Antipyretics are substances that have a fever-reducing effect or can prophylactically protect against fever. This includes substances and compounds from various classes of substances. They differ in their mode of action from other antipyretic agents, such as opiates.
What are antipyretics?
Antipyretics are substances that have a fever-reducing effect or can prophylactically protect against fever. The term antipyretics thus unites diverse substances under itself, which are similar in their effect, but can have different compositions and properties. The best-known antipyretics include paracetamol, acetylsalicylic acid, ibuprofen, naproxen and ketoprofen. Paracetamol belongs to the non-opioid analgesics, i.e. painkillers that differ from opiates in their mode of action. The other antipyretics mentioned also have an anti-inflammatory function in addition to their antipyretic effect. Therefore, they are grouped under the term antirheumatics. To distinguish them in their mode of action from cortisol and its related substances, they are also referred to as nonsteroidal anti-inflammatory drugs. There is no narrow definition of the various antipyretics in chemical terms because of the heterogeneous composition of this class of substances.
Medical application, effect, and use
All antipyretics have in common that they inhibit the synthesis of prostaglandin E2, which is produced in endothelial cells of the hypothalamus. This is a tissue hormone composed of arachidonic acid and is responsible for pain, inflammation and blood clotting, among other things. It triggers pain by irritating the nerve endings, which then send pain signals to the brain. Fever is also triggered by this hormone by activating specific receptors in the region of the hypothalamus where fever reactions are controlled. By inhibiting the synthesis of prostaglandin E2, the blood vessels of the skin are dilated, resulting in increased heat release. This results in increased sweat production, which cools the organism and lowers fever. Inhibition of prostagladin synthesis occurs in different ways. Ibuprofen, for example, inhibits the enzymes involved in the formation of prostagladin, called cyclooxygenases. Naproxen has an additional inhibitory effect on hormone-sensitive lipase, an enzyme that makes fats from food available for the synthesis of hormones. Paracetamol also has an inhibitory effect on cyclooxygenases, but in addition activates certain receptors responsible for the uptake of serotonin, which is an endogenous painkilling hormone. Thus, antipyretics differ in their exact mode of action, but their common function is to knock out prostaglandin E2 to reduce pain, inflammation, and fever.
Herbal, natural, homeopathic, and pharmaceutical antipyretics.
Antipyretics are basically synthetic, medicinal substances. This means that they do not occur as natural substances in the organism, but must be produced artificially. Due to the diversity of individual antipyretics, there are many production routes. The active ingredient of aspirin, for example, is acetylsalicylic acid, which is produced by the so-called Kolbe-Schmitt reaction. Precursors of acetylsalicylic acid, however, also have plant or animal origins. For example, willow bark extracts contain salicin, which is converted to salicylic acid in the human body. In the Kolbe-Schmitt reaction, salicylic acid is the first reactant. Salicylic acid is also found in a secretion that beavers secrete from their anal gland. Several established reaction pathways can be found for the active ingredient paracetamol. In industry, the most common is a reaction in which phenol is acylated with acetic anhydride in the presence of hydrofluoric acid. This produces p-hydroxyacetophenone, which is converted to oxime with hydroxylamine. With the addition of thionychloride, this eventually rearranges to acetaminophen. Paracetamol is usually sold as a monopreparation, but there are also combination preparations containing this active ingredient. If codeine or tramadol are included, these preparations require a prescription, unlike the monopreparation.A very wide range of preparations can be found for the active ingredient ibuprofen, which includes medications approved for infants 6 months and older.
Risks and side effects
Most antipyretics, such as ibuprofen and naproxen, have side effects related to the digestive extract. These include nausea, diarrhea, or gastrointestinal cramps. Less commonly, gastric ulcers, gastritis, or gastrointestinal bleeding may occur. Caution should therefore be exercised when taking these antipyretics, especially in cases of chronic intestinal inflammation. Aspirin can also cause gastrointestinal distress. In addition, it has an inhibitory effect on blood clotting, which is why it should not be taken in conjunction with surgery or during pregnancy. Acetylsalicylic acid is also not approved for use in children under 16 years of age in several countries because in rare cases it can cause fatal Reye’s syndrome. Of all antipyretics, acetaminophen is relatively free of side effects. However, taking acetaminophen can cause an increase in transaminases, certain liver enzymes, which in very rare cases can cause liver dysfunction.
