Sodium Salicylate is a gastric irritant and sodium bicarbonate is often given with it to reduce this effect (however the bicarbonate also increases rate of excretion and this lowers the concentration of salicylate in the blood). Some persons, especially asthmatics, exhibit notable sensitivity to aspirin which may provoke various reactions including urticaria, angioneurotic oedema, rhinitis and severe, even fatal, paroxysmal bronchospasm and dyspnoea. Aspirin increases the bleeding time, decreases platelet adhesiveness, modifies fibrinolyses and in large doses, may cause hypoprothrombinaemia.
The haemorrhagic effects of aspirin on gastric mucosa may be enhanced by anticoagulants. The activity of methotrexate may be markedly enhanced and its toxicity, increased. Aspirin diminishes the effects of uricosuric agents such as probenecid and sulphapyrazone. Barbiturates and other sedatives may mask the respiratory symptoms of aspirin overdosage and have been reported to enhance its toxicity.