The management of chronic pain in older individuals can be challenging. Relieving pain without affecting mental status or causing other complications can be difficult. Every effort should be made to find a remediable cause of the pain.
Non-narcotic options for pain are somewhat limited. Acetaminophen, once thought to be very safe at doses of up to 4 gm per day, has now been found to produce significant elevations in liver function tests in 30% - 40% of patients receiving 4 gm per day. Aspirin is still an effective analgesic for many conditions, but is limited by gastric side effects, salicylate toxicity, and allergy. Nonsteroidal anti-inflammatory drugs (NSAID's), both traditional COX-1 and newer COX-2 inhibitors, have significant renal and cardiac complications, cause salt and fluid retention, and make management of hypertension difficult. The daily, chronic use of NSAID's is very toxic and should be avoided.
Propoxyphene has limited effectiveness, can produce dizziness, constipation, sedation, and is now considered inappropriate for older individuals. Tramadol has both opioid activity and inhibits serotonin and norepinephrine reuptake. It may be a reasonable choice if one is very concerned about the potentially addicting effect of opioids; this should not be a major concern for older patients with chronic pain.
Opioids in older patients have significant side effects. Physical dependence does occur after prolonged administration of one month or more and will result in withdrawal symptoms such as dysphoria, anxiety, and mood volatility as well as tachycardia and sweating. These symptoms can be avoided by gradual tapering of the medications.
Morphine's most significant side effect is respiratory depression, with decreased respiratory rate, minute volume, and tidal exchange. This effect is potentiated with alcohol, sedatives, and analgesic agencies. This medication can also cause nausea, orthostatic hypotension, decreased gastric motility, decreased biliary, pancreatic, and intestinal secretions, decreased peristalsis in the colon, and increased rectal sphinctal tone.
While the duration of morphine analgesia increases with age, the degree does not. Morphine is available in several oral formulations. The long-acting preparations are not generic and can be quite expensive.
The analgesic effect of codeine occurs only when it is demethylated to form morphine. The P450 enzyme CYP2D6 is necessary to convert codeine to morphine. This medication is ineffective as an analgesic in the 10% of Caucasians that lack this enzyme. Codeine is more orally available than morphine.
Oxycodone is not a derivative of codeine. It is derived from the bain, a component of opium. It is 60% orally bioavailable. Controlled release oxycodone has been demonstrated to be effective in a number of conditions, but has a significant potential for abuse and is quite expensive.
Hydrocodone is available in the United States only in combination with acetaminophen or ibuprofen. The significant amount of acetaminophen in each tablet (500 mg. in Vicodin) may limit its daily use.
Hydromorphone is a semisynthetic opioid analgesic, whose onset of action is faster than morphine's, but slower than fentanyl's. It appears to be as effective as morphine for acute and chronic pain, but has a side effect profile similar to morphine.
Fentanyl is a synthetic opioid which is 80 to 100 times more potent than morphine, and is lipid soluble, rapidly crossing the blood brain barrier. The lipid solubility, high potency, and low molecular weight of Fentanyl favors skin absorption and allows it to be utilized as a transdermal patch. The drug forms a depot with upper skin layers and the medication is slowly released into the microcirculation. The medication continues to be absorbed from the cutaneous skin depot after the patch is removed. It takes sixteen to twenty-two hours to decrease blood levels to 50% after the patch is removed, and the elimination half life is even longer in elderly patients. This medication should not be used in narcotic naive patients and should not be used for acute or postoperative pain.
Methadone has good absorption from the GI tract and low cost. In young individuals its half life averages from 15 to 40 hours. This extended duration of action, and great variation in half life, limits its use in older individuals.
Neuropathic pain can be treated by several classes of medications. Tricyclic antidepressants are effective, but have serious side effects of cardiac conduction disturbances, orthostatic hypotension, and potential for acute angle closure glaucoma. Secondary amines (nortriptyline and desiprapine) have fewer side effects than the tertiary amines (e.g. amitriptyline).
Other antidepressants, such as bupropion and venlafaxine (both norepinephrine reuptake inhibitors), have been demonstrated to be effective for neuropathic pain. Duloxetine, a serotonin and norephinephrine reuptake inhibitor, is the first drug to be approved by the FDA for diabetic neuropathy. There have been no studies comparing this drug with other drugs known to be effective for neuropathy.
Antiepileptic medications, which act to inhibit excitatory transmission, also have effectiveness in treating neuropathic pain. Carbamazapine is effective in trigeminal neuralgia and diabetic neuropathy, but limited by leukopenia and hyponatremia. Lamotrigine has been shown to be effective in HIV-related neuropathy and diabetic neuropathy, but has a risk of serious rash and Stevens-Johnson Syndrome.
Gabapentin has been demonstrated to be an effective drug in diabetic neuropathy, using doses of 1600 to 1800 mg. per day. Its major side effect is sedation as well as other CNS effects. It is often difficult to use therapeutic doses in older patients because of sedation and CNS effects. It is synergistic with sustained release morphine for diabetic neuropathy and postherpetic neuropathy.
Pregabalin, a structural analog of gamma amino butyric acid, is effective in postherpetic neuralgia and diabetic neuropathy. Side effects are dizziness, somnolence, peripheral edema, and confusion. There have been no studies comparing this medication with other drugs.
The impact and side effects of pain medications must be monitored closely. The overall impact of pain on one's function may be a better index than visual analog scales. It is best to start with short-acting drugs, moving to extended formulations only after the response to short-acting drugs is clear. Avoid daily use of nonsteroidal anti-inflammatory drugs and watch the total dose of acetaminophen in combination drugs. Do not worry about addiction in these patients. Do monitor carefully, however, for effects on cognition and bowels. Learn the effectiveness, adverse effects, and pharmacology of a few opioids well. Excellent care is not the use of the newest drug, but the use of the most effective drugs in an appropriate manner.
|
