International Patent Applications WO98/31674, WO99/31071 and WO99131090 disclose phthalazinone derivatives having selective PDE4 inhibitory properties. In the International Patent Application WO94/12461 and in the European Patent Application EP 0 763 534 3-aryl-pyridazin-6-one respectively arylalkyl-diazinone derivatives are described as selective PDE4 inhibitors.
In the International Patent Application WO98/37894 the combined application of PDE-inhibitors with adenylat-cyclase-agonists is described. In this context β-sympathomimetics are mentioned as one possible example of an adenylat-cyclase-agonist.
In the International Patent Application WO00/12078 is disclosed the combined application of a PDE4 inhibitor with a beta adrergenic bronchodilator for the treatment of asthma and COPD.