The response to therapy with oral tetracycline has been assessed in three subjects with tropical sprue, all of whom presented with a megaloblastic anemia due to combined folate and vitamin B12 deficiency, and all of whom were shown to have normal absorption prior to treatment of a physiologic dose of 25 µg. of folic acid, as tested by assay of the fecal excretion of a tritium-labeled test dose.
Treatment was associated with clinical and intestinal improvement and a hematologic response in all three subjects. The serum folate concentration rose to normal in one subject and the absorption of a pharmacologic dose of folic acid was normal when tested by microbiologic assay at the termination of the 20 day treatment period in all three. In contrast, both the absorption and serum concentrations of vitamin B12 remained subnormal.
These observations confirm the fact that folate deficiency can be present in some subjects with tropical sprue in whom the absorption of a physiologic dose of folic acid is normal. They suggest that in this circumstance folate repletion and the hematologic response secondary to tetracycline therapy in tropical sprue is mediated by a factor other than the absorption of crystalline folic acid; it is likely that this factor is increased absorption of dietary polyglutamate forms of folate.