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→Aspirin
===Aspirin===
===Aspirin===
Aspirin is the common name for acetyl salicylic acid. This is hydrolysed to an active form, salicylate, which irreversibly binds COX by an acetylation reaction and has a high affinity for COX in platelets. Because of this affinity, the drug has an anti-thrombotic effect which is more pronounced at low doses where platelet production of TXA2 (aggregatory) is inhibited but that of PGI2 (disaggregatory) is not. At higher doses, PGI2 formation is also affected, reducing the dis-aggregatory influence it provides and therefore the anti-thrombotic effects of aspirin. Once COX is bound by salicylate, TXA2 production is inhibited for the life of that platelet, and so new platelets are required to raise body TXA2 levels again. At the low doses required for anti-thrombosis, aspirin has no analgesic or anti-inflammatory properties.
Aspirin is not used very commonly in veterinary medicine, and huge dose variations exist between species. For example, the dose for a dog is 25mg/kg/8 hours, but in the cat is 25mg/kg/day. Half-life also differs between species, being only one hour in the pony but 37.6 hours in the cat.
Oxidisation is the main method of aspirin metabolisation, but some drug is also conjugated to glucuronide. The conjugation reaction cannot be performed by the cat, accounting for the long half-life in this species.
===Paracetemol===
===Paracetemol===