Chronic pain is one of the most prevalent, and disabling condition which hampers a quality life both in personal and professional areas. Clinically, it is sometimes very difficult to assess. Also this is a problem which often remains inadequately treated. Moreover, chronic pain commonly coincides with depression and sleep disturbance, as well as mood and anxiety disorders.
Therefore, it is very important to plan an effective pharmacologic therapy for proper pain management. Here we discuss the major classes of medications as they relate to chronic pain management and thus offer better treatment decisions and combination therapy by increasing your knowledge of the pharmacological options that are available to manage different pain mechanisms.
1. Nonopioid analgesics
Opioid is a compound that acts on the human body like morphine, often used for pain relief. Aspirin and related compounds constitute a class of drugs known as Nonsteroidal Anti-Inflammatory Drugs (NSAIDs). NSAIDs have 3 desirable pharmacological effects: anti-inflammatory, analgesic, and antipyretic (preventing fever) effects. All NSAIDs appear to be equally effective in the treatment of pain disorders.
Acetaminophen has analgesic and anti-pyretic effects similar to NSAIDs. Acetaminophen is a slightly weaker analgesic than NSAIDs, but is a reasonable first-line option because of its more favorable safety profile and low cost.
Tramadol is a drug with a dual activity: one-third of its activity is due to an opioid -like mechanism and two-thirds are due to a mechanism similar to amitriptyline (an antidepressant). It truly represents a multimodal drug to consider for pain management strategies. Tramadol has proven effective to treat osteoarthritis (OA), fibromyalgia (FM), and neuropathic pain (NP). However, it should be used with some caution in persons recovering from substance use disorders. While the degree of physical dependence appears to be relatively mild, patients have reported symptoms of psychic dependence, such as craving tramadol when discontinuing the drug. Daily doses of tramadol should not exceed 400 mg.
3. Opioid analgesics:
Controlled-release opioid analgesics have a major role to play in patients with chronic pain. Studies show that opioids were more effective than placebo for both the pain and functional outcomes of patients with nociceptive and neuropathic pain. Opioids are a reasonable and efficacious treatment for people with chronic pain. The recommended front-line agents include hydromorphone, morphine, and oxycodone used orally on a time-contingent basis.
In case of few anti-depressants, patients often discontinue the medication because side effects occur early, while the analgesia may take several weeks to occur. You must know that with time you will become tolerant to the side effect and analgesia needs some weeks to be evident. In case of pain, an antidepressant is used as a therapy not necessarily associated with psychological problems. Antidepressants work at the spinal level by inhibiting the reuptake of the neural transmitters-norepinephrine and serotonin, and so this potentiates the inhibitory pathway in the spinal cord and in the peripheral nerves by blocking Na channels. Few anti-depressants are:
– Tricyclic antidepressants (TCAs)
Tricyclic antidepressants have the longest track record of any antidepressant class for the treatment of multiple pain conditions. The advantages of TCAs include decades of clinical experience with TCAs for pain management and their low cost. The disadvantages of TCAs are side effects (which may be less when prescribing the lower doses used for analgesia), including cardiovascular effects (e.g., hypertension, postural hypotension, arrhythmias), falling down in older adult patients, and there is also potential lethality with an overdose.
– Serotonin-norepinephrine reuptake inhibitors (SNRIs)
Duloxetine has been proven superior to placebo in patients with pain due to diabetic peripheral neuropathy. Duloxetine is also FDA approved for treating the chronic widespread pain of fibromyalgia. Venlafaxine is reported well in patients with diabetic neuropathy. Venlafaxine may also be useful in other painful conditions, but it does not have the FDA approved indication for pain treatment.
Anticonvulsants have been used for the management of pain since the 1960s and along with antidepressants and constitute the important adjunctive classes of medications for pain management. The clinical impression is that they are useful for chronic neuropathy, especially when the pain is described as sharp or burning. Gabapentin and pregabalin have the strongest evidence for the treatment of pain. They also have peripheral analgesic actions. These actions result in inhibiting the release of excitatory neurotransmitters that are important in the production of pain.
Other drugs worth trying are lamotrigine, clonazepam, and valproate. Carbamazepine and Oxcarbazepine are considered the first effective drugs for trigeminal neuralgia. Carbamazepine and Oxcarbazepine act peripherally on Na channels while the others work at spinal levels by different mechanisms with a common inhibitory effect in the spinal cord.
6. Topical analgesics
A potential advantage of topical agents is avoiding systemic side effects that are often associated with oral medications. Topical analgesics probably have a circumscribed role in treating localized areas of mild to moderate neuropathic or osteoarthritic pain, either as an adjunct with other medications or as an alternative for patients who prefer not to ingest pills. Several topical analgesics are lidocaine, capsaicin, and salicylate.
It is very important for your pain physician to understand the complex nature of chronic pain and the physiological differences between nociceptive pain and neuropathic pain. A thorough understanding of pain mechanisms and good communication between physicians and patients are required to improve patient outcomes. Only then your doctor can choose a multi-level approach with taking into account stepwise selection of medications. A multi-level approach means combining 2 substances from different drug classes, or administering an analgesic with 2 different mechanisms of action. In some circumstances, a single compound capable of addressing both nociceptive and neuropathic pain is desirable.