Effect of lamotrigine on the activities of monoamine oxidases A and B in vitro and on monoamine disposition in vivo.

Recent clinical evidence indicates that the broad spectrum anticonvulsant drug lamotrigine is effective against the depressive phase of bipolar illness and the difficult to treat rapid cycling form of the disorder. However, the molecular mechanism underlying this therapeutic action remains uncertain. Given that inhibition of the A-type of monoamine oxidase (MAO) is a proven antidepressant mechanism, we investigated the effects of lamotrigine on MAO activities in vitro and on monoamine disposition in vivo. In vitro, lamotrigine inhibited rat brain MAO activities with Ki values (MAO-A, 15 microM; MAO-B, 18 microM) potentially within the therapeutic range for this drug. The effects of lamotrigine on the MAO-A activities of rat brain and human liver preparations were almost identical suggesting minimal species or tissue variation. In contrast, there was no (MAO-A) or minimal (MAO-B) reduction in brain MAO activities when assayed ex vivo following the administration of lamotrigine to rats. In vivo brain microdialysis failed to detect meaningful alterations in extracellular hippocampal or frontal cortex monoamine concentrations. Furthermore, lamotrigine did not modulate oral tyramine-induced hypertension in rats or 5-hydroxytryptophan-induced head shaking in mice, providing strong evidence that the drug does not perturb monoamine metabolism in vivo. The absence of observable effects of lamotrigine on monoamine disposition in vivo may be explained by the competitive and highly reversible nature of the interaction of lamotrigine with MAO isoforms. Thus, altered monoamine metabolism in vivo is unlikely to account for the antidepressant action of the drug in bipolar depression.

Drug shortages and implications for pediatric patients.

Drug shortages in the United States continue to be a significant problem that negatively impacts pediatric patients of all ages. These shortages have been associated with a higher rate of relapse among children with cancer, substitution of less effective agents, and greater risk for short- and long-term toxicity. Effective prevention and management of any drug shortage must include considerations for issues specific to pediatric patients; hence, the Pediatric Pharmacy Advocacy Group (PPAG) strongly supports the effective management of shortages by institutions caring for pediatric patients. Recommendations published by groups such as the American Society of Health-System Pharmacists and the American Society for Parenteral and Enteral Nutrition should be incorporated into drug shortage management policies. PPAG also supports the efforts of the Food and Drug Administration (FDA) to not only address but prevent drug shortages caused by manufacturing and quality problems, delays in production, and discontinuations. Prevention, mitigation, and effective management of drug shortages pose significant challenges that require effective communication; hence, PPAG encourages enhanced and early dialogue between the FDA, pharmaceutical manufacturers, professional organizations, and health care institutions.