A more significant risk occurs when the plant becomes infected with mould and the coumarin is converted to the more potent anti-coagulant dicoumarol
. Thus quality control for mould-free products is a significant issue here.
The use of these tests is remarkable because the Quick PT preceded the discovery of the anticoagulant effect of dicoumarol
in spoiled sweet clover and both tests were in use long before there was any understanding of the mechanism of the action of oral anticoagulants or which of the plasma factors were affected by them.
Based on one study published in 1950, dicoumarol
is probably also compatible during nursing.
For example, substantial increases in phenytoin plasma concentrations have been reported in patients receiving concurrent chloramphenicol.(56) Chloramphenicol also appears to inhibit the metabolism of dicoumarol
,(57) chlorpropamide,(58) and tolbutamide.(57) Chloramphenicol probably also inhibits the metabolism of other drugs, but its relatively infrequent use limits our information about these interactions.
A chemical that reduces the blood-clotting ability of animals.
Fungal decomposition of sweet clover results in the formation of dicoumarol
, which is an anticoagulant, but this does not lead to the conclusion that coumarins, per se, cause bleeding.
* Chloramphenicol, dicoumarol
, disulfiram, isoniazid, cimetidine, and some sulfonamides cause increased phenytoin concentrations through enzyme inhibition (21).
It should be noted, however, that simple coumarmns such as umbelliferone, found in many plants -- including chamomile and passion flower, popular components of herbal teas -- are not notably active anticoagulants; however, dicoumarol
, which occurs e.g.