Interaction Between Bactrim and Folinic Acid

HIV patient currently being treated for PCP and Toxoplasmosis

• First line treatment for PCP involves bactrim which has a major interaction with the first line treatment of toxoplasmosis which uses folinic acid
• Interaction between folinic acid and bactrim
• Treatment failure and excess mortality were observed when trimethoprim-sulfamethoxazole was used concomitantly with leucovorin for the treatment of HIV positive patients with Pneumocystis jiroveci pneumonia in a randomized placebo controlled trial. 
• Co-administration of trimethoprim-  sulfamethoxazole and leucovorin during treatment of Pneumocystis jiroveci pneumonia should be avoided. 

References:

1. http://www.drugs.com/disease-interactions/sulfamethoxazole-trimethoprim,bactrim.html
2. http://www.rxlist.com/bactrim-drug/warnings-precautions.htm
3. LEXICOMP