A small amount of ketamine with oxycodone induced an acute hyperactive delirium due to voriconazole, a CYP3A4 inhibitor, in a case of multiple myeloma with cancer pain

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This is a report on a case of delirium due to a small amount of ketamine with voriconazole. A 58 year old male was treated for multiple myeloma and hip pain due to an extramedullary tumor following the administration of oxycodone, and voriconazole was administrated for his suspected mycotic pneumonia. His pain was refractory, so we started the administration of a small dose of ketamine (4 mg/hr) for analgesia, added to oxycodone. About 30 hours later, the delirium appeared but he complained of worsening hip pain, so we added 2 mg of ketamine rapidly. Immediately after the additional administration of ketamine, his delirium became more serious. We think the reason why a small amount of ketamine induced delirium is an interaction of ketamine and voriconazole. Ketamine is metabolized to norketamine, which is thought to be more harmless than ketamine, by cytochrome P 450 (CYP) (a part of by CYP3A4) and voriconazole is an inhibitor of CYP3A4. In cases of patients treated with voriconazole, ketamine should be more carefully administrated.