Acetaminophen

Chapter 35


Acetaminophen






INDICATIONS





Unlabeled Use




• To decrease fever and pain in children receiving DPT vaccination


• Acetaminophen (N-acetyl-p-aminophenol, or APAP) is an OTC medication that is commonly used to alleviate fever and mild pain. It can be used in patients who have experienced gastric irritation with aspirin or NSAIDs. Acetaminophen is similar to aspirin in terms of its effectiveness in decreasing fever and pain. It is the drug of choice for relief of minor pain in children, adults, and the elderly. APAP is different from aspirin in that it has a weak antiinflammatory effect, little GI adverse effect, and no impact on platelet aggregation. It is very well tolerated at recommended dosages. Maximum adult total daily dose is 3000 mg for self-treating users and 4 g/day for those under the care of a clinician. At higher doses, acetaminophen causes hepatotoxicity.


Acetaminophen is a metabolite of phenacetin. Phenacetin was introduced in 1887, was used extensively for many years, and then was taken off the market because its use led to nephropathy. APAP has been in use since 1893 but has become very popular since 1949. APAP has the effectiveness of phenacetin without the adverse reactions. However, acetaminophen overdosage may still cause nephropathy.


The problem most frequently noted with APAP involves difficulty in determining proper dosing in children. The FDA continues to issue safety alerts on various preparations to state that the dosing is confusing. All cough and cold medications that contain acetaminophen and are marketed for children younger than 2 years have been withdrawn from the market. Current guidelines recommend avoiding use of these products PO in children younger than 2 years because of the risk of toxicity associated with improper dosing. For information for patients, go to www.knowyourdose.org. A new formulation of IV acetaminophen for pediatric use went on the market in 2011.


The FDA is asking manufacturers of combination products containing acetaminophen to limit the amount of acetaminophen to no more than 325 mg in each tablet to decrease the risk of overdosage. This will be phased in over a course of years.


The use of acetaminophen in the management of fever is discussed in this chapter. For additional information on the use of APAP in the treatment of pain, see Chapter 43



Therapeutic Overview


Pathophysiology


Fever is an elevation of the setpoint of body temperature. The hypothalamus is the site of the heat-regulating center. The setpoint is elevated through several mechanisms. The most common of these involves the monocyte-macrophages, which, when stimulated, release pyrogenic cytokines such as interleukin-1. These stimulate the heat-regulating center to raise the setpoint. This prompts increased heat production via shivering or decreased heat loss through peripheral vasoconstriction.



Disease Process


It is essential for the clinician to identify and treat the cause of fever and not just the symptoms. Fever is a symptom with many causes, the most common of which is infection. The danger in treating a fever involves the risk that symptoms of a worsening infection may be masked. A fever may be an important indication of antibiotic resistance. Fever of unknown origin is defined as an unexplained case of fever exceeding 38.3°C on several occasions for at least 3 weeks in patients without neutropenia or immunosuppression. Causes of fever and hyperthermia are listed in Table 35-1.





Treatment Principles


Standardized Guidelines






Cardinal Points of Treatment




• Acetaminophen is an OTC medication; many patients self-administer this product for both pain relief and fever reduction.


• APAP use appears relatively straightforward in adults. Maximum adult total daily dose is 3 g/day for self-treating users and 4 g/day for those under the care of a health care provider. However, in all individuals, particularly in children, its use becomes more complicated and presents many opportunities for overdosage. Different dosages are used for different age and weight groups, and many formulations with different strengths are available. APAP is a frequent constituent of other OTC combination products. These formulations change frequently. See Table 35-2 for a list of formulations and strengths. Note the broad array of products with different strengths.


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Jul 22, 2016 | Posted by in PHARMACY | Comments Off on Acetaminophen

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