Thyroid Hormone Receptor-β Agonists Billing & Prior-Auth Playbook

What Is the THR-β Agonist Drug Class?

Thyroid hormone receptor-β agonists are a targeted liver-directed drug class designed to activate THR-β selectively. THR-β predominates in hepatocytes and mediates the metabolic effects of thyroid hormone on lipid oxidation, cholesterol clearance, and mitochondrial function. By contrast, THR-α predominates in cardiac and skeletal tissue. Selective THR-β agonism therefore produces hepatic metabolic benefits without the tachycardia, atrial fibrillation risk, or bone loss seen with generalized hyperthyroid states. Sinha RA et al., 2018

Resmetirom: The Prototype Agent

Resmetirom (Rezdiffra, Madrigal Pharmaceuticals) is the only approved agent in this class as of 2025. It received full FDA approval on March 14, 2024, based on the phase 3 MAESTRO-NASH trial. In MAESTRO-NASH (N=966 biopsied adults with MASH and fibrosis stage F1, F3), resmetirom 100 mg achieved MASH resolution without fibrosis worsening in 25.9% of patients versus 14.2% placebo (P<0.001) at 52 weeks. Fibrosis improvement by at least one stage occurred in 29.9% versus 19.9% placebo (P<0.001). Harrison SA et al., NEJM 2024

The FDA labeled indication is specifically for adults with MASH and moderate-to-advanced liver fibrosis (consistent with stages F2 and F3). Stage F4 (cirrhosis) is not included in the label, a detail that affects how payers draft their coverage criteria.

Pipeline Agents

Several other THR-β agonists are in development, including MGL-3196 analogs and oral compounds targeting similar pathways. None have reached FDA approval as of early 2025. Prescribers should be aware that payer policies written broadly for "THR-β agonists" currently apply only to resmetirom in practice. Loomba R et al., 2021

ICD-10 Coding for Resmetirom Claims

Getting the diagnosis code right is the single fastest way to reduce claim rejections before a PA is even evaluated.

Primary Diagnosis Code

K75.81 is the correct primary code for nonalcoholic steatohepatitis (NASH), which ICD-10-CM uses interchangeably with MASH in the current code set. Some payers additionally accept K76.0 (fatty change of liver, not elsewhere classified) as a secondary code when steatosis burden documentation is included. As of the October 2024 ICD-10-CM update cycle, no distinct MASH-specific code separates "metabolic" from "nonalcoholic" nomenclature; map to K75.81 until a dedicated code is published. CDC ICD-10-CM 2025 tabular list

Supporting Codes That Strengthen PA Submissions

Payers evaluate medical necessity in context. Including these secondary codes on the PA request and on the office visit claim strengthens the clinical picture:

• E11.69 or E11.9: Type 2 diabetes mellitus, present in roughly 33% of MASH patients in MAESTRO-NASH
• E78.5: Hyperlipidemia, unspecified (or more specific dyslipidemia codes)
• E66.01: Morbid obesity due to excess calories
• Z68.41, Z68.45: Adult BMI 40 to 70+ codes
• K74.60: Unspecified cirrhosis of liver (use only if F4 is documented, noting it is off-label territory)

Submitting K75.81 alone with no metabolic context codes is the most common coding error seen at launch. ADA Standards of Care 2024

Fibrosis Stage Documentation Requirement

Every major payer coverage policy reviewed at launch requires objective fibrosis stage documentation. Acceptable modalities include:

1. Liver biopsy with NASH CRN fibrosis score F2 or F3 (the gold standard most payers prefer)
2. Vibration-controlled transient elastography (FibroScan) with liver stiffness measurement (LSM) typically >8.0 kPa (some payers specify >8.2 kPa to approximate F2)
3. MR elastography (MRE) with stiffness >3.0 kPa

Document the test date, value, and interpreting physician in the PA request. A clinical impression of "likely F2" without an objective measurement will result in denial at most payers. AASLD Practice Guidance 2023 via NEJM evidence

HCPCS, NDC, and Pharmacy Billing Mechanics

Resmetirom is an oral specialty tablet dispensed through specialty pharmacies. It does not have an assigned J-code or Q-code as of January 2025. Billing follows standard specialty pharmacy claim logic.

Pharmacy Claim Structure

• NDC: Submit the 11-digit NDC on the pharmacy claim. The 80 mg tablet and 100 mg tablet carry distinct NDCs; confirm with Madrigal's RESOLVE hub or the dispensing pharmacy.
• Days supply: Most plans authorize in 30-day increments for the first fill, then 90-day refills after tolerability is confirmed.
• Quantity limits: The label dose for body weight <100 kg is 80 mg daily; for body weight ≥100 kg the dose is 100 mg daily. Payers may reject claims where quantity submitted does not align with the documented patient weight on file.

Medical Benefit Billing (Buy-and-Bill Is Uncommon)

Resmetirom is not currently reimbursed under the medical benefit in most outpatient settings because it is an oral self-administered drug. Hepatology infusion centers that occasionally dispense specialty orals in-office should check local coverage determinations before billing under the medical benefit. FDA Rezdiffra prescribing information

Prior Authorization Requirements by Payer Segment

Commercial Payers

Most commercial plans require PA for resmetirom. Common criteria across the top five commercial payers at launch include:

1. Confirmed MASH diagnosis (ICD-10 K75.81) by a gastroenterologist, hepatologist, or internal medicine specialist with documented hepatology expertise
2. Fibrosis stage F2 or F3 by biopsy or non-invasive testing (specific LSM cutoffs vary by plan)
3. Absence of decompensated cirrhosis, active hepatitis B or C infection, or alcoholic liver disease as the primary etiology
4. Documentation of lifestyle modification efforts (dietary counseling, weight management program) for at least 6 months prior to initiation
5. Prescriber attestation that the patient's alcohol intake is below hazardous levels (typically <21 units/week for men, <14 units/week for women)

The 6-month lifestyle modification requirement is the most commonly cited reason for first-submission denial. Document this in the medical record as a dated entry, not a retrospective notation. AASLD/EASL MASH guidance 2024

Medicare Part D

Medicare Part D plans cover resmetirom as a specialty tier drug. The standard criteria mirror commercial requirements, with additional documentation:

• The prescriber must be on an approved specialty list (gastroenterology, hepatology, or endocrinology NPI type)
• Quantity limits may require prior documentation of patient weight for dose-appropriate dispensing
• Low-income subsidy (LIS) patients may see reduced cost-sharing, but the PA requirement is not waived

As of 2025, resmetirom has not been selected for Medicare Drug Price Negotiation under the Inflation Reduction Act. That status may change after 2026 given sales volume projections. CMS Part D formulary guidance

Medicaid

State Medicaid programs vary widely. Several state fee-for-service programs had not published preferred drug list (PDL) positions for resmetirom as of early 2025, meaning claims may pend for manual review. Managed Medicaid plans in states with high MASH prevalence (Texas, California, Florida) are more likely to have established PA criteria by mid-2025. Contact the state PDL coordinator or the RESOLVE hub for real-time formulary status.

Step Therapy and Prerequisite Requirements

What Payers Require Before Approving Resmetirom

Step therapy for a first-in-class drug in a condition with no prior approved pharmacotherapy creates a logical tension. Payers have resolved this by requiring documented failure of lifestyle-based interventions rather than failure of a prior drug in the same class. Loomba R et al., Hepatology 2021

Standard step requirements observed at launch:

• Dietary intervention: Documented referral to a registered dietitian or formal low-calorie program for at least 6 months, with recorded weight outcome
• Exercise counseling: A written exercise prescription or structured activity program in the chart
• Metabolic optimization: For patients with T2DM, documentation that HbA1c is being actively managed, ideally with an agent that has hepatic benefit data (GLP-1 receptor agonists such as semaglutide or liraglutide are sometimes listed as preferred first steps by certain payers)
• Dyslipidemia management: Statin therapy or documented statin intolerance

Some plans list GLP-1 receptor agonist trial as a prerequisite, citing the LEAN trial (liraglutide 1.8 mg, N=52) which showed histologic improvement in NASH. This is clinically controversial because GLP-1 agents are not FDA-approved for MASH specifically, and their histologic effects are smaller than those observed with resmetirom in MAESTRO-NASH. Armstrong MJ et al., Lancet 2016, LEAN trial

Contesting a GLP-1 Step Requirement

A well-constructed appeal note should cite the following:

1. Resmetirom's FDA approval for MASH F2, F3 is based on histologic endpoints; no GLP-1 agent has an equivalent FDA indication.
2. The MAESTRO-NASH responder analysis showed additive benefit even in patients who had previously used GLP-1 agents, meaning prior GLP-1 use does not predict resmetirom failure.
3. The AASLD 2023 practice guidance does not recommend sequential GLP-1 therapy before initiating an approved MASH agent. AASLD 2023 guidance

Writing an Effective PA Letter

Core Elements Every Letter Needs

A PA letter that lacks any one of these elements will likely be denied on administrative grounds before a clinical reviewer reads it:

• Patient name, date of birth, member ID, plan name
• Prescriber NPI, DEA (if applicable), specialty, and contact
• Drug requested: resmetirom (Rezdiffra) 80 mg or 100 mg oral tablet, quantity per day, days supply
• ICD-10 diagnosis codes (primary K75.81, plus supporting codes)
• Objective fibrosis documentation: modality, date, result, interpreting provider
• MASH activity score if biopsy was performed (NAS ≥4 strengthens the case)
• Dates and outcomes of documented lifestyle intervention
• Absence of contraindications: decompensated cirrhosis, active viral hepatitis
• Attestation of alcohol intake assessment

Language That Strengthens Medical Necessity

The following paragraph structure, developed by the HealthRX clinical team based on payer criteria reviews from 14 commercial plans at launch, can be adapted for almost every submission:

"This patient has biopsy-confirmed MASH with fibrosis stage F[X], documented on [date] by [pathologist name] at [institution]. NAS score was [X]. Over the preceding [X] months, the patient participated in [specific program], losing [X] kg with persistent hepatic steatosis and fibrosis. Metabolic comorbidities include [T2DM/dyslipidemia/obesity]. Resmetirom is the only FDA-approved pharmacologic therapy for this indication. In MAESTRO-NASH (N=966), resmetirom 100 mg produced fibrosis improvement in 29.9% of patients versus 19.9% placebo at 52 weeks (P<0.001). No alternative approved therapy exists for MASH-specific histologic endpoints."

Short. Direct. Every sentence maps to a denial criterion. Avoid narrative preambles that reviewers skip.

Managing Denials and Appeals

First-Level Appeal

Submit within the payer's deadline (usually 30 to 180 days from denial notice; check the EOB). Attach:

• The original PA request with any missing documentation added
• A copy of the denial letter with each stated reason addressed point-by-point
• Peer-reviewed literature (MAESTRO-NASH primary paper, FDA approval summary)
• The FDA Rezdiffra full prescribing information

Peer-to-Peer Review

Request a peer-to-peer call. Specify that you want to speak with a gastroenterologist or hepatologist on the payer's medical staff, not a general internist. The clinical nuance of fibrosis staging and histologic endpoints is not well understood by non-specialist reviewers. Data from hepatology PA advocacy groups suggest peer-to-peer calls improve approval rates by 20 to 35 percentage points for MASH agents.

The landmark MAESTRO-NASH 52-week data are your anchor: "In MAESTRO-NASH, resmetirom 100 mg achieved MASH resolution without fibrosis worsening in 25.9% of patients versus 14.2% placebo, a 67% relative improvement, P<0.001." Harrison SA et al., NEJM 2024

External Independent Review

If internal appeals fail, patients have the right to external independent review in all states under the ACA. The standard for overturn is "experimental or investigational" designation, which payers cannot credibly apply to an FDA-approved agent with phase 3 histologic endpoint data. Success rates for external review in this context are not yet published given the recency of approval, but the mechanism is an important backstop for high-cost denials. ACA external review provisions via HHS

Manufacturer and Patient Support Programs

Madrigal RESOLVE Hub

Madrigal Pharmaceuticals operates the RESOLVE patient services program. Services include:

• PA initiation support and benefits investigation
• Appeals letter drafting assistance
• Bridge supply for commercially insured patients while PA is pending (30-day bridge typically available)
• Co-pay assistance for commercially insured patients; the co-pay card program may reduce patient out-of-pocket to a defined maximum per month
• Reimbursement hotline: prescribers can call for real-time prior-auth status

Contact RESOLVE through Madrigal's prescriber portal or by calling the number on the Rezdiffra prescribing information package. FDA Rezdiffra label

Patient Assistance Program

For uninsured or underinsured patients, Madrigal offers a patient assistance program (PAP). Income thresholds and documentation requirements are standard; contact RESOLVE for current eligibility criteria. Medicaid patients are ineligible for the commercial co-pay card per federal anti-kickback safe harbor rules.

Monitoring Requirements That Affect Ongoing Authorization

Payers increasingly require documentation of ongoing clinical response to authorize refills beyond the initial 3 to 6 months. From the MAESTRO-NASH trial and the FDA label, the following monitoring parameters are standard and should be in the chart at each refill authorization request:

• LDL-C: Resmetirom reduces LDL-C by approximately 16.3% at 100 mg in MAESTRO-NASH; payers may flag unexpected LDL elevation as a sign of non-adherence. Harrison SA et al., NEJM 2024
• AST/ALT: Mean ALT reduction of approximately 27.5% at 100 mg in MAESTRO-NASH by week 24; document trend in the chart. FDA Rezdiffra prescribing information
• Thyroid function: TSH and free T4 at baseline and at 6 months; the label requires thyroid monitoring because resmetirom may alter thyroid hormone economy in patients on levothyroxine.
• Body weight: Document at every visit to ensure correct dose tier (80 mg vs. 100 mg threshold of 100 kg).

The MAESTRO-NASH 54-month cardiovascular outcomes cohort (MAESTRO-NASH OUTCOMES, ongoing) will generate long-term safety data that payers may incorporate into future criteria revisions. ClinicalTrials.gov NCT04173065

Specialty Pharmacy Selection and Distribution

Resmetirom is distributed through a limited specialty pharmacy network. As of early 2025, the primary network includes Accredo, CVS Specialty, Walgreens Specialty, and AcariaHealth. Not all commercial plans allow free-choice specialty pharmacy; verify the patient's plan-mandated specialty pharmacy before sending the prescription to avoid claim routing failures.

Key Prescription Routing Steps

1. Send the e-prescription to the RESOLVE hub rather than directly to a retail pharmacy; the hub routes to the correct network pharmacy.
2. Confirm the patient's insurance information is current before submission. Specialty pharmacies run benefits verification independently; discrepancies between the office's BV and the pharmacy's BV are a common delay source.
3. For patients with high deductibles, ask the pharmacy to hold the fill until co-pay assistance enrollment is confirmed.

The AASLD-EASL joint working group noted in 2023 that access barriers to MASH pharmacotherapy "represent a significant public health concern" as the estimated global MASH prevalence reaches 4 to 6% of the adult population. Rinella ME et al., Hepatology 2023

Documentation Checklist Before Submitting a PA Request

The following checklist condenses the requirements above into a pre-submission review. Every item should be verifiable in the chart and in the PA submission packet.

| Documentation Item | Minimum Requirement | |---|---| | MASH diagnosis code | K75.81 as primary | | Fibrosis staging modality | Biopsy, FibroScan, or MRE | | Fibrosis stage result | F2 or F3 (objective value required) | | Date of fibrosis assessment | Within 3 years preferred; within 5 years maximum at most payers | | Lifestyle intervention dates | Start date and end date, with provider name | | Weight outcome from lifestyle program | Recorded in kg or lb | | Metabolic comorbidity management | HbA1c, LDL-C, BMI documented | | Alcohol intake assessment | Dated AUDIT-C or AUDIT score or clinical note | | Absence of decompensated cirrhosis | Documented absence of ascites, encephalopathy, variceal bleed | | Prescriber specialty | Gastroenterology, hepatology, or endocrinology preferred |

Submitting a complete packet on the first attempt reduces the average time-to-approval from 18 to 22 business days to 8 to 12 business days based on early specialty pharmacy hub data from the RESOLVE program's first six months of operation. Madrigal Pharmaceuticals investor report Q3 2024