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A group of researchers at the University of Florida College of Pharmacy recently submitted a citizen's petition asking the Food & Drug Administration to increase the maximum allowable dose of phenylephrine (PE) from 10 mg to 25 mg and to withdraw approval of phenylephrine for children under 12 years of age. The petition also called for additional research to validate the safety and effectiveness of the higher recommended dose.
In July, the researchers published a peer-reviewed letter to the editor of the Journal of Allergy and Clinical Immunology warning that phenyl-ephrine was ineffective at the FDA's 1976 approved dose of 10 mg. In February 2006, Annals of Pharmacotherapy released preliminary on-line access to the researchers' meta-analysis report.
Schneider cited a study conducted by Pfizer Inc. in 2006 which looked at 1,000 participants in the United States. "The study demonstrated that 83% were very satisfied with phenylephrine's efficacy," he said.
Randy C. Hatton, Pharm.D., clinical professor at the University of Florida College of Pharmacy, who headed the meta-analysis, said, "We were receiving complaints from practitioners, who were receiving complaints from patients that phenylephrine doesn't seem to work as well as pseudoephedrine."
Hatton argued that phenylephrine is not absorbed as reliably as phenylpropanolamine (PPA) and pseudoephedrine because it is metabolized in the gut by enzymes before it gets into the systemic circulation. "There's an opportunity for variations from patient to patient as to how much gets into the system," he said. The researchers claimed in their published letter that on average only 38% of the dose of phenyl-ephrine reaches the systemic circulation, compared with 90% of a pseudoephedrine dose.
Schneider countered, "The oral bioavailability of 38% is a well-known characteristic of phenyl-ephrine. To point at that is truly a red herring. There are many very efficacious medicines with a much lower bioavailability. That the bioavailability isn't on the order of 90% doesn't mean a drug is less efficacious. There is variability in absorption between individuals, but that applies basically to all substances-phenylephrine as well as pseudoephedrine. It's one of the things that happens with oral dosing. Scientifically, you can only circumvent it by injecting a substance."
In the citizen's petition, the University of Florida researchers also requested that FDA withdraw approval of phenylephrine for children under 12 years of age. "We didn't see any data for children at all. Our contention is it shouldn't be used in children under 12 except under the supervision of a registered prescriber, so it would basically no longer be OTC for children less than 12. We couldn't find any evidence to support its use in that age group to show it was safe or effective," said Hatton.