Effect of tofacitinib on the kidney functions of rheumatoid arthritis patients

The authors evaluated the effect of tofacitinib (Xeljanz) on kidney function in rheumatoid arthritis (RA) patients. 

In RA, high levels of immune system proteins are generated. This causes inflammation, leading to chronic pain and joint damage. In several phase III clinical trials, tofacitinib alone or in combination with other RA drugs has shown effectiveness in reducing the signs and symptoms of RA. It works by blocking certain proteins in the body that can cause inflammation. However based on phase III studies, this drug has also been shown to increase blood creatinine levels, mainly within the first 3 months of use. Creatinine is a non-protein waste product produced by the muscles. The level of creatinine in the blood depends on the glomerular filtration rate (GFR). GFR is a test used to check how well the kidneys are working. Specifically, it estimates how much blood passes through the glomeruli each minute. Glomeruli are the tiny filters in the kidneys that filter waste from the blood.

To understand the impact of tofacitinib on renal functions of RA patients, measurement of the GFR is necessary. 

The authors aimed to assess changes in kidney function with respect to GFR of RA patients following treatment with tofacitinib.

148 patients were included in this study. 97 patients were in group 1 and 51 patients were in group 2. In group 1, patients were randomly assigned to receive 10 mg of tofacitinib twice daily for 43 days (period 1) followed by placebo (harmless pill used in the place of the active drug) twice daily for 29 days (period 2). In group 2, patients received a placebo twice daily for both periods 1 and 2.

During period 1, there was an 8% reduction in measured GFR (mGFR) between patients in group 1 and group 2. During period 2, the average mGFR of patients in group 1 was back to the initial rate measured. At the end of the treatment, there was no difference in mGFR between the two groups. The estimated GFR (eGFR) and blood creatinine levels were similar in both groups at the end of the study. 

The authors concluded that an increase in creatinine and decrease in eGFR in RA patients treated with tofacitinib could indicate a decrease in mGFR.