171, P=0.104). A concentration cut-off predictive of grade III/IV total bilirubin toxicity could not be identified. Patients who developed grade III/IV hyperbilirubinaemia did not show a higher ATV concentration than those who did not develop such toxicity [median 1.29 mg/L (IQR 0.37–2.34 mg/L) vs. TGF-beta inhibitor clinical trial 1.53 mg/L (IQR 0.64–2.10 mg/L), respectively; P=0.697]. For ATV, a relationship between Ctrough and both efficacy and toxicity has been demonstrated . However, as this drug is administered
once daily, in routine clinical practice it can be difficult to monitor Ctrough in patients taking ATV in the evening. We investigated the clinical significance of monitoring mid-dosing interval (C12 h) ATV concentration in the routine clinical out-patient
find more setting. In our clinic, the vast majority of patients taking ATV in the evening (usually after dinner) had an ATV concentration measured in the morning at 12 ± 2 h after drug intake. We hypothesized that this C12 h could be a surrogate estimate of Ctrough and could also reflect drug exposure; as a consequence we investigated whether monitoring this parameter might predict virological response and development of toxicity. In order to study a homogeneous patient population, we selected subjects without significant baseline ATV resistance; therefore, our results can be applied only to individuals harbouring ATV-susceptible virus. We found that a C12 h>0.23 mg/L could independently predict 24-week virological response in patients harbouring an ATV-susceptible virus, without increasing the risk of moderate-to-severe hyperbilirubinaemia. Such an efficacy threshold
C1GALT1 could then be used in clinical practice for TDM in individuals taking ATV in the evening: this would allow one to individualize ATV dosage in order to maximize the probability of treatment success and to reduce the risk of toxicity. The cut-off identified showed a high sensitivity (89.4%) and positive predictive value (85.7%); this means that patients with a mid-dosing interval ATV concentration above this level achieved a very high rate of virological efficacy. However, the lower specificity (33.3%) and negative predictive value (41.2%) mean that a proportion of patients with a concentration below this threshold still maintain virological efficacy, although at significantly lower rates than the previous group. This last observation may have several explanations. First, as a consequence of inter-individual variability, some subjects, especially those administered boosted regimens, might have a reduced clearance of ATV with a less pronounced decay of plasma drug concentration, allowing maintenance of the Ctrough above the minimum effective concentration despite a C12 h lower than the identified mid-dosing interval cut-off. Moreover, as patients were receiving combination regimens, the other antiretroviral drugs coadministered with ATV could have contributed to virological response in individuals with subtherapeutic ATV concentration.