Acetaminophen Actions

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Actions of Acetaminophen in details

The action of the drug on the human body is called Pharmacodynamics in Medical terminology. To produce its effect and to change the pathological process that is happening the body and to reduce the symptom or cure the disease, the medicine has to function in a specific way. The changes it does to the body at cellular level gives the desired result of treating a disease. Drugs act by stimulating or inhibiting a receptor or an enzyme or a protein most of the times. Medications are produced in such a way that the ingredients target the specific site and bring about chemical changes in the body that can stop or reverse the chemical reaction which is causing the disease.
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Pharmacology: Pain is a very common experience and analgesic drugs such as paracetamol plays an important role in providing general pain relief for both acute and chronic pain. Paracetamol is widely recommended as the initial drug of choice for the treatment of mild to moderate musculoskeletal pain and symptomatic osteoarthritis as it is regarded as having a more acceptable safety profile in chronic use than nonsteroidal anti-inflammatory drugs (NSAIDs).

Acetaminophen provides analgesic action via its inhibition activity on the central prostaglandin synthetase and its antipyretic action is thought to be due to selective inhibition of prostaglandin synthesis in the central nervous system (CNS).

Acetaminophen is readily absorbed from the upper small intestine, has absolute oral bioavailability (70-90%) and is extensively metabolized in the liver.

Pharmacokinetics: Acetaminophen formulation consists of a bilayer tablet containing 665 mg of paracetamol: One layer containing an immediate-release (IR) formulation and providing 31% of the total dose and a 2nd layer containing a sustained release (SR) formulation that provides the remaining 69% of the total dose.

Pharmacokinetics of Acetaminophen have been investigated in 2 pivotal biostudies. In the First study, Acetaminophen and Panadol tablets were compared in fed and fasted volunteers. Both were bioequivalent with respect to dose-corrected AUC(0-t) and AUC(0-inf) in both fed and fasted states. The bioavailability of paracetamol from Acetaminophen is not affected by food thus indicating that the formulation can be taken with or without food.

In the Second study, where Acetaminophen was again compared with Panadol; Acetaminophen showed a clear pattern of controlled release of paracetamol, and the formulations were bioequivalent based on the comparison of AUCs for the final 24 hours of the 48-hour dosing period. This shows that there is no additional accumulation of paracetamol from the Acetaminophen formulation. Besides that, steadier concentrations of paracetamol were achieved with Acetaminophen. Thus, Acetaminophen may be particularly appropriate for patients who require repeat doses as it maintains a continuous therapeutic effect when taken every 8 hours (2 x 665 mg tablets per dose).

How should I take Acetaminophen?

Use Acetaminophen exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.

Do not take more of this medication than is recommended. An overdose of Acetaminophen can damage your liver or cause death.

Measure liquid medicine with a special dose-measuring spoon or medicine cup, not with a regular table spoon. If you do not have a dose-measuring device, ask your pharmacist for one.

If you are treating a child, use a pediatric form of Acetaminophen. Use only the special dose-measuring dropper or oral syringe that comes with the specific pediatric form you are using. Carefully follow the dosing directions on the medicine label.

Acetaminophen made for infants is available in two different dose concentrations, and each concentration comes with its own medicine dropper or oral syringe. These dosing devices are not equal between the different concentrations. Using the wrong device may cause you to give your child an overdose of Acetaminophen. Never mix and match dosing devices between infant formulations of Acetaminophen.

You may need to shake the liquid before each use. Follow the directions on the medicine label.

The chewable tablet must be chewed thoroughly before you swallow it.

Make sure your hands are dry when handling the Acetaminophen disintegrating tablet. Place the tablet on your tongue. It will begin to dissolve right away. Do not swallow the tablet whole. Allow it to dissolve in your mouth without chewing.

To use the Acetaminophen effervescent granules, dissolve one packet of the granules in at least 4 ounces of water. Stir this mixture and drink all of it right away. To make sure you get the entire dose, add a little more water to the same glass, swirl gently and drink right away.

Stop taking Acetaminophen and call your doctor if:

This medication can cause unusual results with certain lab tests for glucose (sugar) in the urine. Tell any doctor who treats you that you are using Acetaminophen.

Store at room temperature away from heat and moisture.

Acetaminophen administration

Administration of drug is important to know because the drug absorption and action varies depending on the route and time of administration of the drug. A medicine is prescribed before meals or after meals or along with meals. The specific timing of the drug intake about food is to increase its absorption and thus its efficacy. Few work well when taken in empty stomach and few medications need to be taken 1 or 2 hrs after the meal. A drug can be in the form of a tablet, a capsule which is the oral route of administration and the same can be in IV form which is used in specific cases. Other forms of drug administration can be a suppository in anal route or an inhalation route.
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Take exactly as directed on the label, or as prescribed by your doctor. Do not take in larger or smaller amounts or for longer than recommended.

Do not take more of this medication than is recommended. An overdose of Acetaminophen can damage your liver or cause death.

Measure liquid medicine with a special dose-measuring spoon or medicine cup, not with a regular table spoon. If you do not have a dose-measuring device, ask your pharmacist for one.

If you are treating a child, use a pediatric form of Acetaminophen. Use only the special dose-measuring dropper or oral syringe that comes with the specific pediatric form you are using. Carefully follow the dosing directions on the medicine label.

Acetaminophen made for infants is available in two different dose concentrations, and each concentration comes with its own medicine dropper or oral syringe. These dosing devices are not equal between the different concentrations. Using the wrong device may cause you to give your child an overdose of Acetaminophen. Never mix and match dosing devices between infant formulations of Acetaminophen.

You may need to shake the liquid before each use. Follow the directions on the medicine label.

The chewable tablet must be chewed thoroughly before you swallow it.

Make sure your hands are dry when handling the Acetaminophen disintegrating tablet. Place the tablet on your tongue. It will begin to dissolve right away. Do not swallow the tablet whole. Allow it to dissolve in your mouth without chewing.

To use the Acetaminophen effervescent granules, dissolve one packet of the granules in at least 4 ounces of water. Stir this mixture and drink all of it right away. To make sure you get the entire dose, add a little more water to the same glass, swirl gently and drink right away.

Stop taking Acetaminophen and call your doctor if:

This medication can cause unusual results with certain lab tests for glucose (sugar) in the urine. Tell any doctor who treats you that you are using Acetaminophen.

Store at room temperature away from heat and moisture.

Acetaminophen pharmacology

Pharmacokinetics of a drug can be defined as what body does to the drug after it is taken. The therapeutic result of the medicine depends upon the Pharmacokinetics of the drug. It deals with the time taken for the drug to be absorbed, metabolized, the process and chemical reactions involved in metabolism and about the excretion of the drug. All these factors are essential to deciding on the efficacy of the drug. Based on these pharmacokinetic principles, the ingredients, the Pharmaceutical company decides dose and route of administration. The concentration of the drug at the site of action which is proportional to therapeutic result inside the body depends on various pharmacokinetic reactions that occur in the body.
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Mechanism of Action

The precise mechanism of the analgesic and antipyretic properties of Acetaminophen is not established but is thought to primarily involve central actions.

Pharmacodynamics

Acetaminophen has been shown to have analgesic and antipyretic activities in animal and human studies.

Single doses of Acetaminophen up to 3,000 mg and repeated doses of 1,000 mg every 6 hours for 48 hours have not been shown to cause a significant effect on platelet aggregation. Acetaminophen does not have any immediate or delayed effects on small-vessel hemostasis. Clinical studies of both healthy subjects and patients with hemophilia showed no significant changes in bleeding time after receiving multiple doses of oral Acetaminophen.

Pharmacokinetics

Distribution

The pharmacokinetics of Acetaminophen have been studied in patients and healthy subjects up to 60 years old. The pharmacokinetic profile of Acetaminophen has been demonstrated to be dose proportional in adults following administration of single doses of 500, 650, and 1,000 mg.

The maximum concentration (Cmax) occurs at the end of the 15 minute intravenous infusion of Acetaminophen. Compared to the same dose of oral Acetaminophen, the Cmax following administration of Acetaminophen is up to 70% higher, while overall exposure (area under the concentration time curve [AUC]) is very similar.

Pharmacokinetic parameters of Acetaminophen (AUC, Cmax, terminal elimination half-life [T½], systemic clearance [CL], and volume of distribution at steady state [Vss]) following administration of a single intravenous dose of 15 mg/kg in children and adolescents and 1,000 mg in adults are summarized in Table 5.

Table 5. Acetaminophen Pharmacokinetic Parameters
Subpopulations

Mean (SD)

AUC 0-6h

(mcg× h/mL)

C max (mcg/mL)

(h)

CL

(L/h/kg)

Vss

(L/kg)

Children

38 (8)

29 (7)

3.0 (1.5)

0.34 (0.10)

1.2 (0.3)

Adolescents

41 (7)

31 (9)

2.9 (0.7)

0.29 (0.08)

1.1 (0.3)

Adults

43 (11)

28 (21)

2.4 (0.6)

0.27 (0.08)

0.8 (0.2)

The concentrations of Acetaminophen observed in neonates greater than 32 weeks gestational age at birth treated with 12.5 mg/kg dose are similar to infants, children and adolescents treated with a 15 mg/kg dose, and similar to adults treated with a 1,000 mg dose.

At therapeutic levels, binding of Acetaminophen to plasma proteins is low (ranging from 10% to 25%). Acetaminophen appears to be widely distributed throughout most body tissues except fat.

Metabolism and Excretion

Acetaminophen is primarily metabolized in the liver by first-order kinetics and involves three principal separate pathways: Conjugation with glucuronide, conjugation with sulfate, and oxidation via the cytochrome P450 enzyme pathway, primarily CYP2E1, to form a reactive intermediate metabolite (N-acetyl-p-benzoquinone imine or NAPQI). With therapeutic doses, NAPQI undergoes rapid conjugation with glutathione and is then further metabolized to form cysteine and mercapturic acid conjugates.

Acetaminophen metabolites are mainly excreted in the urine. Less than 5% is excreted in the urine as unconjugated (free) Acetaminophen and more than 90% of the administered dose is excreted within 24 hours.



References

  1. DailyMed. "CAFFEINE; ERGOTAMINE TARTRATE: DailyMed provides trustworthy information about marketed drugs in the United States. DailyMed is the official provider of FDA label information (package inserts).". https://dailymed.nlm.nih.gov/dailyme... (accessed September 17, 2018).
  2. DailyMed. "ASPIRIN; DIPYRIDAMOLE: DailyMed provides trustworthy information about marketed drugs in the United States. DailyMed is the official provider of FDA label information (package inserts).". https://dailymed.nlm.nih.gov/dailyme... (accessed September 17, 2018).
  3. DailyMed. "ACETAMINOPHEN; ASPIRIN; CAFFEINE: DailyMed provides trustworthy information about marketed drugs in the United States. DailyMed is the official provider of FDA label information (package inserts).". https://dailymed.nlm.nih.gov/dailyme... (accessed September 17, 2018).

Reviews

The results of a survey conducted on ndrugs.com for Acetaminophen are given in detail below. The results of the survey conducted are based on the impressions and views of the website users and consumers taking Acetaminophen. We implore you to kindly base your medical condition or therapeutic choices on the result or test conducted by a physician or licensed medical practitioners.

User reports

1 consumer reported administration

When best can I take Acetaminophen, on an empty stomach, before or after food?
ndrugs.com website users have also released a report stating that Acetaminophen should be taken With a meal. In any case, this may not be the right description on how you ought to take this Acetaminophen. Kindly visit your doctor for more medical advice in this regard. Click here to see other users view on when best the Acetaminophen can be taken.
Users%
With a meal1
100.0%


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Information checked by Dr. Sachin Kumar, MD Pharmacology

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