The most effective treatment for isosporiasis is a combination of two drugs: trimethoprim and sulfamethoxazole (TMP-SMX; Bactrim, Septra). To treat isosporiasis, two double-strength TMP-SMX pills are taken twice a day. An alternative is one double-strength pill three times a day. TMP-SMX treatment is usually continued for two to four weeks.
Unfortunately, between 25% and 50% of HIV-positive people are allergic to the sulfur in the SMX half of TMP-SMX. Two of the main symptoms seen in people with allergic reactions to SMX are fever and rash. Very often, the allergy can be so severe that people need to stop taking SMX.
For patients who cannot tolerate SMX, the drug pyrimethamine (Daraprim), combined with folinic acid, can be taken. This combination of drugs is used for a month.
To help control the diarrhea, perhaps in combination with antibiotic therapy, a number of anti-diarrheal drugs can be taken. This include: diphenoxylate (Lomotil), loperamide (Imodium), paregoric, and Pepto-Bismol. And because diarrhea is the direct result of intestinal inflammation caused by the infection, some non-steroidal anti-inflammatory drugs (NSAIDS) may be helpful such as ibuprofen (e.g., Advil). Another drug that has been shown to greatly reduce diarrhea, due to its anti-inflammatory activity, is thalidomide (Thalomid). Women who take this drug should avoid becoming pregnant; thalidomide can cause severe birth defects.
The most effective way to prevent isosporiasis is to avoid its sources —mainly potentially contaminated foods or human feces. This is particularly true for HIV-positive people with compromised immune systems raveling to tropical and subtropical countries where water and food could be contaminated. Drinking bottled water and making sure that food is cooked properly can help reduce the risk of isosporiasis while raveling to tropical and subtropical areas.
Drugs used to prevent isosporiasis (prophylaxis) are, for the most part, the same as those used to prevent Pneumocystis carinii pneumonia (PCP). Trimethoprim-Sulfamethoxazole (TMP-SMX; Bactrim, Septra) is the most effective combination of drugs used to prevent PCP and to treat isosporiasis. And because PCP prophylaxis is generally started when a person's CD4 cell count falls below 200, he or she should be well protected against Isospora belli in the event he or she is exposed to this protozoan.
Bringing or keeping CD4 counts above 200 with antiretroviral (ARV) therapy is also likely to help prevent isosporiasis. A syndrome—called immune reconstitution inflammatory syndrome (IRIS)—where antiretroviral treatment can actually exacerbate the symptoms of an opportunistic infection due to a strengthened immune response, has not been reported with isosporiasis.
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