Drugs of last resort are drugs with the most potent antibiotic, antiviral, or anticancer effect, and for which no (or for cancer, very few) resistant strains are known. They are usually witheld from administration to prevent the development of resistance, and sometimes have unpleasant side effects.

The current broad-spectrum antibiotic drug is ciprofloxacin; there are no known strains of bacteria which are resistant to this drug. Previous to this, vancomycin was the drug of last resort, but since vancomycin-resistant bacteria have appeared, it no longer has this role. If ciprofloxacin-resistant strains appear, there will no longer be a drug of last resort.