Chronic and bedtime use of benztropine with antipsychotics: is it necessary?

Meta-analysis of randomized controlled trials of galantamine in schizophrenia: significant cognitive enhancement

Cognitive impairments are core features of schizophrenia and the best predictor of functional outcome. Cholinergic system and alpha-7 nicotinic acetylcholine (α7nACh) receptors are strongly implicated in the pathophysiologic mechanisms associated with cognitive impairments in schizophrenia. Galantamine is not only a reversible, competitive inhibitor of acetylcholinesterase but also a type I positive allosteric modulator of α7nACh receptors. The objective of this meta-analysis was to examine the efficacy of galantamine for cognitive symptoms of schizophrenia. In the meta-analysis that included six randomized controlled trials (RCTs, N=226), cognitive impairments significantly improved with galantamine compared to placebo, with a small Hedges' g effect size of 0.233. This finding is consistent with other RCTs in schizophrenia with medications with a similar mechanism of action. On the basis of the results from all the failed (although some efficacy has been shown) RCTs to date in schizophrenia, targeting only one pathophysiologic mechanism may be insufficient to detect a clinically meaningful signal. Nicotinergic medications, like any other add-on medications, are unlikely to be effective as stand-alone medications. Hence, these medications may have to be combined with other medications with complementary mechanisms such as glutamatergic/N-methyl-D-aspartate systems to detect a meaningful effect size for the three domains of psychopathology.

Potential Role of Antipsychotic-Galantamine-Memantine Combination in the Treatment of Positive, Cognitive, and Negative Symptoms of Schizophrenia

Schizophrenia is, in part, a cognitive illness. There are no approved medications for cognitive impairments associated with schizophrenia (CIAS) and primary negative symptoms. Cholinergic and glutamatergic systems, alpha-7 nicotinic acetylcholine (α-7nACh) and N-methyl-D-aspartate (NMDA) receptors, kynurenic acid (KYNA), and mismatch negativity have been implicated in the pathophysiology of CIAS and negative symptoms. Galantamine is an acetylcholinesterase inhibitor that is also a positive allosteric modulator at the α4β2 and α7nACh receptors. Memantine is a noncompetitive NMDA receptor antagonist. Galantamine and memantine alone and in combination were effective for cognition in animals and people with Alzheimer's disease. The objective of this article is to critically dissect the published randomized controlled trials with galantamine and memantine for CIAS to highlight the efficacy signal. These studies may have failed to detect a clinically meaningful efficacy signal due to limitations, methodological issues, and possible medication nonadherence. There is evidence from a small open-label study that the galantamine-memantine combination may be effective for CIAS with kynurenine pathway metabolites as biomarkers to detect the severity of cognitive impairments. Given that there are no available treatments for cognitive impairments and primary negative symptoms in schizophrenia, testing of this "five-pronged strategy" (quintuple hypotheses: dopamine, nicotinic-cholinergic, glutamatergic/NMDA, GABA, and KYNA) is a "low-risk high-gain" approach that could be a major breakthrough in the field. The galantamine-memantine combination has the potential to treat positive, cognitive, and negative symptoms, and targeting the quintuple hypotheses concurrently may lead to a major scientific advancement - from antipsychotic treatment to antischizophrenia treatment.

Kynurenine pathway and cognitive impairments in schizophrenia: Pharmacogenetics of galantamine and memantine

The Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) project designed to facilitate the development of new drugs for the treatment of cognitive impairments in people with schizophrenia, identified three drug mechanisms of particular interest: dopaminergic, cholinergic, and glutamatergic. Galantamine is an acetylcholinesterase inhibitor and a positive allosteric modulator of the α₇ nicotinic receptors. Memantine is an N-methyl-D-aspartate (NMDA) receptor antagonist. There is evidence to suggest that the combination of galantamine and memantine may be effective in the treatment of cognitive impairments in schizophrenia. There is a growing body of evidence that excess kynurenic acid (KYNA) is associated with cognitive impairments in schizophrenia. The α-7 nicotinic and the NMDA receptors may counteract the effects of kynurenic acid (KYNA) resulting in cognitive enhancement. Galantamine and memantine through its α-7 nicotinic and NMDA receptors respectively may counteract the effects of KYNA thereby improving cognitive impairments. The Single Nucleotide Polymorphisms in the Cholinergic Receptor, Nicotinic, Alpha 7 gene (CHRNA7), Glutamate (NMDA) Receptor, Metabotropic 1 (GRM1) gene, Dystrobrevin Binding Protein 1 (DTNBP1) and kynurenine 3-monooxygenase (KMO) gene may predict treatment response to galantamine and memantine combination for cognitive impairments in schizophrenia in the kynurenine pathway.

Potential role of the combination of galantamine and memantine to improve cognition in schizophrenia

The Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) and Treatment Units for Research on Neurocognition and Schizophrenia projects were designed to facilitate the development of new drugs for the treatment of cognitive impairments in people with schizophrenia. The MATRICS project identified three drug mechanisms of particular interest: dopaminergic, cholinergic, and glutamatergic. As a group, while people with schizophrenia have moderate cognitive impairment, it is the best predictor of long-term outcome. Unfortunately, there are no approved medications for cognitive impairment in this population. Hence, the development of new pharmacological approaches is critical for reducing illness-related disability. The combination of an acetylcholinesterase inhibitor (AChEI) and memantine is more effective than either medication alone to improve cognition in Alzheimer's dementia. Galantamine is not only an AChEI, but also a positive allosteric modulator of the α4β2 and α7 nicotinic receptors. Hypofunction of N-methyl-d-aspartate (NMDA) receptors has been implicated in the pathophysiology of cognitive symptoms in schizophrenia and hence memantine may positively impact cognition. Memantine decreases the tonic NMDA current and galantamine enhances the action potential mediated by a postsynaptic NMDA current. This results in an increased signal transmission; therefore, a greater signal-to-noise ratio occurs with the combination than memantine alone. Galantamine improves the α-amino-3-hydroxy-5-methyl-4-isoxazol-propionate (AMPA)-mediated signaling which could be neuroprotective and may improve memory coding. The combination of galantamine and memantine may be particularly effective in schizophrenia in order to increase the selective cognition enhancement produced by either medication alone. In the future, multitarget-directed ligands may play a role in the treatment of complex diseases like schizophrenia.