How is vitamin B12 administered to a 9-year-old child weighing 16 kg after an ileal resection?

Vitamin B12 Administration After Ileal Resection in a 9-Year-Old Child

For a 9-year-old child weighing 16 kg after ileal resection, vitamin B12 should be administered as 1000 mcg intramuscularly monthly for life, starting immediately as prophylactic therapy regardless of whether deficiency has been documented. 1, 2

Route of Administration

Intramuscular injection remains the guideline-recommended standard for vitamin B12 supplementation after ileal resection. 1, 2 The parenteral route ensures adequate absorption in patients with ileal malabsorption, bypassing the compromised gastrointestinal absorption mechanism. 3

Alternative Routes (If IM Not Feasible)

While intramuscular administration is preferred, alternative routes may be considered in specific circumstances:

• Oral high-dose therapy: 1200-2400 mcg daily has shown efficacy in treating deficiency in pediatric patients with Crohn's disease, though this is less well-established for ileal resection 1
• Sublingual administration: 1000 mcg daily has demonstrated successful normalization of B12 levels in a 9-year-old with short bowel syndrome and 32 cm residual small intestine 4, 5
• Intranasal hydroxocobalamin: 1500 mcg has shown efficacy in adults with ileal resection, though pediatric data are limited 6

However, these alternative routes should only be considered if intramuscular administration is truly not feasible, as parenteral supplementation remains the reference standard. 1

Dosing Protocol

Prophylactic Supplementation (No Documented Deficiency)

• 1000 mcg vitamin B12 intramuscularly monthly indefinitely 1, 2
• This applies to all patients with >20 cm ileal resection, regardless of current B12 status 1, 2

Treatment of Documented Deficiency (If Present)

If deficiency is already documented with clinical symptoms:

• Loading phase: 1000 mcg intramuscularly every other day for one week 1, 2
• Maintenance: 1000 mcg intramuscularly monthly for life 1, 2

Critical Considerations Based on Resection Length

The extent of ileal resection determines the risk and management approach:

• <20 cm resection: Typically does not cause deficiency; supplementation may not be required 1, 2
• 20-60 cm resection: Variable risk of malabsorption; prophylactic supplementation recommended 2
• >30 cm resection: High risk for B12 deficiency; definite need for lifelong supplementation 1

Since the question does not specify the exact length of ileal resection, assume prophylactic supplementation is indicated and initiate 1000 mcg IM monthly. 1, 2

Monitoring Requirements

Initial Monitoring Schedule

• 3 months after starting supplementation 2
• 6 months after starting supplementation 2
• 12 months after starting supplementation 2
• Annually thereafter 1, 2

Laboratory Parameters to Monitor

• Serum B12: Target >150 pmol/L (>203 pg/mL) 2
• Methylmalonic acid (MMA): If B12 levels are indeterminate (180-350 pg/mL); MMA >271 nmol/L confirms functional deficiency 2
• Homocysteine: Target <10 μmol/L for optimal outcomes 2
• Complete blood count: To assess for megaloblastic anemia 1

Formulation Selection

Hydroxocobalamin is the preferred formulation over cyanocobalamin, particularly in patients who may develop renal complications. 7 Cyanocobalamin requires renal clearance of the cyanide moiety and is associated with increased cardiovascular events in patients with renal dysfunction. 7

Common Pitfalls to Avoid

Never Discontinue Supplementation

Do not stop B12 supplementation even if levels normalize. 2 Patients with ileal resection >20 cm require lifelong supplementation due to permanent malabsorption. 1, 2 Discontinuing therapy after normalization will lead to recurrence of deficiency. 2

Folic Acid Precaution

Never administer folic acid before ensuring adequate B12 treatment. 7, 2 Folic acid can mask B12 deficiency anemia while allowing irreversible neurological damage (subacute combined degeneration of the spinal cord) to progress. 7, 2, 3

Do Not Rely on Oral Absorption

Do not assume oral B12 will be adequate in ileal resection patients. 3 Gastrointestinal absorption of vitamin B12 depends on intrinsic factor and occurs in the terminal ileum. 3 With ileal resection, this absorption mechanism is compromised, making oral supplementation unreliable as primary therapy. 3

Screen for Additional Deficiencies

Patients with ileal resection are also at risk for:

• Fat-soluble vitamin deficiencies (A, D, E, K) due to bile salt malabsorption 1
• Folate deficiency, especially if on sulfasalazine or methotrexate 1, 2

Practical Administration Details

For a 16 kg child receiving intramuscular injections:

• Use 25-27 gauge needle for injection 7
• Vastus lateralis (anterolateral thigh) is the preferred site in children 7
• Avoid the buttock due to risk of sciatic nerve injury 7
• Apply pressure at injection site for 5-10 minutes if thrombocytopenia is present 7

Summary Algorithm

1. Confirm ileal resection >20 cm → Initiate prophylactic B12 supplementation 1, 2
2. Start 1000 mcg hydroxocobalamin IM monthly for life 1, 7, 2
3. Monitor at 3,6,12 months, then annually 2
4. Measure serum B12, MMA if borderline, homocysteine, and CBC 2
5. Never discontinue supplementation 2
6. Ensure adequate B12 before giving folic acid 7, 2