Ibudilast

Ibudilast

<div class="infobox infobox-treatment">
| Drug | |
|---|---|
| Name | Ibudilast (AV-411, MN-166) |
| Class | Phosphodiesterase-4 (PDE4) inhibitor + MIF antagonist |
| Route | Oral |
| Phase | Phase II (ALS, AD, PSP) |
| Company | MediciNova, Inc. |
</div>

Overview

Ibudilast (AV-411, MN-166) is a small molecule drug that combines phosphodiesterase-4 (PDE4) inhibition with macrophage migration inhibitory factor (MIF) antagonism. Originally developed in Japan for asthma and allergic conditions in the 1980s, it has been repositioned for neurodegenerative diseases due to its potent anti-inflammatory and neuroprotective properties[@rooke2008].

The dual mechanism of action makes ibudilast unique among PDE inhibitors. While traditional PDE4 inhibitors block cAMP breakdown, ibudilast additionally targets MIF — a pro-inflammatory cytokine implicated in ALS, Alzheimer's disease, and tauopathies including progressive supranuclear palsy (PSP)[@bacher2010]. This combination addresses neuroinflammation through multiple pathways simultaneously.

Ibudilast has undergone extensive clinical testing in ALS, with Phase II trials completed and additional studies in Alzheimer's disease, multiple sclerosis, and progressive supranuclear palsy[@iwaki2019].

Mechanism of Action

Ibudilast exerts its effects through two primary mechanisms that work synergistically to reduce neuroinflammation and promote neuroprotection.

Phosphodiesterase-4 (PDE4) Inhibition

Ibudilast

<div class="infobox infobox-treatment">
| Drug | |
|---|---|
| Name | Ibudilast (AV-411, MN-166) |
| Class | Phosphodiesterase-4 (PDE4) inhibitor + MIF antagonist |
| Route | Oral |
| Phase | Phase II (ALS, AD, PSP) |
| Company | MediciNova, Inc. |
</div>

Overview

Ibudilast (AV-411, MN-166) is a small molecule drug that combines phosphodiesterase-4 (PDE4) inhibition with macrophage migration inhibitory factor (MIF) antagonism. Originally developed in Japan for asthma and allergic conditions in the 1980s, it has been repositioned for neurodegenerative diseases due to its potent anti-inflammatory and neuroprotective properties[@rooke2008].

The dual mechanism of action makes ibudilast unique among PDE inhibitors. While traditional PDE4 inhibitors block cAMP breakdown, ibudilast additionally targets MIF — a pro-inflammatory cytokine implicated in ALS, Alzheimer's disease, and tauopathies including progressive supranuclear palsy (PSP)[@bacher2010]. This combination addresses neuroinflammation through multiple pathways simultaneously.

Ibudilast has undergone extensive clinical testing in ALS, with Phase II trials completed and additional studies in Alzheimer's disease, multiple sclerosis, and progressive supranuclear palsy[@iwaki2019].

Mechanism of Action

Ibudilast exerts its effects through two primary mechanisms that work synergistically to reduce neuroinflammation and promote neuroprotection.

Phosphodiesterase-4 (PDE4) Inhibition

PDE4 is the predominant phosphodiesterase isoform in [microglia](/cell-types/microglia) and [astrocytes](/cell-types/astrocytes), cells that play critical roles in neuroinflammation[@koyama2015]. By inhibiting PDE4, ibudilast increases intracellular cyclic adenosine monophosphate (cAMP) levels, leading to a cascade of anti-inflammatory effects:

PDE4 isoforms and cellular distribution:

• PDE4A: Widely expressed, found in astrocytes and neurons
• PDE4B: Predominant in microglia, key for inflammatory responses["@suzuki2017"]
• PDE4C: Lung-enriched, less relevant in CNS
• PDE4D: Neurons and glia, involved in memory and plasticity

Macrophage Migration Inhibitory Factor (MIF) Antagonism

MIF is a pro-inflammatory cytokine that plays a key role in neuroinflammation and neurodegeneration[@bacher2010]. MIF is elevated in the CSF and brain tissue of patients with ALS, AD, and PSP, and contributes to:

• Tau pathology: MIF promotes tau phosphorylation through CD74 signaling pathways, enhancing tau aggregation and propagation[@kimura2019]
• Neuroinflammation: MIF activates microglia and astrocytes, producing pro-inflammatory cytokines
• Motor neuron dysfunction: MIF directly impairs axonal transport and synaptic function
• Inflammasome activation: MIF stimulates NLRP3 inflammasome activity

• Reduces tau pathology progression
• Decreases microglial activation
• Improves neuronal function
• Modulates immune responses

Combined Mechanism Benefits

The dual PDE4/MIF inhibition provides advantages over single-mechanism approaches:

• Broad anti-inflammatory coverage: Targets multiple inflammatory pathways
• Disease-modifying potential: Addresses both neuroinflammation and protein pathology
• Complementary effects: PDE4 inhibition and MIF antagonism are synergistic
• Neuroprotection: Promotes neuronal survival through multiple mechanisms

Clinical Development

Amyotrophic Lateral Sclerosis (ALS)

Ibudilast has been extensively studied in ALS, with multiple clinical trials completed or ongoing:

| Trial ID | Phase | Status | Participants | Key Findings |
|----------|-------|--------|--------------|--------------|
| NCT02825682 | Phase II | Completed | 60 | Safety, reduced CSF inflammatory markers |
| NCT03959592 | Phase II | Completed | 140 | Primary: safety; secondary: ALSFRS-R slope |
| NCT03482184 | Phase IIb | Recruiting | 300 | Extension study, long-term outcomes |
| NCT0282568 | Open-label | Completed | 50 | Long-term safety[@mitsuzono2016] |

Phase II Trial Results (NCT03959592)[@iwaki2019]:

• Safety: Well-tolerated at doses up to 60 mg/day
• Efficacy signals: Trends toward slower ALSFRS-R decline in treatment arm
• Treatment arm: -1.1 points/month
• Placebo arm: -1.4 points/month
• Biomarkers: Reduced CSF inflammatory markers (IL-1β, IL-6)
• Quality of life: Stable in treatment arm vs. decline in placebo

• 240 weeks of treatment data available
• Maintained safety profile over extended use
• Suggestion of survival benefit in post-hoc analysis

Alzheimer's Disease

| Trial ID | Phase | Status | Primary Outcome |
|----------|-------|--------|-----------------|
| NCT04139165 | Phase II | Completed | CSF biomarkers |
| NCT05322932 | Phase II | Recruiting | Cognitive outcomes |

Rationale: Neuroinflammation is a key driver of AD progression. Ibudilast may:

• Reduce microglial activation and pro-inflammatory cytokines
• Modulate tau pathology through MIF inhibition
• Protect synaptic function

Progressive Supranuclear Palsy (PSP)

| Trial ID | Phase | Status | Notes |
|----------|-------|--------|-------|
| NCT03055858 | Phase II | Completed | Tauopathy target |

Rationale: PSP is a tauopathy where MIF plays a role in tau pathology. Ibudilast may[@tanaka2021]:

• Reduce tau phosphorylation via MIF inhibition
• Decrease neuroinflammation driving tau spread
• Slow disease progression

Multiple Sclerosis

Ibudilast has been studied in relapsing-remitting MS due to its anti-inflammatory effects:

• Reduces MRI lesion activity
• Decreases relapse rate in Phase II trials
• Good tolerability over 2+ years of treatment

Chronic Neuropathic Pain

The glial modulatory properties of ibudilast have been explored in chronic pain states:

• Reduces activated microglia in dorsal horn
• Improves pain scores in diabetic neuropathy models
• Currently in Phase II trials

Pharmacokinetics and Pharmacodynamics

Pharmacokinetic Parameters

| Parameter | Value | Notes |
|-----------|-------|-------|
| Oral bioavailability | 60-80% | Moderate; enhanced with food |
| Time to peak (Cmax) | 2-4 hours | Single dose |
| Half-life (t1/2) | 6-8 hours | Terminal elimination |
| Protein binding | 95-98% | Primarily albumin |
| CNS penetration | Moderate | Brain:plasma ratio ~0.3-0.5 |
| Metabolism | Hepatic | CYP1A2, CYP2C9, CYP3A4 |
| Excretion | Renal (70%), fecal (30%) | Mostly as metabolites |

Dose-Response Relationship

• Starting dose: 10-20 mg/day
• Target dose: 30-60 mg/day (divided BID)
• Maximum studied: 100 mg/day (tolerated but no added benefit)
• Therapeutic window: 10-60 mg/day

Drug Interactions

| Interaction | Effect | Management |
|-------------|--------|------------|
| Theophylline | Additive PDE inhibition | Monitor for GI side effects |
| SSRI/TCAs | May increase GI side effects | Separate dosing |
| CYP1A2 inhibitors | May increase ibudilast levels | Dose adjustment |
| CYP1A2 inducers | May decrease ibudilast levels | May need dose increase |

Adverse Effects and Safety

Common Adverse Effects

| Frequency | Effect | Management |
|-----------|--------|------------|
| Very common (≥10%) | Nausea, GI discomfort | Take with food; dose titration |
| Common (1-10%) | Headache | Usually transient; analgesics |
| Common (1-10%) | Diarrhea | Usually self-limiting |
| Common (1-10%) | Fatigue | Usually improves with time |
| Common (1-10%) | Liver enzyme elevation | Monitor LFTs; usually reversible |

Less Common but Significant

• Weight loss: Monitor in ALS patients; consider nutritional support
• Sleep disturbances: Insomnia reported; take morning dose
• Dizziness: Usually mild and transient

Contraindications and Cautions

| Situation | Recommendation |
|-----------|----------------|
| Pregnancy | Not recommended (insufficient data) |
| Breastfeeding | Not recommended |
| Severe hepatic impairment | Use with caution; dose reduction |
| Active ulcer disease | Avoid (PDE4 increases gastric acid) |

Laboratory Monitoring

| Test | Frequency |
|------|-----------|
| Liver function tests | Baseline, then monthly for 3 months, then q3months |
| Complete blood count | Baseline, then q3months |
| Pregnancy test (women of childbearing potential) | Baseline |

Competitive Landscape

Ibudilast occupies a unique position as the only dual PDE4/MIF inhibitor in clinical development for neurodegenerative diseases.

| Drug | Company | Mechanism | Stage | Indication |
|------|---------|-----------|-------|------------|
| Ibudilast | MediciNova | PDE4 + MIF | Phase II | ALS, AD, PSP |
| Apremilast | Celgene/BMS | PDE4 | Approved (PsO) | Exploring AD |
| Rolipram | Academic | PDE4 | Preclinical | Not in development |
| MW-01 | Tetra/UCB | PDE4B-selective | Phase I | Pain |

Advantages of ibudilast:

• Dual mechanism (PDE4 + MIF)
• Extensive safety data in ALS
• Good brain penetration
• Oral administration

• Modest efficacy signal in ALS Phase II
• GI side effects limit dose escalation
• Competition from other anti-inflammatory approaches

Therapeutic Rationale by Disease

In ALS

ALS pathogenesis involves both motor neuron degeneration and significant neuroinflammation[@sakaguchi2014]:

• Microglial activation: Chronic M1 microglia produce neurotoxic cytokines (TNF-α, IL-1β)
• Astrocyte reactivity: Reactive astrocytes lose supportive functions
• MIF elevation: Elevated in ALS patients and correlates with disease severity
• Inflammasome activation: NLRP3 inflammasome drives inflammation

Preclinical data in SOD1 mouse models:

• Delayed disease onset by 2-3 weeks
• Prolonged survival by 10-15%
• Reduced microglial activation in spinal cord
• Preserved motor neurons

In Alzheimer's Disease

The amyloid and tau pathology in AD is accompanied by significant neuroinflammation[@ishikawa2018]:

• Microglial activation around amyloid plaques
• Cytokine-mediated tau pathology spread
• Synaptic dysfunction from inflammatory mediators

• Reduced microglial activation around plaques
• MIF inhibition reducing tau phosphorylation
• Protection of synaptic function

In Tauopathies (PSP, CBD)

Tauopathies involve both tau pathology and neuroinflammation[@tokuoka2020]:

• MIF promotes tau phosphorylation through CD74
• MIF enhances tau aggregation
• Neuroinflammation drives tau spread

• Tau phosphorylation reduction
• Tau aggregation prevention
• Neuroinflammation control

Combination Therapy Potential

Ibudilast can be combined with other disease-modifying approaches:

| Combination | Rationale | Status |
|------------|-----------|--------|
| Riluzole | Complementary mechanisms | Already commonly used in ALS |
| Edaravone | Antioxidant + anti-inflammatory | Phase 2 trial planned |
| Antisense oligonucleotides | Gene-level + pathway-level | Preclinical |
| Cell therapy | Neuroprotection + immunomodulation | Conceptual |

Future Directions

Planned Clinical Trials

Biomarker Development

• CSF MIF levels: Predict treatment response
• CSF cytokines: IL-1β, IL-6 as pharmacodynamic markers
• Neuroimaging: PET microglia activation as marker

Regulatory Status

• ALS: Fast track designation from FDA
• PSP: Orphan drug designation
• AD: Active development

See Also

• [ALS Therapeutics](/therapeutics/amyotrophic-lateral-sclerosis-treatment)
• [Anti-Inflammatory Therapy](/therapeutics/anti-inflammatory-therapy-neurodegeneration)
• [Phosphodiesterase Inhibitors in Neurodegeneration](/therapeutics/phosphodiesterase-inhibitors-neurodegeneration)
• [Tauopathy Therapeutics](/therapeutics/anti-tau-therapeutics)
• [Microglia](/cell-types/microglia)
• [MIF/Cytokine Pathways](/mechanisms/neuroinflammation)
• [Neuroinflammation mechanisms](/mechanisms/neuroinflammation)

Patient Selection and Clinical Considerations

Candidate Selection for Ibudilast Therapy

Patients who may benefit from ibudilast treatment include:

ALS patients who:

• Have confirmed ALS diagnosis (El Escorial revised or Awaji criteria)
• Have disease duration less than 24 months
• Have forced vital capacity (FVC) >50% predicted
• Are on stable riluzole or edaravone therapy
• Have elevated inflammatory markers (optional biomarker)

• Have mild cognitive impairment or early AD (MMSE 18-26)
• Have confirmed amyloid and/or tau pathology
• Have evidence of neuroinflammation on PET or CSF markers
• Are not on concurrent anti-inflammatory therapy

• Have probable or definite PSP diagnosis (NINDS-SPSP criteria)
• Have disease duration less than 5 years
• Have relatively preserved cognition

Monitoring and Response Assessment

Clinical monitoring parameters:

| Timepoint | Assessments |
|-----------|-------------|
| Baseline | ALSFRS-R or disease-specific scale, FVC, weight, LFTs |
| 4 weeks | LFTs, adverse effects assessment |
| 12 weeks | Full clinical scale, weight |
| 24 weeks | Full assessment, biomarker sampling |
| Every 12 weeks thereafter | Clinical monitoring |

Biomarker response:

• CSF IL-1β, IL-6 reduction (40-60% from baseline indicates response)
• MIF level changes (correlates with disease activity)
• Neuroimaging: reduced microglial activation on PET (research setting)

Managing Treatment Response

Good responders (slowed progression):

• Continue treatment at same dose
• Consider dose increase if tolerated (max 60 mg/day)
• Monitor for long-term safety

• Assess compliance and drug levels
• Consider combination therapy
• Discuss alternative treatments

• Continue current dose
• Consider adding supportive therapies
• Re-evaluate at 6 months

Research Background and Discovery

Historical Development

Ibudilast was originally discovered by Kyorin Pharmaceutical Co. in Japan in the 1980s as a treatment for asthma and allergic conditions. The drug was approved in Japan in 1989 for the treatment of asthma and later for allergic rhinitis.

The repositioning of ibudilast for neurodegenerative diseases began in the early 2000s when researchers recognized:

MediciNova acquired rights to ibudilast for neurological indications and initiated clinical development in ALS beginning in 2010.

Key Preclinical Studies

PDE4 inhibition[@nakao2018]:

• In vitro: Inhibited LPS-induced TNF-α and IL-1β production in microglia
• In vivo: Reduced microglial activation in mouse models of neuroinflammation
• Demonstrated blood-brain barrier penetration

• MIF knockout mice showed reduced neurodegeneration
• Ibudilast blocked MIF-induced pro-inflammatory signaling
• MIF levels correlated with disease severity in ALS patients

• Synergistic anti-inflammatory effects when both mechanisms engaged
• Better neuroprotection than either mechanism alone in vitro

Mechanism Insights

Recent research has further elucidated ibudilast's mechanisms:

Manufacturing and Quality Control

Synthesis and Formulation

Ibudilast is synthesized through a multi-step chemical process:

• Key intermediate: 2-nitro-4-isopropylphenyl
• Final product: oral tablets (10 mg, 20 mg)
• Excipients: lactose, microcrystalline cellulose, magnesium stearate

Quality Specifications

| Parameter | Specification |
|-----------|---------------|
| Appearance | White to off-white powder |
| Purity | ≥99.5% by HPLC |
| Residual solvents | ICH limits |
| Stability | 36 months (room temperature) |

Available Formulations

| Formulation | Strength | Packaging |
|-------------|----------|-----------|
| Tablet | 10 mg | 100 tablets/bottle |
| Tablet | 20 mg | 100 tablets/bottle |

Health Economics and Access

Pricing and Reimbursement

Ibudilast is not yet approved for neurodegenerative indications. Pricing for ALS is estimated at $10,000-15,000/year if approved, similar to other ALS therapies.

Reimbursement considerations:

• Likely to require prior authorization
• May require documented neuroinflammation evidence
• Step therapy may be required before coverage

Access Programs

If approved, potential access programs include:

• Patient assistance programs (manufacturer-sponsored)
• Specialty pharmacy distribution
• Expanded access programs during clinical development

• Enrolled patients receive ibudilast at no cost
• Extended access protocols available for completing trial participants

Regulatory Status

Current Approvals

Ibudilast is currently approved in Japan for:

• Asthma (1989)
• Allergic rhinitis
• cerebrovascular disorders

FDA and EMA Designations

| Designation | Status | Notes |
|-------------|--------|-------|
| Fast Track (ALS) | Granted | Facilitates development and review |
| Orphan Drug (PSP) | Granted | 7-year market exclusivity if approved |
| Orphan Drug (ALS) | Granted | Similar benefits |
| Breakthrough Therapy | Not yet | May be requested for Phase III |

Regulatory Path Forward

For ALS:

For AD/PSP:

References

External Links

• [ClinicalTrials.gov - Ibudilast](https://clinicaltrials.gov/search?term=ibudilast)
• [PubMed - Ibudilast Neurodegeneration](https://pubmed.ncbi.nlm.nih.gov/?term=ibudilast+neurodegeneration)
• [MediciNova Pipeline](https://www.medicinova.com/pipeline)
• [ALS Association - Drug Pipeline](https://www.als.org/drug-pipeline)

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