Clinical Textbook of Addictive Disorders 3rd ed - R. Frances, S. Miller, A. Mack (Guilford, 2005) WW

17. Pain and Addiction 385adverse effects supervene. The opioid responsiveness of a specific pain syndromecan only be ascertained by dose escalation to limiting adverse effects.The opioid dose is immaterial as long as the patient attains a favorable balancebetween analgesia and adverse effects.Although doses typically stabilize for prolonged periods during long-termmanagement, dose escalation is usually required at intervals to maintain analgesia.In patients with progressive medical illness, this dose escalation is usuallyexplained by a worsening of the pain-producing organic lesion (Nghiemphu &Portenoy, 2000; Portenoy, 1994). As observed previously, experience withlong-term management of pain suggests that tolerance is rarely the “drivingforce” for dose escalation in the clinical setting.Relative potencies have been determined for most pure agonist drugs insingle-dose analgesic assays (Table 17.5). Using potency ratios, equianalgesicdose tables have been created that provide guidance when switching drugs orroutes of administration (Indelicato & Portenoy, 2002). Due to incompletecross-tolerance between opioids, which may result in a potency greater thananticipated for the newly initiated drug, a change from one drug to anothershould always be accompanied by a 25–50% reduction in the calculatedequianalgesic dose. The exceptions to this include methadone, which should bereduced by 75–90% when initiated after treatment with another pure agonistdrug, and transdermal fentanyl, which should be started at the dose indicated inthe package insert (dose reduction already has been built in to these recommendations).The extent to which the equianalgesic dose is reduced by a safetyfactor can be adjusted up or down depending on the clinical condition of thepatient, specifically the severity of the pain, the existence of opioid-related sideeffects, and the severity of medical comorbidities.4. Side effect management. The management of side effects is an essentialpart of opioid therapy. By adequately treating side effects, it is often possible totitrate the opioid to a higher dose and thereby increase the responsiveness ofthe pain. Although respiratory depression fosters the greatest concern, toleranceto this adverse effect develops rapidly, and it is very uncommon if theopioid is titrated according to the accepted dosing guidelines. Constipation isthe most frequent side effect encountered with chronic opioid therapy. Patientsotherwise predisposed to constipation by virtue of advanced age or medicalcomorbidity should be considered for a prophylactic bowel regimen whenopioid therapy is initiated. Although somnolence and mental clouding is frequentat the start of opioid treatment, these effects usually subside in a few days.In the absence of other medical problems, long-term opioid therapy should beaccompanied by clear thinking; the capacity to drive or otherwise function at ahigh level should be considered goals of the treatment. Occasionally, the analgesicresponse is satisfactory but therapy is persistently compromised by somnolenceor mental clouding. One option in this setting, which generally isaccepted by pain specialists, is coadministration of a psychostimulant (such