Porcine insulin has one amino acid difference from human insulin, alanine instead of threonine at the carboxy terminus of the B chain (position B30) and beef insulin differs by two additional alterations of the sequence of the A-chain (threonine and isoleucine at positions A8 and A10 are alanine and valine).

In 1991, Egger et al published information indicating more severe episodes of hypoglycaemia with human insulin. Seventeen patients (33% of the study) were admitted to hospital with coma complicated by seizure or pyramidal signs compared with 17% (10 patients) treated with animal insulin. Animal insulin resulted in no deaths, one patient treated with human insulin died.

The researchers concluded that human insulin has no advantages over highly purified animal insulins. Costs and benefits should be seriously considered as well as availability and method of production.

Hypoglycaemia results when blood glucose levels fall to < 2.8 - 3.8 mmol/l leading to sweating, tremor, restlessness, lack of concentration, visual disturbance, aggressiveness, and sometimes violence. At glucose concentration of 2.0 mmol/l cognitive dysfunction occurs, EEG stimulus becomes incorrect, and third party support is required. At glucose concentration of 1.0 mmol/l diabetic coma, but not necessarily unconsciousness occurs, requiring support from a third party.

Fast acting insulin peaks at 1-2 hours after injection and moderate insulin at 6-8 hours. Long acting insulin's act in 12-18 hours. Snacks are important to avoid hypoglycaemic attacks. Women tend to be reluctant to snack whereas men are comfortable snacking. Exercise can cause low glucose levels for up to 18 hours and may have to be compensated for by reducing insulin intake at night. Excessive alcohol intake can also cause low or disturbed glucose levels for up to 18 hours. The location of the insulin injection site can play an important role when exercise is taken.

Blood glucose must be maintained above a critical level to preserve adequate brain function. To deny the brain glucose leads to loss of neurological and motor control. This can lead to a change in motor responses and cerebral functions.

A diabetic, when treated with animal insulin, is likely to perceive the warning signs of hypoglycaemia as being physiological such as tingling, sweating, tremor and hunger. When treated with human insulin a diabetic is likely to experience warning signs of hypoglycaemia or neuroglycaemia in the form of neurological disturbances such as mental disturbance, unrest, behaviour change, aggression, irritability, appearance of drunkeness and sometimes violence. This was clinically reported in the late 1980's and has led to reports that in a group of 100 patients studied, hypoglycaemia increase was reported by 60%; depression was reported by 26%; memory loss was reported by 14%; muscular weakness was reported by 6%; joint cramp pain was reported by 7%; personality change was reported by 19%. Since the introduction of human insulin in the mid 1980's an increase in violence, suicide, impotence, and untimely death, has been reported to have increased. Tight glucose control can in some instances lead to very low glucose levels occurring during the night leading to the potentially fatal risk of acute hypoglycaemia being encountered during sleep.

The difference in treatment by human insulin, or porcine and beef insulin, may be of particular concern in patients encountering recurrent hypoglycaemia in whom a change from animal to human insulin could exacerbate a worrying tendancy to neuroglycaemia.