Biguanides €“ metformin is the only drug of this class available in the UK and probably acts by inhibiting gluconeogenesis (hepatic production of glucose), increasing its peripheral utilisation and reducing intestinal glucose absorption. Metformin should be started at a low dose and stepped up gradually to minimise the risk of gastrointestinal side effects to the maximum of 2g/day in divided doses. Sustained release metformin tablets are more expensive but may result in fewer gastro-intestinal (GI) adverse effects. Diarrhoea is usually transient, while other GI side effects such as anorexia, nausea and vomiting are more common at higher doses.

Sulfonylureas €“ a sulfonylurea is a first line alternative in certain circumstances (e.g. metformin is contraindicated, the patient is not overweight or rapid control of hyperglycaemia is needed). They act on the beta cells of the pancreas, stimulating release of insulin, but become less effective over time as the beta cells fail. Significant weight gain is an undesirable side effect and agents with long half-lives can lead to insidious development of hypoglycaemia, while those metabolised or excreted via the kidneys can produce hypoglycaemia in patients with end-stage renal failure.

Additional hypoglycaemic treatment €“ other medicines may need to be used to achieve control of blood glucose and these can be found in BNF 6.1.2.3.

Insulin €“ there are various types of insulin (short acting, intermediate acting, long acting, and biphasic). For further information about insulin, see BNF 6.1.1. A National Patient Safety Agency (NPSA) alert highlighted several issues that can lead to errors in insulin prescribing, dispensing and administration, such as inappropriate abbreviations (ml instead of units), wrong injection device, wrong insulin, and wrong dose. This led to the development of an insulin passport, which all patients prescribed insulin should carry at all times and show to any healthcare professional treating them. When dealing with insulin, there are certain risks to be aware of:

• Confusion between similar product names, devices and presentations
• Long acting analogue insulins (e.g. Lantus) are clear in appearance, unlike older intermediate and long acting insulins (e.g. Insulatard), which are cloudy. This may be a problem for patients who identify their insulins visually
• Absorption of insulin is affected by temperature, so when it is in use, insulin must remain out of the fridge
• Insulin mixes must be re-suspended by gentle mixing before administration as not doing so alters the mix
• Patients should be advised against injecting into the same area all the time or using the arms. Repeated injection without rotation of the site can lead to poor control (hypo- and hyperglycaemia), trauma to injection site, infection and varying degrees of insulin absorption due to the different sites. There is also an increased risk of intramuscular injection if using the arms.