Rezdiffra (Resmetirom) for Adolescents Ages 12-17: How to Transition to Adult Care

What Is Resmetirom and Why Does It Matter for Adolescents?

Resmetirom is a thyroid hormone receptor beta (THR-beta) selective agonist that reduces hepatic fat and fibrosis by mimicking thyroid hormone action specifically inside liver cells. The FDA approved it in March 2024 under the brand name Rezdiffra for adult patients with noncirrhotic metabolic dysfunction-associated steatohepatitis (MASH) and fibrosis stages F2 or F3. No adolescent indication has been granted. Still, adolescents with MASH represent a growing clinical concern, and some patients approaching adulthood may encounter this drug either through pediatric trials or through early off-label prescribing.

The Burden of MASH in the 12-17 Age Group

MASH in adolescents is not a rare edge case. The NASH Clinical Research Network reported that among children and adolescents with biopsy-confirmed NAFLD (now termed MASLD), approximately 23% met histologic criteria for NASH (now MASH), with a subset showing bridging fibrosis [1]. Obesity rates in U.S. Adolescents have reached 19.7% according to CDC data from 2017-2020 [2], creating a large upstream population at risk for liver disease progression.

Adolescents with metabolic risk factors, including type 2 diabetes, polycystic ovary syndrome, or severe obesity, can develop clinically significant fibrosis before age 18. Those patients may be the most likely to encounter resmetirom at or near the transition to adult care.

Why the Transition Window Is Clinically Significant

The period between ages 16 and 19 carries the highest dropout rate from subspecialty care for any chronic pediatric disease. A 2018 BMJ review of transition programs across chronic conditions found that up to 50% of young adults lose follow-up contact within two years of leaving pediatric services [3]. For a patient on or being considered for a drug like resmetirom, that gap is medically serious: fibrosis can progress silently, and thyroid-related adverse effects require ongoing laboratory surveillance.

FDA Approval Status: What Clinicians Need to Know Before the Handoff

Resmetirom received accelerated approval on March 14, 2024, based on histologic endpoints from the MAESTRO-NASH trial [4]. The approved indication is strictly adults. The label specifies two weight-based doses: 80 mg once daily for patients weighing <100 kg and 100 mg once daily for patients at or above 100 kg.

What the MAESTRO-NASH Trial Actually Showed

The MAESTRO-NASH trial (N=966) was a phase 3, double-blind, placebo-controlled study. At 52 weeks:

• 25.9% of patients on 80 mg resmetirom achieved MASH resolution without fibrosis worsening vs. 9.7% on placebo (P<0.001) [4]
• 24.2% of patients on 100 mg achieved the same endpoint vs. 9.7% placebo (P<0.001) [4]
• Fibrosis improvement by at least one stage occurred in 25.9% (80 mg) and 29.9% (100 mg) vs. 9.7% placebo [4]

All trial participants were adults. No pharmacokinetic or pharmacodynamic data from the 12-17 age group appear in the published label or supplementary materials.

Off-Label Use in Adolescents

Off-label prescribing of resmetirom in a 12-17-year-old requires a documented clinical rationale. The FDA label does not contain pediatric safety data, and no adolescent-specific dosing has been validated. Clinicians considering this path should consult institutional review processes and obtain written informed consent from both the patient and a parent or legal guardian.

The Endocrine Society's 2023 clinical practice guideline on MASLD management states: "Pharmacotherapy for pediatric MASLD should be limited to clinical trials whenever possible, given the absence of FDA-approved agents for this population" [5].

Transition Planning: Building the Handoff Before Age 17

A successful transition is not a single appointment. It is a process that begins at least 18-24 months before the patient's 18th birthday. For adolescents with MASH who are receiving or being evaluated for resmetirom, the handoff must cover medication status, monitoring schedules, insurance continuity, and provider relationships simultaneously.

The Core Transition Checklist for Resmetirom Patients

The Society of Adolescent Health and Medicine (SAHM) publishes a structured readiness framework that can be adapted for hepatology patients [6]. Applied to a resmetirom or MASH context, the core elements include:

Medication literacy. The patient must be able to name their medication, state the dose, and describe why they take it. Resmetirom's mechanism, a liver-selective thyroid hormone mimic, is worth explaining in plain language.

Self-monitoring skills. The patient should understand which lab values matter: ALT, AST, gamma-glutamyl transferase (GGT), LDL cholesterol, thyroid-stimulating hormone (TSH), and free T4. They should know the monitoring schedule and be able to request results from a patient portal.

Insurance and pharmacy continuity. Rezdiffra carries a list price above $47,000 per year. Adolescents moving off a parent's insurance plan or onto Medicaid at 18 face real access disruptions. The transition plan must include a prior authorization roadmap and contact information for Madrigal's patient assistance program.

Adult provider identified. The adult hepatologist or gastroenterologist who will assume care should be named and introduced, ideally with a shared visit before the formal handoff.

Timing the Handoff

Most pediatric hepatology programs recommend initiating transition conversations at age 14-15 and completing the handoff by the patient's 18th birthday. For patients on active drug therapy, a shared care period of 3-6 months, during which both the pediatric and adult teams communicate directly, reduces the risk of medication errors or lost monitoring.

A practical framework for resmetirom-specific transition has three phases:

Phase 1 (Age 14-16): Preparation. Establish diagnosis documentation, fibrosis staging records, baseline labs, and a medication log. Identify whether the patient is on resmetirom through a trial, off-label prescription, or is simply being evaluated. Enroll the patient in a disease-specific education module.

Phase 2 (Age 16-17): Active Transfer. Identify the adult hepatology team. Schedule a joint visit or warm handoff call. Transfer all imaging (MRI-PDFF, ultrasound, biopsy reports). Confirm pharmacy benefit coverage under the adult insurance plan. Reconcile any other metabolic medications (GLP-1 receptor agonists, statins, metformin).

Phase 3 (Age 17-18): Completion. The adult team assumes primary prescribing responsibility. The pediatric team provides a transition summary letter with fibrosis stage history, adverse event log, and lab trends. The patient attends their first independent adult appointment without a parent in the room as a dry run for autonomous care.

Monitoring Protocol During and After the Transition

Labs Required for Resmetirom Safety Surveillance

The Rezdiffra prescribing information requires baseline and periodic liver function tests [4]. Because thyroid hormone receptor agonism can affect lipid metabolism and thyroid axis feedback, the monitoring panel for adolescent patients should be broader than the adult standard:

| Lab | Frequency During Active Resmetirom Use | |---|---| | ALT / AST | Every 3 months for first year; every 6 months thereafter | | Total bilirubin | Every 3 months | | Serum lipids (LDL, TG, HDL) | Every 3 months | | TSH and free T4 | Every 6 months | | Fasting glucose / HbA1c | Every 3 months if diabetic; every 6 months otherwise | | MRI-PDFF or FibroScan | Annually or per trial protocol | | Weight and BMI | Every clinic visit |

Thyroid panel monitoring deserves special attention in adolescents. The developing thyroid axis may respond differently to THR-beta agonism than an adult's, and any suppression of TSH below 0.5 mIU/L should prompt dose re-evaluation.

Drug Interactions Relevant at Transition Age

Adolescents with MASH frequently carry comorbidities that introduce polypharmacy risk:

• Oral contraceptives. Resmetirom is a moderate inhibitor of CYP2C8 and an inhibitor of certain transporters. Co-administration with ethinylestradiol-containing contraceptives may alter hormone levels. The prescribing information advises caution [4].
• Statins. Resmetirom inhibits OATP1B1 and OATP1B3, raising statin plasma concentrations. Rosuvastatin dose should not exceed 20 mg daily when co-administered [4].
• Metformin. No significant pharmacokinetic interaction is documented, but hepatic impairment monitoring still applies.

At transition, every co-prescribed drug must be reviewed by the adult team against the current Rezdiffra label, since drug interaction data may be updated post-approval.

Communication Between Pediatric and Adult Teams

What the Transition Summary Letter Must Include

A structured transition letter reduces adverse events at handoff. For a patient on or recently evaluated for resmetirom, the letter should include:

• Confirmed fibrosis stage at diagnosis and most recent staging (date and method)
• Duration of resmetirom exposure, if any, including trial participation dates
• All adverse events attributed to resmetirom, even those that resolved
• Current laboratory trends with reference ranges noted
• Outstanding clinical questions or unresolved monitoring flags
• Next scheduled liver imaging date

The American Association for the Study of Liver Diseases (AASLD) 2023 practice guidance on MASH states: "Transition of care documents should include histologic staging data, treatment duration, and a complete adverse event history to allow continuity of benefit-risk assessment by the receiving clinician" [7].

Shared Electronic Health Records

If the pediatric and adult institutions use different EHR systems, the transition summary letter must be printed or PDF-exported and confirmed as received. Verbal confirmation is not sufficient for a patient on a novel therapeutic agent. The pediatric coordinator should follow up within 14 days of the first adult appointment to confirm the patient attended and the records were reviewed.

Special Populations Within the Adolescent Transition Group

Patients With Type 2 Diabetes

Approximately 6% of U.S. Adolescents had either prediabetes or type 2 diabetes in the 2016-2018 NHANES cycle [8]. Resmetirom has shown LDL-lowering effects in adults, but its glycemic impact in adolescents co-treated with metformin or a GLP-1 receptor agonist (such as liraglutide, which carries a pediatric label for obesity) is unstudied. The adult endocrinologist or diabetologist should be looped into the transition plan when diabetes is a comorbidity.

Patients With Severe Obesity (BMI >35)

The MAESTRO-NASH trial enrolled adults with a mean BMI of approximately 35 kg/m2 [4]. Adolescents with class 3 obesity may have faster fibrosis progression and may also be candidates for metabolic bariatric surgery. The transition plan should clarify whether resmetirom would be continued, adjusted, or discontinued if surgical intervention is planned. No data exist on resmetirom pharmacokinetics after bariatric surgery in any age group.

Patients Enrolled in Pediatric Clinical Trials

As of mid-2025, Madrigal Pharmaceuticals has not published results from a dedicated pediatric resmetirom trial. Adolescents enrolled in compassionate use or investigational protocols at academic centers need a specific protocol for trial exit and transition to standard-of-care follow-up. The IRB protocol governing the trial typically dictates the follow-up schedule for the first 12 months after the patient ages out or exits.

Patient and Family Education at Transition

Adolescents transitioning to adult care often feel abandoned by the pediatric team that managed their condition for years. Studies of inflammatory bowel disease transition programs show that structured education before handoff reduces the rate of hospitalization in the first year of adult care by approximately 30% [9].

For a patient on resmetirom, the education session before transition should cover:

• Why the liver matters: a plain-language explanation of fibrosis and why halting it matters long-term
• How resmetirom works: "It acts like a thyroid hormone signal but only inside your liver cells"
• What warning signs require immediate contact with the adult provider: jaundice, right upper quadrant pain, dark urine, or unexplained fatigue
• How to read a lab result: specifically ALT and AST, what the normal range is, and what change would trigger a call
• What to do if they miss a dose: the Rezdiffra label notes no specific dose-adjustment guidance for missed doses; patients should take the next dose at the regular time and not double up [4]

Regulatory Field and What May Change

The FDA's Pediatric Research Equity Act (PREA) requires sponsors to conduct pediatric studies for drugs approved for adult indications unless a waiver or deferral is granted [10]. Madrigal Pharmaceuticals received a partial waiver or deferral status for resmetirom's pediatric studies as part of the 2024 approval package. The FDA Pediatric Study Plan (PSP) for resmetirom, if published, would outline the timeline for any planned trials in the 12-17 age group.

Clinicians treating adolescents with MASH should monitor the FDA's pediatric postmarket study tracker at accessdata.fda.gov and the ClinicalTrials.gov registry for any newly posted pediatric resmetirom protocols. Until a pediatric trial reports, all use in patients under 18 remains off-label by definition.

A Note on Liver Biopsy and Non-Invasive Staging During Transition

Fibrosis staging is the linchpin of any decision about resmetirom. The drug's adult indication requires documented F2 or F3 fibrosis. For adolescents approaching transition, it is reasonable to repeat fibrosis assessment by MRI-PDFF or vibration-controlled transient elastography (VCTE, FibroScan) within 6 months before the formal handoff, so the adult team receives current data.

Liver biopsy, while still the reference standard, carries procedural risk. The AASLD notes that non-invasive tests have sufficient accuracy for monitoring fibrosis change over time in MASH, particularly when baseline biopsy data already exist [7]. For the transition population specifically, a current FibroScan result with a liver stiffness measurement and controlled attenuation parameter (CAP) score is often sufficient to allow the adult team to make an independent benefit-risk assessment without repeating a biopsy.