• Individualize the route, dose, and schedule.
• Once the optimal dose for a 24 hour period has been determined by titration, the analgesic should be given on a scheduled around-the-clock basis. A PRN order can then be used to treat breakthrough pain – pain that occurs before the next scheduled dose of the analgesic. If only PRN medications are used, it may take several hours and higher doses of opioids to relieve pain, leading to a cycle of under-medication and pain, alternating with periods of over medication and potential drug toxicity. Explain to patients that when pain is kept at a satisfactory level throughout the day, they can function at their optimum level.
• Analgesics for chronic pain are more effective when they are given around the clock rather than on a PRN basis. Analgesics should be given at regularly scheduled intervals if a patient is in continuous pain. The first step is establishing the dosage that relieves pain to the patient’s desired level and then to determine how long pain relief lasts. The next dose should be given before the last dose wears off. This practice prevents patients from experiencing the return of pain several times a day, as often occurs when medications are given PRN.
• Healthcare providers should know the dose and duration of action of several opioid analgesics. Although morphine is the most commonly used opioid, several factors should be considered in selecting a different opioid. These factors may include the patient’s prior successful experience with another drug, preference for a drug with a long duration of action, and the need to rotate opioid analgesics as indicated to lessen tolerance.
• Use an opioid with a rapid onset of action whenever possible.
• Give infants and children adequate doses of opioids. The clinical actions and effects of opioids in children and infants older than 6 months are similar to adults. Doses are calculated according to weight. Infants must be monitored very closely for opioid induced adverse side effects.
• Monitor patients closely for pain relief and side effects. Patients receiving opioids require regular assessment, especially when beginning or changing an analgesic regimen. Analgesics benefit patients optimally when the clinician monitors pain relief and side effects frequently and adjusts the regimen accordingly.
• Use caution when changing to a new opioid or a new route of administration. Use an equianalgesic chart (see link below for example) to calculate pain relief equivalencies. One reason patients may have difficulty transitioning from parenteral analgesia to oral analgesia is that the oral doses selected are too low.
• Avoid using meperidine (Demerol) due to its risk of neurotoxicity. Normeperidine, a metabolite of meperidine, is a toxin that stimulates the central nervous system, increasing the risk of anxiety, tremors, myoclonus, (repetitive muscle movements) and seizures. This risk increases when patients receive repetitive doses of meperidine. Patients who receive meperidine for more than 48 hours, those with preexisting renal or central nervous system disease, or individuals who receive doses over 600 mg/24 hours are at especially high risk of meperidine toxicity.
• Keep in mind that patients who have experienced appropriate pain relief on a consistent dose of opioid, who develop an increase in pain, should be evaluated for progressive disease, new pathology, skipped doses, or other causes.
• Do not use placebos to assess the nature of pain.
• Expect physical dependence and prevent withdrawal symptoms by using a tapering schedule.
  

Source: Principles of Analgesic Use in the treatment of acute pain and chronic pain (2003) 5th Ed. The American Pain Society

For an example of an equianalgesic chart, please link to GlobalRPh.com