Oral administration of low molecular weight heparin fractions in rabbits.

A number of studies, including our own, have demonstrated that heparin was not absorbed when administered directly in solution by the oral route. We have attempted to enhance the absorption of orally administered heparin by applying three different approaches: the use of heparin fractions of various molecular weights lower than 6000 D, the complexation of one fraction with glycine (to adjust the ionization of the drug), and the use of gastroresistant capsules administered directly into the stomach. None of these measures resulted in significantly increased absorption, although large doses were administered (15,000 anti-Xa U/kg). New studies will therefore be necessary if heparin and its fractions are to be provided with a satisfactory capacity to be absorbed.