Hydromethylthionine Mesylate (HMTM) for MCI and Mild-to-Moderate Alzheimer Disease
(2026)Objective
To evaluate efficacy of HMTM (tau aggregation inhibitor) vs low-dose MTC in MCI and mild-to-moderate AD
Study Summary
• HMTM 16mg/day failed its primary endpoint at 52 weeks but showed significant cognitive benefit in MCI patients at 78 and 104 weeks, suggesting delayed tau-targeted treatment effects.
Intervention
HMTM 16mg/day oral vs MTC 4mg twice weekly (sub-therapeutic active comparator)
Inclusion Criteria
MCI due to AD or mild-to-moderate AD dementia (MMSE 14–26)
Study Design
Arms: Array
Patients per Arm: 598 total randomized
Outcome
Primary (ADAS-cog13 at 52 weeks): NS. MCI subgroup at 78 weeks: P=0.0291. At 104 weeks: P=0.0308. Moderate AD subgroup: no benefit.
Bottom Line
HMTM 16mg/day failed its primary endpoint at 52 weeks but showed significant cognitive benefit in MCI patients at 78 and 104 weeks, suggesting delayed tau-targeted treatment effects.
Major Points
- Third Phase 3 trial of methylthioninium derivatives for AD. 598 patients randomized to HMTM 16mg/day vs MTC 4mg twice weekly (sub-therapeutic active comparator).
- Primary endpoint (ADAS-cog13 at 52 weeks) was NOT met — no significant difference in overall population.
- MCI subgroup showed significant benefit at extended timepoints: ADAS-cog13 at 78 weeks (P=0.0291) and 104 weeks (P=0.0308).
- Moderate AD subgroup showed no benefit at any timepoint.
- Delayed separation pattern is biologically plausible for disease-modifying mechanism but could represent chance finding given failed primary.
- GI adverse events and chromaturia (blue-green urine) were more common with HMTM — expected pharmacological effects of methylthioninium.
Study Design
- Study Type
- Randomized, double-blind, active-controlled
- Randomization
- Yes
- Blinding
- Double-blind
- Sample Size
- 598
- Follow-up
- 104 weeks
Primary Outcome
| Control | Intervention | HR/OR | P-value |
|---|---|---|---|
| - | - | - | NS (failed) |
Limitations & Criticisms
- Failed primary endpoint — MCI subgroup finding is post-hoc and hypothesis-generating only
- Active comparator (low-dose MTC) rather than true placebo — any treatment effect may be underestimated or confounded
- Third failed Phase 3 for this drug class raises questions about the overall approach
- Delayed separation pattern (78–104 weeks) could be chance finding or selective attrition bias
- Funded by TauRx with investigator conflicts — independent replication needed
Citation
JPAD. 2026.