Source: Medicines and Medical Devices Safety Authority (NZ) Revision Year: 2023 Publisher: Noumed Pharmaceuticals Limited, Auckland, New Zealand
Codeine phosphate is an opioid analgesic with uses similar to those of morphine but is much less potent as an analgesic and has only mild sedative effects. Its primary site of action is at the mu opioid receptors distributed throughout the central nervous system.
Codeine phosphate reduces intestinal motility through both a local and possibly central mechanism of action.
Codeine and its salts are absorbed from the gastro-intestinal tract and onset of analgesic action occurs 30 to 45 minutes after administration, when given orally.
Peak effect is reached within 1 to 2 hours and the duration of analgesic action is 4 hours.
Codeine is readily absorbed from the gastro-intestinal tract and metabolised by O- and N-demethylation in the liver to morphine and norcodeine which, with codeine, are excreted almost entirely by the kidney, mainly as conjugates with glucuronic acid. Most of the excretion products appear in the urine within 6 hours and 40 to 60 percent of the codeine is excreted free or conjugated, approximately 5 to 15 percent as free and conjugated morphine and about 10 to 20 percent free and conjugated norcodeine.
There are no pre-clinical data of relevance to the prescriber which are additional to those included in other sections.
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