Specimen Collection

Collect a trough sample (before the next dose).

Tubes containing gel (SST and PST) are NOT acceptable

4 mL Heparin Blood (Preferred)

4 mL Plain Blood

0.5 mL Paediatric Microsample Blood
Reference Intervals

Units: mg/L

Therapeutic interval : 3 - 15

The quoted therapeutic interval of 3-15 mg/L should only be used as a guide, in conjunction with the individual patient's clinical status .

This therapeutic interval refers to TROUGH samples (before next dose).

Some patients have seizures controlled with levels outside this range, and levels above this range are not always toxic.

Conversion factor: mg/L x 3.9 = umol/L

Uncertainty of Measurement: 12%

Turnaround Time: Within 1 week

Performed Weekly.

Assay Method

Principle : Immunoassay

Diagnostic Use and Interpretation

Lamotrigine plasma level can be significantly influenced by inducers or inhibitors :

- The combination of lamotrigine and valproate may have beneficial effects on seizure frequency, but this combination may result in functionally disabling adverse effects due to the valproate inhibiting lamotrigine metabolism and elimination. The half-life of lamotrigine is perhaps doubled from 30 to 60 hours.

- Conversely, enzyme inducing drugs, such as carbamazepine, phenytoin, phenobarbitone and primidone, accelerate elimination and the half-life of lamotrigine is reduced from 30 to 15 hours.

Lamotrigine level can also be significantly changed during pregnancy or use of oral contraceptive pills due to increase clearance. Therapeutic drug monitoring assists management of pregnant patients with seizures.

References :

1. Hirsch LJ, et al. Neurology 2004; 63(6):1022-6

2. Westly I.S and Morris R.G Seradyn Quantitative Microsphere System Lamotrigine Immunoassay on a Hitachi 911 Analyser Compared with HPLC-UV Ther Drug Monit 2008;30:634-637

3. Harden C.L and Sethi N.K Epileptic disorders in pregnancy: an overview Current opinion in Obstetrics and Gynaecology 2008, 20:557-562

4. Brodtkorb E and Reimers A Seizure control and pharmacokinetics of antiepileptic drugs in pregnant women with epilepsy Seizure 2008 17:160-165

5. Schapel GJ, Black AB, Lam EL et al. Combination vigabatrin and lamotrigine therapy for intractable epilepsy.

Contact Information

Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.

If the query concerns a specific patient please include the NHI number in your email.

If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).

Individual chemical pathologists may be contacted but will not be available at all times.

After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.

Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402

Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052

Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427

Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427

Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427

Specimen Transport Instructions for Referring Laboratories

Centrifuge and separate blood as soon as possible after collection.

If sending within Auckland then sample can be sent refrigerated (2-8 degrees) or at ambient temperature (8-24 degrees).

If sending from outside Auckland then send sample refrigerated (2-8 degrees).

The separated sample is stable up to 7 days at 4 degrees, if testing is delayed then sample should be frozen.

Note: If temperature during shipping is likely to exceed 24 degrees then results may not always be reliable.

Last updated at 15:26:00 06/01/2025