Pharmacology and Medicinal Chemistry of Pain, Analgesic, Anti-inflammatory and Antipyretic Drugs

Dedication

Science has evident that, a mother feels extreme pain during childbirth, generally described as a combination of strong cramping, tightening, and pressure, with some women comparing it to extreme menstrual cramps, bad back pain, or a broken bone. As labor progresses, contractions become more intense, longer, and closer together,labor feels like the worst pains someone can ever imagine, followed by mothers butt feeling like it's going to explode or basically split open. A mother bear this much pain just to bring her child to the earth.

This is just to illustrate the extent to which a mother loves her child! 'Love your mom till the end of your life. The lady with whom you fight almost every day, suffered so much pain just to give you a beautiful life!

This chapter on pain and pain management is dedicated to all beloved mothers without their tolerance and affection, the world doesn’t become so much beautiful. 

Pain 

Pain, in the sense of physical pain, is a typical sensory experience that may be described as the unpleasant awareness of a noxious stimulus or bodily harm. Individuals experience pain by various daily hurts and aches, and sometimes through more serious injuries or illnesses. For scientific and clinical purposes, pain is defined by the International Association for the Study of Pain (IASP) as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage". Pain begins when local tissue damage, a noxious stimuli stimulate inflammatory process that release inflammatory substances, such as-Prostaglandins, Serotonin, Bradykinin, Histamines etc.

In medicine, pain is considered as highly subjective. A definition that is widely used in nursing was first given as early as 1968 by Margo McCaffery: "Pain is whatever the experiencing person says it is, existing whenever he says it does". Pain of any type is the most common reason for physician consultation in the United States, prompting half of all Americans to seek medical care annually. It is a major symptom in many medical conditions, significantly interfering with a person's quality of life and general functioning. Diagnosis is based on characterizing pain in various ways, according to duration, intensity, type (dull, burning, throbbing or stabbing), source, or location in body. Usually pain stops without treatment or responds to simple measures such as resting or taking an analgesic, and it is then called ‘acute’ pain. But it may also become intractable and develop into a condition called chronic pain, in which pain is no longer considered a symptom but an illness by itself. The study of pain has in recent years attracted many different fields such as pharmacology, neurobiology, nursing, dentistry, physiotherapy, and psychology. Pain medicine is a separate subspecialty figuring under some medical specialties like anesthesiology, physiatry, neurology, and psychiatry.

Pain is part of the body's defense system, triggering a reflex reaction to retract from a painful stimulus, and helps adjust behavior to increase avoidance of that particular harmful situation in the future. Given its significance, physical pain is also linked to various cultural, religious, philosophical, or social issues.

Analgesic drugs 

An analgesic (also known as a painkiller) is any member of the diverse group of drugs used to relieve pain (achieve analgesia). The word analgesic derives from Greek an- ("without") and algos ("pain"). Analgesic drugs act in various ways on the peripheral and central nervous systems; they include paracetamol (acetaminophen), the non-steroidal anti-inflammatory drugs (NSAIDs) such as the salicylates, narcotic drugs such as morphine, synthetic drugs with narcotic properties such as tramadol, and various others.

In choosing analgesics, the severity and response to other medication determines the choice of agent; the WHO pain ladder, originally developed in cancer-related pain, is widely applied to find suitable drugs in a stepwise manner. 

The analgesic choice is also determined by the type of pain: for neuropathic pain, traditional analgesics are less effective, and there is often benefit from classes of drugs that are not normally considered analgesics, such as tricyclic antidepressants and anticonvulsants.

Inflammation 

Inflammation (Latin, inflamatio, to set on fire) is the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. It is a protective attempt by the organism to remove the injurious stimuli as well as initiate the healing process for the tissue. Inflammation is not a synonym for infection. Even in cases where inflammation is caused by infection, the two are not synonymous: infection is caused by an exogenous pathogen, while inflammation is the response of the organism to the pathogen.

In the absence of inflammation, wounds and infections would never heal and progressive destruction of the tissue would compromise the survival of the organism. However, an inflammation that runs unchecked can also lead to a host of diseases, such as hay fever, atherosclerosis, and rheumatoid arthritis. It is for that reason that inflammation is normally closely regulated by the body.

Inflammation can be classified as either acute or chronic. Acute inflammation is the initial response of the body to harmful stimuli and is achieved by the increased movement of plasma and leukocytes from the blood into the injured tissues. A cascade of biochemical events propagates and matures the inflammatory response, involving the local vascular system, the immune system, and various cells within the injured tissue. Prolonged inflammation, known as chronic inflammation, leads to a progressive shift in the type of cells which are present at the site of inflammation and is characterised by simultaneous destruction and healing of the tissue from the inflammatory process.

Antiinflammatory drugs

Anti-inflammatory refers to the property of a substance or treatment that reduces inflammation. Anti-inflammatory drugs make up about half of analgesics, remedying pain by reducing inflammation as opposed to opioids which affect the brain.

Antipyretic drugs: Antipyretics (literally "against the fire") are drugs that reduce body temperature in situations such as fever. However, they will not affect the normal body temperature if one does not have a fever. Antipyretics cause the hypothalamus to override an interleukin-induced increase in temperature. The body will then work to lower the temperature and the result is a reduction in fever.

Most are also used for other purposes. For example, the most common antipyretics are aspirin and paracetamol (acetaminophen), which are used primarily as pain relievers. NSAIDs are antipyretic, anti-inflammatory, and pain relievers. There is some debate over the appropriate use of such medications: fever is part of the body's immune response to infection.

Herbal remedies with a fever-reducing effect are called febrifuges, and include catnip, chamomile, sage, wormwood and yarrow.

However, the term febrifuge can also refer to a refrigerant, such as topical alcohol, which cools the body by physically removing heat rather than modifying the body's responses. This is not recommended currently, because alcohol can be transferred through the skin and affect the liver. In addition, alcohol slightly raises the body temperature before it brings it down, which, if the fever is already very high could cause permanent damage.

Some cultures use gallstones as antipyretic antidotes like in China for example, obtained from cow or dog meat.

Further reading 

• Inflammation