How should phenoxymethyl‑penicillin potassium (Penadur) be administered intramuscularly with lidocaine to reduce injection pain?

How to Give Penadur Injection with Lidocaine

Mix 0.5 mL of 1% lidocaine directly with the reconstituted benzathine penicillin G (Penadur) in the same syringe before intramuscular injection to significantly reduce injection pain. This approach is supported by high-quality evidence showing substantial pain reduction without affecting drug efficacy 1, 2, 3.

Preparation and Mixing Technique

Reconstitution Steps:

1. Reconstitute Penadur with sterile water for injection (NOT saline, as this causes precipitation) 4
2. Add lidocaine to the reconstituted penicillin:
   • Use 1% lidocaine solution (without epinephrine)
   • Add 0.5 mL of lidocaine to the standard dose 1
   • For children: use 0.2-0.4 mg/kg lidocaine 3
   • Mix thoroughly in the syringe before injection

Dosing Considerations:

• Calculate lidocaine dose based on ideal body weight 5
• Maximum lidocaine: 120 mg/hour total from all sources 5
• Do not use in patients weighing <40 kg 5

Injection Technique

Use the Z-track injection method for additional pain and induration reduction 6:

• Pull skin laterally before needle insertion
• Insert needle at 90-degree angle into gluteal muscle
• Inject slowly (deep IM injection)
• Wait 10 seconds before withdrawing needle
• Release skin after needle removal

Injection site: Deep intramuscular into gluteal muscle 4

Expected Pain Reduction

The evidence demonstrates:

• Immediate pain reduction: 3.84 points lower on 0-10 scale (from ~6.7 to ~3) 2
• Pain at 5 minutes: 2.85 points lower 2
• Pain at 20 minutes: 1.85 points lower 2
• 87% of patients report at least 2-point pain reduction 1
• Pain relief persists for approximately 30-60 minutes 3, 6

Critical Safety Considerations

Contraindications to Lidocaine:

• Cardiac disease (arrhythmias, heart block)
• Seizure disorders
• Severe hepatic or renal impairment
• Known lidocaine allergy 5

Do NOT combine with other local anesthetics:

• Wait 4 hours after any nerve block before giving lidocaine-mixed injection 5
• Avoid concurrent topical lidocaine preparations 5
• Risk of cumulative local anesthetic toxicity

Monitor for Lidocaine Toxicity:

Early neurological signs appear first 5:

• Perioral tingling or numbness
• Tinnitus (ringing in ears)
• Lightheadedness
• Metallic taste
• Restlessness or agitation

Late cardiovascular signs (more severe) 5:

• Cardiac arrhythmias
• Hypotension
• Bradycardia
• Cardiac arrest (at toxic levels)

Clinical Pitfalls to Avoid

1. Never use saline for initial Penadur reconstitution - causes precipitation 4
2. Do not inject too rapidly - increases pain and systemic absorption of lidocaine 5
3. Do not exceed maximum lidocaine dose - particularly important if patient has received other local anesthetics recently 5
4. Topical lidocaine cream is ineffective - one study showed no benefit when applied to skin before injection 2

Alternative Approach (If Lidocaine Contraindicated)

If lidocaine cannot be used, consider:

• Procaine as alternative diluent (lower quality evidence) 2
• Mepivacaine showed similar pain reduction (mean difference -2.19 points) 2
• Z-track technique alone provides modest benefit 6

Documentation and Consent

While not required for this standard pain-reduction practice, document:

• Lidocaine dose and concentration used
• Any patient-reported allergies to local anesthetics
• Immediate post-injection assessment

The combination of lidocaine dilution with Z-track technique represents the most evidence-based approach to minimize the substantial pain associated with benzathine penicillin G injections, with moderate-to-high quality evidence supporting safety and efficacy 1, 2, 3.