What percent lidocaine (local anesthetic) is mixed with ceftriaxone (antibiotic) for intramuscular injections?

Using 1% Lidocaine with Ceftriaxone for Intramuscular Injections

For intramuscular injections of ceftriaxone, 1% lidocaine solution (without epinephrine) should be used as the diluent to reduce injection pain while maintaining antibiotic efficacy. 1

Evidence for Using 1% Lidocaine with Ceftriaxone

The FDA-approved drug label for ceftriaxone specifically mentions 1% lidocaine solution (without epinephrine) as an appropriate diluent for intramuscular administration 1. This is supported by clinical evidence showing that using 1% lidocaine:

• Significantly reduces pain at the injection site compared to sterile water 2
• Does not alter the pharmacokinetics or bioavailability of ceftriaxone 3
• Maintains stability of the ceftriaxone solution for up to 24 hours at room temperature and 3 days when refrigerated 1

Preparation Method

When preparing ceftriaxone with 1% lidocaine for intramuscular injection:

1. Use only 1% lidocaine solution without epinephrine
2. Follow these reconstitution guidelines:
   • For 500 mg ceftriaxone vial: Add 4.8 mL of 1% lidocaine
   • For 1 g ceftriaxone vial: Add 9.6 mL of 1% lidocaine
   • For 2 g ceftriaxone vial: Add 19.2 mL of 1% lidocaine 1

After reconstitution, each 1 mL of solution will contain approximately 100 mg of ceftriaxone.

Clinical Considerations

• The CDC has noted that "some health-care providers believe that the discomfort of the injection may be reduced by using 1% lidocaine solution as a diluent" when administering ceftriaxone for gonorrhea treatment 4
• A randomized controlled trial demonstrated significantly lower pain ratings at multiple time points (immediately after injection, 10 minutes, 20 minutes, and 6 hours) when using lidocaine as a diluent compared to sterile water 2

Safety Considerations

• Avoid using diluents containing calcium, such as Ringer's solution or Hartmann's solution, as particulate formation can result 1
• The maximum safe dose of lidocaine is 4.5 mg/kg without epinephrine and 7.0 mg/kg with epinephrine for adults 5
• When using 1% lidocaine as a diluent, be mindful of the total lidocaine dose, especially when administering multiple injections
• Rare cases of lidocaine-induced seizures have been reported in non-human primates with central nervous system alterations, suggesting caution in patients with neurological conditions 6

Storage After Reconstitution

When reconstituted with 1% lidocaine solution, ceftriaxone remains stable for:

• 24 hours at room temperature (25°C)
• 3 days when refrigerated (4°C) 1

By using 1% lidocaine as a diluent for ceftriaxone intramuscular injections, you can significantly improve patient comfort while maintaining the efficacy of the antibiotic treatment.