Carbamazepine is a medication belonging to the antiepileptic drug class. It has a narrow therapeutic window and is highly toxic in cases of overdose.
To maintain therapeutic efficacy and minimize the risk of adverse effects, the concentration of carbamazepine in the patient's blood should be monitored regularly. This test enables both the detection of carbamazepine overdose and dose adjustment to achieve the desired therapeutic effect.
Pharmacotherapeutic Group
Antiepileptic drugs.
Pharmacodynamics
Stabilizes the membranes of hyperexcited nerve fibers, inhibits the development of repetitive neuronal discharges, and reduces synaptic transmission of excitatory impulses. Prevents the repetitive generation of sodium-dependent action potentials in depolarized neurons by blocking sodium channels in a use- and voltage-dependent manner.
Pharmacokinetics
After a single dose of a conventional tablet, the maximum plasma concentration (Cmax) is reached after 12 hours. After a single dose of a tablet containing 400 mg of carbamazepine, the mean Cmax of the unchanged active substance is approximately 4.5 μg/mL. Steady-state plasma concentrations are reached within 1-2 weeks, depending on individual metabolic characteristics, as well as the patient's condition, dose, and duration of treatment. Significant interindividual differences in steady-state concentrations are observed within the therapeutic range: in most patients, these concentrations range from 4 μg/mL to 12 μg/mL (17-50 μmol/L). Concentrations of carbamazepine-10,11-epoxide (a pharmacologically active metabolite) reach almost 30% of those of carbamazepine. The bioavailability of different carbamazepine preparations may vary. Carbamazepine is metabolized in the liver.
After a single oral dose, the mean elimination half-life (T½) of unchanged carbamazepine is 36 hours, whereas after repeated administration it is 16-24 hours on average, depending on the duration of treatment.
After a single 400 mg dose of carbamazepine, 72% of the administered dose is excreted in the urine and 28% in the feces.
Overdose
- Central nervous system: CNS depression; disorientation, reduced level of consciousness, drowsiness, agitation, hallucinations, coma, blurred vision, slurred speech, dysarthria, nystagmus, ataxia, dyskinesia, hyperreflexia (initially), hyporeflexia (later), seizures, psychomotor disturbances, myoclonus, hypothermia, mydriasis.
- Respiratory system: respiratory depression, pulmonary edema.
- Cardiovascular system: tachycardia, arterial hypotension, sometimes arterial hypertension, conduction disturbances with widening of the QRS complex; loss of consciousness.
- Gastrointestinal tract: vomiting, delayed gastric emptying, decreased colonic motility.
- Musculoskeletal system: isolated cases of rhabdomyolysis associated with toxic effects have been reported.
- Urinary system: urinary retention, oliguria or anuria, fluid retention; overhydration.
