Acamprosate, a gamma-aminobutyric acid (GABA) analogue used worldwide to treat alcohol dependence, is available in this country (Table 1). The agent appears to reduce discomfort—including restlessness, anxiety, dysphoria, and insomnia—common within the first 6 months of alcohol abstinence. In clinical trials, it prolonged abstinence in alcohol-dependent patients who completed an initial detoxification and were receiving relapse prevention treatment.
HOW IT WORKS
Acamprosate’s chemical structure resembles both GABA and taurine, an endogenous amino acid derivative that enhances GABA-ergic activity.1 The drug’s synthetic structure facilitates its passage across the blood-brain barrier, and the brain mediates its major effect.
Acamprosate: Fast facts
|Maintaining abstinence in alcohol-dependent patients|
|July 29, 2004|
The mechanisms by which acamprosate promotes abstinence in alcohol dependence are unknown. The drug may bind to N-methyl-D-aspartate (NMDA) glutamate receptors and work as a partial antagonist, but direct ligand activity does not appear to cause most of its central actions. Rather, acamprosate interacts with glutamate and GABA to normalize the hyperexcitability that accompanies early abstinence (Table 2).
Acamprosate’s proposed mechanisms of action*
|Neurotransmitter interactions||Pharmacologic effect||Clinical effect|
|Glutamatergic system (NMDA receptor)||Blocks increased glutamate release in nucleus accumbens during alcohol withdrawal; may bind to receptor site as partial antagonist||Decreased arousal, craving, and dysphoria associated with early abstinence|
|GABAergic system (GABAAreceptor)||Normalizes alcohol-induced decrease in basal GABA concentrations in nucleus accumbens||Same as above|
|Taurine||Increases extracellular taurine concentrations in nucleus accumbens; taurine shifts the glutamate/GABA balance in favor of GABAergic activity||Mimics increase in taurine seen with acute alcohol intake, likely facilitating GABA normalization|
|* Based on animal models of alcohol dependence|
|Source: reference 3|
Acamprosate’s bioavailability is relatively poor (11%), so it is prescribed to be taken three times daily. Although patients in clinical practice often have trouble following frequent daily dosing schedules, subjects in one study reportedly had little difficulty adhering to this regimen.2
Acamprosate’s half-life is approximately 13 hours, and it reaches peak plasma concentrations in 3.5 to 9.5 hours. Pharmaceutical studies indicate that food does not significantly affect absorption.
Although 666 mg tid has shown efficacy in clinical trials, the blood level at which acamprosate becomes therapeutic has not been determined.
The drug reaches steady-state blood levels within 1 week, meaning it will not be fully effective for 5 to 7 days but may still reach therapeutic blood levels during that time. Advise patients that adverse effects may not clear for 5 to 7 days after discontinuation.
Acamprosate does not bind with plasma proteins, so it will not interact with drugs that do. The drug, which is renally excreted in an unmetabolized state, has not been found to interact adversely with commonly prescribed antidepressants, anxiolytics, antipsychotics, alcohol, or disulfiram.3 How acamprosate interacts with renally excreted drugs such as lithium is unknown.
In two studies following 24 healthy volunteers4 and 23 alcohol-dependent patients,5 concomitant naltrexone, 50 to 100 mg/d, and acamprosate, 2 to 3 g/d, increased acamprosate plasma concentrations as much as 25%, but did not change plasma levels of naltrexone or its major metabolite. Naltrexone might delay gastric emptying, thereby increasing acamprosate absorption.
Acamprosate with psychosocial treatment increased total abstinent days in:
- 15 randomized, controlled trials (RCT) conducted in Europe6
- a meta-analysis of 12 methodologically comparable RCTs conducted in Europe7
- an open-label trial in France that studied acamprosate as an adjunct to treatment-as-usual in primary care settings.2
Acamprosate may improve patient retention in substance abuse treatment, which predicts favorable outcomes.7 Patients receiving acamprosate and treatment-as-usual reported fewer alcohol-related problems and improved quality of life compared with treatment-as-usual alone.2 Reduced subjective craving for alcohol is difficult to study and has not been sufficiently shown.
In one multi-center, placebo-controlled trial, a subgroup of severely alcohol-dependent patients sought acamprosate/disulfiram therapy. The combination was shown to be safe and increased total abstinent days compared with acamprosate or disulfiram alone, but effectiveness could not be determined because of the self-selection bias of those who requested combined pharmacotherapy.
In one 12-week RCT,8 naltrexone/acamprosate therapy was more effective than acamprosate alone—but not more effective than naltrexone alone—in reducing time to first drink and relapse to heavy drinking.
The multi-center COMBINE (Combining Medications and Behavioral Interventions) study,9 funded by the National Institute on Alcohol Abuse and Alcoholism, is comparing the efficacy of naltrexone, acamprosate, and both agents when given with low-intensity psychosocial treatment or moderate-intensity, alcohol-specific psychosocial treatment. Preliminary safety, tolerability, and adherence results with the acamprosate/naltrexone combination have been promising. Efficacy findings are expected later this year.