The present invention relates compounds of the formula I: oligosaccharide-spacer-GpIIb/IIIa antagonist I, wherein the oligosaccharide is a negatively charged pentasaccharide residue of the structure (I), the charge being compensated by positively charged counterions; the spacer is an essentially pharmacologically inactive linking residue of a length of 15-50 atoms; the GpIIb/IIIa antagonist is a residue derived from tirofiban or an analogue thereof; or a pharmaceutically acceptable salt thereof or a prodrug or a solvate thereof. The compounds of the invention have antithrombotic activity and can be used in treating or preventing thrombotic diseases. ##STR00001##