• Some absorption of inorganic laxative salt ions occurs but, in healthy individuals the amounts are too small to cause toxic effects and the ions are rapidly excreted via the kidney. However, accumulation of magnesium ions can occur in the presence of renal impairment, causing toxic effects in the central nervous system and altered neuromuscular function through hypermagnesaemia. As renal function tends to decline with age, it may be advisable to discourage regular use of magnesium-containing laxatives by elderly patients.
• The main side effects of inorganic osmotic laxatives are nausea and vomiting. In addition, large doses can produce significant dehydration, so sufficient water should always be drunk with a dose to ensure that there is no net loss of body water. Serious adverse effects with lactulose are rare. Relatively minor side effects, although they may be sufficient to discourage compliance, occur in about 20 per cent of patients taking full doses and include flatulence, cramp and abdominal discomfort, particularly at the start of treatment. Lactulose is a disaccharide of galactose and fructose and also includes some lactose. It is therefore not suitable for patients with galactose or lactose intolerance and must be used with caution in patients with diabetes.

Activity

Can you identify any patients who may be using excessive quantities of laxative, either on prescription or OTC? Flag them up on the PMR and ask counter staff to let you know about patients making regular OTC purchase. Consider how to broach and discuss this subject with patients. Under what circumstances would you inform their GP?