- Red, tiger or green top tube
- 5 mL of venous blood
Recommended sample collection time:
| Drug | Route of
Administration | Recommended
Collection
Time |
|---|
| Carbamazepine | PO | For therapeutic monitoring:
- 3-4 days after initiating
therapy, change in dosing
regimen, adding a second drug,
or change in the patient's liver
or GI function - Again 2-4 weeks later
(steady state) - For suspected toxicity:
Immediately and 6 hours after
last dose
|
Additional information
- Note the following times on the lab requisition form and the patient's chart:
- Trough specimen drawn (time)
- Peak specimen drawn (time)
- If orally dosed, time of last dose
- Handle sample gently to prevent hemolysis
- Send sample to lab immediately. If delay is expected, separate serum and refrigerate
- Carbamazepine levels are performed to measure the concentration of antiepileptic drug carbamazepine in the blood
- Carbamazepine is an iminostilbene derivative with a tricyclic structure, and has antiepileptic properties (prevents repeated firing of depolarized neurons) due to its ability to block voltage-dependent sodium channels
- Carbamazepine is used for the treatment of simple and complex partial seizures, neurogenic pain in trigeminal neuralgia and diabetic neuropathy, mania, and bipolar affective disorder
- Antiepileptic drug levels in the therapeutic range are most effective, whereas high levels can be toxic and inadequate levels may lack therapeutic efficacy
- Measured levels are highly dependent on dosing (amount and frequency), patient's body mass, and pharmacokinetic parameters such as bioavailability, volume of distribution, clearance, half-life, and protein binding
- After drug administration, the drug concentration fluctuates between a maximum (peak) and a minimum (trough) level
This section covers Antiseizure medication levels - Carbamazepine. Other sections provide detailed information on other components of Antiseizure medication levels.
- The clinical utility of carbamazepine levels include:
- To monitor compliance with therapeutic regimen in the treatment of epilepsy, prevention of seizures, and sometimes as a mood stabilizer
- To monitor and evaluate change in medication or dosage
- Evaluation of overdose and prevention of toxicity, especially in combination with ethanol
- To monitor in children, elderly people, and persons with poorly controlled seizures or if patient noncompliance is suspected
- To time reinstitution of chronic therapy after overdose
- Carbamazepine toxicity may result from acute overdose or chronic therapy, which may clinically present as:
- Neurologic
- Ocular
- Respiratory depression and apnea
- Cardiovascular
- Bradycardia
- Conduction disorders
- Hypotension
- Urinary retention
- SIADH (hyponatremia)
- Gastrointestinal and hepatic
- Abdominal pain
- Decreased intestinal motility
- Hepatitis
- Hypoglycemia
- Nausea and vomiting
- Pancreatitis (Chemically induced)
- Dermatological effects
- Heme/Lymph effects
- Patients in the first month of pregnancy are at increased risk of delivering fetus's with neural tube defects
- Carbamazepine accelerates the breakdown of estrogens necessitating higher estrogen doses in oral contraceptives
Additional information
- Carbamazepine is absorbed from the GI tract with peak plasma levels occurring at 4-8 hours, with metabolism primarily in the liver by oxidative enzymes, 75-85% is bound to albumin and finally is renally excreted
- Its metabolite, carbamazepine-10,11-epoxide, is active and may achieve up to 50% the concentration of the parent compound
- The oral suspension is more potent (Produces higher peak concentrations than tablets)
- Metabolism of corticosteroids, theophylline, warfarin and haloperidol is increased by carbamazepine
- Many factors must be considered in effective dosing and monitoring of therapeutic drugs including patient age, weight, drug, route of administration, interacting medications, electrolyte balance, protein levels, water balance, conditions that affect absorption and excretion, and ingestion of other substances (foods, herbals, vitamins, and minerals) that can either potentiate or inhibit the intended target concentration
- Factors interfering with test results include:
- Sample collection in serum separator tubes/gel tubes (gel slowly absorbs the drug)
- Serum frozen on cells or left standing on cells for several days
- Hemolysis, lipemic, or icteric specimen
- Hepatic or renal disease
- In critically ill and uremic patients (false increase)
- Related laboratory tests include:
This section covers Antiseizure medication levels - Carbamazepine. Other sections provide detailed information on other components of Antiseizure medication levels.
Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.
| Conv. Units
(µg/mL) | SI Units
(µmol/L) |
|---|
| Total Carbamazepine |
| Therapeutic | 4-12 | 17-51 |
| Toxic | >20 | >85 |
| Free Carbamazepine |
| Therapeutic | 1-3 | 4.2-12.7 |
| Toxic | >3.8 | >16 |
This section covers Antiseizure medication levels - Carbamazepine. Other sections provide detailed information on other components of Antiseizure medication levels.
Elevated serum carbamazepine level is associated with incorrect dosing, overdose, poisoning and toxicity.
Drugs that may increase carbamazepine levels or increase risk of toxicity include:
- Cimetidine
- Clozapine
- Danazol
- Diazepam
- Diltiazem
- Erythromycin
- Haloperidol
- Isoniazid
- Propoxyphene
- Risperidone
- Triacetyloleandomycin
- Tricyclic antidepressants
- Valproic acid
- Verapamil
This section covers Antiseizure medication levels - Carbamazepine. Other sections provide detailed information on other components of Antiseizure medication levels.
Decreased carbamazepine levels are associated with decreased therapeutic effect, inadequate dosing or non-compliance.
Drugs that may decrease carbamazepine levels include:
- Phenobarbital
- Phenytoin
- Primidone
This section covers Antiseizure medication levels - Carbamazepine. Other sections provide detailed information on other components of Antiseizure medication levels.