Intrathecal Riluzole for the Treatment of Patients With Amyotrophic Lateral Sclerosis

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Abstract INTRODUCTION Oral riluzole is the only approved treatment known to improve survival in patients with amyotrophic lateral sclerosis (ALS), with modest efficacy and dosing limited by hepatic toxicity and asthenia. We postulated that a continuous intrathecal (IT) delivery of low daily doses of riluzole could elevate spinal cord (SC) concentrations well above those achievable with oral treatment alone, without increasing side-effects. METHODS A 6-wk and a 24-wk GLP study were conducted to evaluate the safety of IT riluzole in purpose-bred hound dogs. Oral riluzole, equivalent to 50 mg BID in humans, was administered in combination with one of 3 IT doses given through continuous infusion. Plasma, SC, and brain concentrations of riluzole were measured, along with assessments of safety and tolerability. RESULTS In the 6-wk study, when combining the oral and IT routes, IT infusion significantly increased SC concentrations well above those achieved with oral drug administration alone, without increasing brain concentrations. All IT doses in combination with oral administration were well tolerated by the animals. In the 6-mo study, the lowest dose used in the 6-wk study was dropped and a higher dose was added. This highest dose of IT riluzole was not tolerated by the dogs and yielded SC and brain concentrations significantly higher than achieved in any of our previous studies. CONCLUSION Continuous IT administration of riluzole when combined with oral administration can increase the SC concentration of riluzole above those achievable with oral therapy, without increasing the risk for adverse events associated with systemic drug exposure or off-target side-effects in the brain. Therefore, IT riluzole infusion when used in conjunction with oral therapy may safely enhance lower motor neuron neuroprotection and improve the survival benefit of the drug through enhanced SC delivery, and, with a careful selection of IT doses, it could be implemented in patients with ALS.