Introduction C.difficile infection (CDI) is the most serious cause of hospital-acquired diarrhoea. Factors predicting outcome are unclear. We have assessed possible biomarkers of failure to respond to metronidazole in a prospective series of 43 inpatients with CDI.

Methods At diagnosis (T¹) and after 3 days (T²) of metronidazole 400mg tds po (n = 33) or 500mg tds iv (n = 10), we assessed haemoglobin, white cell count (WCC), platelet count, C-reactive protein (CRP), creatinine, albumin, pulse, BP, temperature, stool frequency and Bristol score. Cure was defined as formed stool on 2 consecutive days within 7 days of starting metronidazole; failure was clinical deterioration needing treatment with vancomycin, colectomy and/or death within 28 days. Positive and negative predictive values (PPV, NPV) for failure of metronidazole were calculated.

Results 17 patients failed metronidazole: 7 needed vancomycin and 10 died. Regardless of outcome, there were significant falls in CRP, pulse, stool frequency between T¹ and T²; however, neither WCC and Bristol stool score did not fall in treatment failures (Table). The other measures did not change in either group (data not shown). PPV for treatment failure of increases in WCC and CRP (as separate variables) between T¹ and T² were 67% and 57%, with NPV 75% and 65% (accuracies 72% and 63%), respectively. However, PPV and NPV for treatment failure of increases in both WCC and CRP between T¹ and T² were 100% and 62% (accuracy 75%).

Table. Mean (SEM); ^*p < 0.05, ^**p < 0.001 from T¹

Conclusion No single measure predicted failure to respond to metronidazole. However, all patients showing a rise in both WCC and CRP after 3 days of metronidazole failed treatment (PPV 100%). This simple predictive combination needs confirmation in a validation cohort, but should alert clinicians to the need for prompt escalation of therapy

Disclosure of Interest None Declared.