Many old animals are kept on long-term treatments such as non-steroidal anti-inflammatory drugs (NSAIDS), corticosteroids, diuretics, cardiac stiulants and anticonvulsants. A pre-surgical review of medications is important because they may affect anaesthesia.

Phenytoin and primidone are potentially hepatotoxic when they interwith anaesthetic agents and they also cause CNS depression, so reducing the dose of anaesthetic needed.

Chronic glucocorticoid administration may induce adrenal insufficiency predisposing to cardiac instability during anaesthesia. This is another reason why glucocorticoid administration immediately before induction of anaesthesia has been advocated.

Long-term diuretic administration may cause metabolic alkalosis, hypokalaemia, and sometimes hypomagnesaemia - all of which should be corrected before surgery.