TMP-SMX and PCP

 Q: If Trimethoprim-sulfamethoxazole (TMP-SMX) is used for the treatment of Pneumocystis pneumonia in AIDS patients, which of the following is recommended to be used as an adjuvant treatment? (select one) 

 A) folic acid 

B) folinic acid

C) any of the above 

D) none of the above 

 Answer: D

It is recommended to use folate as an adjuvant treatment while TMP-SMX is in use particularly in prolonged use. TMP-SMX is popularly known with its trade name Bactrim. Trimethoprim (TMP) inhibits human dihydrofolate reductase. In prolong use or with its use in folate deficiency it may lead to megaloblastic changes i.e. macrocytic anemia, thrombocytopenia, and/or leukopenia. 

Folinic acid, also known as leucovorin can be used instead of folic acid. 

Said that this adjuvant treatment should not be used in few specific conditions or one should be preferred over the other like:

• In AIDS patients who develop pneumocystis pneumonia, none should be used as it may lead to treatment failure. 
• If a patient is pregnant and develops pneumocystis pneumonia, folic acid should be added as the risk of neural tube defects would be high. 
• In patients with toxoplasmosis, leucovorin (folinic acid) is preferred as parasites can metabolize folic acid but can't metabolize folinic acid.

#pharmacology

References:

1. Ho JM, Juurlink DN. Considerations when prescribing trimethoprim-sulfamethoxazole. CMAJ 2011; 183:1851. 

2. Safrin S, Lee BL, Sande MA. Adjunctive folinic acid with trimethoprim-sulfamethoxazole for Pneumocystis carinii pneumonia in AIDS patients is associated with an increased risk of therapeutic failure and death. J Infect Dis 1994; 170:912.