Antibiotic-associated hypoprothrombinaemia.

Hypoprothrombinaemia is regarded as a serious adverse effect of antimicrobial therapy. This effect has commonly been attributed to the potential of these drugs to kill intestinal bacteria, a possible source of vitamin K, which is a necessary co-factor in the synthesis of four of the clotting factors. This review examines the evidence for and against this hypothesis, first in experimental animals, then in humans, and assesses the reports of antibiotic associated hypoprothrombinaemia in man, with particular attention to information about the mechanism. The hypothesis that it is the destruction of intestinal bacteria that ultimately results in hypoprothrombinaemia may not be justified. Certain antibiotics, which contain thiol-leaving groups, may produce hypoprothrombinaemia because the thiol group inhibits the vitamin K-dependent step in clotting factor synthesis.