Usage
Benzocaine is a local anesthetic (topical) used to relieve pain and itching caused by conditions such as mouth sores, sore throat, canker sores, teething pain, minor burns, sunburn, insect bites or stings, poison ivy, poison oak, poison sumac, minor cuts, or scratches. It belongs to the pharmacological class of local anesthetics, specifically ester local anesthetics. Benzocaine works by reversibly stabilizing the neuronal membrane, which decreases its permeability to sodium ions. This action blocks nerve impulse initiation and conduction, leading to a localized numbing effect.
Alternate Names
Benzocaine is also known as ethyl 4-aminobenzoate. Brand names include Anbesol, Baby Orajel, Cepacol, Dermoplast, Hurricaine, Orabase, Orajel, Solarcaine, Topicaine, and others.
How It Works
Pharmacodynamics: Benzocaine acts by blocking voltage-gated sodium channels on neuronal membranes. This inhibits the depolarization necessary for nerve impulse transmission, preventing pain signals from reaching the central nervous system.
Pharmacokinetics:
- Absorption: Benzocaine is poorly absorbed through intact skin. Absorption is significantly increased through mucous membranes or broken skin.
- Metabolism: Primarily metabolized in the plasma and, to a lesser extent, in the liver by cholinesterase through hydrolysis.
- Elimination: Excreted in the urine as metabolites.
Mode of Action: Benzocaine binds to the intracellular portion of voltage-gated sodium channels, stabilizing them in their inactive state. This prevents sodium influx into the neuron, hindering depolarization and subsequent nerve impulse propagation.
Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: Benzocaine’s primary mechanism is sodium channel blockade. It does not directly bind to receptors, inhibit enzymes, or modulate neurotransmitters.
Elimination Pathways: Primarily renal excretion of metabolites after plasma and hepatic hydrolysis.
Dosage
Standard Dosage
Adults: Topical application of a 5-20% concentration, 3-4 times daily, as needed. For lozenges, 1 lozenge dissolved slowly in the mouth every 2 hours as needed (generally, use less than 2 days). For sprays, apply 1-3 sprays to the affected area, up to 4 times daily.
Children: Use in children younger than 2 years of age is generally not recommended due to the risk of methemoglobinemia. For children 2 years and older, dosage should be determined by a healthcare professional and is typically lower than adult doses. Lozenges are typically for children 5 years and older.
Special Cases:
- Elderly Patients: Use with caution due to increased risk of methemoglobinemia. Monitor for signs and symptoms.
- Patients with Renal Impairment: No specific dosage adjustments are typically necessary but caution is advised.
- Patients with Hepatic Dysfunction: No specific dosage adjustments are typically necessary but caution is advised.
- Patients with Comorbid Conditions: Use with caution in patients with asthma, bronchitis, emphysema, or heart disease due to an increased risk of methemoglobinemia.
Clinical Use Cases
Benzocaine is not typically used in clinical settings such as intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations. It is primarily used for topical pain relief.
Dosage Adjustments
Dosage adjustments may be necessary based on patient-specific factors, including age, weight, the affected area’s size, and the specific condition being treated. Always follow the advice of a healthcare professional.
Side Effects
Common Side Effects
Mild stinging, burning, or itching at the application site; skin tenderness; redness of the skin; dry white flakes where the medicine was applied.
Rare but Serious Side Effects
Methemoglobinemia (manifested by cyanosis, headache, fatigue, confusion, rapid heart rate, lightheadedness, shortness of breath, pale, blue, or gray skin); allergic reactions (hives, difficulty breathing, swelling of the face, lips, tongue, or throat).
Long-Term Effects
No specific long-term effects have been documented with topical benzocaine use, but prolonged use should be avoided unless under the supervision of a physician.
Adverse Drug Reactions (ADR)
Methemoglobinemia is a serious ADR that requires immediate medical intervention.
Contraindications
Hypersensitivity to benzocaine or other ester-type local anesthetics; secondary bacterial infection of the treated area; children under 2 years of age (for certain formulations); application to large areas of broken or damaged skin.
Drug Interactions
Benzocaine may interact with sulfonamides, potentially antagonizing their therapeutic effect. Anticholinesterases may inhibit benzocaine metabolism. Certain medications can increase the risk of methemoglobinemia when combined with benzocaine (e.g., dapsone, nitrates, other oxidizing agents).
Pregnancy and Breastfeeding
Pregnancy Safety Category: C. Animal studies have not been reported. Benzocaine is generally considered safe for topical use during pregnancy when used as directed and only if clearly needed. Avoid applying benzocaine to the breasts or nipples during breastfeeding, as infants may ingest the drug and develop methemoglobinemia.
Drug Profile Summary
- Mechanism of Action: Blocks voltage-gated sodium channels, inhibiting nerve impulse transmission.
- Side Effects: Stinging, burning, itching, redness, methemoglobinemia (rare but serious).
- Contraindications: Hypersensitivity, secondary bacterial infection, certain age groups.
- Drug Interactions: Sulfonamides, anticholinesterases, oxidizing agents.
- Pregnancy & Breastfeeding: Category C; avoid applying to breasts/nipples.
- Dosage: 5-20% topical application, 3-4 times daily.
- Monitoring Parameters: Observe for signs of methemoglobinemia.
Popular Combinations
Benzocaine is often combined with menthol in topical preparations for enhanced pain relief and a cooling sensation.
Precautions
Pre-screen for allergies to benzocaine or PABA. Avoid use in infants under 2 years old (for certain formulations). Use with caution in the elderly and individuals with asthma, bronchitis, emphysema, or heart disease.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Benzocaine?
A: The recommended dosage varies depending on the formulation, age, and condition being treated. Generally, adults can apply a 5-20% topical formulation 3-4 times daily as needed. For lozenges, one every 2 hours as needed. For children, consult a healthcare professional.
Q2: What is the mechanism of action of Benzocaine?
A: Benzocaine blocks voltage-gated sodium channels, preventing nerve impulse transmission and producing a local anesthetic effect.
Q3: What are the serious side effects of Benzocaine?
A: Methemoglobinemia is a rare but serious side effect. Watch for cyanosis, headache, fatigue, confusion, rapid heart rate, lightheadedness, and shortness of breath. Seek immediate medical attention if these symptoms appear.
Q4: Can pregnant women use Benzocaine?
A: Benzocaine is a Pregnancy Category C drug. It is generally considered safe for topical use during pregnancy when used as directed and only when clearly needed.
Q5: Can breastfeeding mothers use Benzocaine?
A: Avoid applying benzocaine to the breasts or nipples, as the infant could ingest the drug during breastfeeding, leading to a risk of methemoglobinemia. Other topical applications are likely safe.
Q6: What are the contraindications for using Benzocaine?
A: Contraindications include hypersensitivity to benzocaine or other ester anesthetics, secondary bacterial infection at the application site, and use in infants under 2 years of age (certain formulations).
Q7: What are the signs of methemoglobinemia?
A: Cyanosis (bluish skin discoloration), headache, tiredness, confusion, fast heart rate, lightheadedness, and shortness of breath are signs of methemoglobinemia, a serious condition that requires immediate medical attention.
Q8: Can Benzocaine be used for teething pain in infants?
A: Benzocaine use is not recommended for teething pain in infants due to the increased risk of methemoglobinemia.
Q9: What should I do if I suspect an allergic reaction to Benzocaine?
A: Discontinue use immediately and seek medical attention if you experience symptoms like hives, difficulty breathing, or swelling of the face, lips, tongue, or throat.
