Tetracaine Hydrochloride is a potent local anesthetic, belonging to the ester class of local anesthetics. Its appearance is usually a white or off-white crystalline powder, odorless, with a slightly bitter taste and then a numbing sensation. It is easily soluble in water or ethanol. Its anesthetic efficacy is significantly higher than procaine, approximately 10 times that of procaine, and it has stronger penetration and a longer duration, suitable for various clinical scenarios such as surface anesthesia, infiltration anesthesia, conduction block anesthesia, and spinal anesthesia. It is particularly widely used in ophthalmology, otolaryngology surgeries, and epidural anesthesia. Its mechanism of action is by reversibly blocking the voltage-gated sodium channels on the nerve cell membrane, inhibiting sodium ion influx, thereby interrupting the generation and conduction of nerve impulses, resulting in local numbness. However, due to its potency, its toxic side effects are also relatively large. It mainly inhibits the central nervous system and cardiovascular system. Overdose can cause severe adverse reactions such as convulsions, respiratory depression, and arrhythmias. Therefore, when using it, the dosage must be strictly controlled and resuscitation preparations must be made. Despite the risks, benzocaine hydrochloride remains an indispensable important drug in surgical operations and pain management to this day due to its outstanding anesthetic effect.
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Chemical Properties and Physical Characteristics
The chemical name of tetracaine hydrochloride is 4-(butylamino)benzoic acid 2-(dimethylamino)ethyl ester hydrochloride, with the molecular formula C₁₅H₂₄N₂O₂·HCl and molecular weight 300.82. It appears as a white or grayish-white crystalline powder, odorless, with a melting point range of 147–150°C. It is highly soluble in water (1 g/1 mL), soluble in ethanol, but poorly soluble in ether. This high water solubility makes it an ideal choice for mucosal anesthesia, allowing rapid tissue penetration via spray, topical application, or injection.
Pharmacological Mechanism
Tetracaine hydrochloride produces local anesthetic effects by blocking sodium ion channels in nerve cell membranes, thereby inhibiting nerve impulse conduction. Its significantly higher lipid solubility compared to procaine allows faster penetration through mucous membranes and nerve sheaths. Onset occurs within 1-3 minutes, with duration ranging from 20-40 minutes (surface anesthesia) to 2-3 hours (epidural anesthesia). However, this property also results in toxicity levels 10 times higher than procaine. Overdose may trigger severe reactions in the central nervous system and cardiovascular system.
Clinical application scenarios
Tetracaine hydrochloride, as a classic ester-type local anesthetic, has been in use since the 1930s. Due to its potent anesthetic effect and rapid onset characteristics, it has occupied an important position in the field of clinical anesthesia. Its high lipid solubility and strong penetration ability make it the preferred drug for mucosal anesthesia and nerve block. However, its high toxicity also requires strict control of the dosage and operational procedures during clinical application. The following will analyze these from five core application scenarios:
Ophthalmic Surgery: The "Gold Standard" of Precise Anesthesia
Ophthalmic surgeries have extremely high requirements for anesthesia depth and safety. Tetracaine hydrochloride, due to its rapid onset and short duration of action, has become the preferred anesthetic for operations such as corneal foreign body removal, intraocular pressure measurement, and phacoemulsification of cataracts.
Mechanism of action
After instillation of a 0.5%-1% solution into the eye, the corneal nerve conduction can be blocked within 10-20 seconds, and the anesthetic effect lasts for 10-20 minutes, meeting the requirements for short-term operations.
Clinical advantages
Avoid the risk of corneal perforation that may be caused by injection anesthesia;
Reduce operational interference due to the blink reflex of patients;
Repetitive administration can be used to extend the anesthetic duration (with an interval of more than 5 minutes).
Data support
The 0.5% tetracaine hydrochloride eye ointment approved by the FDA is also safe and effective in pediatric patients, and its efficacy is recognized based on extrapolation from adult data.
Otorhinolaryngology and Endoscopy: Reducing discomfort from invasive operations
In nasal endoscopy, laryngoscopy, gastroscopy, colonoscopy, etc., tetracaine hydrochloride reduces the patient's choking reflex and mucosal irritation through surface anesthesia:
Nasal endoscopy and laryngoscopy
A 2% solution is sprayed into the nasal cavity or throat, taking effect within 3-5 minutes, with an anesthesia duration of 20-40 minutes, significantly improving the patient's cooperation during the examination.
Endoscopy
Gastroscopy: Applied to the front end of the gastroscopy or orally in 2% gel form to reduce nausea and vomiting during insertion;
Colonoscopy: Combined with a defoaming agent, it reduces the risk of intestinal spasm.
Innovative application
In painless cystoscopy, bupivacaine hydrochloride gel is used in combination with intravenous anesthesia, which can reduce the dosage of propofol by 30%, shorten the examination time by 15%, and simultaneously improve the postoperative oxygenation level.
Urological procedures: "Lubricants" for catheterization and cystoscopy
Catheterization and cystoscopy often cause patients intense pain. Bupivacaine hydrochloride alleviates discomfort through both local anesthesia and lubrication effects:
Catheterization: Apply 5% gel to the urethral opening or the front end of the catheter. It takes effect after 5 minutes and the anesthetic effect lasts for 20-30 minutes. It is particularly suitable for male patients.
Cystoscopy:
Traditional method: Inject 1% tetracaine hydrochloride solution into the bladder, with an anesthesia duration of 1 hour;
Improved plan: Mixed with lidocaine to extend the anesthesia duration to 2 hours and reduce the patient's movement during the operation.
Risk control: Strictly avoid the solution from entering the blood vessels; otherwise, it may cause a sudden increase in blood drug concentration and lead to poisoning.
Nerve block and epidural anesthesia: "Enhancers" of regional anesthesia
Tetracaine hydrochloride is often used in regional anesthesia in combination with lidocaine to reduce the total amount of the drug by prolonging the action time:
Epidural block
The commonly used concentration is 0.15% - 0.3%, when mixed with lidocaine, the anesthesia duration can be extended to 2 - 3 hours;
Maximum control: a single dose of 80mg, with a total daily dose not exceeding 200mg to reduce the risk of toxicity.
Subarachnoid block
Solution formula: 1ml of 1% tetracaine hydrochloride + 1ml of 10% glucose + 1ml of 3% ephedrine;
Dosage control: a single dose of 10 - 15mg, a maximum of 20mg, to avoid respiratory depression.
Nerve conduction block
Used for brachial plexus and sciatic nerve block, the concentration is 0.1% - 0.2%, a single maximum dose of 100mg;
It is necessary to combine with ultrasound guidance technology for precise positioning to reduce the dosage.
Special Application Scenarios: "Cross-border Exploration" from Anticonvulsant to Muscle Relaxation
Although not a mainstream use, tetracaine hydrochloride demonstrates diverse potential in specific scenarios:
Anticonvulsant effect
By stabilizing the membrane potential of neurons and reducing excessive excitation, it has a certain control effect on absence seizures (requires oral administration, with limited clinical application).
Muscle relaxation assistance
Reduces acetylcholine release at the presynaptic membrane, weakens the excitation transmission at the neuromuscular junction, and is often used in combination with other drugs to achieve muscle relaxation under general anesthesia.
Extended application of analgesia
During trauma, post-operation and childbirth, it exerts analgesic effects by interfering with the transmission of pain signals, but be vigilant of the risk of respiratory depression.
Core principle of clinical application: Balance of safety and efficacy
The toxicity of tetracaine hydrochloride is 10 times that of procaine. Its clinical application must strictly follow the following principles:
Dosage control: Adjust the dosage according to the type of surgery, the patient's weight and age to avoid overdose, which may cause convulsions and respiratory failure.
Contraindication screening: Patients allergic to ester local anesthetics, those with severe heart and kidney dysfunction, and those with myasthenia gravis should be prohibited from using.
Operational norms:
Repeated aspiration during injection to avoid mistakenly entering blood vessels;
Avoid contact of the injection site with iodine agents to prevent drug precipitation and loss of efficacy;
Continuous monitoring of blood pressure, pulse and respiratory function during spinal anesthesia.
Emergency preparedness: Equip with anti-allergic drugs such as epinephrine and dexamethasone to ensure timely treatment of toxic reactions.
Future trends: Integration of precise drug administration and combined anesthesia
With the advancement of medical technology, the application scenarios of tetracaine hydrochloride continue to expand:
Research on sustained-release preparations: Nanometer microsphere technology can extend the duration of anesthesia to 6-8 hours, reducing the risk of repeated administration;
Visualized administration: Ultrasound-guided technology improves the success rate of nerve block and reduces the dosage of drugs;
Comprehensive anesthesia plan: Combined with ropivacaine and lidocaine, it achieves the "rapid onset - long duration" effect while reducing toxicity.
Conclusion
Tetracaine hydrochloride, as a "double-edged sword" in the field of local anesthesia, its clinical value depends on precise dosage control, standardized operation procedures, and strict monitoring of vital signs. In core scenarios such as ophthalmology, otolaryngology, urinary system, and regional anesthesia, it remains an indispensable and highly effective anesthetic drug; and through formulation improvement and technological innovation in the future, its safety and application range are expected to be further enhanced.