Which of the following drug does not act on opioid receptor? (AIIMS Nov 2011)
a. Mu, kappa and delta are three types of opioid receptors.
b. A recently discovered receptor or opioid like receptor is also known and is termed as ‘orphan’ receptor.
c. Each receptor has a unique distribution in brain, spinal chord and periphery.
d. Opioid receptors are G protein coupled and increase permeability of potassium, decrease calcium currents or decrease cAMP.
e. Heroin is diacetylmorphine and is a prodrug, and forms mono acetyl morphine (MAM).
f. MAM is more lipid soluble than morphine and enters brain more freely.
g. Methadone is an isomeric drug and l-methadone is more potent than d-methadone.
h. Ketamine is a phencyclidine derivative and is also a drug of abuse. The drug is best given as an injection intermittent or continuous.
i. It is an isomeric drug and s-isomer is more potent than d-isomer. Ketamine is an NMDA blocker but has long known to interact with opioid receptors.
j. Ketamine activates specific opioid receptors (sigma opioid receptors) in the central nervous system.
k. The sigma opioid receptor has been implicated in many of the symptoms of schizophreniA.
l. Possibly, this is the reason due to which, the drug causes lot of psychomimetics effects such as emergence delirium.
m. These effects can be attenuated by giving diazepam
n. Unique feature of methadone is its long duration and ability to suppress withdrawal in opioid addicts.
o. That is why, it is the drug of choice for opioid detoxification
p. Importantly, buprenorphine, a long acting partial mu agonist can also be used for same purpose and has equal efficacy.
q. It has the advantage of being given sublingually. Methadone is highly protein bound and undergoes de alkylation and cyclization.
r. Metabolism of the drug can be induced by phenytoin or rifampin and these can produce withdrawal symptoms.
s. Abuse potential of the drug is similar to that of morphine
t. Ondansetron, granisetron, Palonosetron, dolasetron, Tropisetron are blockers of 5-HT3 receptors and are considered to be drugs of choice for chemotherapy, radiotherapy and postoperative vomiting.
u. Palonosetron is most potent of them. These drug are well absorbed and extensively metabolized by CYP enzyme system.