Pfizer Inc said that the US Food and Drug Administration has approved Zmax (azithromycin extended release) for oral suspension, a one-dose-only treatment for mild-to-moderate acute bacterial sinusitis (ABS) and community-acquired pneumonia (CAP) in adults.

Using microsphere technology, Zmax delivers a complete course of therapy in a single two-gram dose. In the first 24 hours after a dose of Zmax, the amount of drug that gets into the tissue is three times higher than a standard dose of immediate-release azithromycin. Immediate-release azithromycin has been available in the United States since 1992 under the trade name Zithromax. This "front loading" of Zmax provides high drug levels earlier in the course of infection when the bacterial burden is likely to be highest, a Pfizer release said.

"A single, high-dose antibiotic is an important advance in treating certain types of sinusitis and pneumonia in adults," said Dr Joseph Feczko, chief medical officer at Pfizer. "Results showed that one dose of Zmax was as effective as currently available treatments that must be taken for seven to ten days."

Zmax's innovative microsphere technology allows for release of the medicine in the small intestine rather than in the stomach, which results in a favourable side-effect profile. In addition, the high tissue penetration and long half-life of azithromycin make it possible to deliver the entire course of therapy as a single dose.

"The benefit of this type of short-course, high-dose therapy is that it allows patients to be treated with a single dose of antibiotic," said Dr Michael Niederman, chairman, Department of Medicine, Winthrop University Hospital, and Professor of Medicine, State University of New York at Stony Brook. "An antibiotic taken just once can address compliance issues and may minimize the emergence of antibiotic resistance."

Zmax is indicated for acute bacterial sinusitis due to Haemophilus influenza, Moraxella catarrhalis or Streptococcus pneumonia and community-acquired pneumonia due to Chlamydophila pneumonia, Haemophilus influenza, Mycoplasma pneumonia, or Streptococcus pneumonia in patients appropriate for oral therapy.

The Amax adult clinical research program included outpatients with mild-to-moderate acute bacterial sinusitis and community-acquired pneumonia, and acute bacterial exacerbations of chronic bronchitis (AECB).

Pfizer withdrew its application for the treatment of AECB while the FDA re-evaluates how it reviews investigational antibiotics for this indication.

Zmax offers a safety profile comparable to other antibiotic treatments for certain types of sinusitis and pneumonia and is generally well tolerated. Side effects were generally mild to moderate. Overall, in the pivotal studies the most common treatment-related adverse reactions in adult subjects receiving a single (2 g) dose of Zmax were diarrhoea/loose stools (11.6 per cent), nausea (3.9 per cent), abdominal pain (2.7 per cent), headache (1.3 per cent), and vomiting (1.1 per cent). In the majority of Zmax-treated patients, diarrhoea resolved within two days.

Zmax is contraindicated in patients with known hypersensitivity to azithromycin, erythromycin, or any other macrolide or ketolide antibiotic. If an allergic reaction occurs, discontinue drug and institute appropriate therapy. Physicians should be aware that reappearance of the allergic symptoms may occur when symptomatic therapy for the allergic reaction is discontinued. Pseudomembranous colitis has been reported with nearly all antibacterial agents. It is important to consider this diagnosis in patients who present with diarrhoea.