Cisapride

Cisapride was for a decade the flagship gastrointestinal prokinetic, prescribed extensively for reflux and dysmotility, and its rise and fall fundamentally shaped how every subsequent 5-HT4 agonist has been designed and evaluated. It is a substituted benzamide that acts primarily as a 5-HT4 receptor agonist to enhance gut motility, and it was regarded as effective and useful across a range of upper- and lower-gut disorders ^[1].

Its fatal flaw was cardiac. Cisapride is a potent inhibitor of the human ether-a-go-go-related gene (hERG) potassium channel, and comparative in vitro studies show it prolongs cardiac action potential duration in Purkinje fibre and ventricular preparations, an effect absent in safer prokinetics ^[2]. This translated clinically into QT-interval prolongation and torsades de pointes, particularly when cisapride levels rose because of cytochrome P450 3A4 inhibition by co-administered drugs, culminating in its withdrawal from most markets around 2000.

The cisapride experience directly motivated the entire modern generation of highly selective 5-HT4 agonists. Newer agents such as prucalopride, velusetrag, naronapride, and TD-8954 were explicitly engineered to reproduce cisapride-like prokinetic efficacy while avoiding hERG blockade and, in several cases, cytochrome P450-dependent metabolism ^[3]. Cisapride thus remains a constant reference point in the design rationale and safety framing of the whole class.

Cisapride's defining safety problem is cardiac: hERG channel blockade with QT-interval prolongation and the risk of torsades de pointes and sudden cardiac death, especially in patients taking cytochrome P450 3A4 inhibitors, those with electrolyte disturbances, or those with underlying cardiac disease. These risks led to withdrawal from most markets around 2000, with residual availability only under restricted access programmes. Gastrointestinal effects such as diarrhea and abdominal cramping are otherwise typical of a prokinetic. Any consideration of cisapride requires stringent cardiac and drug-interaction screening.

Cisapride was developed by Janssen Pharmaceutica under the code R-51619 and launched as Propulsid and Prepulsid in the late 1980s and 1990s, rapidly becoming a top-selling prokinetic for reflux and dysmotility. Reports of cardiac arrhythmias accumulated through the 1990s, and mechanistic work identifying hERG channel blockade explained the QT prolongation. Around 2000 the drug was withdrawn from most major markets, an event that became a defining episode in cardiac safety pharmacology and in the routine screening of new drugs for hERG activity.

Cisapride is remembered as both a highly effective prokinetic and the archetypal example of a drug undone by cardiac ion-channel toxicity, and its name is invoked whenever the cardiac safety of a 5-HT4 agonist is discussed. In pharmacology it helped make hERG screening a standard step in drug development. It has no nootropic use and survives clinically only in narrow, tightly controlled settings.