This study aimed to evaluate the relationships between concomitant biologic disease-modifying anti-rheumatic drugs (DMARDs) and prednisolone administration and blood tacrolimus exposure or serum CYP3A4/5-related markers in rheumatoid arthritis (RA) patients without severe disease activity.
Forty-six RA patients treated with oral tacrolimus once daily for maintenance of clinical remission to moderate disease activity were enrolled. The blood concentrations of tacrolimus and its major metabolite were determined at 12 h after the evening dosing. Blood samples for determination of serum markers including 4β-hydroxycholesterol (4β-OHC), 25-hydroxyvitamin D (25-OHD) and interleukin-6 (IL-6), and CYP3A5 genotype were collected.
Most enrolled patients had RA with clinical remission to mild disease activity. Concomitant tocilizumab or low-dose prednisolone administration did not alter the blood tacrolimus exposure. Serum 4β-OHC level was lower in tocilizumab co-treated patients than in the biologic DMARD non-treated patients. The blood tacrolimus concentration was inversely correlated with the serum level of 25-OHD, but not 4β-OHC and IL-6. The serum level of 4β-OHC was positively associated with that of 25-OHD. No correlations were observed between the serum levels of CYP3A4/5 activity markers and IL-6. The patients with the homozygous CYP3A5*3 had the higher blood tacrolimus concentration, while CYP3A5*3 allele was not associated with the serum levels of 4β-OHC and 25-OHD.
Concomitant use of tocilizumab or low-dose prednisolone had no effect on the pharmacokinetics of tacrolimus, while tocilizumab lowered serum 4β-OHC. Blood tacrolimus exposure was negatively associated with serum 25-OHD in RA patients with clinical remission to moderate disease activity.