What is Lidocaine?
Lidocaine falls under the category of medium-acting local anesthetics. Chemically it is an amide. We have a sense of feeling when we touch something. When a local anesthetic is applied on an area of the body for example on your fingertip, you will no more be able to sense the feeling of touch. This happens because, a local anesthetic such as lidocaine, blocks the sensory transmission from the area where it is applied to the central nervous system.
Commercial Synthesis of the drug Lidocaine dates back to the 1940s under the commercial name Xylocaine. Soon after its commercial preparation, the drug was reported to show analgesic as well as anti-arrhythmic properties.
Mechanism of Action
Lidocaine reversibly blocks voltage-gated sodium channels thus blocking the transmission of the action potential. When the drug binds to the active site, it hinders the influx of sodium ions which inhibits the generation and transmission of the action potential. As the drug binds preferably with inactivated, open Na+ channels, so the onset of action is quicker in rapidly firing neuron cells.
Pharmacokinetics of Lidocaine
1. Routes of administration
Lidocaine is administered by intravenous injection or given topically.
2. How long does it last?
The onset of action of Lidocaine is 1-3 minutes, and its duration of action remains 30-120 minutes.
3. Distribution in body tissues
Upon intravenous administration, 60-80% of it remains bound to plasma proteins. The drug also crosses the blood-brain barrier following passive diffusion.
4. Metabolism
Approximately 95% of Lidocaine is metabolized in the liver via N-dealkylation, forming active metabolites.
5. How does Lidocaine eliminate from the body?
Lidocaine excerets out of the body in urine, mostly in the form of metabolites and partly in the form of unchanged drugs. Elimination half-life varies in patients. In normal patients, it ranges from 90 minutes to 120 minutes while in patients with hepatic insufficiency or liver diseases, and patients with cardiovascular failure half-life may increases.
Lidocaine Dosage
For Intravenous administration
Dosage for adults
In adults with an average body weight of 70kg, the required dose of Lidocaine for IV administration loading dose is 1mg to 1.5mg per kg, and maintenance dose is 1mg to 4mg per minute. It should be administered with continuous ECG monitoring.
Dosage for infants and children
Loading dose: 1mg per kg of the body weight and maximum 100mg Intravenous infusion
Maintenance dose: 20 micrograms to 50 micrograms per kg per minute intravenous
Dosage for neonates
Loading dose: 1mg per kg intravenous 1 mg/kg IV load then 20 to 50 mcg/kg/minute IV.
Maintenance dose: 20 micrograms to 50 micrograms per kg per minute intravenous
For Topical Application Cream, Spray, Gel, Solution (OTC)
Dosage for adults
Apply 3 to 4 times per day to the affected area of the skin. Avoid using heavy amounts, particularly over the areas that are exposed or blistered.
Dosage for adolescents and children (2 years to 7 years)
Directions for application are the same as that of adults.
Side Effects
Common side effects associated with Lidocaine include a decrease in blood pressure, skin irritation, redness and itching at the site of injection, nausea, vomiting, dizziness, numbness, swelling, and constipation. Among serious side effects, cardiac arrest, seizures, severe allergic reactions, methemoglobinemia, and irregularities in heart rate have been observed.
What is Lidocaine Used for?
Topical lidocaine is used to treat or reduce pain or itching, certain skin conditions such as burns and minor scrapes, insect bites, mouth sores, and discomfort caused by hemorrhoids. Topical medications are also used to treat anal fissures, itching around the rectum or vagina. Other forms are used to reduce pain during surgical procedures and procedures involving pain such as sigmoidoscopy examination.
Intravenous Lidocaine is commonly used to reduce post-operative pain. Some studies also suggest the perioperative effectiveness of it in reducing post-operative pain management.
Interactions
It may show drug interactions with the following drugs:
Bupivacaine (liposomal), fluvoxamine. B-blockers, cimetidine, saquinavir, succinylcholine, disopyramide, arbutamine, halofantrine and procaine.
Broadly speaking, it interacts moderately with about 62 drugs and shows mild interactions with some 28 drugs.
Lidocaine Contraindications
It is contraindicated when someone is hypersensitive to the drug. Lidocaine IV (Lidocaine HCL) is contraindicated in
- Adam’s stroke syndrome
- Congestive heart failure
- Second and thirs degree heart block (without pacemaker)
- Sinoatrial or atrioventricular heart block (without pacemaker)
- Wolff Parkinson White syndrome
- Atrial fibrillation
- Myasthenia gravis
- Sinus bradycardia
- Decrease in blood volume
- Decrease in blood oxygen levels
- Lidocaine toxicity
- Decreased blood potassium levels
- Deficiency of G6PD
- Partial blockade of heart
- Severe blockage of heart
- Kidney disease (chronic)
Use of Lidocaine in pregnancy and lactating mothers
Lidocaine lies in pregnancy category B drugs which means at doses required for dermatological procedures, it is comparatively safe to use during pregnancy. It appears in breast milk, so it should be used with caution during the lactation period.
Precautions and Warning
Talk to your pharmacist or doctor before using it if you have epilepsy, open sores, heart problems, and low blood pressure.