated, because there is no antimicrobial preservative to control growth introduced during compounding and repeated patient use.
The 20-day supply fits inside a 35-day BUD only if the preparation is dispensed promptly and stored correctly; a 14-day unpreserved BUD would require splitting the dispensed quantity or adding a preservative-containing vehicle.
3. The caregiver says she will 'use a teaspoon from the kitchen and keep it in the fridge next to the juice.' List your counseling points in priority order, including what you would do about the daycare.
Read the worked answer
- Measuring device first: dispense a 1 mL (or 3 mL) oral syringe and mark the 1 mL line. Explain that a household teaspoon delivers roughly 4-6 mL and would give a 4- to 6-fold overdose of a vasodilator; never use a kitchen spoon.
- Shake vigorously for 10-15 seconds before every dose - it is a suspension, and an unshaken dose is not the labeled concentration.
- Storage: refrigeration is correct; keep the bottle closed, upright, and out of a child's reach and out of direct light. Do not store next to food the child can reach, and never leave the syringe where the child can play with it.
- Dosing clock: 0700, 1500, 2300. Since the mother works nights, agree on who gives the 1500 dose and set phone alarms; for a missed dose give it as soon as remembered unless it is nearly time for the next dose, and never double up.
- Daycare: provide a labeled syringe, a written dose card, and a second labeled bottle or pre-measured doses per daycare medication policy; confirm the daycare's authorization-to-administer form is signed.
- Adverse effects to report: flushing, headache, nasal congestion, upset stomach are common; report vision changes, hearing loss, or a painful/prolonged erection (priapism) immediately. Mention that the drug must not be handled by anyone taking nitrates and that it must never be shared.
- Refills: request a refill before day 18; discard remaining suspension at the BUD date.