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Type: Journal article
Title: Lamotrigine and therapeutic drug monitoring: retrospective survey following the introduction of a routine service
Author: Morris, R.
Black, A.
Harris, A.
Batty, A.
Sallustio, B.
Citation: British Journal of Clinical Pharmacology, 1998; 46(6):547-551
Issue Date: 1998
ISSN: 0306-5251
Statement of
Morris, Raymond G.; Black, Andrew B.; Harris, Anne L.; Batty, Andrew B.; Sallustio, Benedetta C.
Abstract: AIMS:To review (retrospectively) the relationships between lamotrigine (LTG) dosage and plasma concentrations based on data generated in a routine therapeutic drug monitoring laboratory from a heterogeneous sample of patients with epilepsy. To distinguish patients taking concomitant anti-epileptic therapy which induced or inhibited drug metabolising enzymes, or a combination of both, together with LTG. To survey medical staff who use a routine LTG assay service with a view to establishing the utility of higher plasma LTG concentrations than those used in early clinical trials. METHODS:All patient assays for LTG received over a 12 month period (339 requests from 149 patients) were reviewed and relationships between dosage and concentration calculated and grouped according to concomitant antiepileptic drug therapy. The doctors requesting the tests were surveyed by questionnaire (n=40 of 67 responded). They were asked for details about the patient's seizure control, rationale used for LTG dosage adjustment and their acceptance of the proposed 'therapeutic range' adopted by the laboratory of 3-14 mg(-1). RESULTS:Linear relationships were demonstrated between LTG dosage and concentration for the 3 treatment groups (LTG plus valproic acid (VPA), LTG plus enzyme inducing antiepileptic drugs, and LTG plus VPA and inducers), however, there were significant differences between groups (P<0.001) with a 4.4 fold difference in dosage: concentration ratios between the LTG plus VPA group and the LTG plus inducers group. The questionnaire showed that the therapeutic range was well accepted by 88% of responders, none of whom considered this higher range to be wrong. CONCLUSIONS:Metabolic inhibition by VPA was shown to have a marked effect on LTG kinetics, suggesting either a significant LTG dosage reduction is required if plasma LTG concentrations are elevated, or alternatively, higher plasma LTG concentrations could be attained from lower dosages. The higher therapeutic range adopted by the laboratory (3-14 mg(-1)) was widely accepted and increasingly applied in clinical practice in the management of patients with epilepsy.
Keywords: Humans; Epilepsy; Valproic Acid; Triazines; Anticonvulsants; Drug Monitoring; Drug Therapy, Combination; Health Care Surveys; Retrospective Studies; Drug Interactions; Lamotrigine
RMID: 0030003437
DOI: 10.1046/j.1365-2125.1998.00835.x
Appears in Collections:Pharmacology publications

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