Pharmacodynamics. Lacosamide is the only antiepileptic/analgesic drug that selectively enhances slow inactivation of voltage-gated sodium channels but without apparent interaction with fast inactivation gating. Slow inactivation is a process like fast inactivation except that it does not produce complete blockade of voltage gated sodium channels, and it occurs over the course of hundreds of milliseconds or more, and recovery from this state takes equally as long.
Lacosamide is sometimes described as having a dual mechanism of action, as it interferes in vitro with the activity of collapsin response mediator protein-2 (CRMP-2), which is involved in neuronal differentiation and control of axonal outgrowth (17). The role of CRMP-2 binding in seizure control, however, has not been established. Electrophysiological characterization of lacosamide binding sites on CRMP-2 has identified a pocket that is important in modulating sodium channel slow inactivation (30).
Pharmacokinetics. Lacosamide is completely absorbed after oral administration with negligible first-pass effect with a bioavailability of approximately 100%. The maximum lacosamide plasma concentrations occur approximately 1 to 4 hours post-dose after oral dosing, and elimination half-life is approximately 13 hours. Steady state plasma concentrations are achieved after 3 days of twice-daily repeated administration. Pharmacokinetics of lacosamide is proportional to dose within a range of 100 to 800 mg with low inter- and intra-subject variability. Compared to lacosamide, the major metabolite, O-desmethyl metabolite, has a longer Tmax (0.5 to 12 hours) and elimination half-life (15 to 23 hours).
Favorable pharmacokinetic characteristics of lacosamide include rapid absorption and high oral bioavailability that is not affected by food and dose-proportional pharmacokinetics with low inter- and intraindividual variability. Lacosamide does not induce or inhibit cytochrome P450 enzymes or known drug transporter systems, and it has low protein binding of less than 15%. Also, because it has multiple elimination pathways, lacosamide has no clinically relevant interactions with commonly prescribed medications (04).
Therapeutic drug monitoring. A simple method based on high-performance liquid chromatography with ultraviolet detection for the quantification of lacosamide in human plasma is available for determination of serum levels of the drug. A small volume of the extracted specimen is injected into a reversed-phase chromatography column, and lacosamide is identified by positive electrospray ionization mass spectrometry in the multiple reaction monitoring, which provides selectivity for quantitative analysis of lacosamide (33). The practical significance of therapeutic drug monitoring is that patients on concomitant strong inducer antiepileptic drugs such as oxcarbazepine, levetiracetam, lamotrigine, and valproic acid, may require a 30% higher dose of lacosamide compared with patients not receiving strongly inducing antiepileptic drug cotherapy to achieve the same plasma drug concentration (07).
Formulations. Lacosamide is available in oral or intravenous formulations, which have been used successfully for the control of status epilepticus. Bioequivalence between the oral tablet and the oral syrup of lacosamide has been established. The bioavailability of the oral lacosamide tablet is like that of a 30- or 60-minute intravenous infusion of lacosamide administered at the same dosage. Intravenous lacosamide is well tolerated when administered as a 15-, 30-, or 60-minute infusion.
Pharmacogenetics. There is no significant effect of CYP2C19 polymorphism on the pharmacokinetics of lacosamide. There are no clinically relevant differences in the pharmacokinetics between CYP2C19 poor metabolizers and extensive metabolizers, but concentrations and the amount excreted into urine of the O-desmethyl metabolite were about 70% reduced in the former as compared to the latter.