Causes of megaloblastosis due to drugs:
(1) interference with vitamin B12 absorption or metabolism
(2) interference with folate absorption or metabolism
(3) acute interference with DNA synthesis
(4) chemotherapy-induced myelodysplasia
Drugs interfering with vitamin B12 (cobalamin) absorption include:
(1) neomycin
(2) metformin or other biguanides
(3) omeprazole or other proton pump inhibitors (PPI)
Chemicals interfering with vitamin B12 metabolism:
(1) nitrous oxide
Drugs interfering with folate absorption or metabolism include:
(1) phenyotin
(2) methotrexate
(3) trimethoprim and trimethroprim-sulfamethoxazole
(4) sulfasalazine
(5) triamterene
(6) pyrimethamine
(7) cholestyramine
Drugs interfering acutely with DNA synthesis:
(1) hydroxyurea
(2) methotrexate
(3) zidovudine
(4) azathioprine
(5) cladribine, fludarabine or other purine nucleoside analogs
(6) chemotherapeutic agents
Drugs causing myelodysplasia:
(1) alkylating agents or other chemotherapeutic agents with or without radiation
Differential diagnosis:
(1) myelodysplastic syndrome not due to medications
(2) alcohol abuse
(3) other causes of vitamin B12 or folate deficiency
