How do you reconstitute ceftriaxone (Ceftriaxone) 1g with lidocaine (Lidocaine) 1%?

Reconstitution of Ceftriaxone 1g with Lidocaine 1%

To reconstitute ceftriaxone 1g for intramuscular injection, add 2.1 mL of 1% lidocaine solution (without epinephrine) to the vial, shake thoroughly until dissolved, which yields a concentration of approximately 350 mg/mL. 1

Standard Reconstitution Protocol

The FDA-approved reconstitution instructions specify the following volumes for achieving different concentrations 1:

• For 350 mg/mL concentration: Add 2.1 mL of 1% lidocaine to the 1g vial
• For 250 mg/mL concentration: Add 3.6 mL of 1% lidocaine to the 1g vial

Step-by-Step Procedure

1. Inject the diluent (1% lidocaine without epinephrine) into the vial 1
2. Shake the vial thoroughly to form a complete solution 1
3. Withdraw the entire contents of the vial into the syringe to equal the total labeled dose 1
4. Inject deeply into the body of a relatively large muscle, using aspiration to avoid unintentional intravascular injection 1

Clinical Evidence Supporting Lidocaine Use

Using 1% lidocaine as the diluent significantly reduces injection pain without altering the pharmacokinetics or efficacy of ceftriaxone. 2 A randomized crossover study demonstrated that lidocaine considerably reduced both the intensity and frequency of pain at the injection site compared to water diluent, while maintaining identical bioavailability (0.96) and elimination parameters 2, 3. Clinical trials confirm that when lidocaine is used for reconstitution, the intramuscular route is well tolerated by patients 4.

Stability Considerations

After reconstitution with 1% lidocaine solution 1:

• At room temperature (25°C): Stable for 24 hours at 100 mg/mL concentration; 24 hours at 250-350 mg/mL concentrations
• Refrigerated (4°C): Stable for 10 days at 100 mg/mL concentration; 3 days at 250-350 mg/mL concentrations

The solution should be protected from light during storage as powder, but protection from normal light is not necessary after reconstitution. 1 The color ranges from light yellow to amber depending on storage duration, concentration, and diluent used 1.

Critical Safety Points

• Only use 1% lidocaine WITHOUT epinephrine for reconstitution 1
• Maximum safe lidocaine dose is 4.5 mg/kg in adults without epinephrine 5
• For a 1g vial reconstituted with 2.1 mL of 1% lidocaine (10 mg/mL), the total lidocaine dose is approximately 21 mg, well below toxic thresholds for any adult 5
• Monitor for local anesthetic systemic toxicity (LAST) including circumoral numbness, facial tingling, slurred speech, and metallic taste, though this is extremely unlikely at these doses 5

Pharmacokinetic Equivalence

Research demonstrates that 1% lidocaine does not alter the bioavailability or elimination parameters of intramuscularly administered ceftriaxone 2. Peak plasma concentrations after 1g IM administration reach approximately 81 micrograms/mL at 2-3 hours, with a half-life of 8.3 hours, providing therapeutic levels for 24 hours against most susceptible organisms 6, 2.

Common Pitfalls to Avoid

• Do not use lidocaine with epinephrine, as this is not FDA-approved for ceftriaxone reconstitution and may alter absorption 1
• Do not use diluents containing calcium (such as Ringer's solution or Hartmann's solution), as particulate formation can result 1
• Do not refrigerate if using immediately, as the 350 mg/mL concentration is stable at room temperature for 24 hours, making refrigeration unnecessary for same-day use 1
• Ensure complete dissolution before withdrawing the dose, as inadequate mixing may result in inaccurate dosing 1