What are the clinical consequences and immediate management steps for a patient who inadvertently injected 25 units (≈0.25 mL) of tirzepatide/l‑carnitine subcutaneously, exceeding the recommended weekly dose?

Immediate Management of Tirzepatide Overdose

This patient injected approximately 1.9 times her prescribed weekly dose (25 units ≈ 0.25 mL = 4.25 mg tirzepatide instead of 13 units ≈ 0.13 mL = 2.21 mg) and requires close monitoring for severe gastrointestinal complications, particularly paralytic ileus and bowel obstruction, which can persist for weeks due to tirzepatide's long half-life.

Primary Clinical Concerns

The most critical ramifications of this tirzepatide overdose are:

Gastrointestinal Complications (Highest Priority)

• Paralytic ileus: A case report documented prolonged paralytic ileus lasting 3 weeks after tirzepatide overdose, requiring gastrointestinal decompression and prokinetic agents 1. The long half-life of tirzepatide causes persistent suppression of intestinal motility.

• Small bowel obstruction: Multiple recent cases describe acute small bowel obstruction with tirzepatide therapy, even at therapeutic doses 2, 3. The overdose significantly increases this risk through impaired gastrointestinal motility.

• Severe nausea, vomiting, and diarrhea: These are the most common side effects, occurring in 25% (nausea) and up to 10% (vomiting/diarrhea) of patients at therapeutic doses 4. An overdose will likely intensify these symptoms.

Life-Threatening Electrolyte Disturbances

Prolonged vomiting and diarrhea from tirzepatide can cause severe electrolyte imbalances leading to cardiac arrest. One case documented ventricular fibrillation from profound hypokalemia (K⁺ 2.2), hypomagnesemia (Mg²⁺ 1.1), and hypocalcemia (corrected Ca²⁺ 5.6) after high-dose tirzepatide 5.

Metabolic Complications

• Starvation-type euglycemic ketoacidosis: Severe appetite suppression and vomiting can trigger high anion gap metabolic acidosis even without diabetes, requiring ICU admission and dextrose infusion 6.

Immediate Management Algorithm

Within First 24-48 Hours:

1. Monitor vital signs and gastrointestinal symptoms closely

   • Watch for severe abdominal pain, distension, inability to pass gas/stool
   • Document frequency of vomiting and diarrhea episodes
   • Check for signs of dehydration and orthostatic hypotension

2. Obtain baseline laboratory studies immediately:

   • Complete metabolic panel with particular attention to:
     • Potassium (target >3.5 mEq/L)
     • Magnesium (target >1.8 mg/dL)
     • Calcium (corrected for albumin)
   • Venous blood gas if vomiting is severe (check for metabolic acidosis, anion gap)
   • Serum ketones if poor oral intake or abdominal pain develops

3. Aggressive electrolyte monitoring and replacement

   • Repeat electrolytes every 6-12 hours if vomiting/diarrhea is significant
   • Replace deficits aggressively before cardiac complications develop 5

Days 2-21 (Extended Monitoring Period):

The long half-life of tirzepatide means complications can develop or persist for weeks 1. Continue monitoring for:

• Progressive constipation or inability to pass stool/gas
• Worsening abdominal pain or distension
• Persistent vomiting despite antiemetics

If Severe Symptoms Develop:

• Obtain CT abdomen/pelvis if severe abdominal pain, distension, or peritoneal signs develop to rule out bowel obstruction 2, 3
• Consider nasogastric decompression if ileus or obstruction is confirmed 1
• Admit for IV hydration if unable to maintain oral intake or electrolyte abnormalities persist

Supportive Care Measures

• Antiemetics: Ondansetron, metoclopramide (though metoclopramide may be less effective given tirzepatide's mechanism)
• Prokinetic agents: May be needed if ileus develops 1
• Small, frequent meals with increased water and fiber intake once tolerating oral intake 4
• Avoid high-fat, spicy foods and alcohol 4

L-Carnitine Component

The L-carnitine component (100 mg) in this formulation is unlikely to cause significant additional toxicity. Standard L-carnitine dosing ranges from 1-3 g/day orally 7, and the overdosed amount (approximately 25 mg) remains well below therapeutic ranges.

Critical Pitfalls to Avoid

• Do not dismiss persistent gastrointestinal symptoms as "expected side effects" - bowel obstruction and ileus are serious complications requiring imaging
• Do not wait for symptoms to worsen before checking electrolytes - cardiac arrest can occur suddenly 5
• Do not assume symptoms will resolve quickly - tirzepatide's long half-life means complications can persist for 2-3 weeks 1

Patient Education

Immediately counsel the patient on:

• Proper dosing technique and syringe measurement (13 units = 0.13 mL, not 25 units)
• Warning signs requiring emergency evaluation: severe abdominal pain, inability to pass stool/gas for >24 hours, persistent vomiting, chest pain, palpitations
• The medication should be held until symptoms completely resolve and only restarted after provider evaluation