Usage
Lidocaine + Prilocaine is prescribed for topical anesthesia of intact skin and genital mucous membranes. It is used to relieve pain and numb the skin prior to procedures such as needle insertions (venipuncture, IV cannulation, vaccinations), minor surgical procedures (wart removal, biopsies), and laser treatments. It’s also used to alleviate pain associated with superficial skin lesions and for the treatment of primary premature ejaculation in adult men. It also can be used in the management of leg ulcers.
Its pharmacological classification is local anesthetic.
The drug works by blocking nerve signals, preventing the sensation of pain.
Alternate Names
Lidocaine/Prilocaine is also known as EMLA (eutectic mixture of local anesthetics). Fortacin is the brand name for a spray formulation specifically indicated for premature ejaculation. Other brand names include Aprizio Pak, Nuvakaan, Nuvakaan II, Prizotral II, Prilovix, Oraqix, and Tempe.
How It Works
Pharmacodynamics: Lidocaine and Prilocaine, both amide-type local anesthetics, act by stabilizing neuronal membranes. This action inhibits the initiation and conduction of nerve impulses, effectively blocking pain signals from the application site. The depth of anesthesia depends on the dose and application time.
Pharmacokinetics:
- Absorption: Absorption is dependent on the application site, the duration of application, and the area covered. Absorption is higher through mucous membranes than through intact skin.
- Metabolism: Both Lidocaine and Prilocaine are metabolized primarily in the liver. Prilocaine can be metabolized to o-toluidine, which can cause methemoglobinemia.
- Elimination: The metabolites are excreted primarily by the kidneys.
Mode of Action: Lidocaine and Prilocaine block voltage-gated sodium channels in nerve cell membranes. This prevents depolarization and thus the conduction of nerve impulses.
Receptor Binding/Enzyme Inhibition: The primary mechanism is sodium channel blockade. While some interaction with other ion channels or receptors may occur, it is not the primary mechanism.
Elimination Pathways: Primarily renal excretion of metabolites after hepatic metabolism.
Dosage
Standard Dosage
Adults:
Dosage varies depending on the procedure and the area to be treated. Common dosages include:
- Minor skin procedures: 2.5 grams over 20-25 cm² for at least 1 hour.
- Major skin procedures: 2 grams per 10 cm² for at least 2 hours.
- Venipuncture/IV cannulation: 1 gram per 10 cm² for at least 1 hour.
- Premature ejaculation: 3 actuations (spray formulation) to the glans penis, maximum 3 doses within 24 hours with at least 4 hours between doses.
Children:
Dosage is weight-based and must be carefully calculated. It is crucial to consult pediatric dosing guidelines and not exceed maximum recommended doses for age and weight. Close monitoring during treatment is essential. For example:
- <3 months, <5 kg: Do not exceed 1 g total dose/application area >10 cm²/>1 hour application time.
- 3-12 months and >5 kg: Do not exceed 2 g total dose/application area >20 cm²/>4 hours application time.
Special Cases:
- Elderly Patients: Use with caution. Smaller application areas are recommended due to potential for age-related liver, kidney, or heart problems, leading to increased systemic absorption.
- Patients with Renal Impairment: Use with caution. Dose adjustments may be needed depending on the degree of impairment.
- Patients with Hepatic Dysfunction: Use with caution. Reduced hepatic function can impair metabolism, increasing the risk of toxicity. Smaller application areas are recommended.
- Patients with Comorbid Conditions: Consider existing conditions (methemoglobinemia, G6PD deficiency) and concomitant medications that could interact with Lidocaine + Prilocaine.
Clinical Use Cases
Dosing for specific clinical scenarios:
- Intubation: Lidocaine/Prilocaine preparations are not typically indicated for direct use during intubation, though tetracaine spray is sometimes used.
- Surgical Procedures: Dosage depends on the size of the area and the type of procedure, as described above.
- Mechanical Ventilation: Not specifically indicated for use with mechanical ventilation.
- Intensive Care Unit (ICU) Use: Use with caution and close monitoring due to potentially unstable patient conditions.
- Emergency Situations: Not typically used in systemic emergency situations, however local anesthesia can be beneficial for certain procedures.
Dosage Adjustments
Dosage adjustments are necessary for patients with hepatic or renal impairment, the elderly, and those with certain comorbid conditions. Smaller application areas and closer monitoring are advised in these populations.
Side Effects
Common Side Effects:
- Mild burning or stinging at the application site
- Redness or swelling
- Changes in skin color (pallor, erythema)
- Itching
- Altered temperature sensation
Rare but Serious Side Effects:
- Methemoglobinemia (especially with Prilocaine)
- Allergic reactions (hives, difficulty breathing, swelling)
- Seizures
- Cardiac effects (bradycardia, arrhythmia)
Long-Term Effects:
Generally, there are no long-term effects associated with short-term topical use. However, prolonged use or application over large areas could potentially lead to systemic toxicity.
Adverse Drug Reactions (ADR):
- Severe allergic reactions (anaphylaxis)
- Methemoglobinemia
- Cardiac arrhythmias
Contraindications
- Hypersensitivity to amide-type local anesthetics
- Congenital or idiopathic methemoglobinemia
- Preterm infants (<37 weeks gestational age)
- Infants <12 months receiving methemoglobin-inducing agents
Drug Interactions
Lidocaine + Prilocaine can interact with several medications, including:
- Class I antiarrhythmics (additive cardiac effects)
- Methemoglobin-inducing agents (e.g., sulfonamides, nitrates, dapsone)
- Certain medications metabolized by CYP450 enzymes
Pregnancy and Breastfeeding
- Pregnancy: Lidocaine and Prilocaine cross the placenta. Use with caution during pregnancy, especially in the first trimester. Although considered generally safe, weigh potential risks and benefits.
- Breastfeeding: Both drugs are excreted in breast milk, but in small amounts. Caution is advised. Monitor infants for potential side effects.
Drug Profile Summary
- Mechanism of Action: Blocks voltage-gated sodium channels, inhibiting nerve impulse conduction.
- Side Effects: Common: Local skin reactions (burning, redness, swelling). Serious: Methemoglobinemia, allergic reactions.
- Contraindications: Hypersensitivity to amides, methemoglobinemia, preterm infants, infants on methemoglobin-inducing agents.
- Drug Interactions: Class I antiarrhythmics, methemoglobin-inducing agents, drugs metabolized by CYP450 enzymes.
- Pregnancy & Breastfeeding: Use with caution; excreted in breast milk.
- Dosage: Varies based on application area, procedure, and patient age/weight. See detailed guidelines above.
- Monitoring Parameters: Monitor for local skin reactions and signs of methemoglobinemia (cyanosis, shortness of breath). In neonates and infants, monitor methemoglobin levels.
Popular Combinations
Lidocaine + Prilocaine is sometimes used in combination with tetracaine spray for enhanced local anesthetic effect, particularly to prevent cough during extubation.
Precautions
- General Precautions: Screen for allergies, methemoglobinemia, hepatic/renal dysfunction, and concomitant medications.
- Specific Populations: Use with caution in pregnant/breastfeeding women, children, the elderly, and patients with hepatic/renal dysfunction.
- Lifestyle Considerations: Advise patients to avoid touching treated area and to protect it from extreme temperatures until sensation returns.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Lidocaine + Prilocaine?
A: The dosage varies considerably depending on the indication, surface area, and patient population. Refer to the detailed dosage guidelines above for specific recommendations.
Q2: How long does the numbing effect of Lidocaine + Prilocaine last?
A: The numbing effect typically lasts for at least 2 hours after application for 1-2 hours. Duration may be shorter for facial applications or vary based on individual factors.
Q3: Can Lidocaine + Prilocaine be used on broken skin?
A: No, it is generally contraindicated for broken skin, open wounds, or irritated areas unless specifically directed by a physician. Increased absorption through damaged skin raises the risk of systemic toxicity.
Q4: What are the signs of methemoglobinemia?
A: Signs of methemoglobinemia include cyanosis (bluish skin discoloration), shortness of breath, fatigue, confusion, and dizziness. If suspected, monitor methemoglobin levels and administer appropriate treatment.
Q5: Can Lidocaine + Prilocaine be used during pregnancy?
A: It can be used cautiously during pregnancy, but it’s important to weigh potential risks and benefits. Consult with a specialist and minimize the dose and application area whenever possible.
Q6: What should I do if Lidocaine + Prilocaine gets in my eyes?
A: Immediately flush the eyes with copious amounts of water or saline. Protect the eyes until sensation returns and seek medical attention if irritation persists.
Q7: Can Lidocaine + Prilocaine be used for teething pain?
A: No, its use for teething pain is not recommended. It can pose risks to infants due to potential for methemoglobinemia and accidental ingestion. Safer alternatives are available.
Q8: How should Lidocaine + Prilocaine cream be stored?
A: Store at room temperature (15-30°C or 59-86°F) away from moisture, heat, and direct sunlight. Do not freeze. Keep the tube tightly closed when not in use.
Q9: What is the difference between Lidocaine + Prilocaine cream and Fortacin?
A: Fortacin is a metered-dose spray formulation of Lidocaine + Prilocaine specifically designed for the treatment of premature ejaculation. The cream formulation is intended for topical anesthesia for various procedures.
Q10: Can Lidocaine + Prilocaine be used during breastfeeding?
A: Lidocaine and Prilocaine are present in breast milk after topical application, but usually in small amounts. Exercise caution and consider the infant’s age and health status. If used, ensure thorough handwashing and prevent the cream from contacting the nipple area.
