Metronidazole and cough suppressant?

Patient: I’m taking Metronidazole to treat C Diff on my 4th relapse but a day before I got the antibiotic I caught a bad cold (or flu?) so i’ve been having fever, bad cough and flem. I’m wondering if there would be any interaction with Metronidazole if I take Tussin DM (a cough suppressant)?I really want to get rid of my cough so i dont have it so hard with the c diff and the strong antibiotic.Thank you.