Antiseizure medications (ASMs) have endocrine related side effects. Long term use of ASMs may result in menstrual irregularities, sexual dysfunction, anovulatory cycles, polycystic ovaries, and reduced fertility. Some ASMs also interfere with glucose and bone metabolism, as well as normal thyroid function. Other ASMs may result in syndrome of inappropriate ADH secretion (SIADH) and hyponatremia. Epilepsy patients treated with ASMs are at risk for bone loss and fractures. This chapter explores the endocrine and hormonal effects of antiseizure medications.

Experimental analysis of drinking in humans has yielded inconsistent results, ranging from no deficits relative to young groups, to substantial deficits. It is possible that cognitive or other factors can account for some of these differences between studies. Age-related dehydration in at-risk human populations may be minimized by ensuring adequate food intake and meal-associated drinking and/or provision of foods with high fluid content. With the exception of hypotension-related stimuli, age-related declines in drinking by rats after about 25% of the life span are small. Increased drinking at younger ages (3–4 mo) seems to be the unexplained anomaly; a generic explanation would be maturation in late adolescence of an as-yet unrecognized inhibitory mechanism.

Key Learning Points

1. 1. Disorders of sodium balance are frequently encountered in critically ill patients.

2. 2. Measurement of serum and urinary electrolytes and osmolality and clinical assessment of volume status are essential components of the diagnostic approach to the patient with an abnormal serum sodium level.

3. 3. Life-threatening neurological complications can arise from both an acute fall in sodium level (<120 mmol/l) and an overly rapid correction of hyponatraemia.

4. 4. Treatment is based on severity of symptoms and underlying causes.

Key Learning Points

1. 1. The syndrome of inappropriate anti-diuretic hormone secretion is the most common cause of hyponatraemia in the hospital setting.

2. 2. It is characterised by impaired water excretion in the setting of persistent or inappropriate release of anti-diuretic hormone.

3. 3. There are a number of causes, the most common being respiratory disorders, malignancy, neurological disorders and drugs.

4. 4. It should be suspected in patients with euvolaemic hyponatraemia who have a low plasma osmolality and a high urine osmolality.

5. 5. Management involves treating the underlying condition and fluid restriction in the first instance.