Severe hypokalaemia caused by flucloxacillin

after exposure to vancomycin, suggesting the same underlying resistance mechanism. 16 During therapy with daptomycin for S. aureus bacteraemia and endocarditis, 16% of the patients failed with a persistent or relapsing infection with increasing isolate MICs. Most of these failures were in deep-seated infections for which a necessary surgical intervention was not performed. 17 In the case of Enterococcus, either a chronic indwelling line or persistent focus of infection was reported for all but two of the seven reported cases of daptomycin clinical treatment failures, and non-susceptibility developed on treatment after an average of 19 days. 4 – 10 The mechanisms of non-susceptibility to daptomycin are thus diverse and not completely understood. Increasing MICs in the setting of pre-exposure to either vancomycin or daptomycin and/or evidence of a persistent focus of infection seem to be a frequent occurrence for clinical failures among both S. aureus and Enterococcus species. Despite lack of experimental data, it is plausible that the mechanisms that explain enterococcal non-susceptibility parallel those for S. aureus. The use of daptomy-cin in patients with prior prolonged vancomycin or daptomycin therapy, or with a focus of infection that cannot be removed, should be undertaken with caution, as clinical failure can occur.