What does it mean when a patient reports injecting 100 units of compounded tirzepatide (Mounjaro)?

Understanding "100 Units" of Compounded Tirzepatide

When a patient reports injecting "100 units" of compounded tirzepatide, this most likely refers to 100 units on an insulin syringe, which typically translates to 1 mL of volume—but the actual dose in milligrams depends entirely on the concentration prepared by the compounding pharmacy.

Critical Clarification Needed

The term "units" is problematic and potentially dangerous with compounded tirzepatide because:

• FDA-approved tirzepatide (Mounjaro/Zepbound) is dosed in milligrams (mg), not units 1
• The maximum approved weekly dose is 15 mg 1
• Compounded formulations vary widely in concentration between pharmacies 2
• "100 units" on an insulin syringe = 1 mL volume, but the mg dose depends on concentration 2

Determining the Actual Dose

You must immediately obtain the concentration from the patient's compounding pharmacy label. Common compounding concentrations include:

• If concentration is 5 mg/mL: 100 units (1 mL) = 5 mg dose
• If concentration is 7.5 mg/mL: 100 units (1 mL) = 7.5 mg dose
• If concentration is 10 mg/mL: 100 units (1 mL) = 10 mg dose
• If concentration is 15 mg/mL: 100 units (1 mL) = 15 mg dose

The patient in the compounded tirzepatide study received 7.5 mg weekly doses, which would be 100 units if the concentration was 7.5 mg/mL 2.

Safety Concerns with Compounded Products

Compounded tirzepatide carries significant risks not present with FDA-approved formulations:

• Dosing errors are the most common adverse event with tirzepatide, increasing 8-fold from 2022 to 2024 3
• Incorrect dose administration showed strong risk signals (ROR 22.15-23.43) 3
• Compounded products lack FDA oversight for quality, sterility, and accurate dosing 4
• Protein degradation from improper storage can create immunogenic or toxic compounds 4
• Contamination risks include abscess formation, cellulitis, and systemic reactions 4

Recommended Clinical Actions

Immediately verify these details with the patient:

1. Obtain the pharmacy label showing exact concentration (mg/mL)
2. Calculate the actual mg dose being administered weekly
3. Confirm injection frequency (weekly is standard) 1
4. Assess for adverse effects: nausea (17-22%), diarrhea (13-16%), vomiting (6-10%), injection site reactions 5, 3
5. Check blood glucose if diabetic, as compounded products may have variable potency 4

Dosing Context

For reference, FDA-approved tirzepatide dosing:

• Starting dose: 2.5 mg weekly for 4 weeks (not therapeutic, for tolerability) 1
• Maintenance doses: 5 mg, 10 mg, or 15 mg weekly 1
• Titration: Increase by 2.5 mg increments every 4 weeks as tolerated 1

If the patient's "100 units" translates to a dose exceeding 15 mg weekly, this represents off-label dosing above the maximum approved dose and warrants immediate discussion about safety and efficacy 1.

Common Pitfall to Avoid

Never assume "units" means the same thing across different compounded formulations. Unlike insulin, which has standardized unit definitions, compounded tirzepatide concentrations are not standardized. Always verify the concentration in mg/mL before making any clinical decisions about dose appropriateness or adjustments 2.