Lack of association between rifampicin plasma concentration and treatment-related side effects in osteoarticular infections

The aim of this study was to assess the frequency of gastrointestinal side effects (GSE) and hepatotoxicity in patients treated with rifampicin for an osteoarticular infection and to determine if there is an association between rifampicin plasma concentrations and side effects. Rifampicin plasma concentrations were prospectively measured before (trough concentration, C0) and 2 ± 0.5 h (peak concentration, C2) after drug intake. The presence of GSE, the alanine transferase (ALT) value, and concomitantly administered medications were recorded on the day rifampicin concentrations were measured. C0 and C2 were compared for differences regarding the presence or absence of side effects. Multivariate analysis was performed, with associated medications being taken into account. Seventy C0 and 57 C2 values were measured in 46 adults after a median treatment of 8 days (range, 1–179). Wide inter‐individual variability was observed for C0 and C2. Thirteen (28%) patients reported GSE at least once. When GSE occurred, C0 (median, 1 mg L−1; range, 0.1–9.9 mg L−1) and C2 (median, 10.3 mg L−1; range, 1.8–40.3 mg L−1) were similar to C0 (median, 0.6 mg L−1; range, 0.1–10.3 mg L−1) and C2 (median, 10.9 mg L−1; range, 2.9–29.0 mg L−1) without GSE. The ALT value was more than normal in only three patients (6.5%) after rifampicin treatment began. The patients received no different associated medications whether or not GSE were present. Multivariate analysis showed no association between rifampicin plasma concentrations and GSE. GSE occur frequently in patients receiving rifampicin for osteoarticular infection but without an association with rifampicin plasma concentrations. Thus, therapeutic drug monitoring of rifampicin is irrelevant in the management of GSE.