ZTLIDO has different bioavailability compared to Lidoderm. In a single-dose, crossover study conducted in 53 healthy volunteers, ZTLIDO (lidocaine topical system) 1.8% demonstrated equivalent exposure (AUC) and peak concentration (C max) of lidocaine to Lidoderm (lidocaine patch 5%). 

Absorption

The amount of lidocaine systemically absorbed from ZTLIDO is directly related to both the duration of application and the surface area over which it is applied. In a pharmacokinetic study, three ZTLIDO topical systems were applied over an area of 420 cm 2of intact skin on the backs of normal healthy volunteers for 12 hours. Blood samples were drawn for determination of lidocaine concentration during the topical system application and for 12 hours after removal of topical systems. The results are summarized in Table 1. 

Repeated application of three Lidoderm patches simultaneously for 12 hours (recommended maximum daily dose), once per day for three days, indicated that the lidocaine concentration does not increase with daily use. The mean plasma pharmacokinetic profile for the 15 healthy volunteers is shown in Figure 1. 

Figure 1

Mean lidocaine blood concentrations after three consecutive daily applications of three Lidoderm patches simultaneously for 12 hours per day in healthy volunteers (n = 15).

The pharmacokinetics of ZTLIDO (n = 3 topical systems) was assessed in 12 healthy volunteers with exposure to external heat source (heating pad at medium setting applied for 20 minutes at Time 0 and 8.5 hours) or undergoing moderate exercise (cycling for 30 minutes at a heart rate of 108 bpm at Time 0, 2.5, 5.5 and 8.5 hours) and compared to pharmacokinetics of ZTLIDO at rest. Exposure to external heat at 0 and 8.5 hours results in increased peak plasma levels of lidocaine with a mean (SD) of 160.3 ± 100.1 ng/mL versus the peak plasma levels observed at rest with a mean (SD) of 97.6 ± 36.9 ng/mL. For this reason, instruct patients not to apply heating pads directly to ZTLIDO. Concentrations returned to normal within 4 hours after the heat was removed. No clinically relevant differences in systemic absorption were observed under exercise conditions with a mean (SD) peak plasma concentration of 90.5 ± 25.4 ng/mL.

A separate study in 12 healthy volunteers showed that there was no effect on ZTLIDO pharmacokinetics when the topical system is applied to the administration site after external heat exposure (heating pad at medium setting applied for 15 minutes prior to the topical system application) or after engagement in exercise (walking at a moderate pace on a treadmill for approximately 20 minutes beginning approximately 30 minutes prior to the topical system application).

Distribution

When lidocaine is administered intravenously to healthy volunteers, the volume of distribution is 0.7 to 2.7 L/kg (mean 1.5 ± 0.6 SD, n = 15). At concentrations produced by application of ZTLIDO, lidocaine is approximately 70% bound to plasma proteins, primarily alpha-1-acid glycoprotein. At much higher plasma concentrations (1 to 4 µg/mL of free base), the plasma protein binding of lidocaine is concentration dependent. Lidocaine crosses the placental and blood brain barriers, presumably by passive diffusion.

Elimination

Metabolism:

It is not known if lidocaine is metabolized in the skin. Lidocaine is metabolized rapidly by the liver to a number of metabolites, including monoethylglycinexylidide (MEGX) and glycinexylidide (GX), both of which have pharmacologic activity similar to, but less potent than that of lidocaine. A minor metabolite, 2,6-xylidine, has unknown pharmacologic activity. The blood concentration of this metabolite is negligible following application of ZTLIDO. Following intravenous administration, MEGX and GX concentrations in serum range from 11 to 36% and from 5 to 11% of lidocaine concentrations, respectively.

Excretion:

Lidocaine and its metabolites are excreted by the kidneys. Less than 10% of lidocaine is excreted unchanged. The half-life of lidocaine elimination from the plasma following IV administration is 81 to 149 minutes (mean 107 ± 22 SD, n = 15). The systemic clearance is 0.33 to 0.90 L/minute (mean 0.64 ± 0.18 SD, n = 15).