Commonly used regime

• In children, an introduction of 5mg/kg/day in two doses increasing over 3-4 wks to 10-20 mg/kg/day in 2 doses provides a reasonable approach.
• Some patients may be controlled on a lower dose. In the young child on a liquid preparation, the dosage may be changed to three times a day in order to achieve steadier levels.
• Carbamazepine is usually avoided in the first year of life due to poor absorption.
• Dosages per kilogram can only be used up to weights of 30-40kgs.
• ‘Start low and go slow.’ Rash is more of a risk when starting with high doses and rapid dose increase. A slow introduction is also preferable to minimise drowsiness or incoordination.

Preparations

• Tablets 400mg CR, 200mg CR, 100mg, 200mg, Suspension 20mg/ml.

Monitoring and levels

• Most would do a baseline LFT and FBC prior to commencing the drug and then repeat in 4-6 wks. Further tests as clinically indicated.
• Drug levels are done for a reason and the timing of the test depends on the indication, e.g. trough for efficacy, peak for toxicity.
• Levels can be useful to titrate dosage, manage potential drug interactions and assess for toxicity.

Formulary

• Australian Medicines Handbook (AMH)
• eMIMS

Incoordination (e.g. gait unsteadiness) or drowsiness can occur when a patient first starts carbamazepine. These are usually transient side effects (unsteadiness resolves over days to a couple of weeks) and the dose can continue to be increased gradually. Commencing slowly lessens these side effects.

Rashes, in particular Steven-Johnsons Syndrome (SJS), is the most important adverse effect to watch for.

• Rash most commonly occurs within 4-6 weeks but can occur at any time.
• Development of rash on carbamazepine warrants an immediate medical review.
• Particularly concerning signs to look out for are red eyes, mucosal involvement, and blistering.
• Suspected SJS requires appropriate (usually inpatient) medical management.
• Research has shown an increased risk of SJS in people of Han Chinese ethnicity with the HLA-B1502 allele. Care should be taken when considering carbamazepine in this population and HLA-B1502 testing is recommended before starting the drug in particular ethnic populations (Han Chinese, Filipinos, Malaysians, South Asians Indians, and Thai).
• The HLA testing in New South Wales can be done via a blood test using the Immunogenetics Request Form.

Other notable side effects

• Neutropenia
• Transaminitis. Mild nonprogressive transaminitis does not necessarily require drug cessation.
• Syndrome of Inappropriate Antidiuretic Hormone secretion (SIADH).
• All anti-seizure medications are potentially teratogenic and this is often dose related.
• For a complete list of adverse effects, appropriate formularies should be consulted.

• Tegretol is an enzyme inducer and therefore can lower valproate and phenytoin levels.
• It will also reduce the efficacy of the oral contraceptive pill.
• Avoid macrolides – particularly erythromycin – as it can alter carbamazepine levels and cause toxicity, including hyponatremia.
• Research has shown an increased risk of SJS in people of Han Chinese ethnicity with the HLA-B1502 allele. Care should be taken when considering carbamazepine in this population and HLA-B1502 testing is recommended before starting the drug in particular ethnic populations (Han Chinese, Filipinos, Malaysians, South Asians Indians, and Thai).
• Most would do a baseline LFT and FBC prior to commencing the drug and then repeat in 4-6 wks. Further tests as clinically indicated.
• Drug levels are done for a reason and the timing of the test depends on the indication, e.g. trough for efficacy, peak for toxicity.  
• Levels can be useful to titrate dosage, manage potential drug interactions and assess for toxicity. 

The HLA testing in New South Wales can be done via a blood test using the Immunogenetics Request Form.

• Pharmaceutical Benefits Scheme
• MIMS (Monthly Index of Medical Specialties)
• AMH (Australian Medicines Handbook)
• eMIMS