Source of insulin

• Animal insulin: extracted and purified from the pancreases of cows (bovine or beef) and pigs (porcine or pork)
• Human insulin: synthetic insulin made in a laboratory
• Analogue insulin: genetically modified human insulin made in a laboratory.

Speed of insulin – onset and duration of action

• Rapid acting: works almost immediately after being injected
• Short acting: works within 30 minutes of being injected
• Intermediate acting: available for the body to use two to four hours after injection and lasts between 12 and 18 hours
• Long acting: available for the body to use two to four hours after injection and lasts 24 hours or longer
• Ultra-long acting: available for the body to use around six hours after injection and lasts 36 hours or longer.

Most of the insulin available in the UK contains 100 units/ml of insulin, but a few are also available in 200, 300 and 500 units/ml. The high strength insulin 500 units/ml is used in patients with severe insulin resistance who require higher insulin doses – up to 2,000 units per day in some cases.

Common insulin injection sites include the stomach, buttocks and thighs. Regular rotation of injection sites is important because subcutaneous administration of insulin can result in lipohypertrophy (lumps under the skin caused by the accumulation of extra fat at the site of injection) or lipoatrophy (loss of fat tissue).