# Compound Dive: Riluzole (CHEMBL1201585)

**Generic name:** Riluzole  
**Brand name:** Rilutek®  
**IUPAC name:** 6-(trifluoromethoxy)-1,3-benzothiazol-2-amine  
**Molecular formula:** C₈H₅F₃N₂OS  
**PubChem CID:** 5070  
**Date of analysis:** 2026-05-04  

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## Summary

Riluzole is a benzothiazole derivative approved for amyotrophic lateral sclerosis (ALS) and under investigation for spinal cord injury (SCI), traumatic brain injury (TBI), and other neurodegenerative conditions. Its neuroprotective effects are attributed primarily to modulation of glutamatergic neurotransmission and inhibition of voltage-gated sodium channels. Below is a structured analysis of its mechanism, CNS-relevant physicochemical properties, drug–drug interaction liabilities, and dosing evidence.

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## (a) Mechanism of Action and Binding Partners

### Primary Pharmacology

Riluzole is a **multimodal neuroprotective agent** with two principal, interrelated mechanisms:

1. **Inhibition of presynaptic glutamate release**  
   Riluzole reduces synaptic glutamate release through use-dependent blockade of voltage-gated sodium channels (VGSCs) on presynaptic terminals. By limiting sodium influx and consequently reducing membrane depolarization, it attenuates calcium-dependent vesicular glutamate release. This diminishes excitotoxic signaling, a key driver of motor neuron death in ALS and secondary injury in SCI/TBI.

2. **Blockade of voltage-gated sodium channels (VGSCs)**  
   Riluzole is a **use-dependent sodium channel blocker** that preferentially binds to the inactivated state of neuronal VGSCs (including Nav1.5 and related neuronal isoforms). This stabilizes the inactivated state, reduces repetitive neuronal firing, and lowers cellular energy demand.

### Secondary / Ancillary Mechanisms (Preclinical Evidence)

- **NMDA receptor antagonism:** In preclinical studies, riluzole non-competitively antagonizes NMDA receptor-mediated currents at high concentrations, though this is considered a secondary effect relative to presynaptic glutamate release inhibition.
- **Enhancement of glutamate reuptake:** Preclinical data suggest riluzole may upregulate activity of excitatory amino acid transporters (EAATs/GLT-1, encoded by *SLC1A2*), facilitating clearance of extracellular glutamate from the synaptic cleft.
- **GABAergic modulation:** Weak positive modulation of GABA-A receptors has been reported in some in vitro systems.
- **Potassium channel effects:** At higher concentrations, blockade of certain potassium channels (e.g., Kv7/KCNQ) has been observed in preclinical models and is being explored for KCNT2-related epilepsy.

### Key Binding Partners / Targets

| Target | Gene | Role in Mechanism | Evidence Level |
|--------|------|-------------------|----------------|
| Voltage-gated sodium channel α-subunit | *SCN5A* (Nav1.5), neuronal Navs | Primary: use-dependent blockade reducing glutamate release | **Clinical + Preclinical** |
| NMDA receptor subunit 1 | *GRIN1* (GluN1) | Secondary: non-competitive NMDAR antagonism | Preclinical |
| NMDA receptor subunit 2A | *GRIN2A* (GluN2A) | Secondary: modulation of NMDAR signaling | Preclinical |
| NMDA receptor subunit 2B | *GRIN2B* (GluN2B) | Secondary: modulation of NMDAR signaling | Preclinical |
| Excitatory amino acid transporter 2 (EAAT2/GLT-1) | *SLC1A2* | Tertiary: enhanced glutamate reuptake | Preclinical |

### Evidence Attribution for Mechanism

- **Preclinical (in vitro / animal):** Sodium channel blockade, glutamate release inhibition, NMDAR antagonism, EAAT upregulation. Extensive literature in rodent ALS models, spinal cord injury, and primary neuron cultures.
- **Clinical trial:** The ALS pivotal trials (Bensimon et al., 1994; Lacomblez et al., 1996) demonstrated a modest survival benefit and delayed need for tracheostomy/ventilation. The mechanism is inferred from preclinical pharmacology and biomarker studies; direct target engagement in human CNS tissue is not readily measurable.
- **Observational:** Real-world ALS cohorts confirm a consistent ~3–6 month survival benefit when initiated early.

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## (b) Physicochemical Properties Relevant to CNS Penetration

### Calculated Properties (PubChem)

| Property | Value | Notes |
|----------|-------|-------|
| Molecular weight | **234.2 Da** | Well below the BBB permeability threshold (~400–500 Da) |
| XLogP | **3.6** | Moderate lipophilicity, favorable for passive BBB diffusion |
| Topological polar surface area (TPSA) | **76.4 Ų** | Slightly above the ideal < 60–70 Ų for high BBB permeability, but still acceptable |
| Hydrogen bond donors (HBD) | **1** | Low HBD count favors passive diffusion |
| Hydrogen bond acceptors (HBA) | **7** | Higher HBA but offset by low HBD and moderate MW |
| Rotatable bonds | **1** | Very rigid structure; high rigidity correlates with better BBB penetration |
| Complexity | 238 | Moderate |
| Charge at pH 7.4 | Neutral (0) | Uncharged at physiological pH, favorable for lipid-mediated BBB crossing |

### Lipinski Analysis

Riluzole **passes all four Lipinski criteria** (MW ≤ 500, logP ≤ 5, HBD ≤ 5, HBA ≤ 10), confirming drug-like oral bioavailability. Importantly:

- It is **NOT an ionic compound**, so logP is well-defined and meaningful for BBB prediction.
- Its **low molecular weight, neutral charge, and moderate lipophilicity** are consistent with efficient blood–brain barrier (BBB) penetration.

### CNS Penetration Evidence

- **Preclinical:** Rodent studies confirm brain-to-plasma ratios of approximately **1.0–2.5**, indicating good CNS penetration. Intranasal nanoformulations achieve even higher direct transport percentages (DTP ~56%) and drug targeting efficiencies (DTE ~229%) in animal models.
- **Clinical:** Human pharmacokinetic data and the therapeutic efficacy in CNS diseases (ALS, SCI) indirectly confirm that riluzole achieves pharmacologically relevant concentrations in brain tissue and CSF. However, comprehensive published human CSF/plasma ratio data from large trials are limited in the accessible literature.

### CNS Penetration Assessment

| Criterion | Riluzole Profile | Verdict |
|-----------|------------------|---------|
| MW < 400 | 234.2 | ✅ Favorable |
| LogP 1–4 | 3.6 | ✅ Favorable |
| TPSA < 90 | 76.4 | ✅ Acceptable |
| HBD ≤ 2 | 1 | ✅ Favorable |
| Neutral charge | Yes | ✅ Favorable |
| **Overall CNS penetrant probability** | — | **High** |

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## (c) Drug–Drug Interactions with Commonly Co-Prescribed Agents

### Metabolic Pathway

Riluzole undergoes extensive hepatic metabolism. Historically, CYP1A2 was considered the major enzyme. However, a **2025 physiologically based pharmacokinetic (PBPK) modeling investigation** (Malik et al., *Clinical and Translational Science*, PMID 40958536) re-evaluated this and proposed updated fractional contributions:

| Enzyme | Estimated Contribution | Notes |
|--------|------------------------|-------|
| **CYP1A1** | ~60% | Extrahepatic expression (lung, intestine) also relevant; historically underestimated |
| **CYP1A2** | ~30% | Hepatic; major historical focus |
| **UGT1A8/UGT1A9** | ~10% | Glucuronidation pathways |

**Evidence type:** This updated fractionation is derived from **PBPK modeling calibrated on single-dose PK data and verified by predicting observed drug–drug interactions (e.g., riluzole + fluvoxamine) and special populations (ALS, SMA, hepatic impairment, advanced age)**. The authors note that formal clinical DDI studies are still needed to confirm.

### Clinically Relevant Interactions

#### 1. CYP1A Inhibitors ⚠️

| Co-agent | CYP Effect | Clinical Impact | Evidence |
|----------|-----------|-----------------|----------|
| **Fluvoxamine** | Strong CYP1A2 inhibitor; weak CYP1A1 inhibitor | ↑ Riluzole plasma concentrations; risk of toxicity (hepatotoxicity, GI effects) | PBPK-verified DDI prediction (Malik et al., 2025); pediatric OCD study cited |
| **Ciprofloxacin** | Strong CYP1A2 inhibitor | Potential ↑ riluzole levels | Inferred from CYP mechanism; label warning |
| **Theophylline** / other CYP1A2 substrates | Competitive inhibition | Potential ↑ riluzole levels | Theoretical / mechanistic |
| **Amiodarone** | CYP1A inhibitor | Potential ↑ riluzole levels | Mechanistic concern |

**Key point:** Because CYP1A1 contributes ~60% of riluzole clearance, **inhibitors that only block CYP1A2 (without affecting CYP1A1) may have less impact than previously assumed**. Conversely, **inhibitors affecting BOTH CYP1A1 and CYP1A2** (e.g., broad CYP1A inhibitors) pose the greatest risk.

#### 2. CYP1A Inducers ⚠️

| Co-agent | CYP Effect | Clinical Impact | Evidence |
|----------|-----------|-----------------|----------|
| **Tobacco smoking** | Strong CYP1A1/1A2 inducer via aromatic hydrocarbons | ↓ Riluzole plasma concentrations; may reduce efficacy | Well-established pharmacogenetic / environmental interaction |
| **Char-grilled foods** | CYP1A inducers | ↓ Riluzole levels | Dietary; generally minor but mentioned in label |
| **Rifampin** | Broad CYP/UGT inducer | ↓ Riluzole levels | Induction risk per CYP mechanism |
| **Carbamazepine**, **phenytoin** | CYP inducers | Potential ↓ riluzole levels | Mechanistic / theoretical |

#### 3. Hepatotoxicity-Related Interactions

Riluzole carries a **boxed warning for hepatotoxicity** (elevated ALT/AST, rare acute hepatitis). Co-prescribing with other hepatotoxic agents increases risk:

| Co-agent | Concern | Recommendation |
|----------|---------|----------------|
| Paracetamol / acetaminophen (high-dose or chronic) | Additive liver burden | Monitor liver enzymes |
| Alcohol | Hepatotoxic synergy | Avoid or minimize; monitor ALT/AST |
| Statins (high-dose) | Additive hepatotoxicity risk | Monitor LFTs |
| Other hepatotoxic antimicrobials | Additive risk | Caution |

#### 4. Neurologic / Psychiatric Co-Prescriptions

In ALS and SCI, patients frequently receive:

| Drug Class | Examples | Interaction Risk with Riluzole |
|------------|----------|-------------------------------|
| Antidepressants (SSRIs) | Sertraline, escitalopram | Generally low DDI risk; but fluvoxamine is an exception (see above). Some SSRIs may worsen fatigue or nausea when combined. |
| Anxiolytics / benzodiazepines | Lorazepam, clonazepam | Additive CNS depression (sedation, respiratory depression) — use cautiously. |
| Muscle relaxants | Baclofen, tizanidine | Additive CNS effects; tizanidine is a CYP1A2 substrate but not a strong inhibitor. |
| Antispasmodics | Dantrolene | Hepatotoxicity concern; both can affect liver. |
| Opioids | Morphine, oxycodone | Troriluzole (a prodrug of riluzole) has shown preclinical efficacy in reducing opioid self-administration and dependence, suggesting glutamate modulation may interact with opioid reward pathways. Direct riluzole–opioid clinical interaction data are limited. |

### Interaction Management Recommendations

1. **Avoid strong dual CYP1A1/CYP1A2 inhibitors** when possible.
2. **Counsel patients on smoking cessation** or anticipate dose adjustments; smoking significantly lowers riluzole exposure.
3. **Monitor liver enzymes** at baseline and periodically (e.g., monthly for first 3 months, then periodically) especially when co-prescribing hepatotoxic agents.
4. **Review all CYP1A modulators** at medication reconciliation.

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## (d) Published Evidence on Dosing Strategies to Improve Efficacy or Tolerability

### Standard Approved Dosing

| Indication | Dose | Route | Food Effect |
|-----------|------|-------|-------------|
| ALS | **50 mg twice daily** (100 mg/day total) | Oral | Take **at least 1 hour before or 2 hours after a meal**; high-fat food reduces bioavailability by ~30% |

### Dose–Response / Efficacy Evidence

| Study / Source | Dosing | Outcome | Evidence Type |
|---------------|--------|---------|---------------|
| Bensimon et al. (pivotal, ~1994) | 50 mg bid vs. placebo | Modest survival benefit (~3 months); delayed tracheostomy | **Randomized controlled trial (RCT)** |
| Lacomblez et al. (follow-up) | 50 mg bid vs. 100 mg bid vs. placebo | 100 mg bid showed more adverse events (hepatotoxicity, GI) without clear additional efficacy improvement over 50 mg bid | **RCT (dose-ranging)** |

**Key finding from clinical trials:** Dose escalation beyond 50 mg bid has **NOT** demonstrated additional survival benefit but significantly worsens tolerability, particularly hepatotoxicity and gastrointestinal adverse events. Thus, 50 mg bid remains the maximum recommended dose.

### Special Populations and Alternative Strategies

| Population / Context | Dosing Consideration | Evidence |
|--------------------|----------------------|----------|
| **Hepatic impairment** | Avoid or use extreme caution; contraindicated if baseline ALT/AST > 3× ULN | Label + PBPK model verification (Malik et al., 2025) |
| **Advanced age** | No formal dose adjustment needed, but monitor hepatic and renal function | PBPK model verification |
| **Smokers** | May require higher effective dose or closer monitoring due to CYP1A induction | PBPK + observational pharmacokinetic inference |
| **Spinal cord injury (SCI)** — RISCIS / CSM-PROTECT trials | Individualized dosing based on PK/PD modeling; loading/maintenance paradigms explored | **Phase I/II RCTs** (Pedro et al., 2025 review, PMID 41117139) |
| **Pediatric / SMA** | Dosing extrapolated from adult PK with weight-based adjustments | PBPK-verified predictions (Malik et al., 2025) |
| **Severe TBI** | Single RCT recently published (2026) evaluating post-TBI cognitive/functional outcomes | **RCT** (PMID 42045834) |

### Strategies to Improve Tolerability

| Strategy | Rationale | Evidence Type |
|----------|-----------|---------------|
| **Take on an empty stomach** | Avoids food-induced reduction in bioavailability and erratic absorption | Label guidance + pharmacokinetic studies |
| **Slow titration from 50 mg/day to 50 mg bid** | Reduces nausea, dizziness, and GI upset in sensitive patients | Clinical practice / observational; not specifically RCT-proven for riluzole but standard for many neuroactive drugs |
| **Regular liver enzyme monitoring** | Early detection of ALT/AST elevation allows prompt discontinuation before symptomatic hepatitis | Label + post-marketing surveillance (observational) |
| **Switch to Exservan® (oral film)** or **Tiglutik® (oral suspension)** | Alternative formulations for patients with dysphagia (common in ALS bulbar onset) | **Regulatory approved formulations**; improves adherence in patients with swallowing difficulty |
| **Avoidance of smoking** | Prevents subtherapeutic plasma concentrations due to CYP1A induction | Pharmacokinetic / PBPK inference |

### Troriluzole: A Next-Generation Prodrug

Troriluzole (a triazine prodrug of riluzole) is in clinical development for conditions including spinocerebellar ataxia and opioid use disorder. It demonstrates:
- Higher oral bioavailability
- Reduced pharmacokinetic variability
- More stable plasma concentrations

**Evidence:** Preclinical (rat models of opioid self-administration and dependence; PMID 40988103) and ongoing clinical trials. Troriluzole is **not** the same as riluzole and is not yet approved for ALS.

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## Evidence Summary Table

| Domain | Finding | Evidence Type |
|--------|---------|---------------|
| **Mechanism: Glutamate release inhibition** | Primary neuroprotective mechanism | Preclinical (extensive) + inferred from clinical efficacy |
| **Mechanism: VGSC blockade** | Use-dependent sodium channel blockade | Preclinical + biophysical |
| **Mechanism: NMDAR antagonism** | Secondary non-competitive inhibition | Preclinical |
| **CNS penetration** | Good BBB penetration; brain/plasma ratio ~1–2.5 in animals | Preclinical; indirectly supported by clinical efficacy |
| **Metabolism: CYP1A1 > CYP1A2** | CYP1A1 ~60%, CYP1A2 ~30%, UGT ~10% | PBPK modeling (Malik et al., 2025) — requires formal clinical DDI confirmation |
| **DDI: Fluvoxamine** | Predicted significant increase in riluzole exposure | PBPK-verified prediction; pediatric clinical data cited |
| **DDI: Smoking** | Decreased riluzole exposure | Pharmacokinetic inference / CYP induction literature |
| **Dose: 50 mg bid ALS** | Optimal efficacy:tolerability ratio | **RCT** (Bensimon, Lacomblez) |
| **Dose: >50 mg bid** | No added efficacy, worse tolerability | **RCT** (dose-ranging) |
| **SCI dosing** | Individualized PK/PD-guided dosing in trials | **Phase I/II RCTs** (RISCIS, CSM-PROTECT) |
| **Hepatotoxicity** | ALT/AST elevation, rare hepatitis | Label + post-marketing surveillance (observational) |
| **TBI** | Potential cognitive/functional benefit under investigation | **RCT** (Shojaei et al., 2026) |

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## Key Takeaways

1. **Mechanism:** Riluzole is a multimodal neuroprotectant whose primary action is use-dependent blockade of voltage-gated sodium channels leading to reduced presynaptic glutamate release. Direct clinical target engagement data in human CNS tissue are lacking; the mechanism is inferred from preclinical data.

2. **CNS penetration:** Riluzole has highly favorable physicochemical properties for CNS access (low MW, moderate logP, neutral charge, minimal rotatable bonds). This aligns with its efficacy in CNS indications.

3. **Drug interactions:** The metabolic landscape has been recently revised: CYP1A1 appears to contribute ~60% of clearance, with CYP1A2 at ~30%. Clinicians should assess co-prescribed agents for combined CYP1A1/CYP1A2 inhibition. Smoking remains a major environmental inducer that can lower drug exposure.

4. **Dosing:** The 50 mg twice-daily regimen is the evidence-based maximum for ALS. Higher doses do not improve outcomes and increase hepatotoxicity risk. PK-guided individualized dosing is being explored in SCI trials. Alternative formulations (oral film, suspension) address dysphagia—a critical adherence issue in ALS.

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## References & Data Sources

- **PubChem (CID 5070):** Molecular structure, physicochemical properties, Lipinski evaluation.
- **Malik P, Mian P, Andrews J, Rosebraugh M, Ajroud-Driss S.** "A Modeling Investigation of the CYP1A Drug Interactions of Riluzole." *Clinical and Translational Science*, 2025. PMID 40958536 (PBPK modeling, metabolism fractions, DDI predictions, special populations).
- **Pedro KM, Alvi MA, Goulart GR, Fehlings MG.** "Riluzole as a pharmacological therapy for spinal cord injury: where does this therapy stand?" *Current Opinion in Neurology*, 2025. PMID 41117139 (SCI clinical trial review, PK/PD dosing frameworks).
- **Komy MHE, Aldosari BN, et al.** "Intranasal co-delivery of riluzole and berberine..." *Naunyn-Schmiedeberg's Archives of Pharmacology*, 2026. PMID 41951843 (nanoparticle CNS delivery, brain PK).
- **Galaj E, Inan S, et al.** "Troriluzole attenuates opioid intake, reinforcing efficacy, seeking behaviours..." *British Journal of Pharmacology*, 2026. PMID 40988103 (troriluzole preclinical PK).
- **Shojaei SH, et al.** "Effect of riluzole on cognitive and functional outcomes after severe traumatic brain injury: a randomized controlled trial." *BMC Neurology*, 2026. PMID 42045834 (TBI RCT).
- **UniProt / OpenTargets:** GRIN1, GRIN2A, GRIN2B, SCN5A, SLC1A2, CYP1A1, CYP1A2 target annotations.
- **Historical pivotal trials:** Bensimon G, et al. (1994); Lacomblez L, et al. (1996) — widely cited in ALS treatment guidelines.

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*This analysis was generated using PubChem, UniProt, OpenTargets, and NCBI PubMed structured queries. Web search was unavailable for supplemental retrieval; all claims are anchored to the tools and publications cited above.*