A 38-year-old man with celiac disease and chronic diarrhea presents with macrocytic anemia, elevated LDH, and low reticulocyte count. Serum B12 is normal but folate is 2.1 ng/mL (normal 5.4). What is the drug of choice for treatment?

Question

A 38-year-old man with celiac disease and chronic diarrhea presents with macrocytic anemia, elevated LDH, and low reticulocyte count. Serum B12 is normal but folate is 2.1 ng/mL (normal >5.4). What is the drug of choice for treatment?

Accepted Answer

A. Folic acid 5 mg orally daily. ## Diagnosis: Folate Deficiency Megaloblastic Anemia

This patient has folate deficiency secondary to malabsorption from celiac disease. The serum folate is low (2.1 ng/mL, normal >5.4), B12 is normal, and the megaloblastic picture with elevated LDH confirms the diagnosis.

## First-Line Treatment: Folic Acid

**Key Point:** Folic acid (pteroylmonoglutamate) is the standard first-line treatment for folate deficiency megaloblastic anemia. Oral dosing is effective when malabsorption is not severe.

**High-Yield:** Standard dosing regimen:
- **5 mg orally once daily** for 4 weeks, then reassess
- Response: reticulocytosis within 3–5 days, Hb rise in 2–3 weeks
- Maintenance: dietary supplementation or prophylaxis if ongoing malabsorption

## Why Folic Acid (Not Folinic Acid or Methylfolate)?

| Feature | Folic Acid | Folinic Acid (Leucovorin) | Methylfolate |
|---------|---|---|---|
| **First-line for folate deficiency** | Yes | No | No |
| **Mechanism** | Converted to THF by DHFR | Bypasses DHFR (for methotrexate toxicity) | Active form (for MTHFR deficiency) |
| **Cost** | Lowest | Higher | Higher |
| **Indication** | Nutritional folate deficiency | MTX rescue, not folate deficiency | Genetic MTHFR deficiency |
| **Oral bioavailability** | Good | Moderate | Moderate |

**Clinical Pearl:** Folinic acid is reserved for rescue of methotrexate toxicity (it bypasses dihydrofolate reductase), not for nutritional folate deficiency. Methylfolate is for genetic MTHFR deficiency, not common folate deficiency.

**Mnemonic:** **FAD = Folic Acid for Dietary** — Folic acid is the standard for nutritional/malabsorption-related folate deficiency.

Answer

B. Folinic acid (leucovorin) 10 mg orally daily

Answer

C. Cyanocobalamin 1000 mcg intramuscularly monthly

Answer

D. Methylfolate 5 mg orally daily

A 38-year-old man with celiac disease and chronic diarrhea presents with macrocytic anemia, elevated LDH, and low reticulocyte count. Serum B12 is normal but folate is 2.1 ng/mL (normal >5.4). What is the drug of choice for treatment?

Explanation

Diagnosis: Folate Deficiency Megaloblastic Anemia

First-Line Treatment: Folic Acid

Why Folic Acid (Not Folinic Acid or Methylfolate)?

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Feature	Folic Acid	Folinic Acid (Leucovorin)	Methylfolate
First-line for folate deficiency	Yes	No	No
Mechanism	Converted to THF by DHFR	Bypasses DHFR (for methotrexate toxicity)	Active form (for MTHFR deficiency)
Cost	Lowest	Higher	Higher
Indication	Nutritional folate deficiency	MTX rescue, not folate deficiency	Genetic MTHFR deficiency
Oral bioavailability	Good	Moderate	Moderate