Tacrolimus drives activity–infection trade-offs

In people taking tacrolimus, an immune-suppressing drug, infection may create a hidden problem: preserving movement could coincide with weaker pathogen control and organ function. The proposed mechanism says infection may alter blood-protein binding and drug handling, raising tacrolimus’s unbound, biologically active fraction while whole-blood troughs, concentrations measured before a dose, appear acceptable. Extra active drug could then weaken pathogen control and contribute to kidney, thinking, or movement problems, making activity seem harmful when exposure is the driver. This remains an untested hypothesis. A test randomizes activity and tracks unbound drug, pathogen levels, and function. A closer link to unbound exposure than to troughs or activity dose would support the proposal.