Acetaminophen in the Treatment of Acute Low Back Pain

Acetaminophen (Tylenol®) is the principle member of the group of drugs classified as para-aminophenol derivatives. While acetaminophen's analgesic and antipyretic (fever reducing) effects are equal to those of aspirin, its anti-inflammatory effects are weak. Its therapeutic effects appear to be secondary to an inhibition of prostaglandin (mediators of inflammation) biosynthesis with a resultant increase in the pain threshold and modulation of the hypothalamic heat-regulating center (a part of the brain that activates part of the nervous system). The effects of acetaminophen are noted predominantly centrally and less peripherally, were it serves as only a weak inhibitor of cyclooxygenase (enzymes that make prostaglandins) and does not inhibit the activation of neutrophils (acts to clear cell debris), as do other NSAIDs (non-steroidal anti-inflammatory drugs).

As an Analgesic
In the setting of acute low back pain, acetaminophen can be effectively utilized as an analgesic. Several studies have shown acetaminophen to be superior to placebo in the treatment of osteoarthritis pain, and because of its efficacy, it has been recommended as a first line agent in osteoarthritis treatment. A 1991 study by Bradley, et al compared the analgesic properties of acetaminophen to ibuprofen in the treatment of pain associated with osteoarthritis of the knee. Over a four-week study period, acetaminophen was found to be as efficacious as both low dose analgesic and high dose anti-inflammatory regimens of ibuprofen (Motrin®) in providing both pain relief and an improved functional outcome.

In a 1982 study, paracetamol, a compound similar to acetaminophen, was compared to diflunisal (Dolobid®), an NSAID and salicylate derivative (an anti-inflammatory agent), in the treatment of chronic low back pain. Thirty patients with a six-month to several year history of low back pain presumed secondary to facet pathology were treated in a randomized fashion for four weeks, and more favorable outcomes were associated with NSAID use.

Dosage and Side Effects
The accepted oral dose of acetaminophen is 325 to 1000-mg every four to six hours, with a 24-hour use not to exceed 4000-mg. Peak plasma levels and analgesic effects are typically noted from 30 to 60 minutes following ingestion. Acetaminophen is generally available without prescription and is relatively inexpensive.

While erythematosus (skin redness, inflammation) or urticarial skin rashes (multiple raised, swollen, itchy skin areas) are occasionally observed, the most serious adverse affect of acute acetaminophen over dosage is hepatotoxicity (harmful effect on the liver). In adults, hepatotoxicity may result from a single dose of 10 to 15-grams. More chronic abuse of acetaminophen has been associated with nephrotoxicity (harmful effect on the kidneys).

Acetaminophen's analgesic effects make it an acceptable medication in the treatment of acute low back pain. It is inexpensive and its use is typically without complications. While effective against mild to moderate pain in some acute back pain situations, it does not offer the patient other desirable effects against inflammation, muscle spasm, nor sleep disturbance. Its efficacy as an analgesic for low back disorders associated with severe pain is more questionable.

Reference:
Malanga GA, et al. Pharmacologic Treatment of Low Back Pain. In Physical Medicine and Rehabilitation State of the Art Reviews, Philadelphia, Hanley and Belfus Vol.13, No.3, October, 1999