Ibuprofen: the pathway in the body
This page shows the biochemical pathway of the active substance Ibuprofen: where it arrives in the body, where it acts and which steps are affected by that. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.
In brief
Ibuprofen belongs to the non-steroidal anti-inflammatory agents. It lays itself into the channel of cyclooxygenase through which arachidonic acid travels to the active site. The channel is occupied while the substance is there — not destroyed.
What this is about
Arachidonic acid is an omega-6 fatty acid and sits in the membranes of almost all cells. Once it is freed, two enzymes convert it — cyclooxygenase 1 and cyclooxygenase 2:
- Both first make the same intermediate, PGH₂. The individual prostaglandins and thromboxane arise from it.
- COX-1 works continuously, among other places in the stomach wall and in the platelets. The prostaglandin E₂ formed there governs mucus, bicarbonate and blood flow of the lining.
- COX-2 arises above all where tissue answers a stimulus; the prostaglandins from it are among the messengers of an inflammatory reaction.
- The same enzymes also convert the omega-3 fatty acid EPA. What sits in the membrane helps decide which messengers arise.
Ibuprofen lays itself into the channel through which the fatty acid travels to the active site, and it does so in both enzymes. What is occupied is the channel; the enzyme is not destroyed: less PGH₂ arises, and all the paths behind it run more slowly — the one in the stomach wall included.
What this means in an individual case depends on many things and belongs in a conversation with a doctor or health practitioner.
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The pathway step by step
- Ibuprofen → Uptake in the gut The substance is absorbed rapidly; the label puts the highest level in the blood at one to two hours after a dose. In the blood it is bound for the most part to albumin. Source 1, 11
- Uptake in the gut → S-ibuprofen isomerase (R to S) An enzyme path of its own converts part of the R form into the S form; the other direction does not happen. The share of the form that acts at the enzyme thereby rises. Source 1, 2
- S-ibuprofen → Breakdown in the liver CYP2C9 In the liver CYP2C9 above all hangs oxygen onto the side chain. The fragments are coupled and leave with the urine; the label calls the excretion complete one day after the last dose. Source 1, 11
- In the cell membrane → Free arachidonic acid cPLA2 · calcium When calcium in the cell rises, the phospholipase cPLA2 travels to the membrane and cuts arachidonic acid out. Only as a free molecule is it converted further. Source 4
- Free arachidonic acid → PGH₂ COX-1 and COX-2 · haem iron, oxygen Cyclooxygenase builds in oxygen and forms a ring; PGG₂ arises. The peroxidase part of the same enzyme, a haem with iron, turns that into PGH₂ — the common precursor of the prostaglandins and of thromboxane. Source 3
- PGH₂ → Prostaglandin E₂ PGE synthases · glutathione Tissue-specific synthases make the individual prostaglandins out of PGH₂. Prostaglandin E₂ arises in the stomach wall continuously and is at the same time among the substances with which the body sets an inflammatory reaction going. Source 5, 7
- PGH₂ → Thromboxane A₂ thromboxane synthase In platelets, thromboxane synthase converts PGH₂ into thromboxane A₂. There this path runs through COX-1. Source 6
- Prostaglandin E₂ → Mucus and bicarbonate EP receptors Prostaglandin E₂ binds to EP receptors of the gastric lining. The cells then release mucus and bicarbonate, and the blood flow of the lining increases. When COX-1 runs more slowly, less prostaglandin E₂ arises for this path. Source 5, 10
- Thromboxane A₂ → Platelets TP receptors Thromboxane A₂ binds at the TP receptor of the platelets. They then change their shape and stick to one another. Source 6
What this active substance affects
- Arachidonic acid — Starting material of cyclooxygenase; by way of PGH₂ the whole series of prostaglandins and thromboxane arises from it Source 3, 4
- EPA (eicosapentaenoic acid) — The same cyclooxygenases also convert EPA; prostaglandins of series 3 arise from it Source 9
What takes part in these steps
- Linoleic acid — Omega-6 fatty acid from food, from which arachidonic acid arises over several steps Source 8
- Calcium — When it rises in the cell, the phospholipase cPLA2 travels to the membrane and frees arachidonic acid Source 4
- Iron — Sits as a haem in the peroxidase part of cyclooxygenase, which converts PGG₂ into PGH₂ Source 3
- Glutathione — Microsomal PGE synthase-1 needs glutathione in order to convert PGH₂ into prostaglandin E₂ Source 7
What the prescribing information states
The US prescribing information for the tablets lists the reactions that occurred in controlled trials in more than 1 of 100 participants; the column rests on about 3,000 participants. This label gives no placebo column alongside it — unlike, for instance, the ones for pantoprazole or ramipril. A row-by-row comparison is therefore not possible here.
How to read the table: because the placebo column is missing, no row shows how often the same report came in without the substance. The one comparison this label does draw it states in its text: at equally effective doses, complaints in the gastrointestinal area occurred about half as often as with acetylsalicylic acid or indometacin.
| Ibuprofen (about 3,000 participants) | |
|---|---|
| Nausea | 3 to 9% |
| Pain in the upper stomach area | 3 to 9% |
| Heartburn | 3 to 9% |
| Dizziness | 3 to 9% |
| Rash | 3 to 9% |
| Diarrhoea | 1 to 3% |
| Abdominal distress | 1 to 3% |
| Nausea with vomiting | 1 to 3% |
| Indigestion | 1 to 3% |
| Constipation | 1 to 3% |
| Abdominal cramps or pain | 1 to 3% |
| Bloating and flatulence | 1 to 3% |
| Headache | 1 to 3% |
| Nervousness | 1 to 3% |
| Itching | 1 to 3% |
| Ringing in the ears | 1 to 3% |
| Decreased appetite | 1 to 3% |
| Fluid retention | 1 to 3% |
The prescribing information lists in addition reactions that occurred less often than in 1 of 100 participants, as well as reports received after approval. By its own account neither a frequency nor a causal relationship can be given for those; they are therefore not listed here.
Sources
- Davies NM. Clinical pharmacokinetics of ibuprofen. The first 30 years. Clin Pharmacokinet 1998 · PubMed 9515184
- Rainsford KD. Ibuprofen: pharmacology, efficacy and safety. Inflammopharmacology 2009 · PubMed 19949916
- Smith WL, DeWitt DL, Garavito RM. Cyclooxygenases: structural, cellular, and molecular biology. Annu Rev Biochem 2000 · PubMed 10966456
- Leslie CC. Regulation of the specific release of arachidonic acid by cytosolic phospholipase A2. Prostaglandins Leukot Essent Fatty Acids 2004 · PubMed 15041029
- Wallace JL. Prostaglandins, NSAIDs, and gastric mucosal protection: why doesn't the stomach digest itself? Physiol Rev 2008 · PubMed 18923189
- Mitchell JA, Kirkby NS, Ahmetaj-Shala B et al. Cyclooxygenases and the cardiovascular system. Pharmacol Ther 2021 · PubMed 32640277
- Samuelsson B, Morgenstern R, Jakobsson PJ. Membrane prostaglandin E synthase-1: a novel therapeutic target. Pharmacol Rev 2007 · PubMed 17878511
- Brenna JT, Kothapalli KSD. New understandings of the pathway of long-chain polyunsaturated fatty acid biosynthesis. Curr Opin Clin Nutr Metab Care 2022 · PubMed 34937850
- Calder PC. Marine omega-3 fatty acids and inflammatory processes: Effects, mechanisms and clinical relevance. Biochim Biophys Acta 2015 · PubMed 25149823
- Dey I, Lejeune M, Chadee K. Prostaglandin E2 receptor distribution and function in the gastrointestinal tract. Br J Pharmacol 2006 · PubMed 17016496
- US prescribing information (United States): Ibuprofen Tablets USP, DailyMed, version of 15 Sept 2026, sections Description and Clinical Pharmacology · Prescribing information
- US prescribing information (United States): Ibuprofen Tablets USP, DailyMed, version of 15 Sept 2026, sections Adverse Reactions and Postmarketing Experience · Prescribing information
Related pathways
- Metamizol — in the cell membrane
As of 2026-09-25. Draft, written by Claude to schema v2; sources checked in PubMed; expert approval pending
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