How do I administer 3.5 ml of lidocaine and Rocephin (Ceftriaxone) via intramuscular (IM) injection when the recommended maximum volume per muscle site is 3 ml?

Administering 3.5 mL IM Injection: Split-Site Technique

When you need to inject 3.5 mL of ceftriaxone reconstituted with lidocaine intramuscularly, divide the volume between two separate injection sites, administering no more than 3 mL at any single muscle location.

Volume Distribution Strategy

• Split the 3.5 mL total volume into two injections: administer 2 mL at one site and 1.5 mL at a second site 1
• The maximum recommended volume per IM injection site is 3 mL in adults and older children 1
• For infants and younger children, use the anterolateral thigh as the preferred site; for adults and older children, use the deltoid muscle 1

Specific Technique for Ceftriaxone with Lidocaine

• Ceftriaxone 1 g is typically reconstituted in 3.5 mL of 1% lidocaine solution for IM administration 2
• This exact formulation (1 g ceftriaxone in 3.5 mL of 1% lidocaine) has been studied and validated in pharmacokinetic trials 2
• The lidocaine diluent significantly reduces injection pain compared to sterile water, with pain reduction evident immediately after injection and persisting for at least 6 hours 3
• Lidocaine does not alter the pharmacokinetics, bioavailability, or elimination parameters of ceftriaxone 4

Site Selection for Split Dosing

• Choose two separate muscle groups to avoid local tissue irritation from excessive volume 1
• Common combinations include: bilateral deltoids (one in each arm) or one deltoid plus one vastus lateralis (thigh) 1
• Maintain at least 1 inch (2.5 cm) separation between injection sites if using the same muscle group 1
• Use the shortest needle length that reaches intramuscular tissue to minimize pain 1

Administration Technique

• Inject slowly at each site to reduce tissue trauma and pain 1
• Apply concurrent manual pressure to the injection site during administration to decrease discomfort 1
• Use separate syringes for each injection site when splitting the dose 1

Critical Safety Considerations

• Never attempt to inject the full 3.5 mL volume at a single site, as this exceeds safe volume limits and increases risk of tissue damage, poor absorption, and pain 1
• The 1% lidocaine concentration used as diluent is well-tolerated and does not require dose adjustment 4, 5
• Document both injection sites in the medical record 1