Norgesic Mechanism of Action

Pharmacology: Pharmacodynamics: Orphenadrine citrate is salt form of orphenadrine. It acts in the central nervous system at the brainstem. It has no direct effect of muscle relaxation. In animal it inhibited specifically to reticular formation (substantia reticularis). Orphenadrine does not have myoneural block activity and had no effect on crossed extensor reflex. It is classified as anticholinergic skeletal muscle relaxant. The complete mechanism of effect is unclear. It may involve with analgesic activity and/or muscle relaxation activity for skeletal muscle. Orphenadrine is o-methyl analog of diphenhydramine which is antihistamine without sedative effect. On the contrary, it stimulated central nervous system mildly.
Paracetamol is the active metabolite of phenacetin and acetanilide. The site and mechanism of the analgesic effect is unclear. Paracetamol reduces fever by direct action on the hypothalamic heat-regulating center, which increases dissipation of body heat (via vasodilation and sweating). The action of endogenous pyrogen on heat-regulating center is inhibited. Paracetamol is almost as potent as aspirin in inhibiting prostaglandin synthetase in the CNS, but peripheral inhibition of prostaglandin synthesis is minimal, which may account for its lack of clinical significant antirheumatic and anti-inflammatory effects. Generally, antipyretic and analgesic effects of paracetamol and aspirin are comparable. Aspirin is clearly superior to paracetamol for relief of pain of inflammatory origin. Paracetamol does not inhibit platelet aggregation, affect prothrombin response, produce GI irritation.
Pharmacokinetics: Orphenadrine is absorbed from the gastrointestinal tract and is almost completely metabolized to at least eight metabolites. Orphenadrine and its metabolites are excreted from the body in the urine, with a half-life of 14 hours.
Paracetamol absorption is rapid and almost complete from the GI tract. Peak plasma concentrations occur within 0.5 to 2 hours, with slightly faster absorption from liquid preparations.