Water intoxication: one of side effects of oxytocin

 Oxytocin has a similar structure to vasopressin (antidiuretic hormone) and can cross-react with the renal vasopressin receptor. If higher doses (eg, 50 milliunits/minute) of oxytocin are administered in large quantities (eg, over 3 liters) of hypotonic solutions (eg, 5 percent dextrose in water [D5W]) for prolonged periods of time (≥7 hours, excessive water retention can occur and result in severe, symptomatic hyponatremia, similar to the syndrome of inappropriate antidiuretic hormone secretion(SIADH). This risk may be as high as 5 percent when the conditions described above are met. Excessive oral, rather than intravenous (IV), intake of hypotonic liquids can have the same effect.

Symptoms of severe acute hyponatremia include headache, anorexia, nausea, vomiting, abdominal pain, lethargy, drowsiness, unconsciousness, grand mal type seizures, and potentially irreversible neurologic injury. 

If water intoxication occurs, oxytocin and any hypotonic solutions should be stopped. Correction of hyponatremia must be performed carefully and consists of restricting water intake and careful administration of hypertonic saline if the patient is symptomatic.

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