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Zithromax

Azithromycin is the first macrolide antibiotic belonging to the azalide group. Azithromycin is derived from erythromycin by adding a nitrogen atom into the lactone ring of erythromycin A, thus making the lactone ring 15-membered. Azithromycin is sold under the brand names Zithromax and Sumamed, and is one of the world's best-selling antibiotics. Azithromycin is used for the treatment of respiratory-tract, soft-tissue and genitourinary infections. more...

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Etymology

Azithromycin's name is derived from the azane-substituent and erythromycin. Its accurate chemical name is

(2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-13- -2-ethyl- 3,4,10-trihydroxy-3,5,6,8,10,12,14-heptamethyl -11--1-oxa- 6-azacyclopentadecan-15-one.

History

A team of Pliva's researchers, Gabrijela Kobrehel, Gorjana Radobolja-Lazarevski and Zrinka Tamburasev led by Dr Slobodan Dokic, discovered azithromycin in 1980. It was patented in 1981, and was later found by Pfizer's scientists while going through patent documents. In 1986 Pliva and Pfizer signed a licensing agreement which gave Pfizer exclusive rights for the sale of azithromycin in Western Europe and the United States. Pliva brought their azithromycin on the market in Central and Eastern Europe under the brand name of Sumamed in 1988, and Pfizer Zithromax in 1991.

Available forms

Azithromycin is commonly administered in tablet or oral suspension. It is also available for intravenous injection.

Mechanism of action

Azithromycin prevents bacteria from growing by interfering with their protein synthesis. Azithromycin binds to the 50S subunit of the bacterial ribosome, and thus inhibits translation of mRNA. Azithromycin has similar antimicrobial spectrum as erythromycin, but is more effective against certain gram-negative bacteria, particularly Hemophilus influenzae.

Pharmacokinetics

Unlike erythromycin, azithromycin is acid-stable and can therefore be taken orally without being protected from gastric acids. It is readily absorbed, and diffused into most tissues and phagocytes. Due to the high concentration in phagocytes, azithromycin is actively transported to the site of infection. During active phagocytosis, large concentrations of azithromycin are released. The concentration of azithromycin in the tissues can be over 50 times higher than in plasma. This is due to ion trapping and the high lipid solubility.

Metabolism

Azithromycin's half-life is approximately 2 days, and it's fairly resistant to metabolic inactivation. Its main elimination route is through excretion in the biliary fluid, and some can also be eliminated through urinary excretion. Azithromycin is excreted through both of these elimination routes mainly in unchanged form.

Side effects

Most common side effects are gastrointestinal; diarrhea, nausea, abdominal pain and vomiting.

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Treating partners immediately reduces recurrence of STDs
From American Family Physician, 7/15/05 by Mark Ebell

Clinical Question: Should the sex partners of patients with gonorrhea or chlamydia be treated immediately, without being examined by a physician?

Setting: Population-based

Study Design: Randomized controlled trial (nonblinded)

Allocation: Uncertain

Synopsis: Patients with gonorrhea or genital chlamydia were identified by laboratory reporting (70 percent), case reports from physicians, and identification of patients as they presented for medical care. Most had chlamydia only (78 percent) and most were women (77 percent); their mean age was 23 years. All 1,860 patients were contacted within the first 14 days after diagnosis of infection and were randomized to one of two groups: (1) usual care, with a recommendation that any sex partners seek care; and (2) expedited treatment, in which patients chose between being given medication for up to three sex partners, or having clinic staff call these partners and offer them medication directly without a clinical evaluation.

The treatment medication was consistent with standard guidelines (i.e., 400 mg of cefixime [Suprax] plus 1 g of azithromycin [Zithromax] for patients with gonorrhea, 1 g of azithromycin for patients with chlamydia). The medication packets also included condoms and information on how to prevent the transmission of sexually transmitted diseases (STDs). It is not clear how allocation was concealed or whether outcomes were assessed blindly.

Patients were contacted 10 to 18 weeks after treatment for repeat testing; approximately one third of patients in each group were lost to follow-up. Among patients with gonorrhea, infection was much less likely at follow-up if they had chosen expedited treatment for their sex partners (3 versus 11 percent; number needed to treat [NNT] = 12.5; P = .01). Among patients with chlamydia, there was a small decrease in the likelihood of infection at follow-up, but it was not statistically significant (11 versus 13 percent). The combined infection rate was slightly lower for patients who received expedited treatment (10 versus 13 percent; NNT = 33; P < .05).

Bottom Line: Giving patients a prescription for their sex partners or having a staff member contact the partners directly to offer treatment without an examination slightly reduces the risk of recurrent infection in the original patient. This is most helpful in patients with gonorrhea. (Level of Evidence: 1b-)

Study reference: Golden MR, et al. Effect of expedited treatment of sex partners on recurrent or persistent gonorrhea or chlamydial infection. N Engl J Med February 17, 2005;352:676-85.

Used with permission from Ebell M. Treating partners immediately reduces STD recurrence. Accessed online April 27, 2005, at: http://www.InfoPOEMs.com.

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