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Reporting a Medication Error

Dosing Error with Sildenafil Oral Suspension and Its Enclosed Dosing Syringe

Published April 19, 2024

Sildenafil (Revatio) is a medicine used to treat pulmonary arterial hypertension (PAH), a narrowing of the small blood vessels in the lungs that results in increased pressure. The condition can affect both adults and children. Sildenafil is available as an intravenous infusion, a tablet, and as an oral liquid suspension (10 mg/mL) which is easier to use for children. The oral suspension comes with a 2 mL oral syringe that only has markings for 5 mg (0.5 mL) and 20 mg (2 mL) (Figure 1). This means that if a 10 mg dose is needed, a volume of 1 mL will be needed to give the correct dose. Since there is not a 1 mL marking on the syringe, the medicine should be drawn up to the 0.5 mL mark twice to give the correct dose. Infants with PAH may need an even smaller dose (less than 0.5 mL) based on their weight. So, parents would not be able to measure the correct dose using the enclosed syringe.

Figure 1. The oral sildenafil suspension comes with a 2 mL oral syringe that only has markings for 5 mg (0.5 mL) and 20 mg (2 mL).

In a recent case, an infant was to receive a dose of sildenafil oral suspension 2.5 mg (0.25 mL) every 8 hours. When the pharmacy dispensed the medicine, the label included instructions to administer 0.25 mL. However, the pharmacy did not remove the enclosed syringe which could not measure 0.25 mL. At home, the parents used the mg dose number (2.5) to measure the medicine. It is possible that the syringe contributed to the confusion since there are no markings for 0.25 mL. The parents probably used the syringe twice to administer 2.5 mL (one 0.5 mL dose plus one 2 mL dose). The error was not discovered until the parents requested a refill which was too early based on the volume originally dispensed. Fortunately, the infant did not have any adverse effects from the higher dose of medicine.

Here's what you can do: When picking up sildenafil oral suspension from your pharmacy, ask to speak to the pharmacist. Open the package in front of the pharmacist and ask how to measure a dose. If the enclosed syringe does not have markings to measure the dose needed, ask the pharmacist for an appropriate size syringe. Then ask the pharmacist to show you how to measure a dose using the syringe. For example, in the case described above, since the dose was less than 1 mL, the pharmacy should have given the parents a 1 mL oral syringe. The pharmacist should have shown them what marking to use to measure the correct dose (0.25 mL). Finally, you should also repeat back, and show the pharmacist how you will measure a dose using the device.

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