The Dusseldorf Upper District Court (OLG Düsseldorf, I-2 U 126/09 vom 29. April 2010 – Harnkatheterset) has compiled a catalogue of preconditions for granting preliminary junctions on patent infringements in a decision called "Harnkatheterset".
As a rule, a prelininary injunction can only be granted if both the infringement and the enforcibility of the patent are clear to such an extend that a revision of the ruling in a later main procedure can not be reasonably expected.
Doubts in the enforcibility do not lead to a rejection of the request for a preliminary injunction if the patent is actually not challenged or if an attack on the patent in suit can not be foreseen in a reliable way.
If the delay for filing an opposition has not yet expired or is not expiring in the near future, reasonable doubts may exist even if the defendant is not able to produce relevant citations challenging the patent provided that the possibility exists that such documents will be found in a search to be carried out before the expiry of the delay for filing oppositions.
If an action challenging the patent is pending, the burden of proof that the action will surely not be successful is shifted to the patentee.
The enforcibility may be assumed with a sufficient degree of certainty only if the patent has survived at least one opposition- or nullity procedure. A deviation from this rule is possible only under exceptional circumstances (see e.g. BGH "Olanzapin").