- Treatment with the following medications are contraindicated with DSF when taken within 7 days prior to the first dose of DSF + Cu: metronidazole, isoniazid, dronabinol, carbocisteine, lopinavir, paraldehyde, ritonavir, sertaline, tindazole, tixanidine, atazanavir. (Note: the following medications are not contraindicated but should be cautioned if taking concurrently with DSF: warfarin, phenytoin, theophylline, chlorzoxazone, chlordiazepoxide, diazepam. If the patient is taking warfarin, INR should be monitored closely. If the patient has to remain on phenytoin, its serum concentration and response should be monitored closely.