In: Anatomy and Physiology
explain the pharmacokinetics process of codeine druge? Absorption( how and how many (MDNS), Distribution, metabolism and excretion??
Codeine is widely used as anti-tussive and analgesic drug and it is known that O-demethylation of codeine into morphine is mediated by the genetically polymorphic enzyme cytochrome P450 2D6 Whereas this O-demethylation reaction accounts only for less than 10% of codeine clearance, it is regarded to be the bioactivation reaction essential for the analgesic activity of codeine preparations. A strong correlation between debrisoquine metabolic ratio (MR), reflecting CYP2D6 activity, and the urinary recovery of codeine and its metabolites formed by O- and N-demethylation has been shown.
the oral absorption is unreliable because of high and variable first-pass metabolism
oral bioavailability is 1/6th to 1/4th of the parenterally administered drug
30% plasma bounded, only a small fraction enters the brain
crosses placenta affect fetus
metabolize in the liver by glucuronide conjugation
restrict across the blood-brain barrier
plasma half life is 2 to 3 hour
effect of parenentral dose last in 4 to 6 hour
elimination complete in 24 hourand morphine is noncumlative