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Acetaminophen Uses, Side Effects Interactions & Warnings

Acetaminophen is an analgesic. This is available over the counter, meaning you do not need a doctor’s prescription to get this drug. Acetaminophen is one of the top-selling drugs worldwide.

Acetaminophen is recommended as the first-line treatment in pain conditions by W.H.O. This drug is approved by F.D.A.

Acetaminophen uses, side effects interactions

Acetaminophen is an analgesic and pain reliever. This drug has antipyretic effects as well. You can use this drug alone or in combination with other drugs to manage pain and reduce fever.

 Acetaminophen can manage mild to moderate pain such as those caused by headache, muscle aches, the common cold. Toothaches and menstrual cramps.

These drugs mainly perform their actions by inhibiting cyclooxygenase (COX) pathways.

Acetaminophen also has a large side effects profile, including allergic reaction, dizziness, diarrhea, nausea, and vomiting, etc.

In this article, we will discuss what acetaminophen is? Why do we use this drug? What is the mechanism of action? And also, what are the common side effects of this drug?

Generic name of Acetaminophen :

  • Acetaminophen

Common brand name of Acetaminophen :

This drug is available under the following brand names:

  • Tylenol
  • Tylenol Arthritis Pain
  • Zydone
  • Ofirmev
  • Pharbetol
  • Premsyn Pms
  • Prolate
  • Ricochet
  • Robaxace
  • Tylenol Ext

Drug class of Acetaminophen :

Acetaminophen belongs to a drug class known as analgesics.

Mechanism of action of Acetaminophen :

The exact mechanism of action of this drug is not fully known. Acetaminophen is not an NSAID but is often characterized alongside them because of its ability to inhibit cyclooxygenase pathways.

Acetaminophen lacks the peripheral anti-inflammatory properties that indicate that acetaminophen inhibits the COX pathway in the C.N.S. only and not in the periphery.

Additionally, according to one study, acetaminophen does not appear to bind to COX 1 and COX 2 enzymes. Rather, it performs its function by binding to another enzyme called COX 3 (COX 3 has not been confirmed to occur in humans).

The reduction in the COX pathway results in decreased production of prostaglandins that results in analgesic and antipyretic effects of acetaminophen.

According to another theory, acetaminophen bound the cox 1 and cox 2 indirectly in the C.N.S. and increased the pain threshold by decreasing the prostaglandin production. Prostaglandins are mainly involved in eliciting pain sensations.

The antipyretic action of acetaminophen is thought to have been caused by its direct action on the heat-regulating regions of the brain, which respond by decreasing body temperature by various mechanisms, e.g., peripheral vasodilation, sweating, etc.

Before taking this medication of Acetaminophen :

  • Tell your physician about allergic to acetaminophen or any of its inactive ingredients,
  • Before starting any medication, read the medication guide or the patient information leaflet usually provided with the drug. In case you have any quarries about the drug, ask your doctor or your pharmacist.
  • Tell your doctor if you are breastfeeding or pregnant. If you become pregnant during the course of your treatment, then inform your doctor.
  • Inform your doctor if you are consuming two or more alcoholic beverages a day.
  • Acetaminophen is present in combination with over 600 over the medication drugs, so if you are currently using any medication, make sure to inform your pharmacist or your physician about it to avoid overdose.

Clinical indication of Acetaminophen :

The clinical indications of acetaminophen include:

  • Treatment of mild to moderate pain
  • Fever
  • For the management of severe pain and fever, it is used with opioids analgesics.
  • Headaches
  • Muscle aches
  • Cold and sore throats
  • Backache
  • Toothache
  • Minor pain of arthritis
  • Premenstrual and menstrual cramps

Dosage of Acetaminophen :

DiseaseDoseRoute of administration
Fever   (adult dose)Parenteral:   For the patient having weight  50kg or more:   1000 mg IV / 6 hours or 650mg / 4 hours Maximum single dose: 1000mg Dosing interval (minimum): 4 hours Maximum dose: 4000mg / 24 hours   For the patients having weight less than 50kg:   15mg / kg IV / 6 hours Dosing interval ( minimum): 4 hours Maximum dose: 75mg / dayIVOralRectal
Oral:   325mg-1000mg / 4 to 6 hours Dosing interval: 4 hours Maximum single dose: 1000mg The maximum dose in a single day: 4000 mg    
Rectal:   325mg-1000mg / 4 to 6 hours Dosing interval: 4 hours Maximum single dose: 1000mg Maximum dose in a single day: 4000 mg  
Pain (adult dose)  Parenteral:   For the patient having weight  50kg or more:   1000 mg IV / 6 hours or 650mg / 4 hours Maximum single dose: 1000mg Dosing interval (minimum): 4 hours Maximum dose: 4000mg / 24 hours   For the patients having weight less than 50kg:   15mg / kg IV / 6 hours Dosing interval ( minimum): 4 hours Maximum dose: 75mg / dayIVOralRectal
Oral:   325mg-1000mg / 4 to 6 hours Dosing interval: 4 hours Maximum single dose: 1000mg The maximum dose in a single day: 4000 mg  
Rectal:   325mg-1000mg / 4 to 6 hours Dosing interval: 4 hours Maximum single dose: 1000mg Maximum dose in a single day: 4000 mg  

Formulations and strengths of Acetaminophen :

This drug is available in various formulations, including:

Dosage formsStrengths
Tablets325mg500mg
Capsules325mg 500mg650mg
Geltabs500mg
Extended-release caplets650mg
Chewable tablets80mg
Oral solution/ suspension160mg/5ml80mg/0.8ml in case of oral drops
Elixer160mg/5ml
Oral syrup160mg/5ml

Side effects of Acetaminophen :

Side effects of a drug vary from person to person. This article does not contain all the possible side effects of acetaminophen. This article will provide you a general idea about the possible side effects that you can face. 

This drug has quite an extensive side effect profile. Some of the common side effects of these drugs include:

  • Swelling of the skin
  • Dizziness
  • Rash
  • Hives
  • Decrease R.B.C.s count
  • Disorientation
  • Shortness of breath

In addition to the side effects above, some patients also experience some of the more serious side effects of acetaminophen, which include:

  • Anaphylaxis (severe allergic reaction): In some cases, acetaminophen can result in a severe allergic reaction. Call your physician immediately if you notice any of the symptoms given below:
    • Difficulty in breathing
    • Itching
    • Blistering of the skin
    • Hives
    • Swelling of the face
  • Severe hepatic (liver) damage: Acetaminophen is processed by our liver. When we consume large amounts of this drug, our liver is unable to detoxify the toxic metabolites that are produced from acetaminophen. These toxic metabolites, if produced in large amounts, can damage our liver. In case of liver damage caused by the acetaminophen, one can experience the following symptoms:
    • Jaundice
    • Nausea
    • Vomiting
    • Pale skin
    • Fever
    • Fatigue
    • Loss of appetite
    • Dark-colored urine
  • Renal toxicity
  • Stevens-johnson syndrome ( a rare condition that affects skin, genitals, mucus, and mouth).
  • Gastrointestinal bleeding
  • Decrease white cell count
  • Decreased platelet count
  • Hyperammonemia
  • Agranulocytosis ( a condition where the body does not produce enough neutrophils)

Contraindication of Acetaminophen :

Do not use acetaminophen :

  • When you have a history of hypersensitivity (allergy)to acetaminophen
  • Acute liver failure
  • Renal impairment
  • Acute liver inflammation e.g., in hepatitis
  • Shock ( a dangerous condition where the body is unable to maintain adequate blood flow)
  • Alcoholics ( or anyone using two or more alcoholic beverages a day)
  • Using other drugs containing acetaminophen

Other considerations of Acetaminophen :

  • Do not try to alter or stop your medication without consulting your physician first.
  • Make sure your doctor knows about your drug history or any other herbal product you are using.
  • Follow the direction of your doctor, and do not try to alter the dose yourself,
  • In case you have missed a dose, do not double the next dose and if you are unsure about the missed dose, ask your physician.

Drug interaction of Acetaminophen :

When your physician or pharmacist prescribes you a medication, they are already aware of any possible interactions. You must not make any change in the medication prescribed to you by your physician.

If you are unsure about the drug interactions or have any queries about your prescription, you can talk to your doctor or pharmacist. You can also keep a list of your medication and show that to your pharmacist or your physician so they may know all the drugs you are using and make their decision accordingly.

Examples of the few of the drugs that can interact with pantoprazole are given below:

  • Busulfan
  • Dapsone
  • Exenatide
  • Flibanserin
  • Imatinib
  • Isoniazid
  • Lomitapide
  • Warfarin
  • Tetracaine
  • Mipomersen
  • Acebutolol
  • Abatacept
  • Acemetacin

Food interactions of Acetaminophen

Acetaminophen is known to interact with alcohol. Using alcohol and acetaminophen simultaneously can increase the risk of hepatotoxicity. So alcohol should be avoided during acetaminophen therapy.

There is no known interaction of acetaminophen with any other food. Always consult your physician if you have any questions regarding your medications.

Overdosage of Acetaminophen :

Overdose may be accidental or purposeful. You should keep in mind that if you miss a dose, do not try to compensate by taking the extra dose when the next dose is due. You can consult your physician or your pharmacist about the doses you missed.

Some of the common symptoms of acetaminophen poisoning include:

  • Bloody or dark urine
  • Continued nausea and vomiting
  • Pain in the right side of the abdomen just below the ribs
  • Confusion
  • Sleepiness
  • Loss of consciousness
  • Jaundice ( skins and eyes appears yellow)

The currently approved antidote to acetaminophen poisoning is N-acetylcysteine (N.A.C.).

Storage:

Following steps must be taken to store medicine properly:

  • Keep your medications in the container they came in.
  • Store your medicine at room temperature
  • Keep your medicine away from moisture and excess heat e,g, bathroom or kitchen.
  • Keep your medications away from the reach of the children to avoid any accidental poisoning, always lock safety caps and immediately place the medications in a safe location.
Abdur Rashid
Medically Reviewed By Abdur Rashid
MSC Public Health, MCSP, MHCPC
BSC (Hon) Physiotherapy
Consultant Neuro-spinal & Musculoskeletal Physiotherapist

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