Physico-chemical interactions between extracts of Hypericum perforatum L. and drugs

The aim of the present study was to investigate physico-chemical interactions between extracts of Hypericum perforatum L. and drugs. The formation of nanoparticles, microparticles and precipitates in aqueous drug-free and drug-containing preparations of H. perforatum L. was investigated. In aqueous infusions of Hyperici herba only small amounts of nano- and microparticles were observed using photon correlation spectroscopy and scanning electron microscopy. In the presence of promethazine nanoparticles are formed. Between 20.3 and 5.3% of the drug is bound to nanoparticles. Maximally 4.3% of the drug is associated with precipitates. Warfarin has a negligible effect on the particle formation in aqueous infusions of Hyperici herba. In further studies dry extracts of H. perforatum were reconstituted in water. Nanoparticles and precipitates are formed in the drug-free preparations. Scanning electron micrographs show almost spherical nanoparticles with a mean diameter between 100 and 300 nm. After addition of promethazine a precipitate is formed. Maximally 12.8% of the drug is associated with the precipitate. In warfarin-containing reconstituted extracts, nano- and microparticles as well as precipitates are observed. The amount of free warfarin in solution is reduced by 36.6% maximally. A loss of the anticoagulant effect which is described in the literature may partly be caused by particle formation.