This was a Phase 3, multicenter, randomized, double-blind, placebo-controlled study conducted in subjects diagnosed with alcohol dependence as defined by the Diagnostic and Statistical Manual of Mental Disorders, 4th Ed. (DSM-IV). Subjects were randomized (2:2:1:1) to receive intramuscular (IM) injections of Medisorb® naltrexone 190 mg, Medisorb naltrexone 380 mg, placebo for Medisorb naltrexone 190 mg, or placebo for Medisorb naltrexone 380 mg (VIVITROL®). Study drug was administered every 4 weeks for a total of 6 injections.

All subjects received standardized biopsychosocial support therapy (BRENDA Approach [Volpicelli, JR [2001]; Guilford Press: New York]) at each visit.

Subjects who completed this study (ie, received 6 injections of study drug and completed all study visits) and continued to meet eligibility criteria were given the option to enroll in extension study ALK21-003EXT (NCT01218971). A second extension, Study ALK21-010 (NCT00156923), was conducted subsequent to ALK21-003EXT.

Primary Inclusion Criteria:

• Diagnosis of alcohol dependence based on Diagnostic and Statistical Manual of Mental Disorders, 4th Ed. (DSM-IV) criteria
• Male or non-pregnant, non-lactating female
• Able to provide TimeLine Follow-Back (TLFB) alcohol consumption information for 90-day period before detoxification and/or screening
• At least 2 episodes of heavy alcohol drinking per week during the 30 days before detoxification and/or screening
• Negative urine toxicological screen for opiates on day of randomization
• Noncustodial, stable residence and phone plus 1 contact with verifiable address and phone

Primary Exclusion Criteria:

• Evidence of hepatic failure including: ascites, prolonged prothrombin time (PT) (international normalized ratio [INR] ≥1.7), bilirubin >10% above upper limit of normal (ULN) and/or esophageal variceal disease
• Active hepatitis and/or aspartate aminotransferase (AST) or alanine aminotransferase (ALT) higher than 3xULN
• History of pancreatitis
• Major depression with suicidal ideation, psychosis, bipolar disorder, or psychiatric disorders that would compromise subject's ability to complete the study
• Current dependence (within past year) per DSM-IV criteria to benzodiazepines, opioids or cocaine
• Use of benzodiazepines and/or Ambien® (zolpidem tartrate) within 7 days prior to first dose of study medication
• Greater than 7 days inpatient treatment for substance use disorders within 30 days of randomization
• Use of any opioids and/or methadone within 14 days of screening, or likely requiring opioid therapy during study period
• Use of oral naltrexone or disulfiram within 14 days of screening
• Known intolerance and/or hypersensitivity to naltrexone, carboxymethylcellulose, or polylactide-co-glycolide (PLG)

Events were recorded starting at baseline through 42 days after the last dose of study drug.