Chemical formula: C₁₀H₈F₂N₄O Molecular mass: 238.194 g/mol PubChem compound: 129228
Rufinamide modulates the activity of sodium channels, prolonging their inactive state. Rufinamide is active in a range of animal models of epilepsy.
Maximum plasma levels are reached approximately 6 hours after administration. Peak concentration (Cmax) and plasma AUC of rufinamide increase less than proportionally with doses in both fasted and fed healthy subjects and in patients, probably due to dose-limited absorption behaviour. After single doses, food increases the bioavailability (AUC) of rufinamide by approximately 34% and the peak plasma concentration by 56%.
Rufinamide oral suspension and rufinamide film-coated tablets have been demonstrated to be bioequivalent.
In in -vitro studies, only a small fraction of rufinamide (34%) was bound to human serum proteins with albumin accounting for approximately 80% of this binding. This indicates minimal risk of drug-drug interactions by displacement from binding sites during concomitant administration of other substances. Rufinamide was evenly distributed between erythrocytes and plasma.
Rufinamide is almost exclusively eliminated by metabolism. The main pathway of metabolism is hydrolysis of the carboxylamide group to the pharmacologically inactive acid derivative CGP 47292. Cytochrome P450-mediated metabolism is very minor. The formation of small amounts of glutathione conjugates cannot be completely excluded.
Rufinamide has demonstrated little or no significant capacity in -vitro to act as a competitive or mechanism-based inhibitor of the following human P450 enzymes: CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4/5 or CYP4A9/11-2.
The plasma elimination half-life is approximately 6-10 hours in healthy subjects and patients with epilepsy. When given twice daily at 12-hourly intervals, rufinamide accumulates to the extent predicted by its terminal half-life, indicating that the pharmacokinetics of rufinamide are time-independent (i.e. no autoinduction of metabolism).
In a radiotracer study in three healthy volunteers, the parent compound (rufinamide) was the main radioactive component in plasma, representing about 80% of the total radioactivity, and the metabolite CGP 47292 constituting only about 15%. Renal excretion was the predominant route of elimination for active substance related material, accounting for 84.7% of the dose.
The bioavailability of rufinamide is dependent on dose. As dose increases, the bioavailability decreases.
Population pharmacokinetic modelling has been used to evaluate the influence of sex on the pharmacokinetics of rufinamide. Such evaluations indicate that sex does not affect the pharmacokinetics of rufinamide to a clinically relevant extent.
The pharmacokinetics of a single 400 mg dose of rufinamide were not altered in subjects with chronic and severe renal failure compared to healthy volunteers. However, plasma levels were reduced by approximately 30% when haemodialysis was applied after administration of rufinamide, suggesting that this may be a useful procedure in case of overdose.
No studies have been performed in patients with hepatic impairment and therefore rufinamide should not be administered to patients with severe hepatic impairment.
A pharmacokinetic study in older healthy volunteers did not show a significant difference in pharmacokinetic parameters compared with younger adults.
Children generally have lower clearance of rufinamide than adults, and this difference is related to body size with rufinamide clearance increasing with body weight.
A recent population PK analysis of rufinamide on data pooled from 139 subjects (115 LGS patients and 24 healthy subjects), including 83 paediatric LGS patients (10 patients aged 1 to <2 years, 14 patients aged 2 to <4 years, 14 patients aged 4 to <8 years, 21 patients aged 8 to <12 years and 24 patients aged 12 to <18 years) indicated that when rufinamide is dosed on a mg/kg/day basis in LGS subjects aged 1 to <4 years, comparable exposure to that in LGS patients aged ≥4 years, in which efficacy has been demostrated, is achieved.
Studies in new-born infants or infants and toddlers under 1 year of age have not been conducted.
Conventional safety pharmacology studies revealed no special hazards at clinically relevant doses.
Toxicities observed in dogs at levels similar to human exposure at the maximum recommended dose were liver changes, including bile thrombi, cholestasis and liver enzyme elevations thought to be related to increased bile secretion in this species. No evidence of an associated risk was identified in the rat and monkey repeat dose toxicity studies.
In reproductive and developmental toxicity studies, there were reductions in foetal growth and survival, and some stillbirths secondary to maternal toxicity. However, no effects on morphology and function, including learning or memory, were observed in the offspring. Rufinamide was not teratogenic in mice, rats or rabbits.
The toxicity profile of rufinamide in juvenile animals was similar to that in adult animals. Decreased body weight gain was observed in both juvenile and adult rats and dogs. Mild toxicity in the liver was observed in juvenile as well as in adult animals at exposure levels lower than or similar to those reached in patients. Reversibility of all findings was demonstrated after stopping treatment.
Rufinamide was not genotoxic and had no carcinogenic potential. An adverse effect not observed in clinical studies, but seen in animals at exposure levels similar to clinical exposure levels and with possible relevance to human use, was myelofibrosis of the bone marrow in the mouse carcinogenicity study. Benign bone neoplasms (osteomas) and hyperostosis seen in mice were considered a result of the activation of a mouse specific virus by fluoride ions released during the oxidative metabolism of rufinamide.
Regarding the immunotoxic potential, small thymus and thymic involution were observed in dogs in a 13-week study with significant response at the high dose in male. In the 13-week study, female bone marrow and lymphoid changes are reported at the high dose with a weak incidence. In rats, decreased cellularity of the bone marrow and thymic atrophy were observed only in the carcinogenicity study.
Environmental risk assessment studies have shown that rufinamide is very persistent in the environment.
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