From the FDA Drug Label
Oxytocin has been shown to have an intrinsic antidiuretic effect, acting to increase water reabsorption from the glomerular filtrate. Consideration should, therefore, be given to the possibility of water intoxication, particularly when oxytocin is administered continuously by infusion and the patient is receiving fluids by mouth Water intoxication with convulsions, which is caused by the inherent antidiuretic effect of oxytocin, is a serious complication that may occur if large doses (40 to 50 milliunits/minute) are infused for long periods. Management consists of immediate discontinuation of oxytocin, and symptomatic and supportive therapy.
To manage the risk of hyponatremia in patients receiving oxytocin, it is essential to be aware of the potential for water intoxication due to the intrinsic antidiuretic effect of oxytocin.
- Monitor patients closely for signs of water intoxication, especially when oxytocin is administered continuously by infusion and the patient is receiving fluids by mouth.
- Be cautious when administering large doses of oxytocin (40 to 50 milliunits/minute) for extended periods.
- If water intoxication occurs, management consists of immediate discontinuation of oxytocin and symptomatic and supportive therapy 1 1.
From the Research
To manage the risk of hyponatremia in patients receiving oxytocin, implement strict fluid intake monitoring and regular serum sodium level checks, as oxytocin has an antidiuretic effect similar to vasopressin, which can lead to dilutional hyponatremia, especially when combined with excessive hypotonic fluid intake 2.
Key Recommendations
- Limit intravenous fluid administration to 1-1.5 L over 24 hours when oxytocin is being administered, preferably using isotonic solutions rather than hypotonic fluids.
- Monitor serum sodium levels every 6-12 hours during oxytocin infusion, particularly in prolonged labor or when higher doses are used.
- Watch for early signs of hyponatremia including headache, nausea, confusion, and lethargy.
- If hyponatremia develops (sodium <135 mEq/L), consider reducing oxytocin infusion rates and adjusting fluid therapy.
- In severe cases (sodium <125 mEq/L or symptomatic patients), oxytocin may need to be discontinued and hypertonic saline administered under specialist supervision.
Rationale
The risk of hyponatremia is particularly significant during labor induction or augmentation when oxytocin may be administered for extended periods 3, 4.
Additional Considerations
- Vasopressin receptor antagonists, such as tolvaptan, may be considered for the treatment of euvolemic or hypervolemic hyponatremia, but their use is limited by high cost and potential side effects 2, 5.
- Pharmacological chaperones, such as SR49059 and L371,257, may potentially be used to enhance clinical response to oxytocin, but further studies are needed to demonstrate their efficacy and safety in vivo 6.