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Executive Summary Information

Compound Acetaminophen (Paracetamol)
Toxicities Cytotoxicity
Mechanisms Metabolic oxidation to the quinone imine NAPQI metabolite, which traps cellular thiols, both protein and GSH, by formation of covalent adducts. Studies of quinone imine analogues suggest additional depletion of thiols by redox cycling.
Comments Acetaminophen is selected based on its chemical mechanism, which is representative of quinones with a high reduction potential.
Feedback Contact Gold Compound Working Group (GCWG)

Leadscope Id LS-32
CAS 103-90-2
DrugBank DB00316
ChemSpider 1906
ChEBI 116450
Pathway DBs
KEGG D00217
Assay DBs
PubChem CID 1983
ChEMBL 112
Omics DBs
Open TG-Gate 00001
pKa 9.48
ToxCast Accepted yes
Toxic Effect Apoptosis
ToxBank Accepted yes
Approved on 2011-06-28
Target COX-2c
Toxicities Cytotoxicity

In Vivo Data ? Compound Assessment
Adverse Events ? High doses can cause acute hepatic necrosis due to production of toxic quinone imine metabolite (NAPQI). From 1998 to 2003, acetaminophen was the leading cause of acute liver failure in the United States, with 48% of acetaminophen-related cases (131 of 275) associated with accidental overdose.


-Larson AM, Polson J, Fontana RJ, Davern TJ, Lalani E, Lee WM et al. Acute Liver Failure Study Group (ALFSG). Acetaminophen-induced acute liver failure: results of a United States multicenter, prospective study. Hepatology, 2005 Dec; 42(6):1364-72.

Toxicity Mechanisms ? Metabolism via CYP2E1 produces a toxic metabolite, N-acetyl-p-benzoquinoneimine (NAPQI). The toxic effects of acetaminophen are due to NAPQI, not acetaminophen itself nor any of the major metabolites. NAPQI is a quinone imine that has both redox cycling activity and alkylating activity. The imine depletes the mitochondrial membrane potential and glutathione to a comparable extent at toxic concentrations. Although glutathione depletion is most readily measured, it is assumed that NAPQI oxidizes/alkylates reactive protein thiols to an extent comparable to glutathione. It is not clear which reactivity, redox or alkylating, dominates the production of toxicity. At high doses high enough to significantly deplete glutathione, cell death is observed.
Therapeutic Target ? Acetaminophen is thought to act primarily in the CNS, increasing the pain threshold by inhibiting both isoforms of cyclooxygenase, COX-1, COX-2, and COX-3 enzymes involved in prostaglandin (PG) synthesis. Unlike NSAIDs, acetaminophen does not inhibit cyclooxygenase in peripheral tissues and, thus, has no peripheral anti-inflammatory affects.

Human Adverse Events

The following data table has been mined from the Adverse Events Reporting System (AERS) of the US FDA. Significant human liver events. The first column ("# Reports") is the number of reports found for the corresponding adverse event reported in the third column ("Adverse Event"). The second column ("Report:Baseline Ratio") is ratio calculated from the number of reports ("# Reports") divided by a calculated expected statistical baseline number of reports.

# Reports Report:Baseline Ratio Adverse Event
2 6.10464 acute fatty liver of pregnancy
227 9.85492 acute hepatic failure
1 13.2267 bile duct cancer non-resectable
2 7.93603 glycogen storage disease type i
25 3.37416 hepatorenal failure
76 4.84060 liver injury

FDA and Label Information

The following link will display all of the currently approved FDA drug products on the market. The web page will contain a table listing all current products by their respective Tradenames and primary active ingredients. The list is navigable by simply clicking on the product of interest, which will in turn list all of the NDA's and ANDA's associated with that product. From here users can click on a specific NDA or ANDA and see documents that have been submitted for the product that the FDA has made available via their website. The types of documents include approval history, letters, reviews and labels.
FDA Approved Products

This next url will perform a search in the FDA's system for all labels for products that contain Acetaminophen as an active ingredient.
FDA Label Search

Since every unique drug product receives a separate label, we have included a link to another resource for a specific Acetaminophen product (ACETAMINOPHEN liquid - by Goldline Laboratories, Inc.) which displays the drug label information.
Acetaminophen liquid label

PubMed references

The following resource link will perform a PubMed query for the terms "acetaminophen" and "liver toxicity".
Acetaminophen Search

The table listed below contains a summarized listing of toxic effect information leveraged from the 6th European Framework Programme project LIINTOP. For a complete listing of the Gold Compound evaluation criteria please see the Gold Compound Evaluation and Comments immediately following the summary table below.





Summary Hepatotoxic Effects from the LIINTOP FP6 Program
Hepatocellular necrosis.gif Apoptosis.gif Transporter inhibition.gif Cholestatic.gif Steatotic.gif Phospholipidosis.gif Hepatocyte function.gif Mithochondria impairment.gif Oxidative stress.gif DNA synthesis genotoxicity.gif Covalent binding.gif Idiosyncrasia metabolic.gif Idiosyncrasia immune.gif Bioactivation required.gif LIINTOP severity.gif References
+ + + + + 3

[1] [2] [3] [4]


  1. Gomez-Lechon, M.J., O’Connor, E., Castell, J.V., Jover, R., 2002. Sensitive markers used to identify compounds that trigger apoptosis in cultured hepatocytes. Toxicol. Sci. 65, 299–308. doi:10.1093/toxsci/65.2.299
  2. Gomez-Lechon, M.J., Ponsoda, X., O’Connor, E., Donato, T., Jover, R., Castell, J.V., 2003. Diclofenac induces apoptosis in hepatocytes. Toxicol. in Vitro 17, 675– 680. doi:10.1016/S0887-2333(03)00105-X
  3. Hynes, J., Marroquin, L.D., Ogurtsov, V.I., Christiansen, K.N., Stevens, G.J., Papkovsky, D.B., Will, Y., 2006. Investigation of drug-induced mitochondrial toxicity using fluorescence-based oxygen-sensitive probes. Toxicol. Sci. 92, 186–200. doi:10.1093/toxsci/kfj208
  4. Kass, G.E., Macanas-Pirard, P., Lee, P.C., Hinton, R.H., 2003. The role of apoptosis in acetaminophen-induced injury. Ann. NY Acad. Sci. 1010, 557–559. doi:10.1196/annals.1299.103

PK-ADME ? Compound Assessment
PK parameters ?
Cmax 325 mg dose4.2 micro-g/ml
Half life2.5 hours.


Cmax 1000 mg dose17.98-20.55 micro-g/ml (formulation dependent)
Half life2.65-2.81 hours


-F.J. Sevilla-Tirado, E.B. González-Vallejo, A.C. Leary, H.J. Breedt, V.J. Hyde and N. Fernández-Hernando, "Bioavailability of Two New Formulations of Paracetamol, Compared With Three Marketed Formulations, in Healthy Volunteers", Methods Find Exp Clin Pharmacol (2003), 25(7): 531-535

Vd = 0.9 L/kg.

An extensive tabulation of human and rat PK parameters along with predictive models for hepatic toxicity is provided by Péry et al. (2013). Plasma half-life = 2.5 hrs in rats. The predicted dose for onset of hepatic toxicities in humans is 500-800 mg/kg based on these predictive models and an observed EC50 of 5 mM for HepaRG cell viability.


-Péry ARR, Brochot C, Zeman FA, Mombelli E, Desmots S, Pavan M, Fioravanzo E, Zaldívar JM (2013) "Prediction of dose-hepatotoxic response in humans based on toxicokinetic/toxicodynamic modeling with or without in vivo data: A case study with acetaminophen", Toxicol. Lett. 220, 26-34.

Therapeutic window ? The recommended daily dose is 4 g/day (60 mg/kg/day). Toxicity has been observed at the recommended dose and (rarely) at doses of 2.5 g/day. Although the therapeutic window is low, a specific toxicity threshold in humans has not been defined.



Gerald Dal Pan, Bob Rappaport, Background Package for June 29-30, 2009 Meeting of the Drug Safety and Risk Management Committee, Anesthetic and Life Support Drugs Advisory Committee and Nonprescription Drugs Advisory Committee.

Species Route LD50 (mg/kg)
Mouse Oral 340
Rat Oral 1900


-Lee W. Drug-induced hepatotoxicity, New England Journal of Medicine, July 31, 2003; 349:474-485.

Metabolically activated ? Approximately 90 to 95% of a dose is conjugated in the liver with glucuronic acid and sulfuric acid. A small percentage of acetaminophen is oxidized by CYP2E1 to form N-acetyl-p-benzo-quinone imine (NAPQI), a toxic metabolite which is then conjugated to glutathione and excreted renally. Accumulation of NAPQI may occur if primary metabolic pathways are saturated.
Enzyme Metabolite Km Vmax
Cytochrome P450 2D6 NAPQI 1760 54.12
Cytochrome P450 1A2 NAPQI 950 0.12
Cytochrome P450 2E1 NAPQI 1290 120.84

Omics and IC50 Data ? Compound Assessment
Gene expression profiles known. ?
Title: Transcription profiling of human hepatocyte and neuron cell cultures following exposure to various chemical compounds
Organism(s): Homo sapiens

Open TG-GATEs Human Liver
Status: Public on Feb. 25, 2011
Title: Genomics Assisted Toxicity Evaluation system study - Human Hepatocytes
Organism(s): Homo sapiens


-Takeki Uehara, Atsushi Ono, Toshiyuki Maruyama, Ikuo Kato, Hiroshi Yamada, Yasuo Ohno, Tetsuro Urushidani. The Japanese toxicogenomics project: application of toxicogenomics. Molecular nutrition & food research. 2010 Feb;54(2): 218-27 pmid:20041446

Series: GSE5595
Status: Public on Sep. 19, 2007
Title: Acetaminophen (APAP) Rat Liver Test Gene Ex
Organism(s): Rattus norvegicus
Summary: Gene expression test data set from rat liver samples exposed to either 150, 1500 or 2000 mg/kg of APAP for 3, 6 or 24 hours.


-Bushel PR, Heinloth AN, Li J, Huang L et al. Blood gene expression signatures predict exposure levels. Proc Natl Acad Sci U S A 2007 Nov 13;104(46):18211-6. pmid:17984051

Series: GSE8858
Title: Liver Pharmacology and Xenobiotic Response Repertoire
Organism(s): Rattus norvegicus


-Natsoulis G, Pearson CI, Gollub J, P Eynon B et al. The liver pharmacological and xenobiotic gene response repertoire. Mol Syst Biol 2008;4:175. pmid:18364709

Title: Transcription profiling time course toxicogenomic profiles in CD-1 mice after nontoxic and nonlethal hepatotoxic paracetamol administration
Organism(s): Mus musculus


- Williams DP, Garcia-Allan C, Hanton G, LeNet JL, Provost JP, Brain P, Walsh R, Johnston GI, Smith DA, Park BK. Time course toxicogenomic profiles in CD-1 mice after nontoxic and nonlethal hepatotoxic paracetamol administration. Chem Res Toxicol. 2004 Dec;17(12):1551-61.

Proteomics profiles known. ? Proteomics and metabonomics in mice with humanized livers.


-Toxicol. Sci. (2007) 32, 205-215.

Proteomic Analysis of Acetaminophen-Induced Changes in Mitochondrial Protein Expression Using Spectral Counting


-Chem. Res. Toxicol., 2011, 24 (4), pp 549-558.

Alterations in the rat serum proteome during liver injury from acetaminophen exposure.


- J Pharmacol Exp Ther (2006) 318: 792-802.

Genomics and Proteomics Analysis of Acetaminophen Toxicity in Mouse Liver.


-TOXICOLOGICAL SCIENCES 65, 135-150 (2002).
Metabonomics profiles known. ? Acetaminophen dosing of humans results in blood transcriptome and metabolome changes consistent with impaired oxidative phosphorylation.


-Hepatology. 2010 Jan;51(1):227-36

Fluxomics profiles known. ?
Epigenomics profiles known. ?
Observed IC50 for in vitro cellular efficacy. ? IC50 values ranging from 4 to 200 uM dependant on cell type and stimulant. 7.2 and 4.2 M for PGE2 and PGF2 respectively for rheumatoid synoviocytes


-Graham et al. Inflammopharmacology, Vol. 9, No. 1,2, pp. 131-142 (2001)

IC50 for isolated enzymes = 110 uM for COX-1 and 26 uM for COX-2.


-Burkhard Hinz, Olga Cheremina, and Kay Brune, "Acetaminophen (paracetamol) is a selective cyclooxygenase-2 inhibitor in man", The FASEB Journal (2008) 22: 383-390.
Observed IC50 for in vitro cellular toxicity studies. ? Paracetamol IC50: 5-8 mM (mouse/human)


-VIOLLON et al Cell Biology and Toxicology Volume 11, Numbers 3-4, 195-227 (1991)

3D HepaTox Chip

Rat IC50: 16.90mM


-Toh et al. Lab Chip, 2009, 9, 2026-2035
IC50 for cell viability
rat hepatocyte14014 uM
3T3 cells80344 uM
Hela31283 uM
HepG229755 uM
-Wang et al. J of Toxicological Sciences Vol. 27 (2002) , No. 3 August 229-237

IC50: 10-20 mM for depletion of GSH and the mitochondrial membrane potential in human hepatocytes.


-Jinghai J. Xu, Peter V. Henstock, Margaret C. Dunn, Arthur R. Smith, Jeffrey R. Chabot, and David de Graaf, “Cellular Imaging Predictions of Clinical Drug-Induced Liver In”, TOXICOLOGICAL SCIENCES 105(1), 97–105 (2008)

In mouse hepatocytes, cytotoxicity is two-phased. Incubation with 1 mM acetaminophen for 2 h leads to protein arylation and depletion of GSH. Cell death is observed at 3-5 h to the same extent independent of whether acetaminophen is washed out at 2 h.


-Reid, A.B., Kurten, R.C., McCullough, S.S., Brock, R.W. and Hinson, J.A. (2005) “Mechanisms of acetaminophen-induced hepatotoxicity: role of oxidative stress and mitochondrial permeability transition in freshly isolated mouse hepatocytes”, J. Pharmacol. Exp. Ther. 312, 509–516.

Physical Properties ? Compound Assessment
Accepted and listed within the ToxCast/Tox21 program. ? Yes - Included in ToxCast Phase I and II Chemicals List
Substance stability. ?
Soluble in buffer solution at 30 times the in vitro IC50 for toxicity. ? Water solubility 14 mg/ml (~100 mM) (25°C)


-YALKOWSKY,SH & HE,Y (2003) from SRC PhysProp Database

Water solubility 16.7 mg/ml (~100 mM) (25°C)


-Mota FL, Carneiro AP, Queimada AJ, Pinho SP, Macedo EA. Temperature and solvent effects in the solubility of some pharmaceutical compounds: measurements and modeling. Eur J Pharm Sci 2009; 37: 499-507.

estimated intrinsic solubility : 17.8 mg/ml
estimated solubility in pure water at pH 5.70: 17.8 mg/ml
estimated solubility in water at pH 7.4: 17.9 mg/ml
Calculations performed using ACD/PhysChem v 9.14

Solubility in DMSO 100 times buffer solubility. ? 5 M Sigma Aldrich A7085 Product details
Vessel binding properties. ?
Vapor pressure. (Non-volatile) ? estimated vapor pressure: 1.94E-06 mmHg (Calculation performed using EPI Suite v4.10)

Calculated/Predicted Properties

Water Solubility Results
pH Sol, mg/ml 9+ 0 10- Graph
2 21.96 18.8 81.2 - Acetaminophen solubility.png
5.5 17.85 - 100 -
6.5 17.85 - 100 -
7.4 17.9 - 99.7 0.3
10 40.62 - 43.9 56.1
Summary Solubility Data
Intrinsic Solubility, mg/ml 17.8454
Intrinsic Solubility, log(S, mol/l) -0.9279
Solubility in Pure Water @pH = 5.7, mg/ml 17.8474
Calculations performed using ACD/PhysChem v 9.14
LogD Results
pH LogD Graph
2 0.25 Acetaminophen logd.png
5.5 0.34
6.5 0.34
7.4 0.34
10 -1.86E-2
Calculations performed using ACD/PhysChem v 9.14
Single-valued Properties
Property Value Units Error
LogP 0.34 0.21
MW 151.16 -
PSA 49.33 -
FRB 2 -
HDonors 2 -
HAcceptors 3 -
Rule Of 5 0 -
Molar Refractivity 42.41 cm3 0.3
Molar Volume 120.95 cm3 3
Parachor 326.03 cm3 4
Index of Refraction 1.62 0.02
Surface Tension 52.8 dyne/cm 3
Density 1.25 g/cm3 0.06
Polarizability 16.81 10E-24 cm3 0.5
Calculations performed using ACD/PhysChem v 9.14
Property Name Value Units Source
pKa 9.48 SPARC v4.5
Estimated VP 1.94E-06 mm Hg EPI Suite v4.10
Estimated VP 2.586E-04 Pa EPI Suite v4.10
Estimated Water Solubility 3.04E+04 mg/L EPI Suite v4.10
WATERNT Frag Water Solubility Estimate 2.37E+05 mg/L EPI Suite v4.10
pKa Results
Acidic/Basic Acidic/Basic Apparent pKa Value Error Source
9 A 15.32 0.7
10 MA 9.86 0.13
9 MB 1.72 0.5
A = Acidic
B = Basic
MA = Most Acidic
MB = Most Basic
Calculations performed using ACD/PhysChem v 9.14

Authors of this ToxBank wiki page

David Bower, Egon Willighagen, Matthew Clark
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