No systematic toxicological testing of Hp has been reported. However, it is to be expected that some preparation-specific toxicological data, such as genotoxicity and potential for drug-drug interaction data, have been submitted to the authorities by manufacturers. Unger and Frank  reported significant inhibition by Hp of the liver drug metabolising cytochrome P450 (CYP) isoenzymes 2C9,2D6 and 3A4 and measured IC50 values, respectively, of 121, 1044 and 335 |g/ml. The implication of these data is that the tested Hp extract may exert clinically important interactions with co-medications. There are a number of shortcomings in the report from Unger and Frank . They aimed to validate a novel high-throughput procedure, and the drug interaction potential of the Devil's Claw extract was not the primary aim. The study contains no details of the nature of the Devil's Claw extract. The assays were not performed under GLP conditions and employed commercial preparations of the CYP isoenzymes. The report also contains no details on the source and method of enzyme preparations - for example it is not clear whether the enzymes were of human origin, although this is implied in the abstract. Finally, no recognised CYP isoenzyme-specific inhibitors or inducers were included, as is required according to accepted guidelines in order to have a comparative control. It needs to be pointed out that there are no reports of drug-drug interactions relating to Hp, despite the widespread use of Hp extracts and the particular concern in recent years to highlight this potential problem with the use of herbal drugs.
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