Penile absorption of EMLA cream in piglets: Implications for use of EMLA in neonatal circumcision

EMLA® (eutectic mixture of lidocaine and prilocaine) cream is currently not recommended for use in infants < 1 month of age because of the potential risk of methemoglobinemia as a result of the o-toluidine metabolite of prilocaine. We studied bioavailability and changes in methemoglobin levels following topical penile exposure to 1 g of EMLA cream for 1 hour in piglets. Lidocaine, prilocaine, and o-toluidine concentrations were measured simultaneously using a high-performance liquid chromatography method. The systemic bioavailability of EMLA was low: 4.0 ± (SD) 4.7% for lidocaine (range 0-13.6; n = 8) and 7.2 ± 5.7% for prilocaine (range 0-14.5; n = 8). The ratio between exposure to o-toluidine with EMLA versus intravenous administration (i.e., AUCemla/AUQv; see text) was also low: 4.2 ± 9.3% (range 0-28.6; n = 9). The mean maximum methemoglobin value after intravenous administration was 1.23 ± 0.64% (range 0.5-3.0; n = 12) and after penile application 0.99 ± 0.36% (range 0.5-2.0; n = 12). The methemoglobin value was elevated significantly above baseline after intravenous administration (p = 0.03), but not after penile application of EMLA. These findings suggest that penile administration of 1 g of EMLA may be safe for neonatal circumcision, but further study is required.