A 35-year-old with chronic plaque psoriasis is started on methotrexate. Folinic acid is given along with it. What is the rationale for giving folinic acid instead of folic acid?
- A Folinic acid has a longer half-life and thus requires less frequent dosing
- B Folinic acid bypasses DHFR inhibition and rescues normal cells without rescuing tumour/dividing skin cells ✓
- C Folinic acid prevents nephrotoxicity of methotrexate
- D Folinic acid reduces systemic absorption of methotrexate
Correct answer: B. Folinic acid bypasses DHFR inhibition and rescues normal cells without rescuing tumour/dividing skin cells
Explanation
Methotrexate inhibits dihydrofolate reductase (DHFR), preventing conversion of dihydrofolate to tetrahydrofolate. Folic acid still requires DHFR to be active, so it would be blocked. Folinic acid (leucovorin) is a fully reduced, active folate that bypasses DHFR and directly replenishes tetrahydrofolate in normal cells, reducing GI and hematological toxicity. However, it is given 24–48 hours after MTX to avoid competing with the therapeutic effect.
Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.