Adverse effects of insulin are mainly those of overdose.6 Because the brain relies on glucose as its
5 The normal (fasting) blood glucose range is 3.9-5.8 mmol/1 (70-105 mg/100 ml).
6 Suicidal overdose (in diabetics) is well recorded. Surgical excision of the skin and subcutaneous tissue at the injection site of an enormous dose of long-acting insulin has been used effectively.
source of energy, an adequate blood glucose concentration is just as essential as an adequate supply of oxygen, and hypoglycaemia may lead to coma, convulsions and even death (in 4% of diabetics under 50 years of age).
It is usually easier to differentiate hypoglycaemia from severe diabetic ketosis than from other causes of coma, which are as likely in a diabetic as in anyone else. It is unsound to advocate blind administration of i.v. glucose to comatose diabetics on the basis that it will revive them if they are hypoglycaemic and do no harm if they are hyper-glycaemic. A minority of comatose insulin-dependent diabetics have hyperkalaemia and added glucose can cause a brisk and potentially hazardous rise in serum potassium (mechanism uncertain), in contrast to nondiabetics in whom glucose causes a fall in serum potassium.
Hypoglycaemia may manifest itself as disturbed sleep (nightmares) and morning headache. For details of treatment see below.
Other adverse reactions to insulin are lipodystrophy (atrophy or hypertrophy) at the injection sites (rare with purified pork and human insulin), after they have been used repeatedly. These are unsightly, but otherwise harmless. The site should not be used further, for absorption can be erratic, but the patient may be tempted to continue if local anaesthesia has developed, as it sometimes does. Lipoatrophy is probably allergic and lipohypertrophy is due to a local metabolic action of insulin. Local allergy also is manifested as itching or painful red lumps.
Generalised allergic reactions are very rare, but may occur to any insulin (including human) and to any constituent of the formulation. Change of brand of insulin, especially to highly purified preparations (or to one with a different mode of manufacture) may rectify allergic problems. But zinc occurs in all insulins (though very little in soluble insulin) and can be the allergen.
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