Sulfadimethoxine, sulfamethoxine, and trimethoprim sulfa are the current drugs of choice for treating coccidian infections in reptiles.
Protozoan parasites are very common in reptiles and consist of unicellular organisms, which for the most part can be observed only with a microscope. This group of parasites includes the better-known amoebae, coccidia, and cryptosporidia organisms and also the lesser-known flagellates, ciliates, and parasites of the bloodstream (e.g., Plasmodium sp. and Haemosporina). Metronidazole and the sulfa drug family are far and away the most commonly employed drugs for this group of parasites.
Sulfadimethoxine (Albon), sulfamethoxine (Bactrovet), and trimethoprim sulfa are the current drugs of choice for treating coccidian infections in reptiles. These sulfa drugs are both antibacterial and anticoccidial. Sulfa drugs in general exert a static, or suppressant, effect on susceptible bacteria and coccidia. Trimethoprim sulfa has a cidal effect against bacteria. Remember that cidal drugs kill and static drugs suppress their targeted agent. Coccidia would be much easier to treat and eliminate if the sulfa drugs were coccidiocidal.
The antibacterial effects of these drugs are due to the inhibition of enzymes in the folic acid pathway, thereby inhibiting bacterial thymidine synthesis. The anticoccidian mode of action is thought to be the interference with para-aminobenzoic acid (PABA), interference with folic acid pathways, or both.
Sulfadimethoxine is dosed at 50 mg/kg PO daily for five days and then given every forty-eight hours until negative fecals are obtained. Trimethoprim sulfa is dosed at 30 mg/kg PO every forty-eight hours until negative fecals are obtained. These drugs are generally well tolerated and can be administered over a long period of time if the reptile is well hydrated. These drugs should be used with caution in debilitated and dehydrated reptiles and strictly avoided in reptiles with renal failure. Appetite suppression has been noted in both chameleons and bearded dragons, but appetites resume once the drug is discontinued.
Excerpt from the book Understanding Reptile Parasites by Roger Klingenberg with permission from its publisher, Advanced Vivarium Systems.