Effect of Chloramphenicol on Reticulocyte Δ‐Aminolaevulinic Acid Synthetase in Rabbits

Summary. Δ‐aminolaevulinic acid (ALA) synthetase activity was determined in reticulocyte mitochondria of rabbits before and while receiving 30–40 mg of chloramphenicol per kilogram per day. Maintenance of chloramphenicol at this dosage caused a 50–60% decrease in ALA synthetase activity; this enzymic activity returned to a normal level 8 days after discontinuation of the drug. Accompanying the decrease in ALA synthetase activity was a 16% reduction in haematocrit and a 30% decrease in reticulocyte count. No significant alterations in the white cell and platelet values were observed. It is hypothesized that chloramphenicol suppresses mitochondrial ALA synthetase, the rate‐limiting step in haem synthesis, and this accounts for the vulnerability of erythroid cells to the drug.