Werdermann K, Jorde W
Dtsch Med Wochenschr. 1979 Sep 14;104(37):1307-11. doi: 10.1055/s-0028-1129089.
The bronchodilator effect of theophylline ethylenediamine was compared with that of a combination of the methylxanthines theophylline, diprophylline and proxyphylline, after administration of slow-release capsules. At an initial dose of twice two capsules the two drug preparations produced similar, therapeutically significant, effects. When reducing the dose to twice one capsule, during long-term treatment, there was a clinically and statistically significantly greater bronchodilator effect among those patients receiving the combined methylxanthine preparation.