## 1 Introduction  
The public spends billions of dollars on prescription drugs which are designed to cure, treat, or prevent diseases. However, when taking any medication, some risks should be taken seriously. Severe adverse drug reactions (ADRs) can lead to patient morbidity [1]. In the U.S., ADRs have been estimated to send 701,547 patients to emergency rooms, hospitalize 117,318 patients each year [2], account for 2-6% of all hospital admissions, and increase the duration of hospital stays and costs [3]. Moreover, over 2 million serious side effects, including 100,000 deaths, occur due to ADRs [4]. In other words, ADRs strain healthcare resources and thus have strong implications for public health [5]. Pharmacovigilance involves the detection, assessment, understanding, and prevention of ADRs [1] that were previously either unknown or poorly understood. Despite progress in pharmacovigilance, the burden on public health of ADRs remains significant [6]. In recent years, data mining of electronic health records (EHRs) has emerged as a promising complementary method for drug safety surveillance [5]. Data mining in pharmacovigilance has attracted significant attention and has the potential to discover complex interactions that defy human recognition [7]. ADRs also occur in Taiwan. In 2017, 15,422 cases of ADRs were reported [8]. According to the statistics of the Taiwan Drug Relief Foundation, from 1999-2017, 1685 drug relief cases were approved in Taiwan, and the relief amount was NT5454,192,519. Of these cases, 610 (36.2%) cases were related to Stevens-Johnson Syndrome (SJS); it was the highest proportion of all drug relief cases [9]. SJS is a severe disease mainly caused by ADRs. To reduce the mortality rate due to SJS, healthcare workers must share the responsibility for safe drug use. SJS was first described in 1922 by two American physicians named [PERSON] and [PERSON] [10]. It is a rare (2-6 cases/million/population/year) disease [11] characterized by widespread epidermal necrosis involving the skin and mucous membranes [12; 13; 14; 15; 16]. SJS is among the most notorious severe cutaneous adverse reactions (SCARS) due to its rapid progression and high mortality rate. The reported mortality rate of SJS is 1-5% [16]. It is an emergency medical condition that usually requires hospitalization [17; 18]. Due to the importance of SJS, thousands of studies have focused on it since 1940 [19]. Studies have indicated that SJS occurs more frequently in women than in men [13; 20]. Although some studies have found that the ages of patients with SJS are age-stratified [21; 22; 19; 23], the patients affected by SJS range from infants to the elderly [23]. One study found that SJS occurred predominantly in children and adolescents [22], yet another study found that many SJS patients were elderly persons with underlying medical conditions that required regular medical treatment [11]. In summary, most of the studies to date have indicated that children and the elderly are more susceptible to SJS. Although the pathogenesis of SJS is not fully understood [24; 25; 26; 16], most studies have found that it is predominantly medication-induced [11; 12; 13; 16; 19; 21; 24; 25; 26; 27; 28]. The proportion of SJS cases attributable to medications is estimated to be greater than 50% [13]. During the treatment of patients with SJS, the first and most important step is to identify and discontinue any possible responsible medications [24]. Although more than 100 medications have been implicated as causes of SJS [12; 13; 29], certain medications have higher probabilities of causing SJS than others. The most common medications associated with SJS are antibacterial sulfonamides, anticonvulsant agents, oxican NSAIDs, allopurniol, chloromezanone, and corticosteroids [12]. Other medications also induce SJS but to a lesser degree, two examples being theophylline [30; 31] and H2-antagonist [32; 33]. Most (85-100%) of the medications \"highly suspected\" of triggering SJS are initiated in treatment less than 8 weeks before that complication.