The cost‐utility of sodium oxybate as narcolepsy treatment

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Narcolepsy is a chronic neurological disorder that affects the regulation of sleep–wake cycles. Patients with narcolepsy suffer a range of symptoms including excessive daytime sleepiness (EDS), cataplexy, disrupted nocturnal sleep, sleep paralysis, and hallucinations, and are more likely than the general population to be affected by other morbidities.1 Based upon clinical information, result of polysomnography (PSG), multiple sleep latency test (MSLT) and determination of cerebrospinal hypocretin 1 level (csf‐hcrt‐1), narcolepsy is classified into type I (hypocretin deficient type, narcolepsy with cataplexy) and type II (narcolepsy without cataplexy, normal csv‐hcrt‐1 level).3
Narcolepsy is associated with significant comorbidities, potential increased mortality rates, and significant personal and familiar limitations affecting education, professional and social life. Consequently, narcolepsy is associated with a significant welfare burden. The adverse consequences for those affected by narcolepsy are potentially severe and comprise disrupted human‐capital investments and labour market behaviour as well as reduced quality of life.4 In spite of this, current knowledge of the epidemiology of narcolepsy does not seem to yield a complete picture of its adverse effects on the society. The burden of narcolepsy imposed on society depends on the organization of the concerned healthcare‐ and welfare systems. However, only a small number of peer‐reviewed studies have been published, for a limited number of societal contexts.11
Pharmacological treatment is the dominating treatment for the symptoms associated with narcolepsy. However, no pharmaceutical treatment is fully effective for both the major symptoms associated with narcolepsy; EDS and cataplexy. Thus, most patients utilize a combination therapy, including two or more drugs. Sodium oxybate was approved by The European Medicines Agency in 2005, for the indication “Treatment of cataplexy in adult patients with narcolepsy”. In 2013, The Swedish Medical Products Agency issued treatment guidelines that recommended sodium oxybate as the first‐line adult treatment for cataplexy and dyssomnia.16 Thus, Sodium oxybate is regarded as a first‐line treatment for both EDS and cataplexy, and may also reduce other central symptoms of narcolepsy, including hypnagogic hallucinations, sleep paralysis and sleep fragmentation.18 The clinical effectiveness and tolerance of sodium oxybate has been demonstrated in several studies.19 Only one study reported on the quality of life associated with sodium oxybate treatment.22 The committee for Medical Products for Human Use performed a review of data on safety and efficacy and concluded that “the risk‐benefit balance of Xyrem in the treatment of narcolepsy with cataplexy in adult patients was favourable”.28
The cost‐effectiveness of competing pharmacological narcolepsy treatments is largely unknown. A small number of published studies report on the cost‐effectiveness of sodium oxybate as compared to alternative treatments.29 The evidence is mixed: Lanting et al. found that the cost‐effectiveness of sodium oxybate falls well above accepted thresholds for the willingness to pay for the produced treatment effects, while Tatar et al. reached the opposite conclusion. However, due to lack of information these studies do not take the effects of narcolepsy, and treatments of narcolepsy, on general healthcare utilization, human capital investments and labour market behaviours into account. Thus, the reported cost‐effectiveness measures overlook major potential benefits of sodium oxybate treatment. In this study, we will contribute to this literature by exploring Danish data on longitudinal healthcare utilization for narcolepsy patients receiving standard treatment (without sodium oxybate) and treatment with sodium oxybate, respectively, to estimate the cost‐effectiveness of sodium oxybate. In both Denmark and Sweden, most narcolepsy treatment combinations comprise metylphenidate rather than modafinil. Thus, we will assume that standard treatment is metylphenidate combined with venlafaxine, while the comparison treatment is Xyrem combined with metylphenidate.

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