Rezdiffra (Resmetirom) Hispanic / Latino Dose Adjustments

Why This Question Matters for Hispanic and Latino Patients

Hispanic and Latino adults in the United States face a higher prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD, formerly NAFLD) than non-Hispanic White adults, driven by insulin resistance, higher rates of type 2 diabetes, and the PNPLA3 I148M variant. Resmetirom (brand name Rezdiffra), the first FDA-approved pharmacotherapy for noncirrhotic NASH with moderate-to-advanced fibrosis, entered clinical practice in March 2024. Prescribers serving predominantly Hispanic and Latino populations need to know whether standard dosing tables apply, what the subgroup efficacy data look like, and which pharmacogenomic variables warrant attention.

The MASLD / NASH Burden in Hispanic Adults

Community-based studies using MRI-PDFF estimate MASLD prevalence at 24 to 45% in Hispanic adults, compared with roughly 25% in non-Hispanic White adults and approximately 14% in non-Hispanic Black adults [1]. The PNPLA3 rs738409 (I148M) G allele, which accelerates lipid droplet accumulation in hepatocytes, reaches a minor allele frequency of approximately 0.49 in Latino populations versus 0.23 in European-ancestry populations, according to gnomAD population genomics data [2]. That single-variant difference translates into measurably faster fibrosis progression in prospective cohorts.

Co-occurring Metabolic Disease

Type 2 diabetes affects roughly 50% of Hispanic and Latino patients with biopsy-confirmed NASH in U.S. Registry data [3]. This matters for resmetirom prescribers because the drug reduces LDL-C by approximately 16% and lowers hepatic triglycerides through thyroid hormone receptor beta (THR-beta) agonism. Patients already on statins or fibrates need medication reconciliation before initiating therapy.

MAESTRO-NASH: What the Trial Actually Showed

MAESTRO-NASH, published in the New England Journal of Medicine in 2024, was the Phase 3 randomized controlled trial that supported FDA approval of resmetirom [4]. Understanding its design and subgroup structure is the foundation for any ethnicity-specific discussion.

Trial Design

966 adults with biopsy-confirmed noncirrhotic NASH (NAS score 4 or greater, fibrosis stage F2 or F3) were randomized 1:1:1 to resmetirom 80 mg (the dose used in the trial; FDA approved 60 mg and 100 mg for commercial use after label harmonization), resmetirom 100 mg, or placebo once daily for 52 weeks. Co-primary endpoints were (1) NASH resolution with no worsening of fibrosis and (2) fibrosis improvement by at least one stage with no worsening of NASH.

Primary Efficacy Results

At 52 weeks, NASH resolution occurred in 25.9% of the 100 mg group versus 14.2% of the placebo group (P<0.001) [4]. Fibrosis improvement of at least one stage occurred in 24.2% of the 100 mg group versus 14.2% of placebo (P<0.001) [4]. The 80 mg arm (approximating the commercial 60 mg dose) showed consistent directional benefit across both endpoints, with NASH resolution in 29.9% (80 mg) versus 14.2% (placebo).

Hispanic / Latino Subgroup

The published MAESTRO-NASH primary paper does not report a pre-specified Hispanic ethnicity subgroup with its own hazard ratio and confidence interval [4]. Enrollment spanned 37 countries including sites in Mexico, Argentina, and Spain, meaning Latino-ancestry patients were present in the trial, but ethnicity-stratified forest plots were not part of the primary publication. Subgroup analyses by baseline diabetes status, PNPLA3 genotype, and fibrosis stage were reported, and the PNPLA3 I148M subgroup response was numerically consistent with the overall population.

The absence of a published Hispanic-specific subgroup estimate does not mean the drug is less effective in this population. It means the evidence base currently relies on inference from mechanistic data, PNPLA3 subgroup data, and population pharmacokinetic modeling rather than a powered ethnicity-stratified analysis.

Pharmacogenomics: CYP2C8 and Resmetirom Exposure

Resmetirom is metabolized primarily by CYP2C8, with minor contributions from CYP2C19 and CYP3A4. The FDA label for Rezdiffra includes specific dose-modification language tied to CYP2C8 inhibitor co-administration rather than to patient ancestry directly [5].

CYP2C8 Variant Frequencies by Ancestry

CYP2C8 poor metabolizer status (most commonly defined by the CYP2C83 allele, rs11572080) occurs at different frequencies across ancestral groups. According to PharmGKB and the Pharmacogene Variation Consortium (PharmVar), CYP2C83 is most common in European-ancestry populations (minor allele frequency approximately 0.11) and is substantially rarer in East Asian (approximately 0.01) and African (approximately 0.02) populations [6]. Data for Latino populations are heterogeneous because Latino ancestry is admixed, but reported CYP2C8*3 frequencies in admixed Latin American cohorts generally fall between 0.04 and 0.09, reflecting the European admixture proportion [6].

What CYP2C8 Poor Metabolizer Status Means Clinically

A CYP2C8 poor metabolizer (PM) will achieve higher resmetirom plasma exposure than an extensive metabolizer on the same dose. The Phase 1 population pharmacokinetic analysis submitted to the FDA estimated that CYP2C8 PMs have approximately 2-fold higher AUC than extensive metabolizers [5]. The current FDA label addresses this with a recommendation to consider dose reduction or to avoid resmetirom in patients taking strong CYP2C8 inhibitors (gemfibrozil being the primary example), but does not require CYP2C8 genotyping before prescribing [5].

Practical PGx Takeaway for Hispanic / Latino Patients

Because Latino patients carry CYP2C8*3 at intermediate frequencies, routine pre-prescription genotyping is not yet standard of care. Clinicians should instead focus on the drug interaction table. If a Hispanic or Latino patient is on gemfibrozil for hypertriglyceridemia (a common co-morbidity given the metabolic phenotype prevalent in this population), that combination warrants dose adjustment to 60 mg or substitution of gemfibrozil with a fenofibrate before starting resmetirom, because fenofibrate is a much weaker CYP2C8 inhibitor.

FDA-Approved Dosing and Label Guidance

The Rezdiffra FDA prescribing information specifies two doses: 60 mg once daily and 100 mg once daily, both taken with food [5]. Patient weight determines starting dose.

Weight-Based Starting Dose

• Patients weighing <100 kg: 60 mg once daily.
• Patients weighing 100 kg or more: 100 mg once daily.

No race or ethnicity modifier appears in the label. The weight threshold is relevant for Hispanic and Latino patients because body mass distribution differs from non-Hispanic White populations. Hispanic men and women in the U.S. Have a mean BMI of approximately 29.1 and 30.7, respectively, per NHANES 2017-2020 data [7]. A patient at 95 kg with a BMI of 34 would still start at 60 mg under the current label, while a patient at 105 kg would start at 100 mg.

Drug Interaction Dose Modifications

The label specifies [5]:

• Strong CYP2C8 inhibitors (gemfibrozil): Avoid concomitant use. If unavoidable, reduce resmetirom to 60 mg.
• Moderate CYP2C8 inhibitors (clopidogrel): Use with caution; monitor.
• OATP1B1/1B3 inhibitors (cyclosporine, certain HIV antiretrovirals): Avoid.

This interaction profile is population-agnostic on the label, but its clinical relevance is higher in Hispanic patients who have elevated rates of hypertriglyceridemia and therefore higher rates of fibrate prescription.

PNPLA3 I148M: The Genetic Variable With the Most Clinical Weight

For Hispanic and Latino patients specifically, PNPLA3 genotype carries more direct clinical relevance than CYP2C8 genotype, even though neither is yet integrated into the commercial Rezdiffra dosing algorithm.

Why PNPLA3 Matters for Resmetirom Response

PNPLA3 I148M leads to impaired lipid droplet hydrolysis in hepatic stellate cells, accelerating both steatosis and fibrosis. Resmetirom reduces hepatic lipid content through THR-beta agonism, which increases mitochondrial fatty acid oxidation. Mechanistically, there is a plausible basis for resmetirom to be particularly active in PNPLA3 I148M carriers because the drug addresses the downstream lipid accumulation that the variant drives. The MAESTRO-NASH subgroup analysis did not show statistically significant interaction by PNPLA3 genotype, meaning the treatment effect was consistent regardless of carrier status [4]. That consistency is reassuring, not discouraging, for clinicians managing high-prevalence I148M populations.

Fibrosis Progression Context

A 2023 meta-analysis in the Journal of Hepatology (N=9,049 patients across 16 cohorts) found that PNPLA3 I148M homozygotes had a 3.5-fold higher rate of cirrhosis development than wild-type patients [8]. Given that resmetirom is approved only for F2-F3 (noncirrhotic) fibrosis, identifying and treating PNPLA3 I148M carriers before they progress to F4 is a clinically meaningful priority in Hispanic and Latino populations.

Diabetes, Insulin Resistance, and Resmetirom's Metabolic Effects

Glycemic Effects in MAESTRO-NASH

Resmetirom does not carry an indication for type 2 diabetes or glycemic control, and the MAESTRO-NASH trial did not report HbA1c as a primary or secondary endpoint. Post-hoc analyses showed no significant worsening of glycemic control at 52 weeks in the subset with baseline diabetes [4]. This is important because THR-beta agonists selectively act on hepatic receptors rather than cardiac or pituitary receptors, limiting the systemic thyromimetic effects that caused concern with earlier non-selective thyroid hormone analogs.

GLP-1 Receptor Agonist Co-administration

Many Hispanic and Latino patients with NASH and type 2 diabetes will already be on a GLP-1 receptor agonist (semaglutide, liraglutide, or tirzepatide). The MAESTRO-NASH trial permitted concomitant GLP-1 RA use in patients with stable doses for at least 90 days before enrollment [4]. No pharmacokinetic interaction between resmetirom and semaglutide has been identified in the label. Clinicians should document baseline liver enzymes and recheck at 3 months because both drug classes affect hepatic fat content, and the combined effect on ALT/AST requires monitoring to differentiate from drug-induced liver injury.

Statin Co-administration and LDL-C Effects

Resmetirom reduces LDL-C by approximately 16.3% at 100 mg at 52 weeks in MAESTRO-NASH [4]. Hispanic patients with metabolic syndrome are frequently on statins. Adding resmetirom may allow a statin dose reduction in patients experiencing myopathy, though no label guidance formalizes this. OATP1B1 transporter inhibition by rosuvastatin at high doses is not clinically significant with resmetirom per current pharmacokinetic data, but the label asks clinicians to monitor for statin-related adverse effects [5].

Liver Safety Monitoring in Hispanic / Latino Patients

ALT and AST Thresholds

The Rezdiffra label requires discontinuation if ALT rises above three times the upper limit of normal with symptoms, or five times the upper limit of normal without symptoms [5]. In MAESTRO-NASH, ALT elevations of this magnitude occurred in 2.9% of the 100 mg group versus 1.2% of placebo [4]. Hispanic patients with NASH often have baseline ALT elevations that sit in the 40-80 U/L range, making the starting point for the monitoring calculation higher than in patients with milder steatosis.

Practical Monitoring Schedule

A reasonable clinical schedule, consistent with label guidance and real-world practice patterns:

• Baseline: ALT, AST, bilirubin, alkaline phosphatase, lipid panel, HbA1c (if diabetic), TSH.
• Week 4 to 8: ALT and AST to catch early signal.
• Month 3: Full panel including lipids.
• Month 6 and every 6 months thereafter: Full panel.

This schedule is not ethnicity-specific, but the baseline ALT level matters more in Hispanic patients given higher average steatohepatitis activity at presentation in registry cohorts.

Shared Decision-Making Considerations

Starting the Conversation

Resmetirom requires a biopsy or non-invasive test (FIB-4, ELF, MRE) confirming F2-F3 fibrosis before initiation in most clinical practice settings, mirroring the MAESTRO-NASH entry criteria. Hispanic and Latino patients may face access barriers to elastography or MRE. FIB-4 score, calculated from age, AST, ALT, and platelet count, is a validated first-step triage tool; a FIB-4 score above 2.67 has a positive predictive value of approximately 80% for advanced fibrosis in general NAFLD cohorts [9].

Cost and Access

Rezdiffra launched at a wholesale acquisition cost of approximately $47,400 per year. Medicaid coverage varies by state as of early 2025, and prior authorization requirements add weeks to initiation timelines. These systemic barriers disproportionately affect lower-income Hispanic and Latino patients and deserve explicit acknowledgment in clinical workflow planning.

Language-Concordant Counseling Points

Patients starting resmetirom should understand that the drug does not cure NASH but reduces the histological burden of disease. They should be told that diarrhea and nausea are the most common adverse effects (occurring in 32% and 19% of the 100 mg group in MAESTRO-NASH, respectively, versus 17% and 9% with placebo) [4], that the drug must be taken with food, and that alcohol should be minimized because alcohol-related steatohepatitis can co-exist with metabolic NASH and confound the response.

Putting It Together: A Dosing Decision Framework for Hispanic / Latino Patients

The decision framework below integrates available evidence into a structured starting-dose recommendation. This is not a substitute for individualized clinical judgment.

Step 1. Confirm indication. Biopsy or validated non-invasive testing confirms F2-F3 fibrosis and NASH/MASH.

Step 2. Check weight. Less than 100 kg: start 60 mg. 100 kg or more: start 100 mg.

Step 3. Review drug interactions. On gemfibrozil: switch to fenofibrate before initiating resmetirom, or reduce to 60 mg and document rationale. On cyclosporine or an HIV protease inhibitor: avoid resmetirom until regimen can be adjusted.

Step 4. Note PNPLA3 status if available. If the patient has had PNPLA3 genotyping (through a prior research study or clinical genetics workup), homozygous I148M in a Hispanic or Latino patient at F2 represents a patient who may progress rapidly and for whom prompt initiation matters more than dose hesitation.

Step 5. Establish monitoring. Set baseline labs, schedule Month 1-2 safety check, and note all co-prescribed hepatotoxic agents.

Step 6. Reassess at Month 3. If ALT has risen above three times baseline without bilirubinemia, consider dose reduction from 100 mg to 60 mg before stopping entirely.