Final answer:
Codeine is primarily metabolized in the liver through hepatic conversion to morphine. The cytochrome P450 enzyme CYP2D6 is instrumental in this process, which is critical for codeine's analgesic effects.
Step-by-step explanation:
Codeine is primarily metabolized through hepatic conversion to morphine. The liver is the main organ responsible for the metabolism of drugs, including opioids. Codeine's metabolism involves the enzyme CYP2D6, part of the cytochrome P450 family, which converts codeine into morphine, a more potent opioid. This process is a crucial pharmacokinetic phase that determines the efficacy and potential toxicity of codeine. While morphine is an active metabolite of codeine that contributes to its analgesic effect, other metabolites may be produced but with lesser therapeutic roles.
The renal and pulmonary systems are also involved in the excretion of drugs, but they are not primarily responsible for the metabolism of codeine. The renal system helps in excreting the metabolic by-products after hepatic metabolism, and the pulmonary system has a negligible role in drug metabolism. Intestinal metabolism does not convert codeine into oxycodone. Thus, hepatic conversion is central to codeine's metabolism.