Drug Interaction Report

Some of the medication in benzocaine topical may be absorbed into the bloodstream following local application. When present in sufficient concentrations in the blood, local anesthetics such as benzocaine topical may cause methemoglobinemia, a rare condition that can lead to oxygen deprivation in tissues and vital organs due to reduced oxygen-carrying capacity of the blood. The risk is increased when combined with other medications that can also induce methemoglobinemia such as nitrofurantoin. Individuals may be more susceptible to developing methemoglobinemia during treatment with these medications if they are very young (especially neonates and infants) or have anemia, diseases of the heart or lungs, blood circulation disorders, liver cirrhosis, shock, sepsis, and certain genetic predispositions such as NADH cytochrome-b5 reductase deficiency, glucose-6-phosphate dehydrogenase deficiency, and hemoglobin M. In addition, use of topical anesthetics on inflamed or abraded areas or broken skin, as well as excessive use such as application of large doses or on larger than recommended areas, can increase absorption and result in high blood levels of the medication. Topical anesthetics that are applied to mucous membranes such as inside the mouth, nose, or throat (e.G., for sore throat; for numbing prior to dental procedures or scoping of the lungs or gastrointestinal tract) may also be absorbed to a significant extent. Close medical supervision is necessary when medications that can cause methemoglobinemia are used together. Do not exceed the recommended dose or frequency and duration of use when treated with products that contain local anesthetics, including some over-the-counter preparations. Signs and symptoms of methemoglobinemia may be delayed by several hours after treatment with topical anesthetics. Patients (or their caregivers) should seek immediate medical attention if they develop a gray discoloration of the skin, mouth, or nail bed; nausea; headache; dizziness; lightheadedness; fatigue; shortness of breath; rapid or shallow breathing; a rapid heartbeat; palpitation; anxiety; or confusion. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.