Pharmacokinetics of a single dose of rimantadine in young adults and children

In vitro and in vivo activities of aminoadamantane and aminoalkylcyclohexane derivatives against Trypanosoma brucei

We reported recently that the bloodstream form of the African trypanosome, Trypanosoma brucei, is sensitive to the anti-influenza virus drug rimantadine. In the present report we describe the trypanocidal properties of a further 62 aminoadamantane and aminoalkylcyclohexane derivatives. Seventeen of the compounds were found to be more active than rimantadine, with four inhibiting growth in vitro of T. brucei by >90% at concentrations of 1 microM. The most active derivative (1-adamantyl-4-amino-cyclohexane) was about 20 to 25 times more effective than rimantadine. We observed a correlation between structural features of the derivatives and their trypanocidal properties; hydrophobic substitutions to the adamantane or cyclohexane rings generally enhanced activity. As with rimantadine, the activity in vitro varied with the pH. T. brucei was more sensitive in an alkaline environment (including a normal bloodstream pH of 7.4) and less sensitive under acidic conditions. Tests for activity in vivo were carried out with a mouse model of infection with a virulent strain of T. brucei. Although the parasitemia was not eliminated, it could be transiently suppressed by >98% with the most active compounds tested. These results suggest that aminoadamantane derivatives could have potential as a new class of trypanocidal agents.

The anti-influenza virus drug rimantadine has trypanocidal activity

We report here that bloodstream forms of the African trypanosome, Trypanosoma brucei, are sensitive to the anti-influenza virus drug rimantadine (50% inhibitory concentration of 1.26 micrograms ml-1 at pH 7.4). The activity is pH dependent and is consistent with a mechanism involving inhibition of the ability to regulate internal pH. Rimantadine is also toxic to the trypanosomatid parasites Trypanosoma cruzi and Leishmania major.

Rimantadine: a clinical perspective

OBJECTIVE

To provide a review of rimantadine, including its antiviral activity, pharmacokinetics, efficacy, adverse effects, drug interactions, and dosage and administration. Information on influenza A virus and clinical features of influenza disease are presented. Comparative data on rimantadine and amantadine are described.

DATA SOURCES

A MEDLINE search restricted to English-language literature published from 1966 through 1994 and an extensive review of journals was conducted.

DATA EXTRACTION

The data on antiviral activity, pharmacokinetics, adverse effects, and drug interactions were obtained from various articles on rimantadine in open and controlled studies. Controlled double-blind studies were evaluated to assess the efficacy of rimantadine in prophylaxis and treatment of influenza A infection.

DATA SYNTHESIS

Over 90% of a rimantadine dose was absorbed in 3-6 hours in healthy adults. Steady-state plasma concentrations have ranged from 0.10 to 2.60 micrograms/mL at doses of 3 mg/kg/d in infants to 100 mg twice daily in the elderly. Nasal fluid concentrations of rimantadine at steady-state were 1.5 times higher than plasma concentrations, which may explain the effectiveness of rimantadine despite a low plasma concentration. Over 75% of a rimantadine dose was metabolized in the liver, and the parent compound and metabolites were almost completely eliminated by the kidneys. The elimination half-life ranged from 24.8 to 36.5 hours, which allows once-daily dosing. Dosage adjustment is recommended for patients with severe renal impairment (creatinine clearance < or = 0.17 mL/s), severe hepatic dysfunction, or elderly nursing home patients. Drug-resistant strains of influenza A virus to rimantadine occurred in several studies with children and/or adults. Clinical significance of drug-resistant strains has not been established. Rimantadine appeared to be effective in 85-90% of individuals for prevention of influenza A illness and in 50-65% for prevention of influenza A infection. Rimantadine reduced the time to a 50% reduction in symptoms by 1-3 days versus placebo. Differences in symptom reduction between rimantadine and placebo after the first 3 days of treatment was not generally clinically significant. The most common adverse effects of rimantadine administration were associated with the central nervous system (CNS) and the gastrointestinal (GI) tract. CNS-related adverse effects occurred in 3.2% of children younger than 10 years of age and 8.4% of adults. In elderly patients, the incidence of CNS-related adverse effects ranged from 4.9% at 100 mg/d to 12.5% at 200 mg/d. GI adverse effects occurred in 8.4% of children younger than 10 years of age, 3.1% of adults, and 2.9% at 100 mg/d and 17.0% at 200 mg/d in the elderly.

CONCLUSIONS

Rimantadine offers some desirable features for the treatment and prophylaxis of influenza A infection. It appears to be an attractive choice in elderly patients with a history of CNS adverse effects from amantadine and in patients with mild or moderate renal impairment. Although approved for twice-daily dosing, rimantadine has a pharmacokinetic profile that would allow once-daily dosing. It is effective for prophylaxis (not postexposure prophylaxis) and treatment of influenza A virus. It also has a low incidence of adverse effects.

Amantadine and rimantadine prophylaxis of influenza A in nursing homes. A tolerability perspective

Amantadine and rimantadine are recommended for the treatment and prophylaxis of influenza A infections, and constitute an integral component of influenza control measures in the nursing home setting. However, optimal use necessitates a thorough understanding of the toxicity profiles of these agents, as well as strategies to reduce the risk of adverse reactions. Adverse reactions of these compounds predominantly involve the gastrointestinal tract and the central nervous system (CNS), including hyperexcitability, slurred speech, tremors, insomnia, dizziness, mood disturbance, ataxia, psychosis and fatigue. Based on data from comparative trials, rimantadine appears to exhibit a lesser propensity to cause adverse CNS reactions than amantadine, but a similar propensity to cause adverse gastrointestinal reactions. Factors enhancing the risk of adverse reactions to these agents include reduced renal function (especially for amantadine), drug-drug interactions with cationic drugs, which inhibit amantadine renal tubular secretion (e.g. trimethoprim, triamterene, and possibly cimetidine and procainamide), elevated peak and trough plasma concentrations, and a history of seizures. Careful attention to published dosage adjustment guidelines for these compounds, avoidance of interacting drugs and avoiding these agents in patients with a history of seizures may be the best means to reduce the risk of toxicity in elderly patients. Rimantadine may have an advantage over amantadine in the elderly population in light of its lesser propensity to cause adverse reactions, less complex dosage adjustment in the case of renal impairment and probable lack of drug-drug interaction potential with cationic drugs.

Efficacy of rimantadine hydrochloride in the treatment of influenza infection of mice

Rimantadine HCl was assessed for its effect on influenza A virus titer in lungs of infected BALB/c mice. Rimantadine administered orally via drinking water, with and without an intraperitoneal prophylactic loading dose, was compared to intraperitoneal administration. Mice were infected with a non-lethal dose of influenza A/Port Chalmers/H3N2 virus and the pulmonary virus titers were determined at intervals over a 21 day period. Prophylactic treatment with rimantadine followed by oral administration resulted in up to a 4 log10 reduction in pulmonary virus titer. The oral doses given to the mice were comparable on a mg/kg/day basis to those recommended for treatment of human infections. Reductions in pulmonary virus titers also occurred after intraperitoneal rimantadine treatment which included a prophylactic dose, but the reductions in pulmonary virus titers were less striking and not consistent over the course of infection. There were no significant reductions in pulmonary virus titers by either route if treatment was started 8 h after exposure to virus.

Multiple-dose pharmacokinetics of rimantadine in elderly adults

To assess the possible effect of aging on rimantadine hydrochloride pharmacokinetics, single- and multiple-dose kinetics were determined in 18 healthy adults with ages between 51 and 79 years. Subjects ingested single 100-mg oral doses of rimantadine after an overnight fast, followed after 5 days by a dosage of 100 mg twice a day for 9.5 days. No differences were observed among the age-stratified groups in measured or derived pharmacokinetic parameters. Peak concentrations in plasma (mean +/- standard deviation) following the single- and multiple-dose regimens, respectively, were 89 +/- 25 and 417 +/- 129 ng/ml for subjects who were 50 to 60 years of age (group 1), 92 +/- 24 and 401 +/- 84 ng/ml for those 61 to 70 years of age (group 2), and 100 +/- 14 and 538 +/- 51 for those 71 to 79 years of age (group 3). The elimination half-life in plasma following multiple doses averaged 33.5 h for group 1, 32.5 h for group 2, and 38.6 h for group 3. Steady-state concentrations in nasal mucus developed by day 5 of dosing (1.5-fold higher than concentrations in plasma), and rimantadine remained detectable in secretions for 5 days after the last dose in 65% of subjects. Stepwise regression analysis suggested that changes in maximum concentration in plasma and area under the concentration-time curve at steady state may be related to creatinine clearance. The results indicate that no important differences in rimantadine multiple-dose pharmacokinetics exist among healthy elderly adults with ages between 51 and 79 years.

[Rimantadine in the prevention and treatment of influenza A]

Although the antiviral properties of rimantadine specifically directed against influenza A viruses have been known for more than 25 years, this compound has not been widely used owing to its narrow specificity. The drug is active and has low toxicity. It should play a major role in the fight against the medical, epidemiological and economic effects of influenza A, but it can only be used under a number of conditions: accurate identification of the circulating virus and early administration of the drug (these two prerequisites being somewhat contradictory), selection of the right targets (contacts of recognized cases, subjects constantly exposed to contagion, etc.) and respect of certain contraindication. On the other hand, the theoretical advantages of this type of prophylaxis are important: it may limit contagion (morbidity) or at least reduce the severity of the cases (mortality); it may also prevent an epidemic from penetrating the population treated and thus reduce the severity and costs of the epidemic. The therapeutic use of rimantadine has not yet been officially recommended, but it already seems very promising. Rimantadine should be used as an adjuvant treatment, side by side with immunization against influenza which it cannot replace.