Both neostigmine and pyridostigmine antagonize the action of hydroxychloroquine.While there may be a link between hydroxychloroquine and hemolytic anemia in those with glucose-6-phosphate dehydrogenase deficiency, this risk may be low in those of African descent.Specifically, the US Food and Drug Administrations (FDA) drug label for hydroxychloroquine lists the following drug interactions:
Digoxin (wherein it may result in increased serum digoxin levels)
Insulin or anti-diabetic medication (wherein it may enhance the effects of a hypoglycemic treatment)
Drugs that prolong QT interval and other arrhythmogenic drugs (as Hydroxychloroquine prolongs the QT interval and may increase the risk of inducing serious abnormal heart rhythms (ventricular arrhythmias) if used concurrently)
Mefloquine and other drugs known to lower the seizure threshold (co-administration with other antimalarials known to lower the convulsion threshold may increase risk of convulsions)
Antiepileptics (concurrent use may impair the antiepileptic activity)
Methotrexate (combined use is unstudied and may increase the frequency of side effects)
Cyclosporin (wherein an increased plasma cyclosporin level was reported when used together). Pharmacology
Pharmacokinetics
Hydroxychloroquine has similar pharmacokinetics to chloroquine, with rapid gastrointestinal absorption, large distribution volume, and elimination by the kidneys. Cytochrome P450 enzymes (CYP2D6, 2C8, 3A4 and 3A5) metabolize hydroxychloroquine to N-desethylhydroxychloroquine. Both agents also inhibit CYP2D6 activity and may interact with other medications that depend on this enzyme. Pharmacodynamics
Antimalarials are lipophilic weak bases and easily pass plasma membranes. The free base form accumulates in lysosomes (acidic cytoplasmic vesicles) and is then protonated, resulting in concentrations within lysosomes up to 1000 times higher than in culture media. This increases the pH of the lysosome from four to six.
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.