Pharmacology: Pharmacodynamics: Paracetamol appears to produce analgesia at a subcorticol site of brain, and may also block pain impulses by a depressant effect on peripheral chemoreceptors, mainly by inhibiting and interfering with the prostaglandin synthesis. Paracetamol lowers body temperature by acting in the hypothalamus to produce antipyresis.
Codeine Phosphate has a central action especially in the cortex, thereby raising the threshold for pain.
Pharmacokinetics: Paracetamol and Codeine phosphate are well absorbed from the gastrointestinal tract. The peak concentrations in plasma are attained in about 1 hour. The half-life is about 1 to 3 hours for Paracetamol and about 2.5 to 3 hours for Codeine Phosphate after therapeutic doses. The duration of action varies between 4-6 hours.
Metabolism and Excretion: Following therapeutic doses, about 80% of the Paracetamol undergoes conjugation with glucoronic acid in the liver, and only 3% is excreted as unchanged drug.
Codeine Phosphate is metabolised in the liver and excreted primarily as an inactive metabolites, two-third of these within 6 hours of ingestion.