Treatment of Intercurrent Hyperammonemia

Protocol for Treatment of Intercurrent Hyperammonemia in Patients with Urea Cycle Defect

This protocol is based on that used by the Division of Medical Genetics, in the Department of Pediatrics at the University of Iowa Hospitals and Clinics.  It is largely based on information obtained from Dr. Saul Brusilow, at The Johns Hopkins Hospital.

Diagnosis and Early Treatment:

It is critical that patients with urea cycle defects (eg, ornithine transcarbamylase 'OTC' deficiency) having intercurrent hyperammonemia have treatment started as soon as possible.  Realizing that vomitting and/or lethargy in a patient with a urea cycle defect can be an early sign of hyperammonemia, a plasma ammonia level should be drawn immediately.  If the ammonia level is 3x the upper limit of normal, or greater than 120 uM, draw a repeat NH3 as well as pH, pCO2, electrolytes, and quantitative amino acids - and START treatment without waiting for the repeat labs to come back.
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Stop any oral or IV protein intake.

Prevent catabolic state:

Start IV glucose and/or intralipid to provide 50-150 kcal/kg/day.
IV insulin infusion to manage hyperglycemia if necessary.

IV Therapy

Priming Infusion:

In 35 mL/kg of a 10% Glucose solution, add

Sodium Benzoate           250 mg/kg (or 5.5 g/M2 for older patients)
Sodium Phenylacetate    250 mg/kg (5.5 g/M2 for older patients)
10% Arginine HCl         2 mL/kg (4.0 g/M2 for older patients)

The solution needs to be infused over 90 minutes, do not repeat.
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Sustaining Infusion:

In 35 mL/kg of a 10% Glucose solution, add

Sodium Benzoate     250 mg/kg  (or 5.5 g/M2 for older patients)
Sodium Phenylacetate  250 mg/kg (5.5 g/M2 for older patients)
10% Arginine HCl   2  mL/kg (4.0 g/M2 for older patients)

Infuse over 24 hours in addition to maintenance fluids.  NOTE: g/M2 refers to grams per meter squared.
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Hemodialysis

If plasma ammonia level does not decrease by 8 hours after the priming infusion, hemodialysis is indicated.

Contact the Division of Medical Genetics, Department of Pediatrics, University of Iowa Hospitals and Clinics for consultation and further information at (319)-356-2674.
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