Arzneimittelinteraktionen

Improvement in the handling of drug-drug interactions

Approximately one in 200 hospitalised patients has a serious adverse drug effect caused by drug-drug interactions (DDIs). Such adverse effects should be avoidable, but current information provided on DDIs is often incomplete and difficult or even impossible to translate into true risk and appropriate tangible action. Clinicians need to know the mean and maximal expected effect of a DDI on clinical endpoints, any dose adjustments required, and how to monitor tolerability and efficacy in patients subject to a DDI. To this end, improved study designs should take the objective of improving treatment explicitly into account, and any existing DDI data should be publicly accessible. Modelling needs to be used more extensively in order to quantitatively predict the effects of DDIs on clinical endpoints in patients and to relate clinical endpoint effects considered as acceptable to respective changes in experimental and clinical studies. Computer-based expert systems will be required to convert such DDI data into recommendations applicable to the individual patient. Therefore, the incorporation of DDIs in a more general procedure for personalisation of drug therapy is desirable.

[Reflux esophagitis]

Gastroesophageal reflux disease (GERD) is one of the most prevalent diseases in the industrialized countries. Approximately 15-25% of adults suffer from reflux symptoms, characterized mainly by heartburn and/or regurgitation. Currently, antisecretory medication with proton pump inhibitors (PPI) or antireflux surgery are the established options for GERD-treatment. PPI are the therapeutic gold standard in acute, long-term or on-demand therapy of GERD. Since PPI do not restore the antireflux barrier but merely suppress acid secretion a life-long tablet adherence is required in most cases. In view of limitations of PPI and the potential risks of laparoscopic surgery, several endoscopic antireflux techniques were developed and may evolve as a valuable third option. However, so far objective long-term data are lacking for choosing the appropriate patient who will benefit most from endoluminal antireflux therapy.

CYP2C19Polymorphism and Proton Pump Inhibitors

Proton pump inhibitors such as omeprazole (esomeprazole), lansoprazole, pantoprazole and rabeprazole are eliminated by the hepatic route and the polymorphic CYP2C19 is mainly involved in their metabolism. In different populations three phenotypes have been identified: extensive metabolizers, poor metabolizers and individuals carrying one wild type and one mutant allele (het extensive metabolizers). Systemic exposure to the proton pump inhibitors as expressed by the AUC (area under the plasma level time profiles) is 5-12-times higher in poor metabolizers than in extensive metabolizers. As the pharmacodynamic response (elevation of intragastric pH) to the proton pump inhibitors is related directly to their AUC, a much higher pH can be monitored over 24 hr in poor metabolizers than in extensive metabolizers. Furthermore, clinical efficacy of all proton pump inhibitors depend on maintaining intragastric pH above certain threshold levels and significantly higher eradication rates of Helicobacter pylori have been observed in patients of the poor metabolizers and het extensive metabolizers phenotype if compared to extensive metabolizers. Likewise, limited data suggest that proton pump inhibitors-induced healing rates in gastro-oesophageal reflux disease are apparently higher in poor metabolizers/het extensive metabolizers than in extensive metabolizers of CYP2C19. Therefore initial genotyping for this enzyme and higher dosage in extensive metabolizers is likely to improve the clinical efficacy of proton pump inhibitors.