Lidocaine is an amide-type local anesthetic agent and tetracaine is an ester-type local anesthetic agent. Both lidocaine and tetracaine block sodium ion channels required for the initiation and conduction of neuronal impulses- which, in certain instances, results in local anesthesia. When applied to intact skin, S-Caine provides local dermal analgesia by the release of lidocaine and tetracaine from the peel into the skin.

Duration of analgesia was evaluated using a pinprick test in 40 adult volunteers. The median duration of analgesia was 11 hours. There was no difference between the 30-minute and 60-minute S-Caine application periods with respect to the mean for time to return of sensation. However, 55% of S-Caine treated subjects still reported diminished sensation at the end of the 13-hour study period.

Absorption: The amount of lidocaine and tetracaine systemically absorbed from S-Caine is directly related to both the duration of application and the surface area over which it is applied, Table 1. Application of 59 g of S-Caine over 400 cm² for up to 120 minutes to adults produces peak plasma concentrations of lidocaine of 220 ng/mL. Tetracaine plasma levels were not measurable (<0.9 ng/mL). Systemic exposure to lidocaine, as measured by C_max and AUC_0-24, was proportional to the application area, and increased with application time up to 60 minutes.

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