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Inborn Errors of Metabolism Medication

  • Author: Debra L Weiner, MD, PhD; Chief Editor: Stephen Kemp, MD, PhD  more...
Updated: Feb 18, 2015

Medication Summary

Emergency medications for inborn errors of metabolism (IEMs) in infants and children include drugs to eliminate toxic metabolites and/or amino acids and enzyme cofactors to compensate for metabolic deficiencies. These and other drugs may be required to maintain and treat the underlying IEM. Some IEMs are treated with replacement enzymes that are FDA approved, designated as orphan drugs, or investigational.[8]

Helpful Web sites for finding information on orphan drug designation include the following:


Ammonium Detoxicants

Class Summary

Treatment of hyperammonemia; enhances elimination of nitrogen. This drug is FDA approved for treatment of hyperammonemia due to urea cycle defects and is available only from a specialty wholesaler, Ucyclyd Pharma (888-829-2593). For more information, see Ammonul prescribing information.

Sodium phenylacetate and sodium benzoate (Ammonul)


Indicated for acute hyperammonemic and associated encephalopathy due to urea cycle defects. For ammonia levels >500-600 mcg/dL, hemodialysis is the preferred treatment; however, sodium phenylacetate and sodium benzoate should be considered if dialysis cannot be initiated immediately. Benzoate combines with glycine to form hippurate, which is excreted in urine. One mol of benzoate removes 1 mol of nitrogen. Phenylacetate conjugates (via acetylation) glutamine in the liver and kidneys to form phenylacetylglutamine, which is excreted by the kidneys. The nitrogen content of phenylacetylglutamine per mole is identical to that of urea (2 mol of nitrogen). Ammonul should be administered with arginine-HCL for carbamyl phosphate synthetase (CPS), ornithine transcarbamylase (OTC), argininosuccinate synthetase (ASS), or argininosuccinate lyase (ASL) deficiencies and should not be given for arginase deficiency. Approved as adjunctive treatment of acute hyperammonemia associated with encephalopathy caused by urea cycle enzyme deficiencies. Preparation contains 100 mg/mL each of sodium phenylacetate and sodium benzoate and comes in 50-mL vials. Must dilute IV dose in at least 25 mL/kg of dextrose 10% up to 600 mL. Do not mix directly with other medications, but it may be piggybacked. Give in addition to daily fluid requirement but decrease maintenance fluid by volume of Ammonul given.


Amino Acid

Class Summary

Essential amino acid used for certain urea cycle defects.

Arginine (R-Gene)


Enhances production of ornithine, which facilitates incorporation of waste nitrogen into the formation of citrulline and argininosuccinate. Provides 1 mol of urea plus 1 mol ornithine per mol of arginine when cleaved by arginase. Preparation is 10% arginine hydrochloride. Can be mixed with sodium phenylacetate and sodium benzoate. If administering separately, mix with sodium bicarbonate.


Enzyme Cofactor

Class Summary

Enzyme cofactors are used to enhance the activity of cofactor-dependent enzymes.



Precursor of pyridoxal, which functions in the metabolism of proteins, carbohydrates, and fats. Also aids in the release of liver- and muscle-stored glycogen and in the synthesis of GABA (within the CNS) and heme. Involved in synthesis of GABA within the CNS. Indicated for seizures of unknown etiology unresponsive to conventional anticonvulsants and for seizures in patients with known pyridoxine-dependent IEM. Give undiluted or mix with other solutions. Incompatible with alkaline or oxidizing solutions and iron salts. Not to be mixed with sodium bicarbonate.


Nutritional Supplement

Class Summary

This agent is used for the treatment of primary and secondary carnitine deficiency.

Levocarnitine (Carnitor)


An amino acid derivative, synthesized from methionine and lysine, required in energy metabolism. Can promote excretion of excess fatty acids in patients with defects that bioaccumulate acyl-CoA esters. Carnitine is indicated for most organic acidemias and is controversial for fatty acid oxidation defects.

Contributor Information and Disclosures

Debra L Weiner, MD, PhD Attending Physician, Division of Emergency Medicine, Children's Hospital, Boston; Assistant Professor, Department of Pediatrics, Harvard Medical School

Disclosure: Nothing to disclose.

Specialty Editor Board

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Wayne Wolfram, MD, MPH Professor, Department of Emergency Medicine, Mercy St Vincent Medical Center; Chairman, Pediatric Institutional Review Board, Mercy St Vincent Medical Center, Toledo, Ohio

Wayne Wolfram, MD, MPH is a member of the following medical societies: American Academy of Emergency Medicine, American Academy of Pediatrics, Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Chief Editor

Stephen Kemp, MD, PhD Former Professor, Department of Pediatrics, Section of Pediatric Endocrinology, University of Arkansas for Medical Sciences College of Medicine, Arkansas Children's Hospital

Stephen Kemp, MD, PhD is a member of the following medical societies: American Academy of Pediatrics, American Association of Clinical Endocrinologists, American Pediatric Society, Endocrine Society, Phi Beta Kappa, Southern Medical Association, Southern Society for Pediatric Research

Disclosure: Nothing to disclose.

Additional Contributors

Garry Wilkes, MBBS, FACEM Director of Clinical Training (Simulation), Fiona Stanley Hospital; Clinical Associate Professor, University of Western Australia; Adjunct Associate Professor, Edith Cowan University, Western Australia

Disclosure: Nothing to disclose.

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Table 1. Clinical and Laboratory Findings of Inborn Errors of Metabolism
Clinical Findings* AA OA UCD CD GSD FAD LSD PD MD
Episodic decompensationX++++X+--X
Poor feeding, vomiting, failure to thriveX++++XX+++
Dysmorphic features and/or skeletal or organ malformationsXX--XX+XX
Abnormal hair and/or dermatitis-XX------
Cardiomegaly and/or arrhythmias-X--XX+-X
Hepatosplenomegaly and/or splenomegalyX++++++XX
Developmental delay +/- neuroregression+++XXX++++
Lethargy or comaX+++++X++--X
Hypotonia or hypertonia++++X+X+X
Abnormal odorX+X------
Laboratory Findings*         
Primary metabolic acidosisX++++X+--X
Primary respiratory alkalosis--+------
Liver dysfunctionXXX+X+XXX
Reducing substancesX--+-----
*Within disease categories, not all diseases have all findings. For disorders with episodic decompensation, clinical and laboratory findings may be present only during acute crisis. For progressive disorders, findings may not be present early in the course of disease.

AA = Amino acidopathy

OA = Organic acidopathy

UCD = Urea cycle defect

CD = Carbohydrate disorder

GSD = Glycogen storage disorder

FAD = Fatty acid oxidation defect

LSD = Lysosomal storage disease

PD = Peroxisomal disorder

MD = Mitochondrial disorder

++ = Always present

+ = Usually present

X = Sometimes present

- = Absent

H = Inappropriately high

L = Inappropriately low

A = Appropriate

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