Neutropenia from Tacrolimus

Post transplant neutropenia has many causes.  Etiology is usually medications, infections, cancer.
In a retrospective evaluation, 28% neutropenia was noted after first year of transplantation.  Most of this was sought to be from MMF-tacrolimus combination.
The drugs we usually consider are: MMF, azathioprine, acyclovir, gancyclovir, bactrim, valcyte.
A recent review on CJASN 2011, presents three patients with pure tacrolimus induced neutropenia and the mechanism behind it. All improved after they were switched to cyclosporine.

Why does it happen?
1. Direct inhibition of myeloid cells
2. effect of the drug on mononuclear accessory cells
3. pharmacokinetic interaction between MMF and tacrolimus
4. autoantibodies against myeloid precursors or mature neutrophils

Ref:
http://www.ncbi.nlm.nih.gov/pubmed/21258040
http://www.ncbi.nlm.nih.gov/pubmed/19538494