The effect of the immunosuppressant FK 506 on peripheral nerve regeneration following nerve grafting

Nerve allografts are highly antigenic and require the continuous use of imm unosuppressive drugs. Neurotoxic complications from immunosuppressant thera py with FK 506 have been noted in the central and peripheral nervous system although an increased rate of axonal regeneration has also been noted. Reg eneration of peripheral nerve grafts was assessed in a rat model clinically and morphometrically after treatment for 2 and 6 weeks with two different doses of FK 506. Good regeneration was noted in all groups at 6 weeks. A si gnificantly higher axon count was observed in both the FK 506 groups after 2 weeks regeneration compared with controls. This beneficial effect was not evident after 6 weeks of regeneration. Whether this is related to a prunin g mechanism or to a down-regulation of regenerative processes in the nerve due to possible neurotoxic effects of FK 506 remains unknown.