Reconstitution Volume for Intramuscular Rocephin (Ceftriaxone)
For intramuscular injection of ceftriaxone, use 1% lidocaine solution in the following volumes: 1.8 mL for 500 mg, 3.6 mL for 1 g, or 7.2 mL for 2 g to achieve a final concentration of 250 mg/mL. 1
Standard Reconstitution Protocol
The FDA-approved reconstitution volumes for intramuscular ceftriaxone using 1% lidocaine (without epinephrine) are 1:
- 500 mg vial: Add 1.8 mL → yields 250 mg/mL concentration
- 1 g vial: Add 3.6 mL → yields 250 mg/mL concentration
- 2 g vial: Add 7.2 mL → yields 250 mg/mL concentration
Alternative Higher Concentration Option
If a more concentrated solution is needed to reduce injection volume, you can use 1:
- 500 mg vial: Add 1.0 mL → yields 350 mg/mL concentration
- 1 g vial: Add 2.1 mL → yields 350 mg/mL concentration
- 2 g vial: Add 4.2 mL → yields 350 mg/mL concentration
The 350 mg/mL concentration is bioequivalent to the 250 mg/mL concentration and does not alter pharmacokinetics or efficacy. 2 This more concentrated formulation reduces injection volume while maintaining the same therapeutic effect. 2
Critical Administration Details
- Inject the diluent into the vial and shake thoroughly to form the solution. 1
- Withdraw the entire contents to equal the total labeled dose. 1
- Inject deeply into a relatively large muscle mass with aspiration to avoid intravascular injection. 1
- Use only 1% lidocaine WITHOUT epinephrine as the diluent for intramuscular administration. 1
Stability After Reconstitution
Once reconstituted with 1% lidocaine solution, ceftriaxone remains stable 1:
- At room temperature (25°C): 24 hours for all concentrations
- Refrigerated (4°C): 3 days for 250-350 mg/mL concentrations, 10 days for 100 mg/mL concentration
Clinical Evidence Supporting Lidocaine Use
Lidocaine as a diluent significantly improves patient tolerance without affecting ceftriaxone pharmacokinetics. 3 Studies demonstrate that 1% lidocaine does not alter peak plasma concentrations, time to peak, area under the curve, elimination half-life, or bioavailability of intramuscularly administered ceftriaxone. 3 The intensity and frequency of injection site pain are considerably reduced with lidocaine compared to water diluent. 4, 3
Common Pitfall to Avoid
Never use diluents containing calcium (such as Ringer's solution or Hartmann's solution) for reconstitution, as particulate formation will result. 1 This is a critical safety concern that can lead to precipitation and potential embolic complications.