TreatmentUpdate60; Volume 7, No. 6 - June 1995
Sean Hosein

(For information on the symptoms and treatment of the life-threatening brain infection toxo, please read TreatmentUpdate 59.) One of the problems faced by doctors is that some patients with toxo may not be able to tolerate standard therapy--a combination of the antibiotic pyrimethamine and a sulpha drug (such as sulphadiazine). Doctors may sometimes substitute clindamycin in place of sulpha drugs. In the EU, some doctors have been experimenting with the antibiotic clarithromycin to prevent or treat toxo. As some of their patients at risk for toxo developed that infection despite use of clarithromycin, they began an investigation to try and understand what happened.

* STUDY DETAILS

Over a period of 20 months, doctors in France treated 21 subjects who had life-threatening MAC infection with a combination of antibiotics that included clarithromycin, which they took for 3 months. Thirteen subjects had anti-toxo antibodies in their blood, suggesting that they had been infected with the parasite that causes toxo (T. gondii). Before being treated for MAC, 1 subject had toxo but had completely recovered. During the 20 months, 4 subjects developed toxo after an average of 4 months of treatment with clarithromycin. None of the other 9 subjects with anti-toxo antibodies developed toxo.

* RESULTS

The researchers tried to find out why some subjects developed toxo. None of the following differences between the two groups of subjects was statistically significant:

- CD4+ cell counts - length of time they had AIDS - chronic diarrhea - weight - use of other anti-toxo drugs

The doctors did find that a difference in drug combinations between the 2 groups was statistically significant. Subjects who developed toxo were more likely to have been using Cipro, ethambutol, ddI and rifampin.

* EXPLANATION

As many people with HIV/AIDS can be using several drugs for different reasons, it is not surprising that these drugs might interact with each other. The researchers think that ddI might have reduced the absorption of clarithromyin while rifampin could have reduced blood levels of clarithromycin. The researchers note that they only had a small number of subjects in their study and that another study with more subjects should be conducted to investigate possible drug interactions.

* WARNING

The researchers warn that clarithromycin should not be given for prevention of toxo/MAC to patients who are also using rifampin. Patients using such a combination may also develop signs/symptoms of toxo.

REFERENCES:

1. Raffi F, Struillou L, Ninin E, et al. Breakthrough cerebral toxoplasmosis in patients with AIDS who are being treated with clarithromycin. Clinical Infectious Diseases 1995;20:1075-1077.

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