Action and Spectrum

Actions and Spectrum: 

• lidocaine and tetracaine are both local anesthetics that work by blocking the sodium channels responsible for transmitting pain signals from nerves to the brain. 
• lidocaine has a rapid onset of action and is commonly used for short procedures or to manage acute pain. Its activity spectrum includes sensory and motor nerves, making it practical for local anesthesia, regional anesthesia, and nerve blocks. 
• tetracaine has a slower onset of action than lidocaine, but its effects last longer. It is often used for more lengthy procedures or postoperative pain management. tetracaine’s spectrum of activity is primarily limited to sensory nerves, making it practical for surface anesthesia, ophthalmologic procedures, and epidural anesthesia. 
• When used together, lidocaine and tetracaine can be applied as a topical cream or gel for surface anesthesia, particularly in dermatology and cosmetic procedures. Combining these two agents produces a faster onset of action and a longer duration of anesthesia than either drug alone. 

Drug Interaction

Adverse Reaction

Frequency defined 

>10% 

Localized blanching (12%) 

Localized erythema (71%) 

Localized edema (12%)  

1-10% 

Other reactions at the site of the application  

<1% 

Application site reactions 

Dizziness 

Pain 

Contact dermatitis 

Skin discoloration 

Allergic reaction 

Paresthesia 

Vesiculobullous rash 

Rash 

Pruritus 

Headache 

N/V 

Infection 

Somnolence 

Blister 

Urticaria 

Black Box Warning

Contraindication / Caution

Contraindications/caution: 

Contraindications: 

• Hypersensitivity: Individuals allergic or hypersensitive to lidocaine or tetracaine should not use these medications. 
• Methemoglobinemia: lidocaine and tetracaine can cause methemoglobinemia, a rare condition that reduces the amount of oxygen the blood can transport. These medications should not be used in patients with a history of methemoglobinemia or those at an increased risk of developing it. 
• Severe liver disease: lidocaine and tetracaine are metabolized in the liver, and their clearance can be reduced in patients with severe liver disease. These medications should be used with caution in patients with liver disease. 
• Cardiac conduction disturbances: lidocaine and tetracaine can affect cardiac conduction, and their use should be avoided in patients with certain cardiac conditions. 
• Pregnancy and breast-feeding: The safety of lidocaine and tetracaine during pregnancy and breast-feeding has not been established, and their use should be avoided unless necessary. 
• Children: lidocaine and tetracaine should be used with caution in children, as they may be more susceptible to systemic toxicity. 

Caution: 

• Use in elderly patients: lidocaine and tetracaine should be used cautiously in elderly patients, as they may be more sensitive to their effects due to age-related changes in metabolism and clearance. 
• Renal impairment: Patients with renal impairment may have reduced clearance of lidocaine and tetracaine, and caution should be exercised when using these medications in this population. 
• Use in patients with neurological conditions: lidocaine and tetracaine can cause CNS depression, and their use should be avoided or used with caution in patients with neurological conditions such as epilepsy, multiple sclerosis, or Parkinson’s disease. 
• Use in patients with hypotension: lidocaine and tetracaine can cause vasodilation and hypotension, and their use should be avoided or used with caution in patients with pre-existing hypotension. 
• Drug interactions: lidocaine and tetracaine can interact with other medications, including antiarrhythmic drugs, beta-blockers, and calcium channel blockers. Caution should be exercised when using these medications in combination with lidocaine and tetracaine. 
• Systemic toxicity: lidocaine and tetracaine can cause systemic toxicity if absorbed in large quantities or misused. Care should be taken to ensure the recommended dose and application method are followed. 

Pregnancy / Lactation

Pregnancy consideration: Insufficient data available 

Lactation: Excretion of the drug in human breast milk is unknown 

Pregnancy category: 

Category A: well-controlled and Satisfactory studies show no risk to the fetus in the first or later trimester.   

Category B: there was no evidence of risk to the fetus in animal studies, and there were not enough studies on pregnant women. 

Category C: there was evidence of risk of adverse effects in animal reproduction studies, and no adequate evidence in human studies must take care of potential risks in pregnant women.    

Category D: adequate data with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits.    

Category X: Drugs listed in this category outweigh the risks over benefits. Hence these categories of drugs need to be avoided by pregnant women.    

Category N: There is no data available for the drug under this category 

Pharmacology

Pharmacology: 

• lidocaine and tetracaine are local anesthetics that work by blocking sodium channels in nerve membranes. This results in the inhibition of nerve impulses, leading to loss of sensation and pain relief. 
• lidocaine is a member of the amide family of local anesthetics, and it has a fast onset of action when applied topically or injected. lidocaine is metabolized by the liver and excreted in the urine. 
• tetracaine is a member of the ester family of local anesthetics, and it has a slower onset of action than lidocaine. tetracaine is metabolized by plasma cholinesterases and excreted in the urine. 
• When used together in a topical preparation, lidocaine and tetracaine produce a faster onset and longer duration of anesthesia than either drug alone. Combining these two agents allows for a complete blockade of nerve impulses, providing more significant pain relief. 

Pharmacodynamics: 

• The pharmacodynamics of lidocaine and tetracaine involves their ability to block the influx of sodium ions through the ion channels of the nerve membrane. This blockade prevents depolarization of the nerve fiber, which inhibits the transmission of nerve impulses and results in a local anesthetic effect. 
• lidocaine and tetracaine have similar mechanisms of action but differ in their chemical structure and potency. lidocaine is a member of the amide class of local anesthetics and has a relatively fast onset of action. It has a moderate duration of action and is often used for minor surgical procedures and dental work. On the other hand, tetracaine is a local ester anesthetic with a slower onset of action but a longer duration of action than lidocaine. It is often used for spinal anesthesia and in ophthalmic procedures. 
• When used together in a topical preparation, lidocaine and tetracaine produce a synergistic effect, resulting in faster onset and longer duration of anesthesia. Combining these two agents allows for a complete blockade of nerve impulses, providing more significant pain relief. 

Pharmacokinetics: 

Absorption 

lidocaine and tetracaine can be absorbed systemically when administered topically, but the degree of absorption positively correlates with the amount of drug applied and the duration of exposure. 

lidocaine has a peak plasma concentration of 148-641 ng/mL, while the peak plasma concentration of tetracaine is not well-established.  

Distribution 

The volume of distribution (Vd) of lidocaine after intravenous administration is 0.8-1.3 L/kg. 

lidocaine is highly protein-bound, with 75% bound to plasma proteins. 

The Vd and protein binding of tetracaine need to be well-established. 

Metabolism 

It is unclear if lidocaine and tetracaine are metabolized in the skin. 

lidocaine is metabolized in the liver, while plasma esterases metabolize tetracaine. 

Both lidocaine and tetracaine are metabolized into ester- and amide-type local anesthetics.  

Elimination and Excretion 

The half-life of lidocaine after intravenous administration is 1.8 hours. 

lidocaine is primarily excreted in the urine (98%) after intravenous administration. 

The elimination of tetracaine needs to be well-established. 

Adminstartion

Administration: 

• lidocaine/tetracaine is most administered topically as a cream or patch for local anesthesia. The cream or patch is applied to intact skin, and the area is covered with an occlusive dressing to enhance absorption. 
• When using the cream, the amount of cream applied and the duration of application should be based on the patient’s age, weight, and the size of the area to be anesthetized. The recommended dose of lidocaine/tetracaine cream is 1-2 g per 10 cm2 of skin, applied 20-60 minutes before the procedure. 
• When using the patch, the patch should be applied to intact skin and left in place for the recommended duration (usually 30-60 minutes) before the procedure. 
• lidocaine/tetracaine can also be administered by injection for local anesthesia in dental and minor surgical procedures. The dose and administration method should be based on the patient’s age, weight, and the nature of the procedure. 

Patient Information Leaflet

Patient information leaflet 

Generic Name: lidocaine/tetracaine 

Why do we use lidocaine/tetracaine? 

lidocaine/tetracaine is a combination of two local anesthetics that are used for various purposes, including: 

• Topical anesthesia: lidocaine/tetracaine cream or patch is applied to the skin before a procedure to provide local anesthesia. It is commonly used for venipuncture, intravenous cannulation, wound debridement, and laser therapy. 
• Local anesthesia in dental procedures: lidocaine/tetracaine can be injected to provide local anesthesia for dental procedures, such as tooth extraction, cavity filling, and root canal treatment. 
• Ophthalmic procedures: lidocaine/tetracaine can be applied topically to the eye to provide local anesthesia for various ophthalmic procedures, such as corneal abrasion, foreign body removal, and suture removal. 
• Anorectal procedures: lidocaine/tetracaine can be used topically to provide local anesthesia for anorectal procedures such as hemorrhoidectomy, fistulectomy, and fistulotomy. 
• Other procedures: lidocaine/tetracaine can be used for minor surgical procedures such as circumcision, skin biopsy, and dermatological procedures.