Lidocaine Dilution for Intramuscular Ceftriaxone (Rocephin)
Mix ceftriaxone with 1% lidocaine solution (without epinephrine) at a concentration of 250 mg/mL or 350 mg/mL for intramuscular injection, using the volumes specified in the FDA-approved reconstitution table. 1
FDA-Approved Reconstitution Volumes
The official FDA label for ceftriaxone provides specific dilution instructions for achieving either 250 mg/mL or 350 mg/mL concentrations when using 1% lidocaine solution (without epinephrine): 1
- 500 mg vial: Add 1.8 mL of 1% lidocaine for 250 mg/mL concentration, or 1.0 mL for 350 mg/mL concentration 1
- 1 gram vial: Add 3.6 mL of 1% lidocaine for 250 mg/mL concentration, or 2.1 mL for 350 mg/mL concentration 1
- 2 gram vial: Add 7.2 mL of 1% lidocaine for 250 mg/mL concentration, or 4.2 mL for 350 mg/mL concentration 1
After adding the diluent, shake the vial thoroughly to form the solution and withdraw the entire contents into the syringe. 1
Clinical Evidence Supporting Lidocaine as Diluent
Lidocaine significantly reduces injection pain without altering ceftriaxone pharmacokinetics. Multiple studies demonstrate that 1% lidocaine as a diluent substantially decreases pain compared to sterile water, with no impact on drug bioavailability or efficacy: 2, 3, 4
- A prospective study of 39 adolescents showed significant pain reduction at all measured time intervals (immediately post-injection, 10 minutes, 20 minutes, and 6 hours) when lidocaine was used versus sterile water 2
- Pharmacokinetic studies confirm that 1% lidocaine does not alter elimination parameters, bioavailability, peak plasma concentration, or half-life of ceftriaxone 3
- Buffered lidocaine offers no additional pain reduction benefit over standard 1% lidocaine 4
Stability and Storage
Ceftriaxone reconstituted with 1% lidocaine solution (without epinephrine) remains stable with less than 10% potency loss for: 1
- 24 hours at room temperature (25°C) for all concentrations (100,250, and 350 mg/mL) 1
- 3 days refrigerated (4°C) for 250 mg/mL and 350 mg/mL concentrations 1
- 10 days refrigerated (4°C) for 100 mg/mL concentration 1
Administration Technique
Inject the reconstituted solution deep into a large muscle mass with aspiration before injection. 1 The FDA label specifies that ceftriaxone should be injected well within the body of a relatively large muscle, and aspiration helps avoid unintentional intravascular injection. 1
Critical Safety Consideration
Never use lidocaine solutions containing epinephrine for ceftriaxone reconstitution. 1 The FDA label explicitly states to use 1% lidocaine solution without epinephrine. 1 Additionally, do not use diluents containing calcium (such as Ringer's solution or Hartmann's solution), as particulate formation can result. 1
Lidocaine Dosing Limits
When using lidocaine as a diluent, be aware of maximum safe lidocaine doses to avoid systemic toxicity, particularly when administering multiple injections or in patients receiving other local anesthetics: 5, 6
- Maximum lidocaine dose without epinephrine: 4.5 mg/kg in adults and 1.5-2.0 mg/kg in children 6
- Do not administer additional local anesthetics within 4 hours of ceftriaxone injection with lidocaine diluent 5, 6
- Each mL of 1% lidocaine contains 10 mg of lidocaine; calculate total dose accordingly 5
Early signs of lidocaine toxicity include perioral numbness, tinnitus, facial tingling, and dizziness—these warrant immediate evaluation. 5, 6