Raychaudhuri S, Abria C, Harmany ZT, et al. - Twenty-four mice with collagen-induced arthritis in the following groups were evaluated in order to judge the capability of in vivo PET using 18F-fluorodeoxyglucose (¹⁸F-FDG) to quantify variations in inflammatory activity in response to tofacitinib, a Janus kinase (JAK) inhibitor, over a timeframe of a few hours to few days in a preclinical model of RA. At about peak plasma levels of the drug following a single tofacitinib administration, a decrease in PET measures in comparison with pretreatment values was noted, implying reduced inflammatory activity. These measures were comparable to those collected following 6 days of daily dosing by tofacitinib. Nevertheless, PET measures at trough plasma levels of the drug from tofacitinib administration were markedly greater compared with those at peak plasma drug levels and comparable to pretreatment measures. Unimportant variations in PET measures for the control animals was seen. Hence, ¹⁸F-FDG PET could identify advances in inflammatory activity happening in response to the JAK inhibitor tofacitinib ie, during peak and trough plasma drug levels, that is within a couple of hours of treatment, and over a span of days.