HCPCS Level II C9055: Injection, brexanolone, 1mg

HCPCS Level II code C9055 designates a billed unit of brexanolone injection (1 mg), a specialty intravenous medication used in monitored infusion settings. This code matters nationally because brexanolone is a high-cost, specialty therapy administered under supervision, affecting coverage, prior authorization, and site-of-care decisions across payers. Key payers included in the analysis are Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find an overview of what C9055 represents clinically and operationally, common payer coverage patterns, and the elements that influence billing and reimbursement for infusion-administered specialty medications. The publication summarizes typical sites of service, expected documentation and billing considerations, and common modifiers used in infusion and specialty drug billing. It also outlines benchmarking metrics and policy trends relevant to high-cost intravenous neuroactive therapies, and highlights where data was not provided. Data not available in the input will be clearly stated where applicable.

Billing Code Overview

HCPCS Level II code C9055 represents Injection, brexanolone, 1mg. This code covers the billed supply or administration unit of brexanolone measured per milligram. The service type is medication administration for an intravenous or infusion therapy containing brexanolone. The typical site of service for this therapy is an outpatient infusion center or hospital outpatient department where monitored intravenous infusions are provided.

Data not available in the input.

Clinical Context

A 28-year-old postpartum woman presents with severe, treatment-resistant postpartum depression within the first three months after delivery. She experiences marked mood disturbance, suicidal ideation, and significant functional impairment despite trials of standard antidepressant therapy. The care team determines inpatient or closely monitored outpatient infusion is required for a continuous intravenous administration of brexanolone.

The clinical workflow typically includes:

Initial psychiatric and medical evaluation with documentation of diagnosis, severity, and prior treatment trials.
Baseline monitoring: vital signs, oxygen saturation, and continuous pulse oximetry if required; pregnancy and lactation counseling as applicable.
Pharmacy preparation and verification of C9055 as the unit billing descriptor for brexanolone, dosing calculated per mg and delivered as a continuous infusion over 60 hours per product protocol.
Admission to a monitored bed (inpatient psychiatric unit, step-down, or ambulatory infusion center with continuous monitoring) for the duration of the infusion.
Continuous nursing observation during infusion for sedation, hypoxia, excessive somnolence, or other adverse effects and periodic reassessments by prescribing clinician.
Post-infusion observation and documentation of clinical response, adverse events, discharge planning, and follow-up psychiatric care.

Coding Specifications

Taxonomy Code	Specialty	Notes
`207Q00000X`	Psychiatry & Neurology	Psychiatrists typically prescribe and oversee brexanolone therapy.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`F53.0`	Postpartum depression (mental)	Primary indication for brexanolone infusion in women with severe postpartum depressive disorder.

F32.2 | Major depressive disorder, single episode, severe without psychotic features | Relevant when postpartum onset presents as a severe major depressive episode qualifying for brexanolone consideration.

F33.2 | Major depressive disorder, recurrent severe without psychotic features | Relevant for recurrent severe episodes in the peripartum period when brexanolone may be considered.

F32.9 | Major depressive disorder, single episode, unspecified | May be used when documentation supports major depression but specifics of severity are not yet coded.

O99.32 | Mental disorders and diseases of the nervous system complicating pregnancy, childbirth and the puerperium — depressive disorders | Used to capture peripartum timing and maternal complication coding when applicable.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`96365`	Intravenous infusion, for therapy, prophylaxis, or diagnosis; initial, up to 1 hour	Billed for the initial infusion management time if applicable for the initial continuous infusion setup (some payors require infusion codes for nursing/administration time in addition to drug HCPCS `C9055`).

96366 | Intravenous infusion, each additional hour (List separately in addition to code for primary infusion) | Billed for each additional hour of monitored infusion administration beyond the initial hour when payors require time-based infusion codes alongside the drug HCPCS.

99199 | Unlisted special service, procedure or report (Hospital inpatient services) | Used for unique monitoring or facility-specific services related to prolonged monitored infusions when no established CPT exists.

99499 | Unlisted evaluation and management service | Occasionally used for complex, non-standard care coordination or prolonged E/M services directly related to the infusion when standard E/M codes are not appropriate.

36415 | Collection of venous blood by venipuncture | Used for baseline or serial laboratory monitoring required before or during infusion (e.g., pregnancy-related labs, metabolic panels).

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Summary & Overview