FDA Warns of Dosing Errors With Antifungal Agent Posaconazole (Noxafil)

Two oral formulations cause confusion

The FDA is cautioning that differences in dosing regimens between the two oral formulations of the antifungal agent posaconazole (Noxafil, Merck) have resulted in dosing errors. To help prevent additional medication errors, the drug labels have been revised to indicate that the two oral formulations cannot be directly substituted for each other but require a change in dose. Direct milligram-for-milligram substitution of the two formulations may result in drug levels that are lower or higher than needed to treat certain fungal infections effectively.

Since the approval of posaconazole delayed-release tablets in November 2013, the FDA has received 11 reports of the wrong oral formulations being prescribed and/or dispensed to patients. One case resulted in death, and an additional case resulted in hospitalization. According to the reports, these outcomes were a result of health care professionals not knowing that the two oral formulations cannot be substituted for each other without adjusting the dose because of differences in how the medication is absorbed and handled by the body.

In addition to changes to the outer carton of posaconazole, Merck revised the prescribing information and the patient information in the drug label to alert patients and their health care professionals that the two oral formulations of posaconazole cannot be substituted for each other.

Posaconazole is approved in two oral formulations: an oral suspension and a delayed-release tablet. It is also approved as an intravenous solution for injection. The drug is used to help prevent certain invasive fungal infections caused by Aspergillus and Candida fungi. Posaconazole is used in patients who have an increased chance of getting these infections because of weakened immune systems. Posaconazole oral suspension is also used to treat thrush, a fungal infection of the mouth or throat area caused by Candida.

The FDA advises prescribers to specify the dosage form, strength, and frequency on all prescriptions they write for posaconazole. Pharmacists should request clarification from prescribers when the dosage form, strength, or frequency is not specified. Patients should talk to their health care professional before they switch from one oral formulation to the other.

Source: FDA; January 4, 2016.