Dosage of BLT (Benzocaine 20%, Lidocaine 10%, Tetracaine 10%) Ointment for a 70-Pound Patient
For a 70-pound (31.8 kg) patient, the maximum safe amount of BLT ointment should be limited to approximately 2.2 grams per application, based on the lidocaine component which is the limiting factor.
Calculation of Maximum Safe Dose
The primary consideration when determining the maximum safe dose of BLT ointment is the lidocaine component, as it has the most clearly established dosing guidelines:
- Maximum safe dose of lidocaine with epinephrine: 7 mg/kg 1
- For a 70-pound (31.8 kg) patient: 31.8 kg × 7 mg/kg = 222.6 mg maximum lidocaine
- BLT ointment contains 10% lidocaine (100 mg/g)
- Therefore: 222.6 mg ÷ 100 mg/g = 2.2 grams of BLT ointment maximum
Application Considerations
When applying BLT ointment:
- Apply to clean, intact skin only
- Avoid application to mucous membranes unless specifically indicated
- Cover with occlusive dressing if appropriate for the procedure
- Allow 20-30 minutes for full anesthetic effect
- Remove completely after the procedure
Safety Precautions
Monitor for signs of local anesthetic toxicity:
- Early signs: circumoral numbness, facial tingling, light-headedness, tinnitus
- Moderate signs: slurred speech, muscle twitching
- Severe signs: seizures, cardiac arrhythmias, respiratory depression 1
Risk factors for toxicity:
- Application to large surface areas
- Application to damaged skin (increases absorption)
- Prolonged application time
- Concurrent use of other local anesthetics
- Hepatic or renal impairment
Special Considerations for Pediatric Patients
For pediatric patients like this 70-pound child:
- Calculate dose based on actual body weight
- Consider using the minimum effective amount
- Limit the area of application
- Avoid application near eyes or mouth
- Monitor the patient closely during and after application
Alternative Approaches
For procedures requiring more extensive anesthesia:
- Consider using plain lidocaine (without benzocaine and tetracaine) which has better established pediatric dosing guidelines
- For laceration repair, LET (Lidocaine-Epinephrine-Tetracaine) solution has specific pediatric dosing: 0.175 mL/kg for children <17 kg; 3 mL for children >17 kg 2
Practical Application Tips
- Measure the amount of ointment using a calibrated device (syringe without needle)
- Apply a thin layer only to the required area
- Document the amount used and time of application
- Have lipid emulsion 20% available for potential toxicity treatment 1
Remember that this maximum dose calculation is based on the lidocaine component only. The presence of benzocaine and tetracaine in the formulation may have additive toxicity effects, so using less than the calculated maximum is prudent.