Side Effects of Leukovorin (Folinic Acid)
Leukovorin is generally well-tolerated with minimal side effects, primarily causing allergic reactions including anaphylaxis and urticaria, with rare reports of hypersensitivity reactions manifesting as flushing, hives, body pain, headaches, and elevated blood pressure. 1
Primary Side Effects from FDA Labeling
The FDA-approved drug label identifies the following adverse reactions 1:
- Allergic sensitization (most significant concern)
- Anaphylactoid reactions
- Urticaria (hives)
- Hypersensitivity reactions following both oral and parenteral administration
Clinical Context-Specific Considerations
When Used as Methotrexate Rescue/Antidote
Leukovorin itself has minimal toxicity when used to counteract methotrexate toxicity. The critical issue is timing—not side effects. As the interval between methotrexate administration and leucovorin rescue increases, effectiveness in counteracting hematologic toxicity decreases 2. The drug should be administered immediately with subsequent doses every 6 hours when methotrexate overdose is suspected 2.
When Combined with Fluorouracil (Cancer Treatment)
A critical warning: leucovorin may enhance fluorouracil toxicity, leading to severe and potentially fatal complications. 1
- Deaths reported from severe enterocolitis, diarrhea, and dehydration in elderly patients receiving weekly leucovorin with fluorouracil 1
- Cardiotoxicity risk of 3% overall when combined with 5-FU, increasing to 15.1% in patients with pre-existing cardiac disease 3
- Cardiac manifestations include myocardial ischemia, supraventricular arrhythmia, and congestive heart failure 3
When Used with Trimethoprim-Sulfamethoxazole
Avoid this combination. Concomitant use with trimethoprim-sulfamethoxazole for Pneumocystis carinii pneumonia in HIV patients was associated with increased treatment failure and mortality 1.
Documented Hypersensitivity Reactions
While rare, case reports document specific hypersensitivity presentations 4:
- Flushing
- Hives
- Body pain
- Headaches
- Elevated blood pressure
- General discomfort
Use in Autism Spectrum Disorder (Recent Evidence)
In recent studies of high-dose folinic acid (2 mg/kg/day) for autism, side effects were generally mild 5, 6, 7:
Most common adverse effects:
- Aggression (9.5%)
- Excitement or agitation (11.7%)
- Insomnia (8.5%)
- Increased tantrums (6.2%)
- Headache (4.9%)
Important note: No significant adverse effects were observed in controlled trials, and the medication was generally well-tolerated 6, 7.
Key Clinical Pitfalls to Avoid
- Do not delay leucovorin administration when treating methotrexate toxicity—effectiveness decreases with time
- Monitor elderly patients closely when combining with fluorouracil due to fatal enterocolitis risk
- Screen for cardiac history before fluorouracil/leucovorin combinations—15-fold increased risk with pre-existing disease
- Avoid combination with trimethoprim-sulfamethoxazole in HIV patients
- Be prepared for anaphylaxis—have resuscitation equipment available for first doses