In a study of the duration of MOR blockade with naltrexone, the drug with a single 50 mg dose showed 91% blockade of brain [11C]carfentanil (a selective MOR ligand) binding at 48 hours (2 days), 80% blockade at 72 hours (3 days), 46% blockade at 120 hours (5 days), and 30% blockade at 168 hours (7 days). The half-time of brain MOR blockade by naltrexone in this study was 72 to 108 hours (3.0 to 4.5 days). Based on these findings, doses of naltrexone of even less than 50 mg/day would be expected to achieve virtually complete brain MOR occupancy. Blockade of brain MORs with naltrexone is much longer-lasting than with other opioid antagonists like naloxone (half-time of ~1.7 hours intranasally) or nalmefene (half-time of ~29 hours).The half-life of occupancy of the brain MOR and duration of clinical effect of naltrexone are much longer than suggested by its plasma elimination half-life. A single 50 mg oral dose of naltrexone has been found to block brain MORs and opioid effects for at least 48 to 72 hours. The half-time of brain MOR blockade by naltrexone (72–108 hours) is much longer than the fast plasma clearance component of naltrexone and 6β-naltrexol (~4–12 hours) but was reported to correspond well to the longer terminal phase of plasma naltrexone clearance (96 hours).
Parkinsons disease
Rimantadine, like its antiviral cousin amantadine, possesses some NMDA antagonistic properties and is used as an antiparkinsonic drug (i.e., in the treatment of Parkinsons disease). However, in general, neither rimantadine nor amantadine is a preferred agent for this therapy and would be reserved for cases of the disease that are less responsive to front-line treatments. Other
Rimantadine is shown to be effective against other RNA-containing viruses. It can treat arboviruses like Saint Louis encephalitis and Sindbis. Other viruses that can be treated with Rimantadine include respiratory synctial and parainfluenza viruses. Rimantadine has also been shown to treat chronic hepatitis C.

Drug interactions
Taking paracetamol (acetaminophen, Tylenol) or acetylsalicylic acid (aspirin) while taking rimantadine is known to reduce the bodys uptake of rimantadine by approximately 12%. Cimetidine also affects the bodys uptake of rimantadine. Taking anticholigenic drugs with amantadine may increase underlying seizure disorders and aggravate congestive heart failure. Side effects
Rimantadine can produce gastrointestinal and central nervous system adverse effects. Approximately 6% of patients (compared to 4% of patients taking a placebo) reported side-effects at a dosage of 200 mg/d. Common side effects include:

nausea
upset stomach
nervousness
tiredness
lightheadedness
trouble sleeping (insomnia)
difficulty concentrating
confusion
anxiety
Rimantadine shows fewer CNS symptoms than its sister drug Amantadine. Synthesis
1-carboxyadamatanones are reduced with sodium borohydride to create racemic hydroxy acid.