How Analgesic Drugs Are Classified
The word analgesia , etymologically, means denial or lack of pain. This is the goal of pain reliever medications. According to the International Association for the Study of Pain (IASP), pain is defined as the unpleasant sensory and emotional experience. This experience is associated with a real or potential tissue injury.
There are two types of pain: acute and chronic. They differ in terms of sensory experience and also in terms of the emotional experience they involve. Thus, they require different analgesic medications.
Acute pain is derived from a tissue injury, and disappears with the healing of it. An example of acute pain is postoperative pain. On the other hand, it is difficult to find a specific tissue lesion that justifies chronic pain. In addition, they are very spread over time. An example of chronic pain is migraine or osteoarthritis.
As we have indicated before, the emotional component is different in acute and chronic pain. In the case of acute pain, it is common to experience irritability, anxiety and anger. In the context of chronic pain, feelings that tend to depression are experienced.
Primary pain relievers
The main goal of primary pain reliever medications is to relieve pain. Therefore, they are useful for different types of discomfort. Three large groups are distinguished.
Pure analgesics-antipyretics
Pain relievers have other functions as well. The vast majority are also antipyretic (fight fever) and anti-inflammatory.
The group that concerns us now is the exception. An example of a pure analgesic-antipyretic is paracetamol. It does not fight inflammation but it does combat fever and pain.
Analgesic-anti-inflammatory drugs (NSAIDs)
NSAIDs owe their function to the block they perform on the enzyme cyclooxygenase (COX). They prevent COX from synthesizing some substances related to the inflammatory process, thus managing to stop it. Examples of NSAIDs are acetylsalicylic acid (aspirin) or ibuprofen.
But there are different types of COX, each with its own function, and there are pain relievers that block each type in specific ways. These drugs are called selective COX inhibitors (selective iCOX). Examples are celecoxib and rofecoxib.
Opioids
Opioid pain relievers activate their specific receptors. In general, when one of these is activated, it hinders nerve transmission. Thus, an activated opioid receptor decreases the nerve transmission of pain.
There are different types of opioids depending on their efficiency and other characteristics. Thus, we find:
- Pure agonists: the most effective. Examples are morphine, codeine, and methadone.
- Partial agonists: slightly less effective. An example is buprenorphine.
- Agonists-antagonists: activate some opioid receptors and block others. An example is pentazocine.
- Mixed: they have other functions apart from opioids. An example is tramadol.
Opioids often cause unwanted effects such as nausea, constipation, or sedation.
Secondary pain relievers
The primary goal of secondary pain relievers is not pain relief. In fact, they were invented to alleviate other conditions. However, they can alleviate some specific type of pain.
Antidepressants
As we have already explained, depressive symptoms are frequently associated with pain, especially chronic pain. Antidepressants can be beneficial in this regard. One of the most used is amitriptyline.
Antiepileptics
Antiepileptic drugs reduce nerve transmission. When used, the nerve transmission of pain decreases. Carbamazepine and lamotrigine are frequently used.
Muscle relaxants
Muscle relaxants can be beneficial especially in pain of muscle origin. If the origin of the pain is a contracture or similar, when using them the muscle will relax and the pain will decrease.
In addition, in these cases they help to achieve the resolution of the pathology. Commonly used muscle relaxants are diazepam, gabapentin, and topiramate.
Local anesthetics
Local anesthetics block nerve transmission in the area where they are applied. Thus, by using local anesthetics in the original area of pain, the pain will disappear or decrease.
They can also be applied to structures through which the painful impulse passes on its way to the higher nerve centers. In this way, the pain will not become conscious, at least in part. Commonly used local anesthetics are lidocaine and pilocarpine.
Corticosteroids
Corticosteroids have a similar effect to NSAIDs in that they act by inhibiting or reducing inflammation. When this happens, the pain caused by it will decrease. A commonly used corticosteroid is prednisone.
Painkillers are very varied and useful
As we have seen, an analgesic drug is one whose objective is to relieve pain. Now, depending on its characteristics, the drug will be classified in one way or another.
