Pain

GENERAL PRINCIPLES

Pain is subjective and therapy must be individualized. Chronic pain may not be associated with any objective physical findings. Pain scales can be employed for quantitation.

TREATMENT

• Acute pain usually requires short-term therapy and often improves with acetaminophen- or NSAID- based regimens.

• Chronic pain requires multimodality management to keep opioid use to a minimum to prevent risk of dependence and subsequent escalation of opioid doses. Higher doses of opioids have been shown to increase the risk of overdose without providing increased pain relief.⁹

• If pain is refractory to medical therapy, then nonpharmacologic modalities, such as nerve blocks, sympathectomy, and cognitive behavioral therapy, may be appropriate.

Opioid Analgesics

• Effects: Opioid analgesics are pharmacologically similar to opium or morphine and are indicated for moderate to severe pain.

• Dosage: Table 1-1 lists equianalgesic dosages.

TABLE 1-1

EQUIPOTENT DOSES OF OPIOID ANALGESICS

^aAn IM: PO ratio of 1:2-1:3 used for repetitive dosing.

Note: Equivalences are based on single-dose studies.

NA, not applicable.

• For acute pain management, the lowest effective dose of immediate-release opioids should be given. Patients with demonstrated tolerance often require higher doses.

• Use of nonopioid pain medications and nonpharmacological pain management strategies to minimize opioid needs is encouraged.

• Both parenteral and transdermal administration are useful in the setting of dysphagia, emesis, or decreased gastrointestinal (GI) absorption.

• Patient-controlled analgesia often is used to control pain in a postoperative or terminally ill patient. Opioid-naive patients should not have basal rates prescribed due to risk of overdose.

• If a patient requires continuous (basal) analgesia, supplementary PRN doses for breakthrough pain of roughly 5%-15% of the daily basal dose can be provided. If frequent PRN doses are required, the maintenance dose should be increased, or the dosing interval should be decreased.

• Severe pain uncontrolled with large doses of opiates, particularly while using patient-controlled analgesia with basal rates, may w arrant consultation with a pain specialist.

î Opioids are relatively contraindicated in acute disease states in which the pattern and degree of pain are important diagnostic signs (e.g., head injuries). They also may increase intracranial pressure.

î Opioid dosage should be adjusted for patients with impaired hepatic or renal function.

î Drugs that potentiate the adverse effects of opioids include phenothiazines, antidepressants, benzodiazepines, and alcohol.

° Tolerance develops with chronic use and coincides with the development of physical dependence, which is characterized by a withdraw al syndrome when the drug is stopped abruptly. It may occur after only 2 weeks of therapy.

° Administration of an opioid antagonist may precipitate withdrawal after only 3 days of therapy.

î The quantity of opioid tablets prescribed at discharge should not exceed the expected duration of pain.

• Adverse and toxic effects

î Central nervous system effects include sedation, euphoria, and pupillary constriction.

î Respiratory depression is dose related and pronounced after IV administration.

î Cardiovascular effects include peripheral vasodilation and hypotension.

î GI effects include constipation, nausea, and vomiting. Stool softeners and laxatives should be prescribed to prevent constipation. Opioids may precipitate toxic megacolon in patients with inflammatory bowel disease.

î Genitourinary effects include urinary retention.

î Pruritus occurs most commonly with spinal administration.

î Opioid overdose

■ Naloxone, an opioid antagonist, should be readily available for administration in the case of accidental or intentional overdose.

■ Naloxone home rescue kits have been shown to reduce opioid overdose mortality.¹⁰ Patients being discharged home on more than 50 morphine milligram equivalents per day have a higher risk of overdose and may benefit from a prescription for intranasal naloxone at discharge.