Pure opiate antagonists are all of the following: (A) Naloxone, (B) Nalorphine, (C) Nalmefene, (D) Naltrexone
Answer is B. , Nalorphine was the first opiod antagonist introduced in 1951 which could reverse morphine action. Later it was found to have agonistic action or kappa re eptor as well, producing lower ceiling analgesia. It is not used clinically because of dysphoric and psychotomimetic effects. Ref KD Tripathi 8th ed.