Paracetamol absorption and elimination

Paracetamol is very well absorbed orally, it is metabolized mainly by the liver and almost completely eliminated in the urine.

Paracetamol is a drug used as an analgesic (pain reliever) and as an antipyretic (to reduce fever). Paracetamol (acetaminophen) is often called Tachipirina, as this is its most widespread trade name: however, it should not be forgotten that there are numerous other trade names, such as Efferalgan, Acetamol, Codamol and many others.

Paracetamol (chemical name N-acetyl-para-aminophenol) is the active metabolite of phenacetin.
Paracetamol increases the threshold to painful stimuli, exerting an analgesic effect against pain of different causes and etiology.

It is available without a prescription and is used as a common self-prescription pain reliever (although reimbursement of 1000 mg acetaminophen is possible if certain conditions exist and when prescribed by prescription). The drug is available in fixed-dose combinations with narcotic analgesics (paracetamol + codeine, such as Tachidol, or paracetamol + tramadol, such as Patrol) and non-narcotics, including aspirin and other salicylates, barbiturates, caffeine (Tachicaff) in preparations for migraine and headache, for insomnia, for dental pain, with antihistamines, antitussives, decongestants, expectorants, in preparations for colds and flu and in treatments for sore throat.

Paracetamol absorption and elimination

Absorption and elimination of paracetamol in our body

The most used dosages of paracetamol in single preparation are 500 mg and 1000 mg. Paracetamol is a valid alternative to aspirin and other anti-inflammatories such as ibuprofen (momnet, Brufen, Nurofen), ketoprofen (Oki, Ketodolo, Arthrosilene, Fastum Gel), naproxen (Naprosyl, Momendol, Naproxene), nimesulide (Algimesil, Aulin, Ledoren), as an analgesic-antipyretic compound; however, its anti-inflammatory effects are very low when compared with pure anti-inflammatories.

In fact, although paracetamol is indicated in the treatment of pain in patients with non-inflammatory osteoarthritis, it does not represent an adequate substitute for non-steroidal anti-inflammatory drugs (NotSteroidal Anti-Inflammatory Drugs, NSAIDs) in chronic inflammatory conditions such as rheumatoid arthritis. Paracetamol is well tolerated and is associated with a low incidence of gastrointestinal side effects, which instead affects all other anti-inflammatory drugs, which can cause gastritis and gastric or duodenal ulcers.

However, an acute overdose of Tachipirina can cause severe liver damage and cases of accidental or deliberate intoxication are continuously increasing, especially for those with chronic painful conditions and who take more than 3-4 g of paracetamol for several consecutive days. Chronic use of less than 2 g / day has not been shown to be associated with hepatic dysfunction.

Paracetamol: absorption, metabolism and elimination

Paracetamol can be taken orally or intravenously, in the hospital. Paracetamol taken orally shows excellent bioavailability (ie it is mostly absorbed). The peak plasma concentration is reached within 30-60 minutes from the time of dosing and the plasma half-life (i.e. the time in which the concentration of the drug in the blood is halved) is approximately 2 hours following administration of therapeutic doses (i.e. after taking a 500 mg tachipirina for example).

The drug is distributed fairly evenly in most body fluids. Its binding to plasma proteins is variable, but is still lower than that of other NSAIDs; only a percentage ranging from 20% to 50% is bound, even by analyzing the proteins at the concentrations found during acute paracetamol intoxication.

More than 90% of the drug can be found in the urine within the first day at the therapeutic dosage, as it is metabolized by hepatic conjugation with glucuronic acid (about 60% of paracetamol), sulfuric acid (about 35% of paracetamol) or cysteine (less than 3%). Side note: Small amounts of hydroxylated and deacetylated metabolites are also found.

The children have a reduced ability to metabolize paracetamol compared to adults, having a reduced activity of glucuronidation of drugs. So the dosages used for adults are not good for children.


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