What is the best course of treatment for a patient with a suspected vitamin B12 deficiency presenting with vomiting?

Treatment of B12 Deficiency Presenting with Vomiting

For a patient with suspected B12 deficiency presenting with vomiting, immediately administer thiamine 200-300 mg daily and vitamin B co strong (1-2 tablets three times daily) to prevent Wernicke's encephalopathy, while simultaneously investigating the underlying cause and initiating B12 replacement therapy. 1

Immediate Management of Vomiting

The vomiting itself is the critical issue requiring urgent attention, as prolonged vomiting creates risk for thiamine deficiency and Wernicke's encephalopathy, which can cause irreversible neurological damage. 1

• Give thiamine supplementation immediately (200-300 mg daily orally, or IV if unable to tolerate oral medications) 1
• Add vitamin B co strong (1-2 tablets three times daily) 1
• If unable to tolerate oral thiamine or clinical suspicion of acute deficiency exists, give intravenous thiamine 1
• Refer back to specialist center for investigation of the vomiting cause if the patient has had bariatric surgery 1

Diagnostic Approach for B12 Deficiency

While managing the vomiting, confirm B12 deficiency status:

• Measure serum total B12 as the initial test (costs ~£2, rapid turnaround) 2
• If B12 <180 pg/mL (<150 pmol/L): confirmed deficiency, initiate treatment immediately 2, 3
• If B12 180-350 pg/mL (indeterminate range): measure methylmalonic acid (MMA) 2, 3
• MMA >271 nmol/L confirms functional B12 deficiency with 98.4% sensitivity 2
• Check complete blood count for megaloblastic anemia (though absent in one-third of cases) 2

B12 Replacement Therapy Based on Clinical Presentation

If Neurological Symptoms Present (including glossitis, paresthesias, cognitive changes):

Hydroxocobalamin 1 mg intramuscularly on alternate days until no further improvement, then transition to maintenance with 1 mg IM every 2 months for life. 4, 5

• Neurological symptoms often present before hematologic changes and can become irreversible if untreated 2
• Tongue symptoms (glossitis, tingling, numbness) represent neurological involvement requiring aggressive treatment 4
• Pain and paresthesias often improve before motor symptoms 4

If No Neurological Involvement:

Hydroxocobalamin 1 mg intramuscularly three times weekly for 2 weeks, followed by maintenance treatment of 1 mg IM every 2-3 months for life. 4, 5

Route of Administration Considerations:

• Avoid intravenous route - almost all vitamin will be lost in urine 6
• Intramuscular or deep subcutaneous injection is the recommended route 6
• Oral B12 is not dependable for pernicious anemia or malabsorption 6
• If vomiting prevents oral intake, parenteral administration is mandatory 1

Critical Pitfalls to Avoid

Never administer folic acid before treating B12 deficiency, as folic acid may mask anemia while allowing irreversible neurological damage to progress (subacute combined degeneration of the spinal cord). 4, 5, 6

• Check folate levels concurrently, but do not treat folate deficiency until B12 treatment has begun 4
• Doses of folic acid >0.1 mg daily may result in hematologic remission while neurologic manifestations progress 6

Do not rely solely on serum B12 to rule out deficiency - standard testing misses functional deficiency in up to 50% of cases. 2

Do not stop B12 injections after symptoms improve - stopping can lead to irreversible peripheral neuropathy. 4

Monitoring During Initial Treatment

• Monitor serum potassium closely in the first 48 hours and replace if necessary 6
• Repeat hematocrit and reticulocyte counts daily from days 5-7 of therapy, then frequently until hematocrit normalizes 6
• If reticulocytes have not increased after treatment, reevaluate diagnosis or treatment 6
• Recheck B12 levels at 3 months, then 6 and 12 months in the first year, followed by annual monitoring 4

Special Populations Requiring Prophylactic Treatment

Even without documented deficiency, give prophylactic hydroxocobalamin 1000 mcg IM monthly indefinitely for: 4

• Ileal resection >20 cm 4, 5
• Crohn's disease with ileal involvement >30-60 cm 4
• Post-bariatric surgery patients 4
• Chronic PPI or metformin use 4

Long-Term Maintenance

Hydroxocobalamin 1 mg IM every 2-3 months for life is standard maintenance after initial loading. 4, 5, 7

• Some patients require monthly dosing (1000 mcg IM) to meet metabolic requirements 4
• Up to 50% of individuals require individualized injection regimens ranging from daily to every 2-4 weeks to remain symptom-free 8
• Do not "titrate" injection frequency based on measuring serum B12 or MMA - base frequency on clinical symptom control 8