# Compound Dive: Riluzole (Rilutek™)
**P ubChem CID:** 5070  
**CHEMBL:** CHEMBL1201585  
**Date:** 2026-05-04

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## 1. Mechanism of Action & Binding Partners

### 1.1 Primary Pharmacological Action
Riluzole is an antiglutamate agent approved for the treatment of amyotrophic lateral sclerosis (ALS). Its mechanism is **multifaceted** rather than mediated through a single high-affinity molecular target:

| Target/Pathway | Effect | Evidence Level |
|----------------|--------|---------------|
| **Glutamate release inhibition** | Blocks voltage-gated sodium channels (VGSCs) on presynaptic terminals, reducing glutamate release | Preclinical (cell & animal models) + indirect clinical support |
| **NMDA receptor antagonism** | Reduces NMDA-evoked responses; protects against excitotoxic calcium influx | Preclinical (in vitro electrophysiology) |
| **AMPA/kainate receptor blockade** | Inhibits AMPA/kainate receptor-mediated currents | Preclinical |
| **EAAT2/GLT-1 upregulation** | Enhances astrocytic glutamate reuptake via excitatory amino acid transporter 2 (SLC1A2 / EAAT2 / GLT-1) | Preclinical (cell culture, rodent models) |
| **CK1δ kinase inhibition** | ATP-competitive inhibitor of casein kinase 1 delta (IC₅₀ ≈ 16.1 µM); links TDP-43 proteinopathy and glutamate excitotoxicity | **Preclinical** (computational docking + in vitro enzyme assay) |
| **GABA-A receptor potentiation (modest)** | Weak positive allosteric modulation reported in some models | Preclinical |

### 1.2 Binding Partners & Structural Biology
- **No classic high-affinity protein target** (e.g., no nanomolar Kd for a single receptor). Riluzole is a **multi-target ligand** (polypharmacology) at micromolar concentrations.
- **VGSCs**: Use-dependent blockade of Naᵥ channels, particularly persistent sodium currents in motor neurons. This is the most widely cited presynaptic mechanism.
- **Glutamate transporters (EAAT2/GLT-1)**: Riluzole increases expression and/or activity of the astrocytic glutamate transporter EAAT2, which is downregulated in ALS patients. This restores synaptic glutamate clearance.

> **Evidence Note on CK1δ**: The proposed CK1δ mechanism (Bissaro et al., 2018) is **preclinical only**—found via computational modeling and in vitro kinase assays. It has not been validated in ALS patient tissue or clinical biomarker studies and should be regarded as a mechanistic hypothesis, not an established clinical target.

### 1.3 Disease-Relevant Rationale
In ALS, motor neurons are uniquely vulnerable to **glutamate excitotoxicity** due to:
- Low expression of calcium-binding proteins (e.g., calbindin).
- Reduced GluR2 subunit in AMPA receptors, rendering them calcium-permeable.
- **Loss of EAAT2/GLT-1** expression on astrocytes, impairing glutamate clearance.

Riluzole counteracts these vulnerabilities through the multifactorial mechanisms above.

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## 2. Physicochemical Properties Relevant to CNS Penetration

### 2.1 Key Molecular Properties
| Property | Value | CNS Relevance |
|----------|-------|---------------|
| **Molecular formula** | C₈H₅F₃N₂OS | Small molecule (234.2 Da) |
| **Molecular weight** | 234.2 g/mol | ✓ Well below BBB cutoff (~400–500 Da) |
| **XLogP** | 3.6 | Optimal lipophilicity for passive BBB crossing (target 1–3, acceptable up to 5) |
| **TPSA** | 76.4 Ų | Moderately polar; acceptable for BBB penetration (<90 Ų preferred) |
| **H-bond donors (HBD)** | 1 | Low |
| **H-bond acceptors (HBA)** | 7 | Acceptable for oral absorption |
| **Rotatable bonds** | 1 | Low—rigid core, compact |
| **Charge** | 0 | Neutral at physiological pH—facilitates passive diffusion |

### 2.2 CNS Penetration Assessment
Riluzole displays **favorable CNS penetration characteristics**:
- **LogP ~3.6**: Lipophilic enough to cross the blood-brain barrier (BBB) by passive diffusion, yet not so lipophilic as to cause excessive plasma protein binding or peripheral sequestration.
- **Small size (234 Da)**: Facilitates paracellular and transcellular BBB transit.
- **Neutral charge**: No ionization penalty at physiological pH.
- **Low HBD/few rotatable bonds**: Aligns with CNS-penetrant drug design principles.

> **Clinical correlation**: The oral dose of 100 mg/day produces therapeutically relevant CNS concentrations, confirming adequate BBB penetration.

### 2.3 Human Pharmacokinetics
| Parameter | Value |
|-----------|-------|
| **Absolute oral bioavailability** | ~60% (range 50–60%) |
| **Absorption** | Rapid; Tmax ≈ 1.0–1.5 hours |
| **Food effect** | High-fat meals decrease AUC by ~20% and Cmax by ~45% |
| **Elimination half-life** | ~12 hours (range 9–15 h) |
| **Steady-state** | Reached in ~5 days with BID dosing |
| **Accumulation** | ~2-fold with repeated BID dosing |
| **Primary metabolism** | CYP1A2 (major), with possible contribution from CYP1A1 |
| **Active metabolite** | N-hydroxy-riluzole (rapidly eliminated) |
| **Smoking effect** | Clearance ↑ ~20% (CYP1A2 induction by tobacco) |
| **Race effect** | Japanese patients: clearance ~50% lower than Caucasians (body-weight normalized) |

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## 3. Drug–Drug Interactions (DDIs) with Commonly Co-Prescribed Agents

### 3.1 Metabolic Pathway
Riluzole is a **CYP1A2 substrate** (also possibly CYP1A1). Therefore, drugs that inhibit or induce CYP1A2 can significantly alter riluzole exposure.

### 3.2 High-Risk Interactions (CYP1A2 Inhibitors)

| Co-Prescribed Agent | Drug Class / Use in ALS | Interaction Mechanism | Clinical Significance |
|---------------------|------------------------|----------------------|----------------------|
| **Ciprofloxacin** | Antibiotic (respiratory infections in ALS) | **Strong CYP1A2 inhibitor** | ↑ Riluzole AUC/Cmax. **Avoid co-administration** or monitor for increased adverse effects (hepatotoxicity, nausea, asthenia). |
| **Fluvoxamine** | SSRI (depression, pseudobulbar affect) | **Strong CYP1A2 inhibitor** | Significant ↑ in riluzole exposure. **Contraindicated or use with extreme caution.** |
| **Mexiletine** | Antiarrhythmic (used off-label for muscle cramps in ALS) | CYP1A2 inhibitor | ↑ Riluzole exposure. Monitor liver function and adverse effects. |
| **Amiodarone** | Antiarrhythmic | CYP1A2 inhibitor | Potential ↑ in riluzole levels. |
| **Cimetidine** | H2 blocker (GERD in ALS) | CYP1A2 inhibitor | Moderate interaction. Consider PPI alternative (e.g., omeprazole has fewer CYP1A2 issues). |

### 3.3 Moderate / Clinically Relevant Interactions

| Co-Prescribed Agent | Drug Class / Use in ALS | Interaction | Guidance |
|---------------------|------------------------|-----------|----------|
| **Amitriptyline** | Tricyclic antidepressant (neuropathic pain, sialorrhea) | No direct CYP1A2 interaction of major concern, but overlapping CNS depression | Monitor for additive CNS effects. Note: amitriptyline is metabolized by CYP2C19/CYP3A4, not primarily CYP1A2. |
| **Baclofen** | Muscle relaxant (spasticity in ALS) | No major metabolic interaction | Additive CNS depression possible (drowsiness, dizziness). |
| **Gabapentin** | Anticonvulsant (neuropathic pain) | No major metabolic interaction | Generally safe; no CYP-mediated DDI. |
| **Quetiapine** | Atypical antipsychotic (behavioral symptoms) | Minimal CYP1A2 relevance (quetiapine primarily CYP3A4) | Low DDI risk via metabolism. Additive sedation possible. |
| **Olanzapine** | Atypical antipsychotic | Olanzapine is a CYP1A2 substrate, not a strong inhibitor | Low bidirectional DDI risk. |
| **Fluoxetine** | SSRI (depression) | Fluoxetine inhibits **CYP2D6** (not CYP1A2) | No major pharmacokinetic DDI with riluzole. Monitor serotonergic effects. |
| **Sertraline** | SSRI (depression) | Minimal CYP1A2 effect | Generally compatible. |

### 3.4 Inducers That Lower Riluzole Efficacy

| Co-Prescribed Agent | Mechanism | Effect |
|---------------------|-----------|--------|
| **Cigarette smoking** | CYP1A2 induction | Clearance ↑ ~20%; may reduce riluzole exposure. Counsel patients to disclose smoking status. |
| **Carbamazepine** | CYP1A2 / CYP3A4 / UGT inducer | Likely ↓ riluzole levels. Use caution. |
| **Phenytoin** | CYP inducer | Likely ↓ riluzole levels. |
| **Rifampin** | Broad CYP/UGT inducer | Likely ↓ riluzole levels. |
| **Charred meat, cruciferous vegetables** | Dietary CYP1A2 induction | Minor effect; not clinically significant at usual intake. |

### 3.5 Interactions from Product Label / Clinical Data
- **Grapefruit juice**: No clinically significant effect on riluzole pharmacokinetics (rat study showed no change in absorption or metabolism; limited human data but generally considered low risk).
- **Alcohol**: Not a pharmacokinetic interaction, but alcohol may worsen hepatotoxicity risk (riluzole carries a black-box warning for liver injury).

> **Evidence classification**: Most DDI data are derived from **in vitro** (human liver microsome) and **animal** (Wistar rat) studies. Human clinical DDI studies with strong CYP1A2 inhibitors are limited; the riluzole label recommendations are largely **extrapolated from metabolic profiling** rather than large-scale clinical interaction trials.

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## 4. Dosing Strategies to Improve Efficacy or Tolerability

### 4.1 Approved and Evidence-Based Dosing

| Dosing Schedule | Evidence Base | Outcome |
|----------------|--------------|---------|
| **100 mg/day (50 mg BID)** | **Pivotal RCT** (Bensimon et al., NEJM 1994, n=155; dose-ranging study 1996, n=959) | Modest survival benefit (~2–3 months); slowed decline in muscle strength. |
| **200 mg/day (100 mg BID)** | Dose-ranging RCT (1996) | Also showed survival benefit, but **higher adverse effects** (elevated ALT/AST, nausea, asthenia). Not superior enough to justify routine use over 100 mg/day. |
| **50 mg/day** | Dose-ranging RCT (1996) | Less effective than 100 mg/day. |

### 4.2 Disease-Stage Considerations
- **Post-hoc analysis** (Lancet Neurology, 2018) of the original dose-ranging data found that **riluzole 100–200 mg/day prolonged survival primarily in late-stage ALS (stage 4, the final stage before death)** (HR 0.55 vs placebo).
- Early-stage benefit is more controversial and may relate to trial design rather than biological ineffectiveness.

> **Evidence classification for stage-specific efficacy**: **Retrospective/subgroup analysis** of RCT data—not a prospective stratified trial.

### 4.3 Tolerability and Dose Adaptation

| Adverse Effect | Frequency | Management Strategy |
|----------------|-----------|---------------------|
| **Nausea** | Common (~10–20%) | Take with food (**but** food reduces bioavailability ~20–45%). If intolerable, consider Tiglutik® oral suspension or Exservan® oral film for easier titration/splitting. |
| **Asthenia / fatigue** | Common | Dose reduction to 50 mg/day may be considered, though efficacy data at this dose are weaker. |
| **Hepatotoxicity** (elevated ALT >3× ULN) | ~5–10% | **Contraindicated** in baseline ALT/AST >3× ULN. Monitor LFTs at baseline, monthly ×3, then quarterly. Discontinue if ALT >5× ULN or clinical jaundice. |
| **Dizziness / somnolence** | Common | Slow titration from 50 mg/day to 100 mg/day over 2 weeks may improve tolerability (**clinical practice**, not formally tested in RCTs). |

### 4.4 Alternative Administration Routes (Investigational)

| Route | Status | Rationale / Findings |
|-------|--------|---------------------|
| **Intrathecal (IT) infusion** | **Phase I/II clinical trials** (NCT ongoing) | Overcomes poor CNS penetration concerns; achieves **2–3× higher spinal cord tissue concentrations** than oral dosing. Two human ALS cases reported tolerability at doses up to 0.2 mg/hr. |
| **Oral film (Exservan®)** | FDA-approved formulation (2019) | For patients with dysphagia (common in ALS). Bioequivalent to tablets. |
| **Oral suspension (Tiglutik®)** | FDA-approved (2018) | Easier dose titration; designed for ALS patients with swallowing difficulties. |

> **Evidence classification for IT riluzole**: Early **clinical trial data** (safety/pharmacokinetic cohorts); not yet powered for efficacy endpoints.

### 4.5 Special Populations
| Population | Recommendation | Evidence Base |
|------------|---------------|---------------|
| **Smokers** | May need dose adjustment (clearance ↑ 20%), but standard 100 mg/day still used. | PK data from labeling; no prospective dose-optimization trial. |
| **Japanese patients** | Lower clearance (~50% of Caucasians); monitor for toxicity at standard doses. | PK population analysis (post-hoc). |
| **Hepatic impairment** | Contraindicated if baseline ALT/AST >3× ULN. Use caution in mild impairment. | Label guidance; no dedicated PK trial. |
| **Elderly** | More sensitive to effects; age-related hepatic decline warrants closer LFT monitoring. | Label guidance; no age-specific RCT. |

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## 5. Summary of Evidence Levels

| Claim | Evidence Type | Strength |
|-------|--------------|----------|
| Riluzole 100 mg/day prolongs survival in ALS | **Randomized controlled trial** | High |
| Dose-response: 100 mg ≈ 200 mg for survival; 50 mg inferior | **RCT (dose-ranging)** | High |
| Glutamate release inhibition via VGSC blockade | **Preclinical** (electrophysiology, animal) | Moderate (indirect clinical support) |
| EAAT2/GLT-1 upregulation | **Preclinical** (cell & rodent) | Moderate (mechanistic hypothesis) |
| CK1δ inhibition as MOA | **Preclinical only** (in silico + in vitro) | Low (hypothesis) |
| CYP1A2 is major metabolic enzyme | **In vitro** (HLM) + **animal PK** | Moderate |
| Ciprofloxacin ↑ riluzole exposure | **Animal PK** (rat) | Moderate (extrapolated to humans) |
| Intrathecal riluzole achieves higher CNS levels | **Phase I/II clinical trial** | Moderate (safety/PK only) |
| Riluzole efficacy greatest in late-stage ALS | **Retrospective subgroup analysis** of RCT | Low–Moderate (hypothesis-generating) |
| Food reduces riluzole bioavailability | **Clinical PK study** | High |
| Smoking increases riluzole clearance | **Clinical PK / population analysis** | Moderate |

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## 6. Key References

1. Bensimon G, Lacomblez L, Meininger V. A controlled trial of riluzole in amyotrophic lateral sclerosis. **N Engl J Med**. 1994;330(9):585–591. (RCT, n=155)
2. Lacomblez L, et al. Dose-ranging study of riluzole in ALS. **Lancet**. 1996;347(9013):1425–1431. (RCT, n=959)
3. Bissaro M, et al. Targeting Protein Kinase CK1δ with Riluzole. **ChemMedChem**. 2018;13(24):2567–2573. (Preclinical MOA)
4. Malik R, et al. A Modeling Investigation of the CYP1A Drug Interactions of Riluzole. **Clin Transl Sci**. 2025. (In silico DDI modeling)
5. Ravi PR, Vats R, Kora UR. Effect of ciprofloxacin and grapefruit juice on oral pharmacokinetics of riluzole in Wistar rats. **J Pharm Pharmacol**. 2013;65(12):1781–1790. (Animal DDI)
6. Paganoni S, et al. Intrathecal administration of riluzole in amyotrophic lateral sclerosis. **Neurosurgery**. 2023. (Clinical IT PK)
7. Paganoni S, et al. Riluzole, disease stage and survival in ALS. **Lancet Neurol**. 2018;17(6):506–507. (Post-hoc stage analysis)
8. RILUTEK (riluzole) Prescribing Information. Sanofi. (FDA label)

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*Disclaimer: This document is assembled from public-domain pharmacological, clinical trial, and regulatory sources for analytical purposes. It does not constitute medical or prescribing advice.*