Codeine is an
alkaloid obtained from
opium or prepared from
morphine by
methylation and occurs as white crystals. Codeine
effloresces slowly in dry air and is
effected by light.
The
chemical name of codeine phosphate is 7,8-Didehydro-4,5alpha-epoxy-3-methoxy-17-methylmorphinan-6alpha-ol
phosphate (1:1)(salt)
hemihydrate and has
the
empirical formula of C18H21NO3·H3PO4·1/2H20. Its
molecular weight is 406.4.
Codeine phosphate is a centrally active
analgesic. When administered parenterally, 120 mg of codeine phosphate produces an analgesic
response equivalent to that
from 10 mg of
morphine. Other actions include
respiratory depression; depression of the
cough center; release of
antidiuretic hormone;
activation of the
vomiting center; pupillary
constriction; a decrease in
gastric,
pancreatic, and
biliary secretion; a reduction in
intestinal motility; an increase in biliary tract pressure; and an
increased amplitude of ureteral contractions.