The Importance of Drug Adverse Effects Compared with Seizure Control for People with Epilepsy

Abstract

Antiepileptic drugs (AEDs) have been shown to reduce the severity and frequency of seizures for most patients. However, many patients experience adverse effects in order to maintain seizure control. A stated preference discrete choice experiment (DCE) was used to explore the preferences of people with epilepsy regarding the adverse effects and seizure control of AEDs. The main adverse effects of AEDs were identified through a literature search and expert consultation. In addition, a national epilepsy patient advocacy group helped to identify important attributes and commented on the attributes we had already identified. The DCE included five attributes related to adverse effects (alopecia, nausea, skin rash, concentration effects and weight change) plus seizure control and cost (to estimate willingness to pay [WTP]). A cost attribute was included in the DCE in order to estimate people's WTP for changes in attribute levels. Five hundred members of a national patient advocacy group with a diagnosis of epilepsy were presented with pairs of hypothetical drug profiles with varied levels of adverse effects, seizure control and cost; they were then asked to indicate which drug they preferred. Questions were also included to collect sociodemographic data (including income) and information regarding experience of adverse effects and medication. The survey was administered via the post and the Internet. Data were analysed using a random effects probit model. A total of 148 surveys were returned. All attributes were significant and had the expected polarity, i.e. participants showed a preference for less severe adverse effects, greater seizure control and less cost. To achieve 100% seizure control and no adverse effects, participants were willing to pay 709 pounds sterlings (1105 US dollars) per month, 95% CI 451 pounds sterlings, 1278 pounds sterlings (1 pound sterling = 1.56 US dollars, 2002 exchange rate). Participants' WTP was significantly influenced by different adverse effects; for example, people with epilepsy were willing to pay only 174 pounds sterlings (271 US dollars) per month for a drug that provided seizure freedom but also caused hair loss. Segmented models showed that seizure frequency has a significant negative impact on respondents' income levels. Also, women were willing to pay twice as much as men to avoid weight gain. Participants were also willing to trade changes in seizure control for improvements in adverse effects. Participants placed a high value on gaining total seizure control with no adverse effects. This study underlines the importance that people with epilepsy place on reducing adverse effects. The study also revealed how preferences for AEDs vary in different subgroups. Management of epilepsy is usually aimed at minimising seizures within a tolerable level of adverse effects. The present study suggests that people with epilepsy have strong preferences for reducing adverse effects as well as improving seizure control. These data may be considered useful when making medical management decisions in epilepsy.