Clinical data
Trade namesEmflex, many others
AHFS/Drugs.comInternational Drug Names
Routes of
ATC code
Legal status
Legal status
  • UK: POM (Prescription only)
Pharmacokinetic data
Protein binding80–90%
MetabolismHydrolysis, glucuronidation
Elimination half-life4.5±2.8 (up to 16) hrs
Excretion40% renal, 50% biliary
  • 2-[2-[1-(4-Chlorobenzoyl)-5-methoxy-2-methylindol-3-yl]acetyl]oxyacetic acid
CAS Number
PubChem CID
CompTox Dashboard (EPA)
ECHA InfoCard100.053.077 Edit this at Wikidata
Chemical and physical data
Molar mass415.83 g·mol−1
3D model (JSmol)
Melting point150 to 153 °C (302 to 307 °F)
  • Clc1ccc(cc1)C(=O)n3c2ccc(OC)cc2c(c3C)CC(=O)OCC(=O)O
  • InChI=1S/C21H18ClNO6/c1-12-16(10-20(26)29-11-19(24)25)17-9-15(28-2)7-8-18(17)23(12)21(27)13-3-5-14(22)6-4-13/h3-9H,10-11H2,1-2H3,(H,24,25) checkY
 ☒NcheckY (what is this?)  (verify)

Acemetacin is a non-steroidal anti-inflammatory drug (NSAID) used for the treatment of osteoarthritis, rheumatoid arthritis, lower back pain, and relieving post-operative pain. It is manufactured by Merck KGaA under the tradename Emflex. It is no longer available in the UK (since 2018),[1] however is available in other countries as a prescription-only drug.[2]

Medical uses

Acemetacin has proven effective in the treatment of osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, and other kinds of rheumatoid inflammation, as well as in post-operative and post-traumatic pain and attack of gout.[3][4] Application of a single dose of acemetacin for post-operative pain is not well supported by studies.[5]


Contraindications are basically the same as with other NSAIDs: hypersensitivity reactions to NSAIDs in the past (typically asthma or skin reactions), gastrointestinal or cerebral bleeding, peptic ulcer, haematopoietic disorders (anaemia, leukopenia), and during the third trimester of pregnancy.[3][6]

Adverse effects

Common side effects (in about 1–10% of patients) include gastrointestinal problems typical of NSAIDs, such as nausea, diarrhoea, stomach pain, and peptic ulcer; central nervous effects like headache and dizziness; and skin reactions. Gastrointestinal tolerability is better than that of the related drug indometacin. Severe allergic reactions and haematopoietic disorders occur in fewer than 0.01% of patients.[3][4]


The following interactions, typical of NSAIDs, have been described:[3][4]


Main article: Non-steroidal anti-inflammatory drug § Mechanism of action

Acemetacin acts as an inhibitor of cyclooxygenase (COX), producing the anti-inflammatory and analgetic (pain relieving) effects. In the body, it is partly metabolized to indomethacin, which also acts as a COX inhibitor. The same mechanism is responsible for the antipyretic and antiplatelet effects, which are however not clinically used, as well as for the typical NSAID adverse effects.[3][4]

An advantage of acemetacin is that it reduces gastric damage as compared to indometacin, possibly because acemetacin has less effect on the increase of leukotriene B4 synthesis and tumor necrosis factor (TNF) expression, leading to less induction of leukocyte-endothelial adherence.[7][8]


Metabolism of acemetacin. Cleaving of the glycolic acid ester (green) activates the substance to indometacin, cleaving of the methoxy ether or the 4-chlorobenzoate (orange) inactivate it.

The substance is quickly and almost completely absorbed from the gut. Highest blood plasma concentrations are reached after two hours. It is bound to plasma proteins to 80–90%. Concentrations in the synovial fluid and membranes, muscle and bone are higher than in the blood.[3]

Apart from the active metabolite indometacin, a number of inactive metabolites are found after application of acemetacin: the O-desmethyl-, des-4-chlorobenzoyl-, and O-desmethyl-des-4-chlorobenzoyl derivatives of both indometacin and acemetacin, as well as all of these substances' glucuronides (mediated at least partly by the enzyme UGT2B7[9]). Elimination half-life is 4.5±2.8 hours (in some individuals up to 16 hours) under steady state conditions. 40% are eliminated via the kidney, and 50% via the faeces.[3][4]


Acemetacin is the glycolic acid ester of indometacin. It is a fine, slightly yellowish, crystalline powder that melts at 150 to 153 °C (302 to 307 °F). It is polymorphic, with four known anhydrous (water-free) and two monohydrate crystalline forms.[4]

Society and culture

Brand names

Other brand names include Zadex (Hungary), Rheutrop (Austria), Acemetadoc, Acephlogont, Azeat, Rantudil (Germany, Hungary, Mexico, Poland, Portugal, Turkey), Gamespir (Greece), Oldan, Reudol (Spain), Tilur (Switzerland), ACEO (Taiwan), Ost-map (Egypt).


  1. ^ "Acemetacin capsules for pain and inflammation - Emflex". 29 March 2023.
  2. ^ International Drug Names: Acemetacin.
  3. ^ a b c d e f g Haberfeld H, ed. (2015). Austria-Codex (in German). Vienna: Österreichischer Apothekerverlag.
  4. ^ a b c d e f Dinnendahl V, Fricke U, eds. (2003). Arzneistoff-Profile (in German). Vol. 1 (18 ed.). Eschborn, Germany: Govi Pharmazeutischer Verlag. ISBN 978-3-7741-9846-3.
  5. ^ Moore RA, Derry S, McQuay HJ (July 2009). "Single dose oral acemetacin for acute postoperative pain in adults". The Cochrane Database of Systematic Reviews. 2019 (3): CD007589. doi:10.1002/14651858.CD007589.pub2. PMC 4170991. PMID 19588437.
  6. ^ UK Drug Information on Emflex.
  7. ^ Chávez-Piña AE, McKnight W, Dicay M, Castañeda-Hernández G, Wallace JL (November 2007). "Mechanisms underlying the anti-inflammatory activity and gastric safety of acemetacin". British Journal of Pharmacology. 152 (6): 930–8. doi:10.1038/sj.bjp.0707451. PMC 2078220. PMID 17876306.
  8. ^ Chávez-Piña AE, Vong L, McKnight W, Dicay M, Zanardo RC, Ortiz MI, et al. (November 2008). "Lack of effects of acemetacin on signalling pathways for leukocyte adherence may explain its gastrointestinal safety". British Journal of Pharmacology. 155 (6): 857–64. doi:10.1038/bjp.2008.316. PMC 2597236. PMID 18695646.
  9. ^ "Acemetacin". Retrieved 16 September 2016.