Lidocaine as a diluent for administration of benzathine penicillin G

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Benzathine penicillin G is recommended for secondary prophylaxis of rheumatic fever. Its main disadvantage is local pain and discomfort associated with the injection. Lidocaine as a diluent may reduce this discomfort. We compared the administration of benzathine penicillin G with two diluents; sterile water and lidocaine hydrochloride 1% for penicillin concentrations and pain of injection.


In a randomized double blind, crossover trial, 18 children ages 11 to 19 years who required prophylactic treatment for rheumatic fever were randomly divided into two groups. One received an injection of benzathine penicillin G diluted with 3.2 ml of sterile water, followed 1 month later by an injection of benzathine penicillin G diluted in lidocaine hydrochloride 1%; the second group received the same regimen in the reverse order. Serum penicillin concentrations and subjective pain sensation were determined after each injection.


Peak serum penicillin concentrations at 24 h after injection were similar for both preparations (0.100 μg/ml for water, 0.102 μg/ml for lidocaine), as were the other serum values measured throughout the month. After 28 days detectable concentrations (≥0.020 μg/ml) were found in 44 and 29% of the subjects, respectively (P = 0.4). Urine penicillin concentrations on Day 28 were 1.81 ± 0.25 and 2.31 ± 0.25 μg/ml, respectively. The pain score immediately after the injection was significantly lower with the lidocaine than with the sterile water dilution.


Use of lidocaine hydrochloride as a diluent for benzathine penicillin G does not change the penicillin concentration in body fluids and significantly reduces the pain of injection. We suggest the use of lidocaine hydrochloride 1% as a diluent for benzathine penicillin G.

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