CurrentNeighborhood Health Plan of Rhode IslandPolicy N/A

Carglumic acid (Carbaglu) — Coverage Criteria for Hyperammonemia

This policy governs prior authorization and coverage criteria for carglumic acid (Carbaglu) as adjunctive or maintenance therapy for hyperammonemia due to N-acetylglutamate synthase (NAGS) deficiency and for acute hyperammonemia in propionic acidemia (PA) or methylmalonic acidemia (MMA); it affects providers requesting coverage and members receiving this medication.

Policy Summary

PayerNeighborhood Health Plan of Rhode Island

PolicyCarglumic acid (Carbaglu) — Coverage Criteria for Hyperammonemia

Policy CodePolicy N/A

Change TypeNo material changes

Effective DateN/A

Next Review DateN/A

Key ActionSubmit prior authorization with diagnostic confirmation (enzymatic, biochemical, or genetic testing) and baseline plasma ammonia results; authorization up to 12 months may be granted.

SourceLink

POLICY UPDATE CHANGES

No material clinical or coverage changes in this revision.

12 monthstypical authorization period

NAGS, PA, MMAspecific diagnoses considered

baseline and follow-up ammoniarequired laboratory documentation

FDA-approved onlycoverage limited

Coverage Criteria for Carglumic Acid (Carbaglu)

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inv-01: NAGS deficiency (initial)

Covered when ALL of the following are met:

NAGS deficiency initial coverage: Diagnosis of N-acetylglutamate synthase (NAGS) deficiency is confirmed by enzymatic, biochemical, or genetic testing

supports NAGS indication

Baseline ammonia: Member has elevated plasma ammonia levels at baseline

required for initial authorization

inv-02: PA or MMA (acute hyperammonemia)

Covered as adjunctive therapy when ALL of the following are met:

PA/MMA acute episode: Diagnosis of propionic acidemia (PA) or methylmalonic acidemia (MMA) with acute hyperammonemia

Used adjunctively with other ammonia-lowering therapies (alternate pathway medications, hemodialysis, dietary protein restriction) per product labeling

inv-03: Reauthorization criteria

Reauthorization covered when ALL of the following are met:

NAGS reauthorization: Member with NAGS deficiency is experiencing benefit from therapy as evidenced by a decrease in ammonia levels from baseline

Authorization of up to 12 months may be granted

PA/MMA reauthorization: Member with methylmalonic acidemia or propionic acidemia demonstrates disease stability or improvement while on therapy

Authorization of up to 12 months may be granted

inv-04: Not medically necessary

Exclusions: All other indications not listed (beyond FDA-approved and compendial uses) are considered experimental/investigational and not medically necessary

Requests for non-approved indications may be denied

All indications other than the listed FDA-approved indications and compendial uses are considered experimental/investigational and not medically necessary.

Use of carglumic acid for indications beyond NAGS deficiency, acute hyperammonemia due to propionic acidemia (PA) or methylmalonic acidemia (MMA), or other compendial uses is considered experimental/investigational and not medically necessary.

Diagnosis Confirmation and Covered Indications

inv-16: Diagnosis confirmation for NAGS deficiency

Diagnosis may be confirmed by enzymatic, biochemical, or genetic testing to meet coverage criteria.

Confirmed diagnostic method: Diagnosis confirmed by enzymatic assay, biochemical testing, or genetic testing for NAGS (documentation must be submitted with initial prior authorization request)

Enzymatic, biochemical, or genetic testing acceptable to meet diagnostic confirmation requirement

Laboratory documentation: Baseline plasma ammonia level documented at initiation and follow-up ammonia measurements available to demonstrate clinical response for continuation/reauthorization

Follow-up labs should show a decrease in ammonia for continued authorization

Coding and Monitoring

Laboratory monitoring

Required baseline testEnzyme assay, biochemical, or genetic testing results confirming NAGS deficiency must be submitted with initial requests.

Baseline ammonia levelLab results documenting elevated plasma ammonia at baseline are required for initial authorization.

Continuation criterionContinuation/reauthorization requires laboratory results documenting a reduction in plasma ammonia from baseline.

Authorization durationAuthorization of up to 12 months may be granted when diagnostic confirmation and baseline ammonia criteria are met.

Provider Actions, Authorization, and Documentation

Prior Authorization

Prior Authorization Required

Prior authorization is required. Authorization may be granted for up to 12 months when diagnostic confirmation and baseline plasma ammonia criteria are met.

Authorization up to 12 months when: diagnosis confirmed by enzymatic, biochemical, or genetic testing; baseline elevated plasma ammonia documented.

Note

Adjunctive Therapy Requirement

During acute hyperammonemic episodes, carglumic acid (Carbaglu) must be used as adjunctive therapy alongside other ammonia‑lowering treatments.

Concomitant administration with alternate pathway medications, hemodialysis, and dietary protein restriction is recommended during acute episodes.
For maintenance therapy, concomitant use of other ammonia‑lowering therapies and protein restriction may be needed based on plasma ammonia levels.

Documentation Required

Required Documentation

Required documentation must be submitted with initial and continuation prior authorization requests to support the diagnosis and assess treatment response.

Initial requests: enzyme assay, biochemical, or genetic testing results confirming NAGS deficiency; and laboratory results documenting baseline plasma ammonia levels.
Continuation requests: laboratory results demonstrating a reduction in plasma ammonia levels from baseline.

Definitions

Acute hyperammonemia — definition and clinical context

DefinitionAn episode of markedly elevated plasma ammonia requiring urgent ammonia‑lowering interventions; includes acute hyperammonemia from NAGS deficiency and acute episodes in propionic acidemia (PA) or methylmalonic acidemia (MMA).

Treatment contextCarglumic acid (Carbaglu) is indicated as adjunctive therapy to standard of care during acute episodes; use with alternate pathway medications, hemodialysis, and dietary protein restriction is recommended.

Patient populationIndicated in pediatric and adult patients as adjunctive therapy for acute hyperammonemia due to NAGS deficiency, PA, or MMA.

Chronic hyperammonemia due to NAGS deficiency — definition

DefinitionOngoing elevated plasma ammonia managed with maintenance carglumic acid therapy in pediatric and adult patients with NAGS deficiency; protein restriction or other ammonia‑lowering therapies may be needed based on ammonia measurements.

IndicationCarbaglu is indicated as maintenance therapy for chronic hyperammonemia due to NAGS deficiency.

Concomitant measuresDuring maintenance therapy, concomitant use of other ammonia‑lowering therapies and dietary protein restriction may be required depending on plasma ammonia levels.

Background

Carglumic acid (Carbaglu) is indicated to treat acute and chronic hyperammonemia caused by N-acetylglutamate synthase (NAGS) deficiency and as adjunctive therapy for acute hyperammonemia in propionic acidemia (PA) and methylmalonic acidemia (MMA). It functions as a synthetic analog of N-acetylglutamate to activate carbamoyl phosphate synthetase I, promoting ammonia detoxification; during acute episodes it should be used alongside standard ammonia-lowering measures.