OTC analgesics and drug interactions: clinical implications

Abstract

The risk of drug interactions with concurrent use of multiple medications is a clinically relevant issue. Many patients are unaware that over-the-counter (OTC) analgesics can cause potentially serious adverse effects when used in combination with other common medications such as anticoagulants, corticosteroids, or antihypertensive agents. Of particular significance is the increased risk of upper abdominal gastrointestinal adverse events in patients who take traditional nonsteroidal anti-inflammatory drugs (NSAIDs). This risk is dose dependent and further increased in patients who take more than one NSAID or use NSAIDs in combination with certain other medications. Some NSAIDs may also mitigate the antiplatelet benefits of aspirin and may increase blood pressure in patients with hypertension. Clinicians should be aware of potential drug interactions with OTC analgesics when prescribing new medications. Additionally, patients should be properly counseled on the appropriate and safe use of OTC analgesics.

Figure 1

The risk for upper GI bleeding with aspirin, ibuprofen, and acetaminophen (adapted from reference [4], with permission). OTC = over the counter.

Figure 2

The effect of aspirin alone and of ibuprofen plus aspirin on platelet cyclooxygenase-1 (COX-1). A) The platelet prostaglandin (PG) G/H synthase-1 (COX-1) is depicted as a dimer, and the arachidonic acid substrate gains access to the catalytic site through a hydrophobic channel that leads to the core of the enzyme. B) Aspirin works by inhibiting access of arachidonic acid to the catalytic site by irreversibly acetylating a serine residue at position 529 in platelet COX-1. Interpolation of the bulky acetyl residue then permanently prevents metabolism of arachidonic acid into the cyclic endoperoxides PGG2 and PGH2. Because PGH2 is metabolized by thromboxane synthase into thromboxane A₂, aspirin prevents the formation of thromboxane A₂ by the platelets until new platelets are created. C) Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, are competitive inhibitors of the catalytic site, and cause the reversible inhibition of thromboxane A₂ formation during the dosing interval. Therefore, prior occupancy of the catalytic site by ibuprofen prevents aspirin from gaining access to its target serine (reproduced from reference [26], with permission).