All of the following about meperidine are true except (DNB Dec 2010)
|A||Has shorter half-life then morphine|
|B||Greater spasmogenic action then morphine|
|D||Better oral availability|
Although pethidine is chemically unrelated to morphine, it has many similar actions; has been shown to interact with opioid receptors and its actions are blocked by naloxone. Important differences in comparison to morphine are enumerated below.
a. Dose-to-dose 1/10th in analgesic potency; however, analgesic efficacy approaches near to morphine and is more than codeine;
b. After intramuscular, injection the onset of action is more rapid but duration is shorter (3 - 4 hours);
c. Does not effectively suppresses cough;
d. Spasmodic action on smooth muscles is less marked; miosis, constipation and urinary retention are less prominent; liability to induce biliary spasm is less;
e. It is equally sedative and euphoriant and has similar abuse potential. The degree of respiratory depression is equivalent to morphine at equianalgesic dose.
f. Causes less histamine release and is safer in asthmatics;
g. Has got local anesthetic action, and corneal anesthesia is produced after systemic doses; and
h. It is well absorbed, oral: parenteral activity ratio is high (1/3 to 1/2).