Pain treatment

Management of continuous pain

Continuous pain will have a known cause, such as cancer or other chronic disease states. Hyman and Cassem (1989) suggested the following in the management of pain in such patients.

• Give analgesics on a fixed schedule rather than prn
• Observe for constipation
• Monitor for tolerance. An increase in dose of 50% is often necessary after 2 weeks
• Do not consider addiction in a terminally ill patient. Even in the non-terminally ill, the risk is <1%
• Give 2-3x the regular dose at bedtime so the patient can sleep
• If bone or inflammatory pain is present, give antiprostaglandin drugs (e.g., NSAIDs)
• Begin narcotics either orally or rectally
• Use adjunctive behavioral treatment

Management of chronic pain

Chronic pain has persisted for at least 6 months and the original stimulus for the pain is now gone. Chronic opiates are seldom a reasonable solution. The ideal plan is an integrative one that is focused on modulating pain rather than curing it. Medications tend to be underutilized in the treatment of chronic pain.

Opioids

Opiates vary in potency and a table of equivalency is here.

When used in the treatment of neuropathic pain, opioids do provide direct analgesic effects as opposed to just counteracting unpleasantness. One study found that continuous-release morphine gave rise to more pain relief from post-herpetic neuralgia than did tricyclic antidepressants.

When considering urine toxicology, it is important to remember the metabolism of opioids. For example, codeine is a pro-drug that is metabolized by 2D6 to morphine. Therefore, someone taking codeine would likely have a toxicology screen positive for codeine and morphine. However, if a patient were only taking morphine and was positive for codeine, then he/she was obtaining additional codeine.

Although long-term use does expose the patient to tolerance, there is evidence that tolerance is enhanced by chronic pain itself.

The fear of addiction tends to limit the use of opioids in the treatment of nonmalignant pain. However, this fear is often out of proportion with reality. ★In patients without a history of abuse, the incidence of abuse after narcotics is about 0.03%. The risk factors for problematic prescription of opioid use are:

• past cocaine use; history of alcohol or cannabis use
• lifetime history of substance use disorder
• family history of substance abuse
• heavy tobacco use
• history of severe depression or anxiety

In patients with a history of abuse, opiates should be dosed and titrated just as in other patients.

In general, a constant, as opposed to intermittent, schedule of dosing opioids should be maintained. Opioids with a longer duration and slow onset usually have less euphoric effect. In addition, pain alters opioid effects in that there is significantly less euphoria and fewer effects of morphine withdrawal. ★Note that methadone when used for analgesia requires a 6-hour dosing window. In addition, tolerance of the analgesic effect of methadone develops more slowly than for other opioids.

The most common side effect of chronic opioid therapy is decreased GI motility, which leads to vomiting, constipation, and abdominal pain. The "narcotic bowel" occurs when a patient attempts to taper off opioids, then pas painful constipation, which requires increases in opioid dose.

Some people have suggested that the most desirable patient for longer term use of opioids has the following characteristics:

• no substance abuse disorder
• reliable
• history of medication compliance
• willing to engage in recovery
• recognizes that opioids are only part of the solution
• good family support with no substance abusers at home

Some people report opioid allergies. ★There are several things to bear in mind regarding opioid allergies:

Opioids release histamine from mast cells

- Pruritis, urticaria may not mean allergy

Allergies, when they occur, tend to be to entire chemical families:

- Diphenylheptanes: methadone, propoxyphene

- Phenylpiperidines: meperidine, fentanyl

- Phenanthrenes: codeine, hydromorphone, morphine, oxycodone, hydrocodone

Rashes more likely from inactive additives.

Important interactions

★There are several important interactions to be aware of with opioids.

• Meperidine cannot be given concomittantly with MAOIs.
• Tramadol also has serotonergic activity and can potentiate serotonin syndrome

Opioid tapers

Some patients with chronic pain may not respond to opioids. In these situations, you may have to taper them off of an opioid. ★There are several strategies for tapering opioids.

There are several stages of opioid withdrawal that occur at specific time points, as shown in this table.

Antidepressants

The first report of tricyclic antidepressants in the treatment of trigeminal neuralgia was in 1960 and used imipramine. Since this time, the uses of tricyclic's in the treatment of chronic pain is legion. Somewhat oddly, the analgesic effects of tricyclic antidepressants occurs independent of changes in mood. Antidepressants vary in their efficacy in treating neuropathic pain, as shown in this table.

Tricyclics. Tricyclic antidepressants are the most commonly used and the most studied in the treatment of neuropathic pain, especially with burning, numbness, or tingling sensations. The tertiary amines (amitriptyline, doxepin, imipramine) inhibit reuptake of norepinephrine more so than serotonin. The reverse is true of secondary amines (desipramine, nortriptyline). ★Though the research is not clear, in general tertiary amines are felt to be more effective in the treatment of neuropathic pain. Thus, noradrenergic activity tends to be associated with better analgesia than serotonergic activity alone. Medications with balanced noradrenergic and sertonergic activity (e.g., imipramine, amitriptyline, doxepin) are considered more effective.

★The analgesic effects of antidepressants is usually independent of the presence of depression or improvement in mood.

SSRIs. The data supporting the efficacy of SSRIs in the management of chronic pain is less consistent than that for tricyclics. This is summarized in the table. It is generally the case that fluoxetine does not seem to have much effect.

Others. Venlafaxine and duloxetine inhibit presynaptic reuptake of serotonin and norepinephrine, although duloxetine is more potent. Duloxetine is approved for the treatment of diabetic neuropathy.

Anticonvulsants

Some anticonvulsants can be of benefit in treating chronic pain. Phenytoin was used for trigeminal neuralgia as far back as 1940, though carbamazepine is most widely studied for its use in neuropathic pain. Valproic acid is effective in the treatment of neuropathic pain and migraine. Gabapentin (typically at higher doses) can reduce neuropathic pain and phantom limb pain. Lamotrigine may also be effective with phantom limb pain, diabetic neuropathy, trigeminal neuralgia, and poststroke pain.