Azithromycin (Zithromax) is an antibiotic that belongs to the macrolide class of drugs. It is licensed for treating respiratory tract infections, infections of the middle ear, skin and soft tissue infections, and chlamydia. It is manufactured by Pfizer.

Azithromycin is an effective treatment for Mycobacterium avium intracellulare (MAI), cryptosporidiosis, bacillary angiomatosis and toxoplasmosis^[1][2][3]. Azithromycin is also effective in preventing MAI in people with advanced HIV infection who are unresponsive to anti-HIV therapy with a CD4 cell count below 100 cells/mm³ at a dose of 1200mg once a week^[4][5][6].

Some doctors also use azithromycin to treat syphilis with a single dose of 2000mg^[7]. However, an azithromycin-resistant strain of syphilis has recently been found in HIV-positive gay men in the United States and Ireland^[8]. A single case report has also shown that a 1000mg dose of azithromycin can cure early Lymphogranuloma venereum (LGV)^[9].

Nausea is a frequent side effect of azithromycin at the dose of 600mg once a day used to treat MAI. Other side effects include diarrhoea, abdominal pain and loose stools. The tablets contain lactose, to which some people are allergic. There is an increased risk of side-effects if it is taken at the same time as some anti-histamines and the anti-mycobacterial rifabutin (Mycobutin).

Azithromycin is best taken on an empty stomach to maximise absorption, and should be taken at least two hours apart from antacids or ddI (didanosine, Videx / VidexEC), which will interfere with absorption. There are no known interactions between azithromycin and any currently available protease inhibitors or non-nucleoside reverse transcriptase inhibitors (NNRTIs).