Intramuscular Injections and Lignocaine

Availability

• Lignocaine HCL 2% (no preservative) (100mg/5ml)
• Lignocaine HCL 2% (preservative) (200mg/10ml)

Rationale

• One of the major disadvantages of IM injection of penicillins, such as benzathine penicillin G, is pain at the injection site.
• Farhadi et al. reported that the average pain intensity in patients receiving IM injection of benzathine penicillin was described as "severe" with a mean visual analog scale (VAS) score of 7.4/10
• Injection pain can be greatly reduced by administering drugs in combination with local anesthetics like lidocaine.
• Lidocaine is a sodium-channel-blocking drug and an extremely versatile local anesthetic agent which has remained a widely used agent due to its potency, rapid onset and intermediate duration of action

Stability

• A few studies have examined the influences of lidocaine as a diluent on pharmacokinetics of IM penicillins or cephalosporins in human and none showed any changes in pharmacokinetic parameters of these antibiotics when mixed with lidocaine
• Patel et al. investigated the effect of lidocaine 1% as a diluent on the pharmacokinetics and tolerance of IM ceftriaxone and showed that lidocaine neither changed parameters nor altered its bioavailability
• Amir et al. compared concentration and injection pain of benzathine penicillin G between two diluents, either sterile water or lidocaine hydrochloride 1%. They found that although lidocaine significantly reduced injection pain, it did not change penicillin concentration in body fluids

Toxicity

• Despite potential toxicity of lidocaine, its usual dose for IM penicillin injections is 10-60 mg (1-3 mL of lidocaine 1% or 2%) which is significantly less than the recommended maximum dose for local anesthetics without epinephrine (4.5 mg/kg)

Administration Recommendations

	Vol of Lignocaine 2%	Diluent Solutions	Used to Reconstitute:
1.	1.75 ml	1.75 ml of NS, 1/2NS, D5, NSD5	1g Ceftriaxone powder
2.	0.25ml	WFI	1.2 MU Benzathine Penicillin powder in at least 3ml of WFI 0.6 MU (2 ml) 2.4MU (5 ml)

References:

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3464756/
2. Product Leaflets
3. https://www.health.govt.nz/.../nursing_guidance_-_administering_im_penicillin.pdf