Usage
Benzocaine + Metronidazole is prescribed for the treatment of mouth sores (ulcers) and other localized oral infections susceptible to metronidazole.
Pharmacological Classification:
- Benzocaine: Local anesthetic, topical analgesic
- Metronidazole: Antibacterial, antiprotozoal
Mechanism of Action:
This combination medication works through two distinct mechanisms:
- Benzocaine: Blocks voltage-gated sodium channels, inhibiting nerve impulse transmission and producing a localized anesthetic effect to reduce pain sensation.
- Metronidazole: Disrupts DNA synthesis and structure in susceptible anaerobic bacteria and protozoa, leading to cell death.
Alternate Names
- Benzocaine and Metronidazole
- Boromet Dental Gel (Brand name in some regions)
How It Works
Pharmacodynamics:
- Benzocaine: Produces localized anesthesia by reversibly binding to sodium channels on neuronal cell membranes, inhibiting nerve impulse initiation and propagation.
- Metronidazole: Enters microbial cells and undergoes reductive activation, forming cytotoxic metabolites that disrupt DNA structure and function. This leads to microbial cell death.
Pharmacokinetics:
- Benzocaine: Minimally absorbed systemically when applied topically to intact oral mucosa. Metabolized primarily by plasma cholinesterases. Eliminated via urinary excretion.
- Metronidazole: Well absorbed after oral administration, achieving peak plasma concentrations within 1-2 hours. Metabolized in the liver primarily via oxidation and glucuronidation. Excreted primarily in the urine, with some fecal elimination.
Receptor binding, enzyme inhibition, or neurotransmitter modulation:
- Benzocaine: Binds to voltage-gated sodium channels.
- Metronidazole: Forms cytotoxic metabolites that interact with DNA.
Elimination pathways:
- Benzocaine: Primarily renal excretion.
- Metronidazole: Primarily renal excretion, some fecal elimination, hepatic metabolism.
Dosage
Standard Dosage
Adults:
Topical application to the affected area 2-4 times daily, or as directed by a healthcare professional. Do not swallow.
Children:
Consult a healthcare professional for pediatric dosing recommendations. Use in children under 2 years of age is generally not recommended for benzocaine.
Special Cases:
- Elderly Patients: Monitor for potential systemic absorption, particularly with prolonged use. Dosage adjustments may be necessary.
- Patients with Renal Impairment: Dosage adjustment for metronidazole may be necessary in severe renal impairment.
- Patients with Hepatic Dysfunction: Dosage adjustment for metronidazole may be required in severe hepatic impairment. Caution is advised with benzocaine due to potential systemic toxicity.
- Patients with Comorbid Conditions: Patients with G6PD deficiency, methemoglobin reductase deficiency, or heart, lung, or blood vessel disease are at an increased risk of methemoglobinemia with benzocaine use.
Clinical Use Cases
This combination is not typically used in settings like intubation, surgical procedures, mechanical ventilation, ICU use, or emergency situations. It is primarily indicated for localized oral infections and ulcers.
Dosage Adjustments
Refer to special cases above.
Side Effects
Common Side Effects
- Tingling or burning sensation at the application site.
Rare but Serious Side Effects
- Methemoglobinemia (especially with prolonged use or in susceptible individuals).
- Allergic reactions (rash, itching, hives, swelling).
Long-Term Effects
With prolonged or excessive use of benzocaine, there is a potential risk of methemoglobinemia.
Adverse Drug Reactions (ADR)
Methemoglobinemia is a serious ADR that can occur with benzocaine use.
Contraindications
- Known hypersensitivity to benzocaine or metronidazole.
- Children under 2 years of age (for benzocaine).
Drug Interactions
- Benzocaine: May interact with other drugs metabolized by plasma cholinesterases.
- Metronidazole: Disulfiram-like reaction with alcohol. May interact with warfarin, lithium, and certain other medications.
Pregnancy and Breastfeeding
- Pregnancy: Consult a healthcare professional before using during pregnancy. Metronidazole is generally avoided in the first trimester.
- Breastfeeding: Topical benzocaine is unlikely to affect the infant if applied away from the breast. Metronidazole is present in breastmilk; short courses are generally considered compatible with breastfeeding.
Drug Profile Summary
- Mechanism of Action: Benzocaine blocks sodium channels, producing local anesthesia. Metronidazole disrupts DNA in anaerobic microbes.
- Side Effects: Local irritation, methemoglobinemia (benzocaine).
- Contraindications: Hypersensitivity, children <2 years (benzocaine).
- Drug Interactions: Alcohol (metronidazole).
- Pregnancy & Breastfeeding: Use with caution.
- Dosage: Topical application 2-4 times daily.
- Monitoring Parameters: Observe for signs of methemoglobinemia, especially with prolonged use.
Popular Combinations
This combination itself is a popular fixed-dose combination used in clinical practice.
Precautions
- Avoid contact with eyes and nose.
- Do not swallow the product.
- Monitor for signs of methemoglobinemia.
- Consult a doctor before use in pregnancy or breastfeeding.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Benzocaine + Metronidazole?
A: Topical application 2-4 times daily to the affected area in adults. Consult a healthcare professional for pediatric dosing.
Q2: What are the main contraindications for this combination?
A: Hypersensitivity to benzocaine or metronidazole, and use in children under 2 years of age (for benzocaine).
Q3: Can pregnant or breastfeeding women use this medication?
A: Consult a healthcare professional. Metronidazole is generally avoided in the first trimester. Topical benzocaine use is generally safe if applied away from the breast.
Q4: What are the primary side effects?
A: Transient local irritation, such as burning or tingling. Methemoglobinemia is a rare but serious side effect, especially with prolonged use or in susceptible individuals.
Q5: How does metronidazole work?
A: It acts as an antiprotozoal and antibacterial agent by disrupting DNA synthesis and structure within susceptible organisms.
Q6: How does benzocaine work?
A: It’s a local anesthetic that blocks nerve impulse transmission by inhibiting sodium channels on nerve cell membranes.
Q7: What should I do if I accidentally swallow this medication?
A: Contact a healthcare professional or poison control center immediately. While small amounts are unlikely to cause systemic toxicity, it’s crucial to seek medical advice.
Q8: Are there any drug interactions I should be aware of?
A: Metronidazole can have a disulfiram-like reaction with alcohol. Concurrent use of certain medications like warfarin or lithium should also be discussed with a doctor.
Q9: How should I store this medication?
A: Store at room temperature away from light and moisture. Keep out of reach of children.
