The physician must try to determine why the patient has not responded well. Lack of compliance is unquestionably the commonest reason. This can be checked by noting from the medical records how many prescriptions have been collected. If a patient has been taking antibiotics regularly then Staph, epidermidis should be resistant to  that antibiotic.  If it is not, the  physician should re-address the problem with the patient. Some physicians may have access to Wood's rays. Tetracycline fluoresces yellow; if the skin fluoresces yellow at least it is bearing some tetracycline. A negative test does not, however, necessarily exclude  the patient from having taken the therapy.