Measurement of serum lamotrigine by high performance liquid chromatography using a phenyltriazine as internal standard

Determination of lamotrigine in human plasma by HPLC-PDA. Application to forensic samples

PURPOSE

Therapeutic drug monitoring of plasma lamotrigine (LTG) has customarily been carried out in order to prevent some its adverse effects. For forensic purposes, determination of LTG in plasma is an useful tool in cases of accidental overdose or suicidal attempts. Currently, there are several analytical methods available including some based on LC tandem mass spectrometry techniques, but simple and accessible LC-UV methods still can be useful for the purpose. Here we report on a new high-performance liquid chromatography method for the determination of lamotrigine in human plasma which has been developed and validated including selectivity, sensitivity, accuracy, precision and recovery studies.

METHODS

Lamotrigine and the internal standard chloramphenicol were extracted from plasma using liquid-liquid extraction using small volumes of buffer and ethylacetate. Detection was monitored at 305.7 and 276.0 nm for lamotrigine and chloramphenicol, respectively.

RESULTS

The method was linear concentration dependence within the range of 0.1-10 µg/ml, with a mean coefficient of correlation r = 0.993. The limit of detection (LOD) was 0.04 µg/ml and the limit of quantification (LOQ) was 0.1 µg/ml. Intra and interday precision values were lower than 9.0% at all concentrations studied. The intra and interday accuracy values ranged from - 7.6 to 10.1%. Recovery was found to be 98.9% or higher. The method here described was successfully applied to 11 postmortem blood samples received at the Forensic Sciences Institute of Santiago de Compostela (Spain).

CONCLUSION

A new HPLC method for the determination of lamotrigine in human plasma was developed and validated. A liquid-liquid extraction using small volumes of buffer and ethylacetate was optimized. The proposed method is suitable for forensic toxicological analysis.

Interference from Indian diet on the internal standard in a commercial method for the measurement of urinary metanephrines by high-performance liquid chromatography with electrochemical detection

Introduction:

Urinary metanephrines are widely used in the diagnosis of catecholamine secreting tumours. Over the past two years we have been using the commercial Recipe® ClinRep® Complete Kit for Metanephrines in Urine coupled with high-performance liquid chromatography and coulometric detection. It was noticed that the internal standards on the patient chromatograms were sporadically raised due to interference.

Methods:

The interference had identical chromatographic and electrochemical properties to the Recipe® internal standard (undisclosed identity). Inspection of the patient names showed it seemingly had a higher frequency and magnitude in patients of Indian origin. The source of the interference was tracked by dietary observation and intervention to curry leaves, a common component of Indian foods.

Results:

The interference was chromatographically and electrochemically indistinguishable from the internal standard. The mass spectrum of the pentafluoropropionate derivative of the interference matched the Recipe® internal standard and was identified as methoxyhydroxybenzylamine by library match.

Conclusion:

The component co-elutes exactly with internal standard and artifactually decreases the metanephrine and normetanephrine results. It is surprising that it has not been described previously. Patients being assessed for catecholamine secreting tumours should be advised to withdraw from eating Indian foods at least 24 h prior to commencement of urinary collection.