Dopamine D2 and D3 Agonist Pramipexole May Enhance Cognitive Function in Bipolar I Disorder
Anil Malhotra from the Zucker Hillside Hospital found that pramipexole (Mirapex), a dopamine D2 and D3 agonist used in the treatment of Parkinson’s disease, improved measures of processing speed and working memory in euthymic bipolar patients (whose average age was 42) when compared with placebo in an adjunctive clinical trial.
Editor’s Note: Bipolar patients in a euthymic phase have consistently been shown to have some degree of cognitive dysfunction that is typically correlated with the number of prior depressive and/or manic episodes they have experienced. This is one of the first studies to directly target this cognitive dysfunction with a pharmacotherapeutic agent.
Pramipexole may be of additional value among depressed patients, because in two small, placebo-controlled studies, one led by Carlos Zarate at the National Institute of Mental Health and one led by Joseph F. Goldberg in New York, pramipexole has been shown to exert acute antidepressant effects in bipolar patients in the depressive phase of the illness. The new data from Malhotra raise the possibility that there could be a two-for-one benefit when pramipexole is used in the depressive phase of bipolar illness—improvement in both depression and cognition.
Other approaches to improving cognition in patients with bipolar disorder
Anti-Alzheimers’s Drug Memantine (Namenda) May Augment the Antidepressant Effects of Lamotrigine
At the 65th Annual Scientific Convention of the Society of Biological Psychiatry in May, Amit Anand reported that the anti-Alzheimer’s drug memantine (20 mg/day) was superior to placebo in augmenting the acute antidepressant effects of lamotrigine. These data are of particular interest since one of the assumed mechanisms of action of lamotrigine is to decrease the release of glutamate.
Memantine is a drug approved for the treatment of Alzheimer’s disease and is a partial antagonist (blocker) of glutamate NMDA receptors. This suggests that the dual actions of inhibiting glutamate’s release pre-synaptically (with lamotrigine) and blocking glutamate receptor activity post-synaptically (with memantine) combine to produce a better effect than that of lamotrigine alone.
Dual Drug Treatment for Alzheimer’s
The two main classes of drugs for the treatment of Alzheimer’s disease currently include cholinesterase inhibitors, which increase brain acetylcholine levels, and memantine (Namenda), which is a partial blocker of glutamate receptors. Treating patients with both types of drugs in combination may help their cognitive functioning.
The brains of patients with Alzheimer’s are deficient in acetylcholine. Acetylcholinesterase breaks down acetylcholine, so the first class of Alzheimer’s drugs inhibits these esterases and makes more acetylcholine available.
Memantine works a different way. Glutamate is the major excitatory neurotransmitter in the brain. Excesses of glutamate may be toxic to cells, so memantine’s ability to partially block glutamate receptors may explain the drug’s effectiveness in Alzheimer’s.
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