This category includes individual antibiotic classes listed in different categories by WHO, including the HPCIA macrolides. For those substances proposed for inclusion in this category, there are in general alternatives in human medicine in the EU but there are few alternatives in veterinary medicine for certain indications. Antibiotic classes that may select for resistance to a substance in Category A through specific multiresistance genes have also been placed in this category. These antibiotics should only be used when there is no available substance in Category D that would be clinically effective.