Lamotrigine

Absorption

Lamotrigine is rapidly and entirely absorbed with minimal first-pass metabolism effects, with a bioavailability estimated at 98%. Cmax is reached in the range of 1.4 to 4.8 hours post-dose, but this depends on the dose administered, concomitant medications, and epileptic status. The rate and extent of lamictal absorption is considered equivalent between the compressed tablet form taken with water to that of the chewable dispersible tablets, taken with or without water.

Toxicity

The oral LD50 in mouse and rat is 205 mg/kg and 245 mg/kg, respectively.
Fatal cases of overdose of up to 15g of lamotrigine have been reported. Overdose with lamotrigine has been manifested by ataxia, nystagmus, increased seizures, decreased level of consciousness, coma, and intraventricular conduction delay. Though no known antidote exists for lamotrigine, hospitalization and general supportive measures should be employed in the case of a suspected lamotrigine overdose. Gastric lavage and emesis may be warranted with simultaneous protection of the airway. It is uncertain at this time whether hemodialysis is an effective means of removing lamotrigine from the sytemic circulation.

Description

Lamotrigine is a new mazine, glutamate inhibitor anticonvulsant that significantly reduces the incidence of refractory partial seizures. The drug is reported to produce fewer CNS side effects than diazepam or sodium phenytoin. It is also indicated as add-on therapy for the treatment of generalized seizures not satisfactorily controlled by other anti-epileptics.

Chemical properties

It is a white to cream coloured powder that is soluble in isopropanol and somewhat soluble in water. It has a melting point of 216-218°C and readily dissolves in organic solvents like benzene, toluene, and hot ethanol.

Originator

Burroughs Wellcome (United Kingdom)

The Uses of Lamotrigine

Lamotrigine is an anticonvulsant. Inhibits glutamate release, possible through inhibition of Sodium, Potassium and Calcium currents. Used in treatment of bipolar depression.

Indications

Lamotrigine is indicated as adjunctive therapy for the following seizure types in patients ≥2 years of age: partial seizures, primary generalized tonic-clonic seizures, and generalized seizures due to Lennox-Gastaut syndrome.
It is also indicated for the process of conversion to drug monotherapy for those at least 16 years of age or older with partial seizures and currently are receiving treatment with carbamazepine, phenytoin, phenobarbital, primidone, or valproate as the single antiepileptic drug (AED).
In addition to the above, lamotrigine is also indicated for the maintenance treatment of bipolar I disorder, delaying the time to mood episodes (which may include mania, hypomania, depression, mixed episodes) in adults at least 18 years or older, who have been treated for acute mood symptoms with standard therapy.
Limitations of use
It is important to note that lamotirigine should not be used in the treatment of acute mood episodes, as efficacy has not been established in this context.

Background

Lamotrigine is an antiepileptic drug belonging in the phenyltriazine class. It is used in the treatment of both epilepsy and as a mood stabilizer in bipolar disorder. Lamotrigine is the first medication since lithium granted Food and Drug Administration (FDA) approval for the maintenance treatment of bipolar type I. It is approved for use in more than 30 countries.
Lamotrigine has relatively few side-effects and does not require laboratory monitoring. While it is indicated for epilepsy and bipolar disorders, there is evidence that lamotrigine could have some clinical efficacy in certain neuropathic pain states.

What are the applications of Application

Lamotrigine is a sodium channel protein inhibitor

Definition

ChEBI: Lamotrigine is a member of the class of 1,2,4-triazines in which the triazene skeleton is substituted by amino groups at positions 3 and 5, and by a 2,3-dichlorophenyl group at position 6. It has a role as an anticonvulsant, an antimanic drug, an antidepressant, a non-narcotic analgesic, a calcium channel blocker, an excitatory amino acid antagonist, an EC 3.4.21.26 (prolyl oligopeptidase) inhibitor, an environmental contaminant, a xenobiotic and a geroprotector. It is a member of 1,2,4-triazines, a primary arylamine and a dichlorobenzene.

Preparation

The preparation method of Lamotrigine involves several steps. 2,3-dichlorobenzoic acid is chlorinated to 2,3-dichlorobenzoyl chloride, then reacted with cuprous cyanide, condensed with aminoguanidine, and finally cyclized under the action of potassium hydroxide Lamotrigine.
Two key methods for the synthesis of lamotrigine have been reported.
https://www.sciencedirect.com/topics/chemistry/lamotrigine
A novel process for the synthesis of lamotrigine and its intermediate
https://patents.google.com/patent/WO2007069265A1/en

brand name

Lamictal (Glax oSmithKline).

Therapeutic Function

Anticonvulsant

World Health Organization (WHO)

Lamotrigine is a relatively new antiepilepsy agent acting through stabilization of neuronal membranes and preventing liberation of neurotransmitters.

Biological Functions

Lamotrigine has a broad spectrum of action and is effective in generalized and partial epilepsies. Its primary mechanism of action appears to be blockage of voltagedependent sodium channels, although its effectiveness against absence seizures indicates that additional mechanisms may be active. Lamotrigine is almost completely absorbed from the gastrointestinal tract, and peak plasma levels are achieved in about 2 to 5 hours. The plasma half-life after a single dose is about 24 hours. Unlike most drugs, lamotrigine is metabolized primarily by glucuronidation. Therefore, it appears likely that lamotrigine will not induce or inhibit cytochrome P450 isozymes, in contrast to most AEDs.

General Description

Lamotrigine is an antiepileptic drug belonging in the phenyltriazine class. It is used in the treatment of both epilepsy and as a mood stabilizer in bipolar disorder. Lamotrigine is the first medication since lithium granted Food and Drug Administration (FDA) approval for the maintenance treatment of bipolar type I. It is approved for use in more than 30 countries.

Biological Activity

Anticonvulsant. Inhibits glutamate release, possibly through inhibition of Na + , K + and Ca 2+ currents.

Mechanism of action

Lamotrigine has been found effective against refractory partial seizures. Like phenytoin and CBZ, its main mechanism of action appears to be a blockade of sodium channels that is both voltage- and used-dependent. It also inhibits the high-threshold calcium channel, possibly through inhibition of presynaptic N-type calcium channels, and also blocks glutamate release. The most probable explanation for lamotrigine's efficacy is its ability to produce a blockade of sodium channel repetitive firing. In addition, lamotrigine appears to reduce glutaminergic excitatory transmission, although the mechanism for this action remains unclear.

Pharmacokinetics

Lamotrigine likely prevents seizures and prevents mood symptoms via stabilizing presynaptic neuronal membranes and preventing the release of excitatory neurotransmitters such as glutamate, which contribute to seizure activity.
A note on cardiovascular effects
The metabolite of lamotrigine, 2-N-methyl metabolite (formed by glucuronidation), is reported to cause dose-dependent prolongations of the PR interval, widening of the QRS complex, and at higher doses, complete AV block. Although this harmful metabolite is only found in trace amounts in humans, plasma concentrations may increase in conditions that cause decreased drug glucuronidation, such as liver disease.

Pharmacokinetics

Following oral administration, lamotrigine is absorbed rapidly and completely, exhibiting linear pharmacokinetics and modest protein binding (55%). Lamotrigine is metabolized predominantly by N-glucuronidation and subsequent urinary elimination of its major metabolite, the quaternary 2-N-glucuronide (80–90%), the minor 5-amino-N-glucuronide (8–10%), and unchanged drug (8–10%). Lamotrigine's usual elimination half-life of 24–35 hours is reduced to 13–15 hours in patients taking enzymeinducing AEDs. The presence of valproate increases the lamotrigine half-life substantially by inhibiting N-glucuronidation, necessitating a reduction in dose to avoid toxicity. Hepatic disease patients may demonstrate a reduced capacity to for lamotrigine glucuronidation, thus reducing its rate of clearance.

Clinical Use

Lamotrigine is a 5-phenyl-1,2,4-triazine derivative indicated as monotherapy or as an adjunct for partial seizures in adults, as adjunct in patients with Lennox-Gastaut syndrome, and as adjunct for partial seizures in children 2 years of age and older. Lamotrigine may have additional benefit in combating myoclonic and typical absence seizures. It is approved for use in the maintenance treatment of bipolar disorder.

Side Effects

The usefulness of lamotrigine is limited by the increased incidence of serious rashes, particularly in children or patients taking valproate. This increase, however, may be attenuated by very slow dose escalation, because most rashes appear within the first 8 weeks of treatment. The drug should be discontinued if a rash appears at any time. Additionally, lamotrigine may be associated with development of myoclonus after 2 to 3 years of drug treatment. Additional common side effects associated with lamotrigine therapy include dizziness, diplopia, headache, ataxia, blurred vision, somnolence, and nausea.

Synthesis

The reaction of the Grignard compound of 2,3-dichloroiodobenzene with CO2 in diethyl ether gives 2,3-dichlorobenzoic acid, which is converted to the corresponding acyl chloride by refluxing with SOCl2. The reaction of 2,3-dichlorobenzoyl chloride with cuprous cyanide and KI in refluxing xylene yields 2,3-dichlorobenzoyl cyanide. Finally, this compound is cyclized with aminoguanidine in DMSO to yield lamotrigine .

Metabolism

Lamotrigine is mainly glucuronidated, forming 2-N-glucuronide conjugate, a pharmacologically inactive metabolite. The total radioactivity detected after a 240mg radiolabeled dose of lamotrigine during clinical trials were as follows: lamotrigine as unchanged drug(10%), a 2-N-glucuronide (76%), a 5-N-glucuronide (10%), a 2-N-methyl metabolite (0.14%), as well as various other minor metabolites (4%).

Metabolism

Lamotrigine is extensively metabolised in the liver by UDP-glucuronyl transferases and excreted almost entirely in urine, principally as an inactive glucuronide conjugate. It slightly induces its own metabolism. Only about 2% of lamotrigine-related material is excreted in faeces.

storage

Room temperature

References

https://my.clevelandclinic.org/health/drugs/20217-lamotrigine-tablets
https://pubchem.ncbi.nlm.nih.gov/compound/Lamotrigine
https://go.drugbank.com/drugs/DB00555
The_Renal_Drug_Handbook_The_Ultimate