Obtaining past medical history is just common sense.
Previous cardiovascular disease increases the risk of arrhythmias
Previous chronic respiratory disease will increase the adverse effects from respiratory depressant drugs
Previous epilepsy increases the risk of seizures with proconvulsant drugs
Previous renal or hepatic disease may reduce the clearance of some drugs
Myotonic dystrophy is a contraindication to aminoglycoside therapy (just thrown in to see if you're still awake)