What are Analgesics? Opioid and Non-Opioid Painkillers

What is an analgesic?

An analgesic is any type of drug that relieves pain although this may only be a partial relief at times. It should not be confused with anesthetics that block pain and other impulses in the nerves to a degree that there is numbness. Analgesics are commonly referred to as painkillers or pain-killers and is among the more widely used type of drug in the modern pharmacy of today. The term ‘analgesic’ encompasses many class of drugs, all of which relieve pain to varying degrees and different mechanisms.

What is pain?

In most instances, pain serves as the body’s warning signal to alert you of damage or impending damage to living tissue. Inflammation is the body’s response to tissue injury and one of the symptoms of inflammation is pain. The release of different chemicals associated with inflammation irritates the pain receptors, known as nocioceptors, which leads to pain. Similarly, damage or irritation of the nerve can also lead to pain even when the surrounding tissue is intact.

The pain receptors have a certain threshold level which once reached, then allows the pain impulses to reach the brain. This ensures that the human body is not constantly in pain from everyday activities, minor bumps and moderate pressure. Although pain serves as a warning signal of damage and will only ease once the offending agent has been removed or the damaged tissue heals, it some cases it may be present despite there being no damage or injury. This is known as neuropathic pain or if it is a result of mental or emotional factors then it is known as psychogenic pain.

Action of analgesics

Analgesics work in one of two ways to relieve pain :

• Reduces inflammation.
• Blocks nerve impulses.

Non-opioids

Non steroidal anti-inflammatory drugs (NSAID’s) reduce inflammation thereby relieving the pain and in this sense it may be referred to as an analgesic. Examples of NSAID’s includes ibuprofen, paracetamol (acetaminophen) and aspirin. Many of these type of drugs are harsh on the lining of the stomach and is not advisable for long term use. It falls under the broad category of non-selective COX inhibitors.

Another type of NSAID that is also used for pain relief is the COX-2 (cyclooxygenase-2) inhibitors, which are not as harsh on the gastric lining. These drugs have received negative publicity since they have been linked with an increased risk of heart attacks and strokes in long term use and certain brands of COX-2 inhibitors have been removed from the market. Example of a COX-2 inhibitor is celecoxib which is still available while other COX-2 inhibitors like the previously popular rofecoxib is no longer available.

These drugs are known as non-opioids.

Picture of ibuprofen from Wikimedia Commons

Opioids

Other analgesics may act on the central or peripheral nervous system to either reduce the impulses sent by the pain receptors to the brain or block the perception of pain in the brain. Opioids are one type of analgesics that act on the central nervous system to block the perception of pain, which can also be viewed as an increased tolerance to pain.

These scheduled drugs may either be classified as :

• Weak opioid analgesics like codeine.
• Strong opioid analgesics like morphine.

Acute pain is often due to inflammation and an NSAID, sometimes used in combination with other class of analgesic drugs, is usually sufficient for pain management. However in chronic pain, analgesics that act on the central nervous system may be necessary. The danger of these type of drugs is that they have narcotic effects and are usually addictive. Other drugs that may have pain-relieving properties include psychotropic drugs like  tricyclic antidepressants.

Side Effects of Analgesics

NSAIDs, or non-opioid analgesics, are most widely used and if used in small to moderate doses over a short period of time, the side effects are minimal. However, long term NSAID use may cause :

• Peptic ulcers
• Loss of appetite
• Nausea
• Indigestion
• Abdominal pain
• Diarrhea

In these event of toxic doses or in a person with drug hypersensitivity, there may also be breathing problems, skin rashes, liver dysfunction and acute kidney failure.

Opioids have more severe side effects even with small doses and in short term use. This includes :

• Drowsiness
• Confusion
• Cognitive impairment
• Poor memory
• Slurred speech
• Slow breathing
• Retention of urine
• Low blood pressure

It may also cause skin rashes and other effects like NSAIDs when used in high doses. The reduced activity of the heart and drop in body temperature may eventually contribute to death.