A Pharmacist's Guide to OTC Therapy: Comparing Nonprescription Analgesics

Ms. Terrie is a clinical pharmacy writer based in Haymarket, Virginia.

An estimated 17% to 23% of the population use an OTC analgesic each week to treat a variety of conditions, including headaches, fever, toothache, musculoskeletal injuries and disorders, and menstrual cramps.¹ Currently available oral OTC analgesics include acetaminophen, nonsteroidal anti-inflammatory drugs (NSAIDs [ibuprofen and naproxen]), and salicylates (aspirin, magnesium salicylate, and sodium salicylate). Criteria in selecting an appropriate analgesic include a thorough assessment of the patient’s medical, medication, and allergy history.

Acetaminophen

Acetaminophen is an effective analgesic and antipyretic, though it does not have any anti-inflammatory activity.² Acetaminophen is effective in relieving mild-to-moderate pain of nonvisceral origin.² The drug is absorbed rapidly from the gastrointestinal (GI) tract and metabolized in the liver to inactive glucuronic and sulfuric acid conjugates.² The onset of activity occurs about 30 minutes after oral administration; the duration of activity is about 4 hours, but can last 6 to 8 hours when using the controlled-release/extendedrelease formulations.²

At doses >4 g/day, acetaminophen is potentially hepatoxic.² Acetaminophen poisoning is the leading cause of acute liver failure in the United States and one of the primary reasons for communicating with poison control centers.² An estimated 50% of acetaminophenrelated acute liver failure cases are due to unintended chronic overdoses.² The FDA is currently considering a June 30, 2009, advisory committee recommendation calling for stronger warnings and dose limits because of concerns over potential hepatic problems.³

Elderly patients are at greater risk for the adverse reactions associated with salicylates and NSAIDs; therefore, acetaminophen is generally the recommended analgesic for this patient population when appropriate.² Although acetaminophen is considered to be the analgesic of choice for individuals currently taking warfarin, it can elevate an individual’s international normalized ratio, and patients should be advised to avoid routine use of acetaminophen when possible and always consult their primary health care provider before using any OTC analgesic.² Patients should also be advised that concurrent use of acetaminophen and alcohol can increase the risk of hepatoxicity.²

Nonsteroidal Anti-inflammatory Drugs

These agents have analgesic, antipyretic, and anti-inflammatory activity and also are considered to be useful in managing mild-to-moderate pain of nonvisceral origin.² A dose of 220 mg of naproxen sodium appears to be comparable in effectiveness with 200 mg of ibuprofen.² Both agents have onsets of activity of about 30 minutes after oral administration; however, naproxen sodium has a longer duration of action.² The analgesic effect from naproxen sodium may last up to 12 hours, whereas ibuprofen lasts 6 to 8 hours.²

The most common adverse effects associated with the use of NSAIDs include dyspepsia, nausea, heartburn, and epigastric pain. These agents produce less GI upset and bleeding when compared with aspirin.² Patients should be instructed to take NSAIDs with food, milk, or antacids if they experience GI upset. Examples of clinically significant drug interactions associated with NSAIDs include bisphosphonates, digoxin, beta-blockers, angiotensin converting enzyme (ACE) inhibitors, diuretics, anticoagulants, and methotrexate.² Patients with a history of impaired renal function, congestive heart failure, or medical conditions that compromise renal hemodynamics should not selfmedicate with NSAIDs.²

Some studies have reported that the use of NSAIDs is associated with an increased risk of myocardial infarction, heart failure, hypertension, and stroke.^2,4 The American Heart Association recommends that patients with, or at risk for, cardiovascular disease (hyperlipidemia, hypertension, and diabetes) should avoid the use of NSAIDs.^2,4 It is also recommended that patients use the lowest possible dose for the shortest duration.^2,4 The FDA recommends that patients use NSAIDs for no more than 10 days, unless otherwise directed by a physician.²

Salicylates

Salicylates are indicated for the treatment of osteoarthritis, rheumatoid arthritis, and other rheumatologic disorders, as well as for temporary relief of mild-to-moderate pain related to muscular aches and back pain; these agents also have antipyretic activity.²

Aspirin also is indicated for the prevention of thromboembolic events in high-risk patients.² Examples of clinically significant drug—drug interactions associated with aspirin include valproic acid, beta-blockers, ACE inhibitors, diuretics, anticoagulants, methotrexate, and sulfonylureas.² The maximum analgesic dose for self-medication with aspirin is 4 g/day; however, dosages of 4 to 6 g/day may be needed to produce anti-inflammatory effects.² Aspirin and other salicylates should not be administered to patients ≤15 years who are recovering from chickenpox or influenza.² Patients with gout or diabetes should avoid the use of aspirin unless otherwise directed by their physician. Patients with renal impairment should consult their primary health care provider prior to using aspirin or other salicylates.²

An estimated 50% of patients who take aspirin experience upper GI symptoms.² Individuals with risk factors for upper GI bleeding should avoid the use of aspirin, as well as individuals on anticoagulants and those with hepatic and renal disorders or heart failure.²

Evaluating Efficacy

Various clinical studies have been conducted to compare the efficacy and safety of the various OTC analgesics. For example, Perrott et al summarized studies testing the efficacy and safety of single-dose acetaminophen and ibuprofen for treating pain or fever in pediatric patients.⁵ The study concluded that in children, single doses of ibuprofen (4-10 mg/kg) and acetaminophen (7-15 mg/kg) have similar efficacy for relieving moderate-to-severe pain; ibuprofen (5-10 mg/kg) was a more effective antipyretic than acetaminophen (10-15 mg/kg) at 2, 4, and 6 hours post-treatment.^2,5

In another study, Prior et al evaluated and compared the efficacy and safety of single doses of 1000 mg of acetaminophen and 375 mg of naproxen versus placebo over a 6-hour period in the treatment of tension headaches. They concluded that for episodic tension headaches, 1000 mg of acetaminophen appears to provide pain relief that is comparable with/equivalent to 375 mg of naproxen.^2,6

Other studies have concluded that aspirin and nonacetylated salicylates are thought to be comparable in antiinflammatory efficacy; however, some health care professionals believe that aspirin is the superior analgesic and antipyretic.² In addition, various studies have reported the comparable efficacy of aspirin and acetaminophen on a milligram- for-milligram basis in a number of pain models (ie, postoperative pain, episiotomy pain, oral surgery pain, and cancer pain). The results of a placebocontrolled study reported that 2 hours after taking either 500 or 1000 mg of aspirin or 500 or 1000 mg of acetaminophen, both aspirin groups and the acetaminophen group taking 1000 mg produced superior pain relief compared with the placebo group.²

Studies also have shown that ibuprofen is as effective as aspirin in treating various types of pain, such as dental, dysmenorrheal, and episiotomy; however, NSAIDs are preferred for selftreatment of inflammatory disorders, because aspirin must be dosed near the self-care maximum to achieve antiinflammatory effects.²

Conclusion

Patients with preexisting medical conditions and women who are pregnant and lactating should consult their physician prior to using any of these products. It is imperative for pharmacists to remind patients to adhere to the recommended dosages and duration of use unless otherwise directed by a physician, as well as the warnings listed by the products’ manufacturers. Patients who are not achieving adequate pain relief with the use of OTC analgesics should be advised to consult their primary care physician for other available treatment options.