Hydroxyzine or Phenothiazine
42. Would coadministration of either hydroxyzine or phenothiazine be beneficial for A.J.'s pain?
The addition of hydroxyzine (Vistaril, Atarax) to an analgesic regimen is thought to potentiate the analgesia of the opioid analgesic.20,146,147 Whether this is a true analgesic effect or a consequence of its sedating properties is unclear. An additional benefit related to the antihistamine properties of hydroxyzine is prevention of opiate-induced nausea and itching.
Phenothiazines, as with antihistamines, often are administered concomitantly with opioids to “enhance” analgesia. Claims of enhanced analgesia are not supported by well-designed studies, however. Many of these studies lack double-blinding, cross-over of patients, placebo control, or appropriate instruments capable of evaluating pain. Another problem in the design of studies evaluating the combination of a phenothiazine or antihistamine with an opioid is the failure to differentiate between analgesia and sedation. Two excellent reviews summarize the studies that demonstrate analgesia with antihistamines and discuss the proposed mechanisms of action.148,149
All phenothiazines, except for methotrimeprazine, initially demonstrated antianalgesic effects in experimental pain studies. Clinicians now realize that experimental pain is not a completely valid model to assess the response of a patient in pain. These studies could not assess the anxiolytic properties of the phenothiazines and the effect a reduction in anxiety has on pain perception. Furthermore, cancer and chronic pain cause anxiety, and anxiety worsens pain perception and, consequently, pain severity. This reinforcement cannot be overestimated and helps explain the apparent benefit many patients obtain from the combination of hydroxyzine with an opioid.
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