Memantine has been associated with a moderate decrease in clinical deterioration with only a small positive effect on cognition, mood, behavior, and the ability to perform daily activities in moderate to severe Alzheimer's disease. There does not appear to be any benefit in mild disease.
Memantine is, in general, well-tolerated. Common adverse drug reactions (≥1% of people) include confusion, dizziness, drowsiness, headache, insomnia, agitation, and/or hallucinations. Less common adverse effects include vomiting, anxiety, hypertonia, cystitis, and increased libido.
Like many other NMDA antagonists, memantine behaves as a dissociative anesthetic at supratherapeutic doses. Despite isolated reports, recreational use of memantine is rare due to the drug's long duration and limited availability. Also memantine seems to lack most of the psychoactive effects recreational users are usually looking for, such as euphoria or hallucinations.
Memantine is a low-affinity voltage-dependent uncompetitiveantagonist at glutamatergic NMDA receptors. By binding to the NMDA receptor with a higher affinity than Mg2+ ions, memantine is able to inhibit the prolonged influx of Ca2+ ions, particularly from extrasynaptic receptors, which forms the basis of neuronal excitotoxicity. The low affinity, uncompetitive nature, and rapid off-rate kinetics of memantine at the level of the NMDA receptor-channel, however, preserves the function of the receptor at synapses, as it can still be activated by physiological release of glutamate following depolarization of the postsynaptic neuron. The interaction of memantine with NMDA receptors plays a major role in the symptomatic improvement that the drug produces in Alzheimer's disease. However, there is no evidence as yet that the ability of memantine to protect against NMDA receptor-mediated excitotoxicity has a disease-modifying effect in Alzheimer's, although this has been suggested in animal models.
Serotonergic (5-HT3 receptor)
Memantine acts as a non-competitive antagonist at the 5-HT3 receptor, with a potency similar to that for the NMDA receptor. Many 5-HT3 antagonists function as antiemetics, however the clinical significance of this serotonergic activity in the treatment of Alzheimer's disease is unknown.
Cholinergic (nicotinic acetylcholine receptor)
Memantine acts as a non-competitive antagonist at different neuronal nicotinic acetylcholine receptors (nAChRs) at potencies possibly similar to the NMDA and 5-HT3 receptors, but this is difficult to ascertain with accuracy because of the rapid desensitization of nAChR responses in these experiments. It can be noted that memantine is an antagonist at Alpha-7 nAChR, which may contribute to initial worsening of cognitive function during early memantine treatment. Alpha-7 nAChR upregulates quickly in response to antagonism, which could explain the cognitive-enhancing effects of chronic memantine treatment. It has been shown that the number of nicotinic receptors in the brain are reduced in Alzheimer's disease, even in the absence of a general decrease in the number of neurons, and nicotinic receptoragonists are viewed as interesting targets for anti-Alzheimer drugs.
Dopaminergic (D2 receptor)
Memantine acts as an agonist at the dopamine D2 receptor with equal or slightly higher affinity than to the NMDA receptors.
Sigmaergic (σ1 receptor)
It acts as an agonist at the σ1 receptor with a low Ki of 2.6 µM (2600 nM). The consequences of this activity are unclear (as the role of sigma receptors in general is not yet that well understood). Due to this low affinity, therapeutic concentrations of memantine likely are too low to have any sigmaergic effect. However, excessive doses of memantine for recreational purposes may indeed activate this receptor.
Memantine was first synthesized and patented by Eli Lilly and Company in 1968 as an anti-diabetic agent, but it was ineffective at lowering blood sugar. Later it was discovered to have CNS activity, and was developed by Merz for dementia in Germany; the NMDA activity was discovered after clinical trials had already begun. Memantine was first marketed for dementia in Germany in 1989 under the name Axura.
In the US, some CNS activities were discovered at Children's Hospital of Boston in 1995, and Children's licensed patents covering uses of memantine outside the field of ophthalmology to Neurobiological Technologies (NTI) in 1995. In 1998 NTI amended its agreement with Children's to allow Merz to take over development.
In 2000 Merz partnered with Forest to develop the drug for Alzheimers in the U.S. under the name Namenda.
In 2000 Merz partnered with Suntory for the Japanese market and with Lundbeck for other markets including Europe; the drug was originally marketed by Lundbeck under the name Ebixa.
Sales of the drug reached $1.8 billion for 2014. The cost of Namenda was $269 to $489 a month in 2012.
In February 2014 as the July 2015 patent expiration for memantine neared, Actavis, which had acquired Forest, announced that it was launching an extended release (XR) form of memantine that could be taken once a day instead of twice a day as needed with the then-current "immediate release" (IR) version, and that it intended to stop selling the IR version in August 2014 and withdraw the marketing authorization. This is a tactic to thwart generic competition called "product hopping". However the supply of the XR version ran short, so Actavis extended the deadline until the fall. In September 2014 the attorney general of New York, Eric Schneiderman, filed a lawsuit to compel Actavis to keep selling the IR version on the basis of antitrust law.
In December 2014, a judge granted New York State its request and issued an injunction, preventing Actavis from withdrawing the IR version until generic versions could launch. Actavis appealed and in May a panel of the Second Circuit Court of Appeals upheld the injunction, and in June Actavis asked that its case be heard by the full Second Circuit panel. In August 2015 Actavis' request was denied.
^Schneider, LS; Dagerman, KS; Higgins, JP; McShane, R (August 2011). "Lack of evidence for the efficacy of memantine in mild Alzheimer disease". Archives of Neurology. 68 (8): 991–8. doi:10.1001/archneurol.2011.69. PMID21482915.
^ abMorris H, Wallach J (2014). "From PCP to MXE: a comprehensive review of the non-medical use of dissociative drugs". Drug Testing and Analysis. 6 (7–8): 614–32. doi:10.1002/dta.1620. PMID24678061.
^Swedberg MD, Ellgren M, Raboisson P (2014). "mGluR5 antagonist-induced psychoactive properties: MTEP drug discrimination, a pharmacologically selective non-NMDA effect with apparent lack of reinforcing properties". The Journal of Pharmacology and Experimental Therapeutics. 349 (1): 155–64. doi:10.1124/jpet.113.211185. PMID24472725.
^ abParsons CG, Stöffler A, Danysz W (November 2007). "Memantine: a NMDA receptor antagonist that improves memory by restoration of homeostasis in the glutamatergic system — too little activation is bad, too much is even worse". Neuropharmacology. 53 (6): 699–723. doi:10.1016/j.neuropharm.2007.07.013. PMID17904591.
^Lipton SA (October 2007). "Pathologically activated therapeutics for neuroprotection". Nature Reviews Neuroscience. 8 (10): 803–8. doi:10.1038/nrn2229. PMID17882256.
^Rammes G, Rupprecht R, Ferrari U, Zieglgänsberger W, Parsons CG (2001). "The N-methyl-D-aspartate receptor channel blockers memantine, MRZ 2/579 and other amino-alkyl-cyclohexanes antagonise 5-HT(3) receptor currents in cultured HEK-293 and N1E-115 cell systems in a non-competitive manner". Neuroscience Letters. 306 (1–2): 81–4. doi:10.1016/S0304-3940(01)01872-9. PMID11403963.
^Aracava Y, Pereira EF, Maelicke A, Albuquerque EX (March 2005). "Memantine blocks alpha7* nicotinic acetylcholine receptors more potently than n-methyl-D-aspartate receptors in rat hippocampal neurons". J Pharmacol Exp Ther. 312 (3): 1195–205. doi:10.1124/jpet.104.077172. PMID15522999.
^Peeters M, Romieu P, Maurice T, Su TP, Maloteaux JM, Hermans E (Apr 2004). "Involvement of the sigma 1 receptor in the modulation of dopaminergic transmission by amantadine". Eur J Neurosci. 19 (8): 2212–20. doi:10.1111/j.0953-816X.2004.03297.x. PMID15090047.
^Aarsland, D; Ballard, C; Walker, Z; Bostrom, F; Alves, G; Kossakowski, K; Leroi, I; Pozo-Rodriguez, F; Minthon, L; Londos, E (July 2009). "Memantine in patients with Parkinson's disease dementia or dementia with Lewy bodies: a double-blind, placebo-controlled, multicentre trial". Lancet Neurology. 8 (7): 613–8. doi:10.1016/S1474-4422(09)70146-2. PMID19520613.
^Johansson, C; Ballard, C; Hansson, O; Palmqvist, S; Minthon, L; Aarsland, D; Londos, E (February 2011). "Efficacy of memantine in PDD and DLB: an extension study including washout and open-label treatment". International Journal of Geriatric Psychiatry. 26 (2): 206–13. doi:10.1002/gps.2516. PMID20665553.
^Haghighi M, Jahangard L, Mohammad-Beigi H, Bajoghli H, Hafezian H, Rahimi A, Afshar H, Holsboer-Trachsler E, Brand S (2013). "In a double-blind, randomized and placebo-controlled trial, adjuvant memantine improved symptoms in inpatients suffering from refractory obsessive-compulsive disorders (OCD)". Psychopharmacology. 228 (4): 633–40. doi:10.1007/s00213-013-3067-z. PMID23525525.
Lipton SA (2005). "The molecular basis of memantine action in Alzheimer's disease and other neurologic disorders: low-affinity, uncompetitive antagonism". Current Alzheimer Research. 2 (2): 155–65. doi:10.2174/1567205053585846. PMID15974913.