ISDN vs isosorbide dinitrate

ISDN

isosorbide dinitrate

noun

  • A coronary vasodilator C₆H₈N₂O₈ (trademark Isordil) used especially in the treatment of angina pectoris. 

How often have the words ISDN and isosorbide dinitrate occurred in a corpus of books? (source: Google Ngram Viewer )