Benzocaine

Benzocaine blocks µ1 wild-type Na+ currents in a dose-dependent manner with IC50 of 0.8 mM in HEK293T cells. Benzocaine (1 mM) blocks about 55% of wild-type Na+ current but about 95% of µ1-N1584A mutant current. Benzocaine (1 mM) blocks about 55% of wild-type µ1 currents, but about 80% of µ1-I1575A mutant current. ^[1] Benzocaine results in a biphasic (protective/inductive) concentration-dependent hemolytic effect upon rat erythrocytes, with an effective Benzocaine:lipid molar ratio in the membrane for protection (RePROT), onset of hemolysis (ReSAT) and 100% membrane solubilization (ReSOL) of 1.0:1, 1.1:1 and 1.3:1, respectively. ^[2] Benzocaine and 4-hydroxybenzoate interact with the open and inactivated channels during repetitive pulses, but during the interpulse the complex dissociates too fast to accumulate sufficient use-dependent block of Na+ currents. ^[3] Benzocaine (500 μM) reduces the peak and steady-state currents and increases the amplitude of the inactivating component from 21.7% to 30.2% (n=7, P<0.05), so that benzocaine-induced block at the end of pulses to +60 mV averaged 30.9% (n=7). Benzocaine (500 μM) significantly accelerates the initial phase of deactivation (τf=27.2±2.6 ms, n=7, P<0.01), but does not modify the slow phase of tail current decline. Benzocaine binds with high affinity to an intracellular binding site to produce 'agonist' effects and to a low affinity subsite, which is also located in the inner mouth, to produce the blocking effects. Benzocaine and extracellular K(+) interact to modify the voltage-dependence of channel opening. ^[4]

Benzocaine is absorbed rapidly and similarly through both viable and nonviable skin of the hairless guinea pig, the absorption of the two acidic compounds, benzoic acid and PABA, is greater through nonviable skin. ^[5]