Does probenecid increase tigecycline's bioavailability?

No. Probenecid is used to reduce renal clearance of some drugs (by inhibiting renal organic acid transporters) and can increase the plasma levels of certain antibiotics that are renally cleared. Tigecycline, however, is eliminated mainly by biliary/fecal routes and is given IV with essentially 100% bioavailability via that route. Its renal excretion is minimal, so inhibiting renal secretion with probenecid would not meaningfully increase tigecycline exposure or bioavailability.

In short: there is no clinically meaningful interaction between probenecid and tigecycline, and probenecid does not increase tigecycline’s bioavailability. If you’re using both, monitor as clinically indicated, but no dosing adjustment is needed for this reason.