Delivery vehicle leads to increased bioavailability of azithromycin

Key Points

Miami-Azithromycin 1% ophthalmic solution (AzaSite, Inspire Pharmaceuticals) is more soluble and able to remain on the ocular surface for a longer period than it would otherwise because of the patented drug delivery vehicle (DuraSite, InSite Vision) with which it is paired, according to Terrence P. O'Brien, MD.

"That means that the drug levels are much higher than what we've seen with other antibiotics, and that's an exciting bonus of the vehicle, allowing us to achieve very high drug levels for both therapeutic purposes and preventive purposes," said Dr. O'Brien, holder of the Charlotte Breyer Rodgers Distinguished Chair in Ophthalmology and director of the refractive surgery service, Bascom Palmer Eye Institute, Palm Beach Gardens, FL, and Miller School of Medicine, University of Miami.

The vehicle contains polycarbophil, he said.

He said that he and his colleagues have been using the drop to treat posterior and anterior blepharitis as well as conjunctivitis.

"The azithromycin has been wellsuited for ophthalmic use because it has a broad spectrum of activity, and it's known for its high tissue penetration," Dr. O'Brien said.

Single-dose study

He discussed a single-dose study conducted by Inspire Pharmaceuticals that compared azithromycin 1% with moxif loxacin 0.5% (Vigamox, Alcon Laboratories) to assess the achievable concentrations of the drugs in 41 healthy human adult eyes. After one dose of either drop was instilled in the conjunctiva, the conjunctiva was sampled at 30 minutes, 2 hours, 12 hours, and 24 hours (three to six subjects per time point). Researchers used liquid chromatographic-mass spectrometric assays to determine tissue concentrations.

"This was really striking because the levels of azithromycin were 15-fold higher than the moxifloxacin, and, more importantly, they were sustained in the tissue for a much greater period-24 hours after a single dose," he said.

"In addition to its antibacterial properties, this agent has unique immunomodulatory properties that result in an anti-inf lammatory effect," Dr. O'Brien said. "This is a bonus; not only can you treat the infectious aspect, you actually can suppress inf lammation. And for chronic diseases such as blepharitis or chronic conjunctivitis, this is really an exciting, new phenomenon to have dual action of an antibiotic having anti-inflammatory properties."