Usage
- Tetracaine is prescribed for short-term local anesthesia of the eyes, nose, throat, and skin. It is used for various procedures, such as minor surgical procedures, tonometry, removal of foreign bodies from the eye, and diagnostic procedures. It is also used to numb the eye before certain eye exams or other procedures. Topical tetracaine can also provide temporary relief of pain and itching caused by minor burns, skin irritations, or rashes.
- Pharmacological Classification: Local anesthetic.
- Mechanism of Action: Tetracaine reversibly blocks nerve conduction by inhibiting sodium ion influx through voltage-gated sodium channels in neuronal cell membranes. This prevents the initiation and propagation of action potentials, thereby producing local anesthesia.
Alternate Names
- Amethocaine (international nonproprietary name).
- Brand Names: Pontocaine, Tetcaine, Viractin, Altacaine, and various generic formulations.
How It Works
- Pharmacodynamics: Tetracaine binds to the intracellular portion of voltage-gated sodium channels in nerve axons, preventing depolarization and blocking nerve impulse transmission. This action is reversible, and nerve function returns as the drug is eliminated from the site of action.
- Pharmacokinetics:
- Absorption: Rapidly absorbed from mucous membranes, including the eyes. Absorption is slower through intact skin.
- Metabolism: Primarily metabolized by plasma esterases through hydrolysis to para-aminobenzoic acid (PABA) and diethylaminoethanol.
- Elimination: Excreted primarily in the urine as metabolites.
- Mode of Action: Binds to the intracellular portion of voltage-gated sodium channels, blocking sodium influx and preventing nerve impulse initiation and propagation.
- Receptor Binding: Binds to voltage-gated sodium channels.
- Elimination Pathways: Renal excretion following rapid metabolism by plasma esterases. A small fraction is excreted unchanged in the urine.
Dosage
Standard Dosage
Adults:
- Ophthalmic: 1-2 drops of 0.5% solution instilled into the eye(s) as needed. For minor surgical procedures, 1-2 drops may be instilled every 5-10 minutes, not exceeding 5 doses.
- Topical/Cutaneous: Apply a thin film to the affected skin area as needed. For percutaneous local anesthesia before venipuncture or venous cannulation, up to 5g (approx. 5 tubes) of 4% tetracaine base gel can be applied, then covered with an occlusive dressing. Remove after 30 minutes (venipuncture) or 45 minutes (cannulation). May repeat application after a minimum of 5 hours. Max cumulative dose: 7g in 24 hours.
- Spinal anesthesia: 2–5 mg for saddle block, 5 mg for perineum, 10 mg for lower extremities. Administer a 1% solution diluted 1:1 in cerebrospinal fluid (CSF) at a rate of 1 mL every 5 seconds.
Children:
- Ophthalmic: Safety and efficacy in children have been extrapolated from adult data. Similar dosing as in adults is often used, but under strict medical supervision.
- Topical/Cutaneous: For children >1 month to <5 years, apply up to 1g (approx. 1 tube) of 4% tetracaine base gel. For children ≥5 years, adult dosing may be used.
- Spinal anesthesia: Safety and effectiveness have not been established.
Special Cases:
- Elderly Patients: Use with caution, as they may be more sensitive to the effects of tetracaine. Dose reduction may be necessary.
- Patients with Renal Impairment: Caution is advised, and dose adjustment may be required.
- Patients with Hepatic Dysfunction: Use with caution, as tetracaine is metabolized in the liver.
- Patients with Comorbid Conditions: Use with caution in patients with cardiovascular disease, hyperthyroidism, or decreased plasma esterase levels.
Clinical Use Cases
- Intubation: Topical application to the trachea and larynx before intubation.
- Surgical Procedures: Infiltration or topical application for minor surgical procedures.
- Mechanical Ventilation: Not typically used.
- Intensive Care Unit (ICU) Use: Limited use, mainly for specific procedures like central line placement.
- Emergency Situations: Limited use, with caution.
Dosage Adjustments: Dosage modification is necessary for patients with renal or hepatic impairment, and the elderly.
Side Effects
Common Side Effects
- Stinging, burning, or redness at the application site.
- Blurred vision (ophthalmic use).
- Runny nose, nasal congestion, watery eyes, sneezing (nasal use).
- Sore or numb throat (throat use).
Rare but Serious Side Effects
- Allergic reactions (rash, hives, itching, swelling, difficulty breathing).
- Methemoglobinemia (cyanosis, shortness of breath, fatigue, confusion).
- Seizures.
- Cardiac arrest.
Long-Term Effects
- Corneal damage with prolonged ophthalmic use.
Adverse Drug Reactions (ADR)
- Anaphylaxis.
- Methemoglobinemia.
Contraindications
- Hypersensitivity to tetracaine, PABA, other ester-type local anesthetics, or any component of the formulation.
- Use in patients receiving sulfonamides (PABA interference).
Drug Interactions
- Sulfonamides: Tetracaine’s metabolite, PABA, antagonizes the antibacterial action of sulfonamides.
- Other Local Anesthetics: Additive effects, potentially increasing the risk of systemic toxicity.
- Cholinesterase Inhibitors: May prolong the duration of action of tetracaine.
- Methemoglobin-inducing Agents: Increased risk of methemoglobinemia.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: C (data are lacking, use only if potential benefit outweighs risk).
- Fetal Risks: Potential for fetal bradycardia and methemoglobinemia.
- Breastfeeding: Limited data suggest minimal risk with single doses; an alternative drug may be preferred.
Drug Profile Summary
- Mechanism of Action: Blocks voltage-gated sodium channels, inhibiting nerve impulse transmission.
- Side Effects: Stinging, burning, blurred vision, allergic reactions, methemoglobinemia.
- Contraindications: Hypersensitivity, concurrent sulfonamide therapy.
- Drug Interactions: Sulfonamides, other local anesthetics, cholinesterase inhibitors.
- Pregnancy & Breastfeeding: Category C; use with caution.
- Dosage: Varies depending on route and indication; see detailed dosage section.
- Monitoring Parameters: Heart rate, blood pressure, respiratory rate, oxygen saturation (especially during spinal anesthesia).
Popular Combinations
- Often combined with other local anesthetics (e.g., lidocaine) for enhanced effect or longer duration.
- Epinephrine may be added to prolong the anesthetic effect and reduce bleeding.
Precautions
- General Precautions: Pre-screening for allergies and medical conditions that may affect drug metabolism or increase risk of adverse reactions.
- Specific Populations: Use with caution in pregnant/breastfeeding women, children, and the elderly.
- Lifestyle Considerations: Patients should avoid driving or operating machinery until the anesthetic effects have worn off.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Tetracaine?
A: Dosage varies depending on route, indication, and patient-specific factors. Refer to the detailed dosage section above.
Q2: What are the common side effects of tetracaine?
A: Common side effects include stinging, burning, blurred vision, runny nose, and sore throat.
Q3: What are the serious side effects of tetracaine?
A: Serious side effects include allergic reactions, methemoglobinemia, seizures, and cardiac arrest.
Q4: Is tetracaine safe to use during pregnancy?
A: Tetracaine is a Pregnancy Category C drug. Use only if the potential benefit outweighs the risks.
Q5: Can tetracaine be used during breastfeeding?
A: Limited data are available. Single doses are likely low risk, but an alternative drug might be preferred.
Q6: What are the contraindications to using tetracaine?
A: Contraindications include hypersensitivity to tetracaine, PABA, or other ester-type local anesthetics, and concurrent use of sulfonamides.
Q7: What drug interactions are important to consider with tetracaine?
A: Important drug interactions include sulfonamides, other local anesthetics, and cholinesterase inhibitors.
A: Tetracaine is rapidly metabolized by plasma esterases.
Q9: What is the duration of action of tetracaine?
A: The duration of action varies depending on the route of administration and the specific procedure. It typically ranges from 30 minutes to several hours.
Q10: How should tetracaine be administered?
A: Tetracaine can be administered topically (eye drops, cream, ointment, gel), by injection (spinal anesthesia), or as a solution for nasal or throat application. The specific method depends on the clinical indication.
