Influenza A viruses; ion channels NMDA, M2; CDK2; Bcl-2; Bax

The suppression of SARS-CoV-2 replication by amantadine sulfate (0-500 µM, 26 hours) ranges in IC50 values from 83 to 119 µM [4]. The growth of HepG2 and SMMC-7721 cells is markedly inhibited by amantadine sulfate (0-100 µg/mL, 24-72 hours) [6]. Inducing apoptosis, amantadine sulfate (0-75 µg/mL, 48 hours) stops the cell cycle in the G0/G1 phase [6]. In 48 hours, amantadine sulfate (0-75 µg/mL) decreases Bcl-2, increases Bax protein and mRNA levels, and decreases cell cycle-related genes and proteins (cyclin D1, cyclin E, and CDK2) [6].

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Since the SARS-CoV-2 pandemic started in late 2019, the search for protective vaccines and for drug treatments has become mandatory to fight the global health emergency. Travel restrictions, social distancing, and face masks are suitable counter measures, but may not bring the pandemic under control because people will inadvertently or at a certain degree of restriction severity or duration become incompliant with the regulations. Even if vaccines are approved, the need for antiviral agents against SARS-CoV-2 will persist. However, unequivocal evidence for efficacy against SARS-CoV-2 has not been demonstrated for any of the repurposed antiviral drugs so far. Amantadine was approved as an antiviral drug against influenza A, and antiviral activity against SARS-CoV-2 has been reasoned by analogy but without data. We tested the efficacy of Amantadine in vitro in Vero E6 cells infected with SARS-CoV-2. Indeed, amantadine inhibited SARS-CoV-2 replication in two separate experiments with IC50 concentrations between 83 and 119 µM. Although these IC50 concentrations are above therapeutic amantadine levels after systemic administration, topical administration by inhalation or intranasal instillation may result in sufficient amantadine concentration in the airway epithelium without high systemic exposure. However, further studies in other models are needed to prove this hypothesis.[4]

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Hepatocellular carcinoma (HCC) is one of the most aggressive malignancies worldwide, and its incidence associated with viral infection has increased in recent years. Amantadine is a tricyclic symmetric amine that can effectively protect against the hepatitis C virus. However, its antitumor properties remain unclear. In the present study, the effects of Amantadine on tumor cell viability, cell cycle regulation and apoptosis were investigated. The growth of HepG2 and SMMC‑7721 cells (HCC cell lines) was detected by an MTT assay. Flow cytometry was used to investigate cell cycle regulation and apoptosis. Reverse transcription‑quantitative polymerase chain reaction and western blot analysis were also performed to examine the expression of cell cycle‑ and apoptosis‑related genes and proteins, including cyclin E, cyclin D1, cyclin‑dependent kinase 2 (CDK2), B‑cell lymphoma 2 (Bcl‑2) and Bax. Our results demonstrated that amantadine markedly inhibited the proliferation of HepG2 and SMMC‑7721 cells in a dose‑ and time‑dependent manner and arrested the cell cycle at the G0/G1 phase. The levels of the cell cycle‑related genes and proteins (cyclin D1, cyclin E and CDK2) were reduced by amantadine, and apoptosis was significantly induced. Amantadine treatment also reduced Bcl‑2 and increased the Bax protein and mRNA levels. Additionally, Bcl‑2/Bax ratios were lower in the two HCC cell lines following amantadine treatment. Collectively, these results emphasize the role of amantadine in suppressing proliferation and inducing apoptosis in HCC cells, advocating its use as a novel tumor-suppressive therapeutic candidate [6].

Amantadine sulfate (25 mg/kg, IP, once day for 3 days) can reduce surgery-induced neuroinflammation and learning and memory deficits [5].
Surgery increased the time to identify the target box in the Barnes maze when tested 1 day [22 (median) (11-66) (interquartile range) of control group vs. 158 (29-180) of surgery group, n = 15, P = 0.022) or 8 days after the training sessions and reduced context-related freezing behavior in the fear conditioning test. These effects were attenuated by Amantadine (25 (14-90), n = 15, P = 0.029 compared with surgery group at 1 day after the training sessions in Barnes maze) and intracerebroventricular GDNF. Amantadine increased GDNF that was co-localized with glial fibrillary acidic protein, an astrocytic marker, in the hippocampus. Intracerebroventricular injection of an anti-GDNF antibody but not the denatured antibody blocked the effects of amantadine on cognition. Surgery induced neuroinflammation that was inhibited by amantadine. Lipopolysaccharide increased interleukin 1β production from C8-B4 cells. This effect was inhibited by GDNF [5].

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Amantadine attenuated surgery-induced learning and memory impairment [5]
The time to identify the target box during the 4-day training sessions of Barnes maze test was reduced with increased training sessions in the control rats, rats received anesthesia only, rats received amantadine only and rats received surgery plus Amantadine. This time on day 4 was significantly shorter than that on day 1 for these four groups of rats. This effect was not apparent in the rats after surgery alone. Surgery had a significant effect on the time needed to identify the target box in the training sessions [F(1,28) = 5.625, P = 0.025]. This effect was abolished by amantadine [F(1,28) = 0.840, P = 0.367; compared with control group]. Amantadine or anesthesia only did not have a significant effect on the time to identify the target box during the training sessions [F(1,28) = 0.063, P = 0.804; F(1, 14) = 0.074, P + 0.790] (Figs. 1 and 2). When the rats were tested 1 day after the training sessions, the time to identify the target box for the rats subjected to surgery was longer than that for the control rats. This prolongation was attenuated by amantadine. A similar change pattern occurred when the test was performed 8 days after the training sessions. However, anesthesia and amantadine alone did not affect the time to identify the target box whether the test was performed 1 day or 8 days after the training sessions (Fig. 1B and 2B). Rats in the surgery group but not in the anesthesia only group or amantadine group had less context-related freezing behavior in the fear conditioning test than control rats. This surgical effect was abolished by amantadine (Fig. 1C). There was no difference in the tone-related freezing behavior among the control rats, rats received amantadine, rats received surgery and rats received surgery plus amantadine (Fig. 1C and 2C).

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Amantadine attenuated surgery-induced neuroinflammation [5]
The expression of Iba-1 (a microglial marker), IL-1β and IL-6 in the hippocampus was significantly increased at 6 and 24 h after the surgery. These increases were abolished by amantadine (Figs. 3 and 4). Similarly, Iba-1 expression in the hippocampal dentate gyrus region was also increased at 10 days after the surgery and this increase was blocked by Amantadine (Fig. 5). These results suggest that surgery induces neuroinflammation that was inhibited by amantadine.

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Amantadine increased the expression of GDNF that inhibited microglial activation [5]
Amantadine significantly increased GDNF in the hippocampus (Fig. 7). GDNF was mainly co-localized with GFAP, an astrocytic marker, but was not co-localized with Iba-1 (Figs. 7A and 7B). Some GDNF appeared to be around NeuN, a neuronal marker (Fig. 7C). Surgery also increased GFAP but this increase was not affected by Amantadine in the hippocampus (Figs. 7A and 7E).

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Amantadine-induced attenuation of learning and memory impairment after surgery was inhibited by anti-GDNF antibody [5]
Similar to the control rats, rats in antibody only group and the surgery plus Amantadine plus boiled antibody group had a decreased time to find the target box with increased training sessions. This time on the training day 4 was shorter than that on training day 1 for these two groups of rats. This effect was not apparent for rats in the surgery plus amantadine plus anti-GDNF antibody group. The anti-GDNF antibody was found to have a significant effect on the time to identify the target box during the training sessions [F(1,14) = 19.009, P < 0.001; compared with control) (Fig. 9A). The time to identify the target box on day 1 after the training session was not different among control rats, rats received antibody, rates received surgery plus amantadine plus anti-GDNF antibody or rats received surgery plus amantadine plus boiled antibody. However, rats subjected to surgery plus amantadine plus anti-GDNF antibody required much longer time than control rats or rats received surgery plus amantadine plus boiled antibody to identify the target box on day 8 after the training sessions (Fig. 9B). Similarly, rats subjected to surgery plus amantadine plus anti-GDNF antibody also had less context-related freezing behavior than control rats or rats received surgery plus amantadine plus boiled antibody in the fear conditioning test. However, the tone-related freezing behavior was not different among the three groups (Fig. 9C).

S-Protein—ACE2 Binding Assay [4]
The compounds were tested for their ability to inhibit the binding of SARS-CoV-2 spike protein (S protein) to ACE2 using the SARS-CoV-2 spike: ACE2 Inhibitor Screening Assay Kit. In brief, the SARS-CoV-2 spike protein was coated to a 96 microwell plate at 1 µg/mL in phosphate buffered saline. Unbound protein was removed and unspecific binding sites in the wells are blocked. Then, the blocking solution was removed, and the diluted compounds and control samples were added to the wells. After pre-incubation of the coated spike protein with the compounds, the His-tagged ACE2 protein was added and incubated together with the compounds to allow binding to the spike protein. After washing and blocking, the bound ACE2 protein was detected by an anti-His-antibody coupled to horse radish peroxidase (HRP). The detection was performed using a chemiluminescent HRP substrate and reading the luminescence intensity in a microtiter-plate reader. The luminescence signal of each sample containing diluted compound was divided by the luminescence in absence of any inhibitor, and the resulting values were plotted against the concentration of the compound.

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Antiviral Activity Assay with RT-PCR Readout (1st Experiment) [4]
Exponentially growing Vero E6 cells were seeded into a 48-well plate at a density of 8 × 104 cells per well and were incubated overnight. Medium was removed and cells were infected in triplicate with SARS-CoV-2 (hCoV-19/Italy/INMI1-isl/2020 at an MOI of 0.01 in 300 µL of medium containing different inhibitor concentrations. Amantadine was solubilized in sterile water and further diluted with medium to concentrations of 500 µM, 100 µM, 20 µM, 4 µM, and 8 nM. Remdesivir was solubilized in DMSO and diluted with medium to concentrations of 50 µM, 10 µM, 2 µM, 0.4 µM, and 80 nM. Remdesivir MOCK control contained according amounts of DMSO.

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Antiviral Activity Assay with Nucleocapsid Protein Readout (2nd Experiment) [4]
Exponentially growing Vero E6 cells were seeded into a 96-well plate at their optimal density in complete medium; 24 h later, cells were infected with SARS-CoV-2 (viral strain INMI1) at 0.01 moi (multiplicity of infection) and then exposed to different concentrations of the drugs (0–0.1–1–10–100–300 μM for Amantadine for 72 h. Drug dilutions were performed in culture medium. Replicates for each concentration point were examined. At the end of the incubation period, antiviral activity was examined through both ELISA (quantifying SARS-CoV-2 nucleoprotein) as well as a cytoprotection assay (toxicity effect examined through an inverted microscope).

Cell Viability Assay[4]
Cell Types: Vero E6 Cell
Tested Concentrations: 500 µM, 100 µM, 20 µM, 4 µM and 8 nM
Incubation Duration: 26 hrs (hours)
Experimental Results: Causes concentration-dependent reduction of virus (IC50=83 µM) 26 post-infection The nucleic acid concentration in the supernatant is 10-500 µM. Results in a concentration-dependent reduction of viral nucleic acid in the cytoplasm (IC50=119 µM) 26 hrs (hours) post-infection.

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Cell proliferation assay[6]
Cell Types: Human HCC cell lines (HepG2 and SMMC-7721) and normal liver cells (L02 cells)
Tested Concentrations: 0, 1, 2, 5, 10, 25, 50 and 100 µg/mL
Incubation Duration: 24, 48 and 72 hrs (hours)
Experimental Results: Inhibited cell proliferation in a time- and dose-dependent manner in HepG2 and SMMC-7721 cells.

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Cell cycle analysis[6]
Cell Types: HepG2 and SMMC-7721 Cell
Tested Concentrations: 0, 10, 25, 50 and 75 µg/mL
Incubation Duration: 48 hrs (hours)
Experimental Results: Significant increase in the number of HepG2 and SMMC-7721 cells in G0/G1 phase in a dose-dependent manner, and Dramatically diminished the numbe

Animal/Disease Models: Fischer 344 rats (4 months old, male, 290-330 g, 15 rats per group) [5]
Doses: 25 mg/kg
Route of Administration: IP, one time/day for 3 days (first dose in 15 minutes before administration)
Experimental Results: Inhibited surgery-induced neuroinflammation and learning and memory impairment, increased GDNF (glial cell line-derived neuronal neuron) co-localized with hippocampal glial fibrillary acidic protein (an astrocyte marker) nutritional factors).

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Four-month old male Fischer 344 rats weighing 290 – 330 g were randomly assigned to: 1) control group (not being exposed to surgery or any drugs), 2) Amantadine group, 3) surgery group (right carotid artery exposure), and 4) surgery plus Amantadine group in the first experiment. Each group had 15 rats. In the second experiment, the rats were assigned to: 5) control group, 6) anti-GDNF antibody group, 7) surgery plus amantadine plus boiled anti-GDNF antibody group, and 8) surgery plus amantadine plus anti-GDNF antibody group. Each group had 8 rats. In the third experiment, the rats were randomly assigned to: 7) control group, 8) anesthesia only group, and 9) surgery plus GDNF group. Each group had 8 rats. GDNF and the anti-GDNF antibody were injected intracerebroventricularly. One week later, these rats were started to be tested in Barnes maze and then fear conditioning. Separate rats were assigned to 1) control group, 2) surgery group, and 3) surgery plus amantadine group (n = 6 per condition) and sacrificed at 6 h, 24 h or 10 days after the surgery for Western blotting and immunohistochemistry.

Amantadine was dissolved in normal saline and injected intraperitoneally at 25 mg/kg/day for three days with the first dose at 15 min before surgery. Similar injections were performed in the amantadine only group except that no surgery and anesthesia were performed. The amantadine dose was chosen based on previous studies.[5]

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Absorption, Distribution and Excretion
Amantadine is well absorbed orally from the gastrointestinal tract.
It is primarily excreted unchanged in the urine by glomerular filtration and tubular secretion.
3 to 8 L/kg [healthy subjects]
0.2 - 0.3 L/hr/kg
0.10 +/- 0.04 L/hr/kg [healthy, elderly male]
Rapidly and almost completely absorbed from gastrointestinal tract.
Amantadine is distributed into breast milk.
Elimination: Renal; >90% excreted unchanged in urine by glomerular filtration and renal tubular secretion. Rate of excretion rapidly increased in acid urine. In dialysis: Only small amounts (approximately 4%) removed from the blood by hemodialysis.
Distributed into saliva, tear film, and nasal secretions; in animals, tissue (especially lung) concentrations are higher than serum concentrations. Crosses the placenta and blood-brain barrier; distributed into breast milk. Cerebral spinal fluid concentrations were 52% of corresponding plasma concentrations in one patient. VolD - 4.4 + or - 0.2 L/kg (normal renal function); 5.1 + or - 0.2 L/kg (renal failure).
For more Absorption, Distribution and Excretion (Complete) data for AMANTADINE (7 total), please visit the HSDB record page.

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Metabolism / Metabolites
No appreciable metabolism, although negligible amounts of an acetyl metabolite have been identified.
Eight metabolites of amantadine have been identified in human urine. One metabolite, an N-acetylated compound, was quantified in human urine and accounted for 5-15% of the administered dose. Plasma acetylamantadine accounted for up to 80% of the concurrent amantadine plasma concentration in 5 of 12 healthy volunteers following the ingestion of a 200 mg dose of amantadine. Acetylamantadine was not detected in the plasma of the remaining seven volunteers..
No appreciable metabolism, although negligible amounts of an acetyl metabolite have been identified. Amantadine is well absorbed orally from the gastrointestinal tract. The mechanism of its antiparkinsonic effect is not fully understood, but it appears to be releasing dopamine from the nerve endings of the brain cells, together with stimulation of norepinephrine response. The antiviral mechanism seems to be unrelated. The drug interferes with a viral protein, M2 (an ion channel), which is needed for the viral particle to become "uncoated" once it is taken inside the cell by endocytosis. Metabolites are excreted in the urine (A308).
Route of Elimination: It is primarily excreted unchanged in the urine by glomerular filtration and tubular secretion.
Half Life: Mean half-lives ranged from 10 to 14 hours, however renal function impairment causes a severe increase in half life to 7 to 10 days.

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Biological Half-Life
Mean half-lives ranged from 10 to 14 hours, however renal function impairment causes a severe increase in half life to 7 to 10 days.
Amantadine pharmacokinetics were determined in 24 normal adult male volunteers after the oral administration of a single amantadine hydrochloride 100 mg soft gel capsule. ... The half-life was 17 + or - 4 hours (range: 10 to 25 hours). Across other studies, amantadine plasma half-life has averaged 16 + or - 6 hours (range: 9 to 31 hours) in 19 healthy volunteers.
Normal renal function: 11 to 15 hours. Elderly patients: 24 to 29 hours. Renal function impairment, severe: 7 to 10 days. Hemodialysis: 24 hours.
The elimination half-life increases two to three fold or greater when creatinine clearance is less than 40 mL/min/1.73 sqm and averages eight days in patients on chronic maintenance hemodialysis.

Toxicity Summary
The mechanism of its antiparkinsonic effect is not fully understood, but it appears to be releasing dopamine from the nerve endings of the brain cells, together with stimulation of norepinephrine response. It also has NMDA receptor antagonistic effects. The antiviral mechanism seems to be unrelated. The drug interferes with a viral protein, M2 (an ion channel), which is needed for the viral particle to become "uncoated" once it is taken inside the cell by endocytosis.

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Hepatotoxicity
Despite widespread use, there is little evidence that amantadine when given orally causes liver injury, either in the form of serum enzyme elevations or clinically apparent liver disease.
Likelihood score: E (unlikely cause of clinically apparent liver injury).

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Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
It is probably best to avoid amantadine during breastfeeding because of its potential negative effect on lactation.
◉ Effects in Breastfed Infants
Relevant published information was not found as of the revision date.
◉ Effects on Lactation and Breastmilk
Amantadine is a dopamine agonist. Clinical studies using amantadine dosages of 100 mg 2 or 3 times daily have demonstrated a decrease in serum prolactin and decreased galactorrhea in patients taking dopaminergic neuroleptic drugs such as phenothiazines, haloperidol and loxapine.[1][2] No studies have been reported on the effects of amantadine on the milk supply in nursing mothers. The maternal prolactin level in a mother with established lactation may not affect her ability to breastfeed.

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Protein Binding
Approximately 67% bound to plasma proteins over a concentration range of 0.1 to 2.0 µg/mL.

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Toxicity Data
LD50: 800 mg/kg (Oral, Rat)
LD50: 700 mg/kg (Oral, Mouse)

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Interactions
The anti-influenza A activities of amantadine and ribavirin were investigated seperately and in combination. In ferret tracheal ciliated epithelium, the combination of drugs synergistically delayed the virus-induced cytopathic effect.
Concurrent use /of alcohol/ with amantadine is not recommended since this may increase the potential for CNS effects such as dizziness, lightheadedness, orthostatic hypotension, or confusion.
Concurrent use /of anticholinergics, or other medications with anticholinergic activity; tricyclic antidepressants; other antidyskinetics; antihistamines; or phenothiazines/ with amantadine may potentiate the anticholinergic-like side effects, especially those of confusion, hallucinations, and nightmares; dosage adjustments of these medications or of amantadine may be necessary; also, patients should be advised to report occurrences of gastrointestinal problems promptly since paralytic ileus may occur with concurrent therapy.
Concurrent use /of opioid- and anticholinergic-containing antidiarrheals/ with amantadine may potentiate the anticholinergic-like side effects; although significant interaction is unlikely with usual doses of opioid- and anticholinergic-containing antidiarrheals, significant interaction may occur if these medications are abused.
For more Interactions (Complete) data for AMANTADINE (10 total), please visit the HSDB record page.

[1]. Emergence of amantadine-resistant influenza A viruses: epidemiological study. J Infect Chemother. 2003;9(3):195-200.

[2]. Amantadine: the journey from fighting flu to treating Parkinson disease. Neurology. 2012;78(14):1096-1099.

[3]. A review of compounds exhibiting anti-orthopoxvirus activity in animal models. Antiviral Res. 2003 Jan;57(1-2):41-52.

[4]. Amantadine Inhibits SARS-CoV-2 In Vitro. Viruses. 2021 Mar 24;13(4):539.

[5]. Amantadine alleviates postoperative cognitive dysfunction possibly by increasing glial cell line-derived neurotrophic factor in rats. Anesthesiology. 2014 Oct;121(4):773-85.

[6]. Amantadine inhibits cellular proliferation and induces the apoptosis of hepatocellular cancer cells in vitro. Int J Mol Med. 2015;36(3):904-910.

Amantadine sulfate is an alkylammonium sulfate salt obtained by combining amantadine and sulfuric acid in a 2:1 ratio. Used as an antiviral and antiparkinson drug. It has a role as an antiparkinson drug, an antiviral drug, a dopaminergic agent, a NMDA receptor antagonist and a non-narcotic analgesic. It contains an adamantan-1-aminium.
Amantadine Sulfate is the sulfate salt of amantadine, a synthetic tricyclic amine with antiviral, antiparkinsonian, and antihyperalgesic activities. Amantadine appears to exert its antiviral effect against the influenza A virus by interfering with the function of the transmembrane domain of the viral M2 protein, thereby preventing the release of infectious viral nucleic acids into host cells; furthermore, this agent prevents virus assembly during virus replication. Amantadine exerts its antiparkinsonian effects by stimulating the release of dopamine from striatal dopaminergic nerve terminals and inhibiting its pre-synaptic reuptake. This agent may also exert some anticholinergic effect through inhibition of N-methyl-D-aspartic acid (NMDA) receptor-mediated stimulation of acetylcholine, resulting in antihyperalgesia.
An antiviral that is used in the prophylactic or symptomatic treatment of influenza A. It is also used as an antiparkinsonian agent, to treat extrapyramidal reactions, and for postherpetic neuralgia. The mechanisms of its effects in movement disorders are not well understood but probably reflect an increase in synthesis and release of dopamine, with perhaps some inhibition of dopamine uptake.

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Therapeutic Uses
Antiparkinson Agents; Antiviral Agents; Dopamine Agents
Amantadine is used in the management of certain aspects of fatigue associated with multiple sclerosis, including lowered energy level, deceased sense of well-being, decreased perceived attention and memory, and diminished problem solving ability. /NOT included in US or Canadian product labeling/
Amantadine is indicated in the treatment of idiopathic parkinsonism (paralysis agitans; shaking palsy), post-encephalitic parkinsonism, drug-induced extrapyramidal reactions, symptomatic parkinsonism following injury to the nervous system caused by carbon monoxide intoxication, and parkinsonism associated with cerebral arteriosclerosis in the elderly. /Included in US product labeling/
Amantadine is indicated as a primary agent in the prophylaxis and treatment of respiratory tract infections caused by influenza A virus strains in high-risk patients (including those with pulmonary or cardiovascular disease, the elderly, and residents of nursing homes and other chronic care facilities who have chronic medical conditions), hospital ward contacts of high-risk patients, immunocompromised patients, those in critical public service positions (eg, police, firefighters, medical personnel), in high-risk patients for whom the influenza vaccine is contraindicated, and patients with severe influenza A viral infections. It is effective against all strains of influenza A virus that have been tested to date, including Russian, Brazilian, Texan, London, and others. It may be given as chemoprophylaxis concurrently with inactivated influenza A virus vaccine until protective antibodies develop. However, it should be emphasized that vaccination of high-risk persons each year is the single most important measure for reducing the impact of influenza. No well-controlled studies have examined whether amantadine prevents complication of influenza A in high-risk persons. Resistant strains of influenza A have been reported in patients receiving rimantadine; these resistant strains were also apparently transmitted household contacts. Rimantadine has a similar chemical structure, spectrum of activity, and mechanism of action to amantadine, and drug-resistant strains of virus have cross-resistance to amantadine and rimantadine. /Included in US product labeling/
For more Therapeutic Uses (Complete) data for AMANTADINE (6 total), please visit the HSDB record page.

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Drug Warnings
Swine influenza (H1N1) viruses contain a unique combination of gene segments that have not been reported previously among swine or human influenza viruses in the US or elsewhere. The H1N1 viruses are resistant to amantadine and rimantadine but not to oseltamivir or zanamivir.
Suicide attempts (resulting in death in some patients) have been reported rarely in patients receiving amantadine, many of whom received short courses of the drug for influenza prophylaxis or treatment. The manufacturer states that the incidence and pathophysiology of these suicide attempts are not known. Suicide ideation or attempts have been reported in patients with or without a prior history of psychiatric disorders. Amantadine can exacerbate mental status in patients with a history of psychiatric disorders or substance abuse. Patients with suicidal tendencies may exhibit abnormal mental states including disorientation, confusion, depression, personality changes, agitation, aggressive behavior, hallucinations, paranoia, other psychotic reactions, somnolence, or insomnia.
Possible neuroleptic malignant syndrome (NMS) has been reported in patients receiving amantadine and was associated with dosage reduction or withdrawal of the drug. NMS is potentially fatal and requires immediate initiation of intensive symptomatic and supportive care. Patients should be observed closely when the dosage of amantadine is reduced or the drug is discontinued; this precaution is especially important in patients receiving concomitant therapy with an antipsychotic agent.
Nausea is one of the most frequent adverse effects of amantadine and has been reported in 5-10% of patients receiving the usual dosage of the drug. Anorexia, constipation, diarrhea, and dry mouth have been reported in 1-5% and vomiting has been reported in up to 1% of patients receiving amantadine. Abdominal discomfort or dysphagia also has been reported. The incidence of adverse GI effects is comparable for amantadine and rimantadine.
For more Drug Warnings (Complete) data for AMANTADINE (19 total), please visit the HSDB record page.

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Pharmacodynamics
Amantadine is an antiviral drug which also acts as an antiparkinson agent, for which it is usually combined with L-DOPA when L-DOPA responses decline (probably due to tolerance). It is a derivate of adamantane, like a similar drug rimantadine. The mechanism of action of amantadine in the treatment of Parkinson's disease and drug-induced extrapyramidal reactions is not known. It has been shown to cause an increase in dopamine release in the animal brain, and does not possess anticholinergic activity.

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At present, three licensed antiviral influenza agents are available in Japan: amantadine, zanamivir, and oseltamivir. These antiviral agents can be used for controlling and preventing influenza, but they are not a substitute for vaccination. Amantadine is an antiviral drug with activity against influenza A viruses, but not influenza B viruses. Persons who have influenza A infection and who are treated with amantadine can shed sensitive viruses early in the course of treatment and later shed drug-resistant viruses, especially after 5-7 days of therapy. Such persons can benefit from therapy even when resistant viruses emerge. In screening for amantadine susceptibility, enzyme-linked immunoassays, plaque reduction assays, and TCID50/0.2 ml titration are employed. The molecular changes associated with resistance have been identified as single-nucleotide changes, leading to corresponding amino acid substitutions in one of four critical sites, amino acids 26, 27, 30, and 31, in the transmembrane region of the M2 protein. The polymerase chain reaction (PCR)-restriction fragment length polymorphism analysis method is quite useful. Resistant viruses have been circulated in outbreak situations at nursing homes where amantadine was used not only for treating influenza virus infection but also for Parkinson's disease. Measures should be taken to reduce contact, as much as possible, between persons taking and those not taking antiviral drugs for treatment or chemoprophylaxis.[1]

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Objective: To explore how amantadine transitioned from an anti-flu drug to antiparkinsonian agent. Methods: A review of the historical literature on the use of amantadine from 1966 to the present was performed. Results: Amantadine was originally introduced and utilized as an antiviral medication. A single patient noticed relief in her Parkinson disease (PD) symptoms after taking amantadine for a flu infection, and this observation sparked an interest, and several important studies that eventually led to a new drug indication. Conclusion: Amantadine has over the years fallen out of favor as a drug to address influenza infection; however, it has become part of the arsenal utilized for early symptomatic treatment of PD, as well an option for treating dyskinesia.[2]

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Several animal models using mice (most frequently), rabbits, or monkeys have been used to identify compounds active against orthopoxvirus infections. The treatment of vaccinia virus infections has been well studied in models involving infection of scarified skin or eyes, or resulting from intravenous, intraperitoneal, intracerebral, or intranasal virus inoculation. Cowpox virus has been used in intranasal or aerosol infection studies to evaluate the treatment of lethal respiratory infections. Rabbitpox, monkeypox, and variola viruses have been employed to a lesser extent than the other viruses in chemotherapy experiments. A review of the literature over the past 50 years has identified a number of compounds effective in treating one or more of these infections, which include thiosemicarbazones, nucleoside and nucleotide analogs, interferon, interferon inducers, and other unrelated compounds. Substances that appear to have the greatest potential as anti-orthopoxvirus agents are the acyclic nucleotides, (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (cidofovir, HPMPC) and 1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl)methyl]cytosine (cyclic HPMPC), and the acyclic nucleoside analog, 2-amino-7-[(1,3-dihydroxy-2-propoxy)methyl]purine (S2242). Other classes of compounds that have not been sufficiently studied in lethal infection models and deserve further consideration are thiosemicarbazones related to methisazone, and analogs of adenosine-N(1)-oxide and 1-(benzyloxy)adenosine.[3]

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Background: Postoperative cognitive dysfunction is a clinical entity that is associated with poor outcome. We determined the effectiveness of amantadine in reducing surgery-induced cognitive impairment and the role of glial cell line-derived neurotrophic factor (GDNF) in this effect. Methods: Four-month old male Fischer 344 rats were subjected to right carotid exposure under intravenous anesthesia. Some rats received intraperitoneal injection of 25 mg/kg/day amantadine for 3 days with the first dose at 15 min before the surgery or intracerebroventricular injection of GDNF or an anti-GDNF antibody at the end of surgery. One week later, rats were started to be tested by Barnes maze and fear conditioning. Hippocampus was harvested at 6 h, 24 h or 10 days after the surgery for biochemical analysis. C8-B4 cells, a microglial cell line, were pretreated with 1 ng/ml GDNF for 30 min before being exposed to 5 ng/ml lipopolysaccharide for 2 h.[5]

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In conclusion, amantadine inhibits viral replication in the Vero E6 cell system. In this study, a functionally relevant interference with the binding of the viral spike protein to ACE2 on target cells could not be shown, with the limitations discussed above. The question was triggered by the predicted docking with close contact of amantadine to Tyr489 and Phe456 in the receptor-binding domain (RBD) of SARS-CoV-2; SARS-CoV-2 RBD (residues Arg319–Phe541) interacts with the N-terminal peptidase domain of ACE2 (residues Ser19–Asp615), which might have indicated a potential antiviral mode of action of amantadine, but our data do not substantiate the in silico hypothesis. Inhibition of a viroporin as an alternative mode of action needs to be analyzed in future studies. In a recently published preprint, amantadine inhibited the recombinant SARS-CoV-2 viroporin protein E and the putative SARS-CoV-2 viroporin Orf10. The authors observed in the Xenopus laevis oocyte model a 77% inhibition of the protein E ion channel-mediated current at 10 µM amantadine, which appears even more potent than the inhibition of the overall virus replication in the more complex eukaryotic cell culture model at an IC50 of 83–119 µM that we have found; these data indicate that viroporin inhibitors merit a closer look. Finally, so far, amantadine appears to also affect the known SARS-CoV-2 mutations because few or no mutations have been identified in protein E or Orf10 in mutated SARS-CoV-2 lineages collected from patients in India. Lineage B 1.1.7 neither contains mutations in protein E nor in Orf10. Nevertheless, a single amino acid exchange can reduce the efficacy of a small molecule, as happened with the influenza A virus years ago.

C10H17N.H2O4S

249.32716

400.239

C, 59.97; H, 9.06; N, 6.99; O, 15.98; S, 8.00

31377-23-8

Amantadine;768-94-5;Amantadine hydrochloride;665-66-7

124108

Typically exists as solid at room temperature

1.066g/cm3

225.7ºC at 760 mmHg

300 °C

96ºC

5.656

4

6

0

27

225

0

S(O)(O)(=O)=O.C12(N)CC3CC(CC(C3)C1)C2

MYWTWSQFJLXGGQ-UHFFFAOYSA-N

InChI=1S/2C10H17N.H2O4S/c2*11-10-4-7-1-8(5-10)3-9(2-7)6-10;1-5(2,3)4/h2*7-9H,1-6,11H2;(H2,1,2,3,4)

adamantan-1-amine;sulfuric acid

Amantadine Sulfate; Amantadine sulphate; 1-Aminoadamantane Sulfate; 1-Aminoadamantane sulphate; ...; 31377-23-8 (sulfate);

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)