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Facts About Analgesics (Painkillers)

Drugs Designed to Relieve Pain

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Updated August 20, 2014

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What Are Analgesics?

Simply put, analgesics are a class of drugs used to relieve pain. The pain relief induced by analgesics occurs either by blocking pain signals going to the brain or by interfering with the brain's interpretation of the signals, without producing anesthesia or loss of consciousness. There are basically two kinds of analgesics: non-narcotics and narcotics.

It should be noted that some references include aspirin and other non-steroidal anti-inflammatory drugs (NSAIDS) in the class of analgesics, because they have some analgesic properties. Aspirin and NSAIDS primarily have an anti-inflammatory effect, as opposed to being solely analgesic.

Non-Narcotic Analgesics

Acetaminophen is the most commonly used over-the-counter, non-narcotic analgesic. Acetaminophen is a popular pain-reliever because it is both effective for mild to moderate pain relief and relatively inexpensive. It must be emphasized though that the safety of acetaminophen is tied to proper use of the drug (use according to specific prescribing instructions). If acetaminophen is not used according to the directions on the label, serious side effects and possible fatal consequences can occur. For example, taking more than 4,000 mg/day or using it longterm can increase the risk of liver damage. The risk of liver damage with acetaminophen use is also increased by ingesting alcohol. Make sure you discuss with your doctor the maximum allowable dose of acetaminophen and any other guidelines for its use.

Many people do not realize that acetaminophen is found in more than 600 over-the-counter drugs. It can be found in combination with other active ingredients in many cold, sinus, and cough medications. The cumulative effect of acetaminophen must be considered if you are talking multiple drugs which contain acetaminophen.

How can acetaminophen damage the liver? Acetaminophen changes into metabolites which are eliminated from the body. By taking more than the recommended maximum daily dose of acetaminophen, more toxic metabolites are produced than can be eliminated.

Narcotic Analgesics

There are two types of narcotic analgesics: the opiates and the opioids (derivatives of opiates). Opiates are the alkaloids found in opium (a white liquid extract of unripe seeds of the poppy plant).

Opioids are any medication which bind to opioid receptors in the central nervous system or gastointestinal tract. According to Wikipedia, there are four broad classes of opioids:

  • Endogenous opioid peptides (produced in the body: endorphins, dynorphins, enkephalins)
  • Opium alkaloids (morphine, codeine, thebaine)
  • Semi-synthetic opioids (heroin, oxycodone, hydrocodone, dihydrocodeine, hydromorphone, oxymorphone, nicomorphine)
  • Fully synthetic opioids (pethidine or Demerol, methadone, fentanyl, propoxyphene, pentazocine, buprenorphine, butorphanol, tramadol, and more)

Opioids are used in medicine as strong analgesics, for relief of severe or chronic pain. Interestingly, there is no upper limit for the dosage of opioids used to achieve pain relief, but the dose must be increased gradually to allow for the development of tolerance to adverse effects (for example, respiratory depression). According to eMedicine, "Some people with intense pain get such high doses that the same dose would be fatal if taken by someone who was not suffering from pain."

There have been debates over the addictive potential of opioids vs. the benefit of their analgesic properties for treating non-malignant chronic pain, such as chronic arthritis. Some experts believe opioids can be taken safely for years with minimal risk of addiction or toxic side effects. The enhanced quality of life which opioids may provide the patient must be considered.

Side Effects / Adverse Reactions of Opioids:

Common side effects and adverse reactions:

  • nausea
  • vomiting
  • drowsiness
  • dry mouth
  • miosis (contraction of the pupil)
  • orthostatic hypotension (blood pressure lowers upon sudden standing)
  • urinary retention
  • constipation and/or fecal impaction

Less common side effects and adverse reactions:

  • confusion
  • hallucinations
  • delirium
  • hives
  • itch
  • hypothermia
  • bradycardia (slow heart rate)
  • tachycardia (rapid heart rate)
  • raised intracranial pressure
  • ureteric or biliary spasm
  • muscle rigidity
  • flushing

Most severe side effects and adverse reactions:

  • respiratory depression
  • fatal overdose

More Information on Specific Analgesics

Sources:

Types of Drugs - Analgesics. Arthritis Today Magazine. 6/11/07.
http://www.arthritistoday.org/treatments/drug-guide/types-of-drugs/drug-guide-analgesics.php

Pharmacologic Management of Pain. Primer on the Rheumatic Diseases. John H. Klippel.

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