Carbamazepine

Absorption

The bioavailability of carbamazepine is in the range of 75-85% of an ingested dose. After one 200 mg oral extended-release dose of carbamazepine in a pharmacokinetic study, the Cmax carbamazepine was measured to be 1.9 ± 0.3 mcg/mL. The Tmax was 19 ± 7 hours. After several doses of 800 mg every 12 hours, the peak concentrations of carbamazepine were measured to be 11.0 ± 2.5 mcg/mL. The Tmax was reduced to 5.9 ± 1.8 hours. Extended-release carbamazepine demonstrated linear pharmacokinetics over a range of 200–800 mg.
Effect of food on absorption
A meal containing high-fat content increased the rate of absorption of one 400 mg dose but not the AUC of carbamazepine. The elimination half-life remained unchanged between fed and fasting state. The pharmacokinetics of an extended-release carbamazepine dose was demonstrated to be similar when administered in the fasted state or with food. Based on these findings, food intake is unlikely to exert significant effects on carbamazepine absorption.

Toxicity

Toxicity information Oral LDLO (female): 1920 mg/kg/17W (intermittent); Oral LDLO (male): 54 mg/kg/9D (intermittent) Oral LD50 (rat): 1957 mg/kg
Overdose information
The initial signs of carbamazepine overdose occur 1-3 hours post ingestion. These signs and symptoms may vary in case of an overdose between carbamazepine and other drugs. Carbamazepine may cause various cardiovascular, neurological, respiratory, urinary symptoms as well as laboratory abnormalities including leukocytosis, reduced leucocytes, acetonuria, and glycosuria.
Neuromuscular symptoms may occur initially, followed by mild cardiac symptoms such as tachycardia, hypertension, or hypotension. Higher doses of carbamazepine may cause more severed cardiovascular effects. Restlessness, muscular twitching, tremor, dilated pupils, nystagmus, psychomotor disturbances, and other neurological symptoms may occur. Hyperreflexia in the initial stages of overdose may be followed by hyporeflexia. Nausea, vomiting, urinary retention, dizziness or drowsiness may also occur. In cases of overdose, contact the local poison control center. Ensure to provide supportive and symptomatic treatment, which may include monitoring and careful supervision by a medical professional. The possibility of overdose with multiple drugs must be considered in the case of carbamazepine overdose. Maintain an adequate airway, oxygen, in addition to ventilation. Vital signs should be monitored.

Description

Carbamazepine is a synthetic iminostilbene derivative structurally similar to imipramine, a tricyclic antidepressant. While unrelated structurally, carbamazepine shares a similar therapeutic action with phenytoin. Carbamazepine was first discovered in 1953 by Swiss chemist Walter Schindler. Throughout the 1960s, antimuscarinic was used and marketed for trigeminal neuralgia and as an anticonvulsant. By the 1970s, it was being used as a mood stabilizer for patients with bipolar disorder.

The Uses of Carbamazepine

Carbamazepine (CBZ) is a first generation anticonvulsant and mood stabilizing compound that has been used as a therapeutic in the context of neuropathic pain, epilepsy, and affective disorders. It exerts its effects by blocking voltage-gated sodium channels (IC50 = 640 μM), making fewer of these channels available to subsequently open, which leads to decreased high-frequency repetitive firing of action potentials. The estimated IC50 values for inhibition of Nav1.7-, Nav1.3-, and Nav1.8-type channels by CBZ following prolonged inactivation have been reported as 406, 900, and 138 μM, respectively. CBZ can also inhibit L-type Ca2+ channels (IC50 = 974 μM) and has been shown to potentiate GABAA receptors (IC50 >3 mM).

What are the applications of Application

Carbamazepine is a sodium channel protein inhibitor

Background

Carbamazepine, also known as Tegretol, is an anticonvulsant drug and analgesic drug used to control seizures and to treat pain resulting from trigeminal neuralgia. It was initially approved by the FDA in 1965. Aside from the above uses, this drug is also given to control the symptoms of bipolar 1. Interestingly, carbamazepine was the first anticonvulsant used to treat individuals with bipolar disorder.

Indications

Carbamazepine is indicated for the treatment of epilepsy and pain associated with true trigeminal neuralgia. In particular, carbamazepine has shown efficacy in treating mixed seizures, partial seizures with complex symptoms, and generalized tonic-clonic seizures. Carbamazepine is also indicated for the treatment of manic episodes and mixed manic-depressive episodes caused by bipolar I disorder. Some off-label, unapproved uses of carbamazepine include the treatment of alcohol withdrawal syndrome and restless leg syndrome.

Pharmacokinetics

General effects
Carbamazepine treats seizures and the symptoms of trigeminal neuralgia by inhibiting sodium channels. In bipolar 1 disorder, carbamazepine has been found to decrease mania symptoms in a clinically significant manner according to the Young Mania Rating Scale (YMRS). Carbamazepine has a narrow therapeutic index.
A note on genetic variation and carbamazepine use
In studies of Han Chinese ancestry patients, a pronounced association between the HLA-B*1502 genotype and Steven Johnson syndrome and/or toxic epidermal necrolysis (SJS/TEN) resulting from carbamazepine use was observed.

Metabolism

Carbamazepine is largely metabolized in the liver. CYP3A4 hepatic enzyme is the major enzyme that metabolizes carbamazepine to its active metabolite, carbamazepine-10,11-epoxide, which is further metabolized to its trans-diol form by the enzyme epoxide hydrolase. Other hepatic cytochrome enzymes that contribute to the metabolism of carbamazepine are CYP2C8, CYP3A5, and CYP2B6. Carbamazepine also undergoes hepatic glucuronidation by UGT2B7 enzyme and several other metabolic reactions occur, resulting in the formation of minor hydroxy metabolites and quinone metabolites. Interestingly, carbamazepine induces its own metabolism. This leads to enhanced clearance, reduced half-life, and a reduction in serum levels of carbamazepine.