Narcotic Analgesics (Opioids) 81given by parenteral route. It is excreted un-
changed in urine. Side effects include dizzi-
ness, sedation, miosis, respiratory depres-
sion, sweating and vomiting.
It is indicated in moderate to severe pain,
premedication to surgery, pain due to myo-
cardial infarction and in postoperative pain.
BUTORPHANOL
It is a kappa agonist. It produces anal-
gesia equivalent to nalbuphine and
buprenorphine but produces more sedation.
It is used in postoperative pain and re-
nal colic pain.
NALOXONE
It is N-allyl analogue of oxymorphone,
have a high affinity for mu receptor and
lower affinity at delta and kappa sites. It
selectively antagonizes the respiratory de-
pression produced by opioids. After intra-
venous administration, it antagonizes all
actions of morphine. It also blocks the ac-
tions of endogenous opioid peptides.
It is inactive orally because of high first
pass metabolism in liver. Metabolised by
glucuronidation in liver. The main use of
naloxone is in the treatment of acute opioid
overdose (acute morphine poisoning). It
also precipitates withdrawal syndrome
when administered to morphine addicts.
The constricted pupils of addicts dilate af-
ter administration of naloxone. This has
been used as a diagnostic tool for opioid
addiction.NALTREXONE
It is a pure antagonist and chemically
related to naloxone. It is more potent than
naloxone and because of its longer dura-
tion of action, it can be used as maintenance
drug for morphine addicts. It has no eu-
phoric effect and no physical dependence
liability. It is effective orally. It is also
claimed to be beneficial in decreasing crav-
ing for alcohol in alcoholics. Side effects
include gastrointestinal disturbances and
muscular pain.