Why is it recommended to check eosinophil counts when prescribing naltrexone (Naltrexone) or Vivitrol (Naltrexone)

Checking Eosinophils When Prescribing Naltrexone or Vivitrol

Eosinophil monitoring is not a standard recommendation when prescribing naltrexone or Vivitrol; the primary recommended laboratory monitoring is liver function testing at baseline and every 3-6 months due to the risk of hepatotoxicity at supratherapeutic doses. 1

Standard Monitoring for Naltrexone

The established guideline-based monitoring for naltrexone includes:

• Liver function tests (LFTs) at baseline and every 3-6 months are the primary recommended laboratory monitoring, as naltrexone has been associated with hepatic injury at supratherapeutic doses 1
• No routine eosinophil monitoring is mentioned in primary care guidelines for substance misuse treatment with naltrexone 1

Why Eosinophils Might Be Considered

While not a standard recommendation, there is emerging case report evidence of rare but serious eosinophilic reactions:

• Acute eosinophilic pneumonia (AEP) has been reported as a rare complication of injectable naltrexone (Vivitrol), presenting with dyspnea, hypoxia, and bilateral pulmonary infiltrates within hours to days of administration 2, 3
• These cases showed peripheral eosinophilia on initial presentation and required bronchoscopy with bronchoalveolar lavage showing eosinophil predominance (up to 66% eosinophils) 2, 3
• Eosinophilic pustular folliculitis has been reported with oral naltrexone, representing a cutaneous eosinophilic reaction 4

Clinical Context

The confusion about eosinophil monitoring may arise from:

• Cross-contamination with eosinophilic esophagitis guidelines, where eosinophil counts are central to diagnosis and monitoring, but these guidelines are unrelated to naltrexone therapy 1, 5
• The fact that 10-50% of patients with substance use disorders may have concurrent atopic conditions that could cause peripheral eosinophilia independent of naltrexone 1

Practical Recommendation

For routine naltrexone/Vivitrol prescribing:

• Obtain baseline LFTs and repeat every 3-6 months 1
• Eosinophil monitoring is not routinely indicated
• If acute respiratory symptoms develop (dyspnea, cough, hypoxia) within days of naltrexone administration, obtain a complete blood count with differential to evaluate for eosinophilia as part of the workup for drug-induced AEP 2, 3
• If cutaneous reactions occur, consider checking eosinophils as part of the evaluation for drug-induced eosinophilic skin reactions 4