"Clinically relevant" new drug interactions

The concomitant intake of drugs with the potential to cause drug interactio ns is frequent. In contrast, adverse effects due to drug interactions accou nt for only a small fraction of all adverse effects. A reproducible evaluation of the clinical relevance of drug interactions is lacking. We now can accurately define the potential of a drug to cause int eractions, primarily by comparative investigations within a drug class. Whe ther or not the selection of the drug based on this information is useful f or the patient is unknown. Therefore, usually it is to be recommended to abandon therapeutically reaso nable drug combinations with a risk for interactions only if equivalent the rapeutic options are available. Several actual examples on interactions wit h selective serotonin re-uptake inhibitors, HMG-CoA reductase inhibitors, m ibefradil, sildenafil, protease inhibitors and with grapefruit juice are di scussed.