How common is Sulfa drug in medicine?

No. Keflex is a cephalosporin antibiotic which is chemically related to a penicillin. It does not contain a sulfa group in its structure, so it is not a sulfa drug.

Sulfa drugs are the group drugs that includes antibiotic characteristics.they use to treat infection.

no, sulfate is a salt, like a prefix to a word (like "ed" or "ing") sulfa is short for sulfonamide antimicrobials

True all medicines are drugs but not all drugs are medicines or legal anyway.

Drugs included in medicines is thou. because in medicines use drugs as too to treatment to patios. Both drugs and medicines are inter related these two item can't be along.