Action of Certain Narcotic Analgesics

The meehanism of aetion of certain narcotic analgesics included in this chapter are discussed 

Its most important action is on the brain more specifically its higher functions. It has been observed that an initial transitory stimulation is usually followed by a distinct depression of the brain, its higher functions, and above all its medullary centres. Besides, the spinal functions and reflexes are normally stimulated. Interestingly, it causes a visible change in perception in such a manner that the patient shows more to tolerance to pain and discomfort perhaps due to possible interference with pain conduction . 

Because of its high addition potential and abuse, the drug is classified as Schedule II drug under the Controlled Substances Act. 

Codeine is chiefly metabolized in the liver where it imdergoes o-demethylation, N-demethylation and partial conjugation with glycuronic acid. It is mostly excreted in the urine as narcodeine and morphine (both as its free and conjugated form). It is found to be less apt than morphine to produce nausea, vomitting, constipation and miosis. It also causes addiction liabilities resulting into enhanced tolerance limits. 

Naloxone is a specific antagonist in the situations arising from acute intoxication . 

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