Pharmacology of Eluxadoline (Viberzi)
Eluxadoline is a minimally absorbed, locally-acting mixed opioid receptor modulator (μ- and κ-opioid receptor agonist, δ-opioid receptor antagonist) FDA-approved for treating irritable bowel syndrome with diarrhea (IBS-D) in adults. 1, 2
Mechanism of Action
Eluxadoline acts locally in the enteric nervous system through its mixed opioid receptor activity 1, 2:
- μ-opioid receptor agonist (binding affinity Ki = 1.8 nM): Provides antidiarrheal effects and visceral analgesia by modulating spinal neuron responses 3
- κ-opioid receptor agonist (Ki = 55 nM in guinea pig): Contributes to analgesic potency
- δ-opioid receptor antagonist (Ki = 430 nM): Designed to reduce constipation risk compared to pure μ-agonists
The drug's minimal systemic absorption (absolute bioavailability not determined, but very low oral bioavailability) means it works peripherally in the gut without significant central nervous system effects 2, 4. Interestingly, while initially thought to act purely peripherally, recent evidence demonstrates eluxadoline produces visceral analgesia centrally by attenuating lumbo-sacral (L6-S1) spinal neuron responses, not by inhibiting visceral sensory afferents 3.
Dosing
Standard dose: 100 mg orally twice daily with food 1, 2
Reduced dose of 75 mg twice daily is required for: 1, 2
- Patients unable to tolerate 100 mg dose
- Mild to moderate hepatic impairment (Child-Pugh Class A or B)
- Concomitant use of OATP1B1 inhibitors
- Moderate to severe renal impairment (eGFR <60 mL/min/1.73 m²)
- End-stage renal disease not yet on dialysis (eGFR <15 mL/min/1.73 m²) 5
Food effect is significant: Taking with a high-fat meal decreases Cmax by 50% and AUC by 60%, which is why the drug must be taken with food 2.
Metabolism and Pharmacokinetics
Absorption and Distribution:
- Cmax: 2-4 ng/mL after 100 mg dose
- Tmax: 1.5-2 hours (median)
- Plasma protein binding: 81%
- Linear pharmacokinetics with no accumulation on twice-daily dosing 2
Elimination:
- Half-life: 3.7-6 hours
- 82% excreted in feces, <1% in urine
- Minimal involvement of CYP450 and UGT pathways 2
Special populations:
- Hepatic impairment: Exposure increases 6-fold (mild), 4-fold (moderate), and 16-fold (severe) 2
- Renal impairment: Cmax increases 3.7-fold and AUC 4.7-fold in severe impairment; 2.4-fold and 5.9-fold respectively in ESRD 5
Absolute Contraindications
Eluxadoline is strictly contraindicated in patients: 2
- Without a gallbladder (highest risk for pancreatitis and sphincter of Oddi spasm)
- Known/suspected biliary duct obstruction or sphincter of Oddi disease
- Alcoholism, alcohol abuse, or >3 alcoholic beverages per day
- History of pancreatitis or structural pancreatic disease
- Severe hepatic impairment (Child-Pugh Class C)
- History of chronic/severe constipation or mechanical GI obstruction
- Known hypersensitivity to eluxadoline
Critical clinical pitfall: The absence of a gallbladder is an absolute contraindication—all serious pancreatitis and sphincter of Oddi spasm cases in clinical trials occurred in patients without gallbladders 1, 6.
Adverse Effects
Common adverse effects (vs placebo): 1
- Constipation: 8% (vs 2.5% placebo)
- Nausea: 7% (vs 5% placebo)
- Abdominal pain: 7% (vs 4% placebo)
- Discontinuation rate due to adverse events: 8% (vs 4% placebo)
Serious adverse effects:
Pancreatitis: 0.3% (5/1666 patients in safety population) 1, 7
- Risk: 3 more per 1000 patients (high certainty evidence) 1
- Most cases occurred within 1 week of starting treatment, some after just 1-2 doses 2
- All serious cases occurred in patients without gallbladders 1, 6
- Fatal cases have been reported 2
Sphincter of Oddi spasm: 0.5% (10/1839 eluxadoline-treated patients) 6
- Risk: 5 more per 1000 patients (high certainty evidence) 1
- Manifests as acute abdominal pain with elevated aminotransferases or lipase
- All occurred in patients without gallbladders 6
- 8 of 10 events occurred with 100 mg dose within 1 week of initiation 6
Abuse potential: Low but present 2
- Eluxadoline produced small but significant increases in "Drug Liking" and "High" scores in abuse potential studies
- Euphoria reported in 14-28% of recreational opioid users
- Risk of psychological dependence exists, though physical dependence appears minimal
- Classified as a controlled substance
Clinical Efficacy Context
Eluxadoline is more effective for stool consistency and urgency than abdominal pain, making it ideal for IBS-D patients with predominant diarrhea rather than those with severe abdominal pain as the primary complaint 1. The 2022 AGA guidelines provide a conditional recommendation for its use based on moderate certainty evidence 1.
Patient monitoring: Instruct patients to immediately stop eluxadoline and seek medical attention if they develop acute abdominal or epigastric pain radiating to the back or shoulder, especially with nausea and vomiting 2.