Acamprosate

Indications

• FDA-approved for maintenance of abstinence from alcohol in adults with alcohol dependence who are already abstinent, alongside psychosocial treatment.
• Listed with naltrexone as first-line pharmacotherapy for alcohol use disorder by the APA 2018 guideline and the VA/DoD 2021 guideline.
• Best matched to patients whose stated goal is complete abstinence, whereas naltrexone chiefly reduces heavy drinking days.
• Preferred when hepatic disease, ongoing opioid analgesia or opioid agonist therapy makes naltrexone unsuitable or contraindicated.
• Not effective for managing acute alcohol withdrawal and has no role in detoxification; benzodiazepines or phenobarbital cover that phase.
• Off-label trials in gambling disorder, anxiety, tinnitus and fragile X syndrome exist but the evidence is too thin to support routine use.

Mechanism of action

• Structural analog of taurine and homotaurine that modulates glutamatergic transmission, with NMDA receptor modulation and mGluR5 antagonism proposed.
• Restores the glutamate-GABA balance disrupted by chronic alcohol, damping the hyperglutamatergic rebound that follows withdrawal.
• Reduces protracted withdrawal symptoms such as insomnia, anxiety, dysphoria and restlessness that commonly drive a return to drinking.
• Has no effect on alcohol reward or intoxication and produces no disulfiram-like reaction if the patient drinks.
• No action at opioid, dopamine, GABA-A or benzodiazepine receptors, so there is no sedation, euphoria or abuse liability.

Pharmacokinetics

• Oral bioavailability is only about 11% and food reduces absorption further, yet dosing with meals is advised because it aids adherence.
• Not metabolized at all: the drug is excreted unchanged by the kidneys, so there is no hepatic clearance and no CYP450 involvement.
• Elimination half-life is 20-33 h, with steady-state plasma concentrations reached after roughly 5 to 7 days of three-times-daily dosing.
• Supplied as enteric-coated delayed-release tablets that must be swallowed whole; crushing or chewing destroys the coating.
• Renal function alone governs exposure, which is why creatinine clearance drives every dose adjustment and the contraindication.

Dosing

• Standard adult dose is two 333 mg delayed-release tablets (666 mg) three times daily with meals, begun as soon as abstinence is achieved.
• Start after withdrawal is complete, ideally within days of the last drink; delaying initiation reduces the chance of sustained abstinence.
• Reduce to one 333 mg tablet three times daily when creatinine clearance is 30-50 mL/min, and check renal function before starting.
• Contraindicated when creatinine clearance is 30 mL/min or less; there is no safe reduced dose in severe renal impairment.
• Continue through a lapse rather than stopping, since benefit accrues over months and relapse is not a reason to discontinue.
• No taper is needed on stopping, and no hepatic dose adjustment is required at any stage of liver disease.

Adverse effects

• Diarrhea is the signature adverse effect, reported in roughly 10-17%, usually mild, dose-related and improving after the first weeks.
• Nausea, flatulence, abdominal pain, pruritus, dry mouth and asthenia occur but rarely force discontinuation on their own.
• Anxiety, depression, insomnia and, uncommonly, suicidal ideation have been reported; the label calls for monitoring of mood.
• No hepatotoxicity, no sedation, no cognitive impairment and no abuse potential, which distinguishes it from most relapse-prevention options.
• Acute kidney injury and hypercalcemia have followed massive overdose; treatment is supportive with attention to calcium and renal function.
• Three-times-daily dosing and a large pill burden are the main practical causes of discontinuation rather than toxicity.

Monitoring

• Baseline serum creatinine with calculated creatinine clearance, repeated periodically and whenever the clinical picture changes.
• Screen for depression and suicidal ideation at each visit, since both alcohol use disorder and the drug label flag this risk.
• Track drinking days, heavy drinking days and craving with the timeline followback or AUDIT-C at every follow-up.
• Check adherence explicitly given the three-times-daily schedule; pill counts or pharmacy refill data are more reliable than self-report.
• Reassess overall benefit at 3 months and consider adding or switching to naltrexone, disulfiram or off-label topiramate if drinking persists.

Interactions

• No clinically significant drug interactions have been identified, because acamprosate is neither metabolized nor protein-bound to any degree.
• Studied without interaction alongside alcohol, diazepam, disulfiram and imipramine, so combination with these agents needs no dose change.
• Naltrexone raises acamprosate peak and total exposure, but the combination is well tolerated and no dose adjustment is recommended.
• Contraindicated in severe renal impairment, and caution is warranted with nephrotoxic agents such as NSAIDs or aminoglycosides.
• Safe to combine with antidepressants, antipsychotics and mood stabilizers, which makes it useful in complex psychiatric comorbidity.

Special populations

• Pregnancy: animal data show skeletal malformations at high doses and human data are limited, so use only if the benefit clearly outweighs risk.
• Lactation: excretion into human milk is unknown; most authorities advise avoiding it or monitoring the infant closely if used.
• Pediatric safety and effectiveness have not been established and there is no established dose for patients under 18 years.
• Geriatric patients often have reduced creatinine clearance despite a normal creatinine, so calculate clearance before prescribing.
• Hepatic impairment requires no adjustment at any Child-Pugh class, making acamprosate the preferred agent in cirrhosis.

Clinical pearls

• Choose it when the goal is total abstinence and the liver is the problem; no hepatic dosing needed.
• Renal function is the only dose lever: cut to 333 mg TID at CrCl 30-50, stop at 30 or less.
• Diarrhea early is expected and usually settles; do not abandon the drug in the first two weeks.