Three New Pfizer Studies Show a Single Dose of Azithromycin Microspheres is as Effective as Multi-Dose Treatment for Respiratory Tract Infections in Adults

WASHINGTON -- Three head-to-head studies

presented during the 44th annual Interscience Conference on Antimicrobial

Agents and Chemotherapy (ICAAC) in Washington show that Pfizer Inc.'s new

investigational microsphere formulation of azithromycin, which is dosed as a

one-time-only oral antibiotic, is comparable to other frequently prescribed

treatments for some of the most common respiratory tract infections in adult

patients.  Azithromycin has been available in the United States since 1992

under the tradename Zithromax. 


Pfizer sponsored the studies and has

submitted the data for review by the Food and Drug Administration (FDA).  The

Company is seeking approval for the treatment of adult respiratory tract

infections, including acute bacterial exacerbations of chronic bronchitis

(AECB) acute bacterial sinusitis (ABS) and community acquired pneumonia (CAP).


These three studies showed that with one dose, azithromycin microspheres

provides a complete course of therapy for the treatment of AECB, ABS and CAP.

Azithromycin microspheres was compared to a seven-day regimen of

clarithromycin XL for the treatment of CAP and to seven- and 10-day courses

of levofloxacin for the treatment of AECB and ABS, respectively.


"Given the efficacy of a one-time-dose for these common infections and the

assured compliance, the hope would be that this type of regimen can help

minimize the emergence of antibiotic resistance," said Michael Niederman,

MD, chairman of the Department of Medicine at Winthrop-University Hospital,

Mineola, N.Y. and professor of medicine at the State University of New York at

Stony Brook.  "Antibiotic resistance is a growing problem in the treatment of

community respiratory tract infections, and one of the factors that

contributes to its development is patients taking an incomplete course of



Study Results


In two of three multicenter, randomized, double-blind, double-dummy trials

presented, azithromycin microspheres was compared to levofloxacin.  One study

examined azithromycin microspheres (2.0 g) and levofloxacin (500 mg/day for

seven days) in 446 subjects with AECB.  The clinical cure rate in the

azithromycin microspheres group was comparable (95 percent) to the

levofloxacin group (96 percent).  Chronic bronchitis is characterized by

excessive cough and sputum production on most days for at least three months

during at least two consecutive years with intermittent acute exacerbations.

AECB are usually manifested as an increase in dyspnea (difficult or labored

breathing), sputum volume and/or sputum purulence (pus).(1)


Azithromycin microspheres was also compared to levofloxacin (500 mg/day

for 10 days) in 541 patients with ABS.  Clinical success rates were

comparable -- 94.5 percent of patients treated with azithromycin microspheres

and 92.8 percent of levofloxacin-treated patients.  ABS is an acute infection

of the sinuses that can cause purulent nasal discharge, nasal congestion,

fever and facial pain or tenderness(2).


In another study presented during the meeting, the new formulation of

azithromycin was compared to clarithromycin XL (1 g/day for seven days) in 501

randomized subjects with mild-to-moderate CAP.  Treatment with azithromycin

microspheres resulted in comparable pathogen eradication rates (91.8 percent)

vs. clarithromycin XL (90.5 percent).  The clinical success rate in the

azithromycin microspheres group was 92.6 percent vs. 94.7 percent in the

clarithromycin XL group.  CAP is a lung infection acquired outside of

hospitals or extended-care facilities.(3)


"A one-dose-only treatment is a significant advance, giving physicians and

patients an option that can effectively treat the most common respiratory

tract infections that occur in adults, while also providing an additional

benefit regarding noncompliance with therapy," said Joseph Feczko, MD,

president of Worldwide Development, Pfizer Inc.


The new formulation of azithromycin microspheres offers a safety profile

comparable to other antibiotic treatments for common respiratory tract

infections and is generally well tolerated.  In clinical studies, side effects

were generally mild and resolved within two days for the majority of patients.

The most common adverse events on day one were diarrhea/loose stools

(11.7 percent), nausea (3.9 percent), abdominal pain (2.7 percent) and

vomiting (1.1 percent).(4)  Patients with known hypersensitivity to

azithromycin, erythromycin or any macrolide or ketolide antibiotic should not

take azithromycin microspheres.


The new azithromycin formulation allows for delayed release of drug, which

occurs in the small intestine instead of in the stomach, maintaining

tolerability.  This, together with the long half-life of azithromycin

microspheres, makes it possible to deliver the entire two-gram dose as a

single dose regimen.


Pfizer Inc. discovers, develops, manufactures and markets leading

prescription medicines for humans and animals and many of the world's best-

known consumer brands. 




    (1) Niederman, Michael S.  "Nationalise: North American Taskforce on

        Improving Outcomes in AECB and LRTIs - Implementation, Strategies and

        Education." Supplement to Consultant. Oct 2002, Vol 42, Num 12, pgs.


    (2) Piccirillo JF.  "Acute Bacterial Sinusitis." New England Journal of

        Medicine. 2004; 351:902-910. Number 9

    (3) Schmitt SK. "Community-Acquired Pneumonia." The Cleveland Clinic

        Foundation. 2004.

    (4) Pfizer product insert: Azithromycin microspheres.



Source:  Pfizer, Inc