Locain (Lidocaine): Uses, Side Effects, Dosage & More

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March 12, 2026

On March 12, 2026

Lidocaine (Lignocaine) Drug Class: Amide-type Local Anesthetic | Class Ib Antiarrhythmic Available Forms: Injection, Gel, Spray, Medicated Patch/Plaster, Eye Drops, Viscous Solution, Ointment

What Is Locain?

Locain is a brand-name medication containing Lidocaine (Lignocaine) as its active ingredient. It is one of the most widely used local anesthetics in the world, approved for both anesthetic and cardiac antiarrhythmic purposes. The FDA first approved lidocaine in November 1948, and it remains a cornerstone drug in medicine, dentistry, and emergency care.

Unlike general anesthetics, Locain does not cause unconsciousness. It simply prevents pain signals from reaching the brain in a specific, localized region of the body.

How Does Locain Work?

Locain belongs to the amide-type local anesthetic family. It works by blocking sodium (Na⁺) channels in nerve cell membranes, which stops pain signals from being generated and conducted to the brain.

In the heart, it reduces ventricular depolarization and decreases automaticity in the His-Purkinje system — making it effective against dangerous heart rhythm problems. As a Class Ib antiarrhythmic agent, it also acts as an NMDA antagonist, which is why it can help with difficult-to-treat neuropathic pain.

Note: Locain’s effectiveness is reduced at inflammation sites due to local acidosis and increased blood flow, which interfere with sodium channel activity.

Uses & Indications

Locain is prescribed across a wide range of medical settings. Here is a breakdown by category:

Local & Surgical Anesthesia

Numbing skin or tissue before surgical or medical procedures
Infiltration anesthesia, nerve blocks, and IV regional anesthesia
Dental procedures one of the most common uses worldwide
Endotracheal intubation as an anesthetic lubricant

Topical Uses

Skin ulcers, minor burns, insect bites, and haemorrhoids
Sore mouth or throat and reducing gagging during dental X-rays
Nasal and throat passages before endoscopic procedures

Urological Procedures

Pain relief during urinary catheterization
Treatment of painful urethritis
Urethral dilation and cystoscopy

Neuropathic Pain (PHN)

The Locain 700 mg medicated plaster is specifically approved for post-herpetic neuralgia (PHN) — the nerve pain that persists after a shingles infection.

Cardiac Uses (Injection Only)

Acute ventricular tachyarrhythmias
Ventricular dysrhythmias following cardiac surgery
Emergency management of ventricular tachycardia and fibrillation

Other Uses

Adjuvant analgesic for acute and chronic pain
Reducing hypertensive response during tracheal intubation
Studies show lidocaine 5% spray may significantly improve premature ejaculation when applied 10–20 minutes before intercourse

Available Dosage Forms

Locain comes in several forms depending on the medical need:

Form	Common Use
Injection (0.5%–2%)	Nerve blocks, regional anesthesia, cardiac arrhythmias
Gel	Burns, haemorrhoids, urethral procedures
Medicated Plaster (700 mg)	Post-herpetic neuralgia
Spray	Mucosal anesthesia (throat, nose)
Viscous Solution	Mouth/throat soreness, dental impressions
Ointment	Topical skin anesthesia
Eye Drops	Short ophthalmic procedures

Dosage Guidelines

Always follow your doctor’s prescribed dosage. The information below is for general reference only.

Topical Gel (Adults)

Apply to the affected area 3–4 times daily
Typical dose: 15 ml every 3 hours
Maximum: 8 doses in any 24-hour period

Injection (Adults)

Without epinephrine: up to 4.5 mg/kg, not exceeding 300 mg
With epinephrine: up to 7 mg/kg, not exceeding 500 mg
Always use the lowest concentration that produces the required effect

Medicated Plaster

Apply once daily for up to 12 hours per 24-hour period
Up to 3 plasters may be used simultaneously if needed
Plasters can be cut to size before removing the release liner

Children

Dosage must always be determined by a doctor based on body weight
Use with extreme caution in children under 3 years of age
Never use lidocaine viscous solution for infant teething pain

Missed Dose

Apply as soon as you remember
If it is nearly time for the next dose, skip the missed one
Never apply double doses at the same time

Side Effects

Most people tolerate Locain well at recommended doses. However, side effects can occur, especially if too much is absorbed into the bloodstream.

Common / Mild Side Effects

Dizziness or light-headedness
Drowsiness or sedation
Numbness or tingling around the lips and tongue
Tinnitus (ringing in the ears)
Headache and restlessness
Metallic taste in the mouth
Redness, burning, or swelling at the application site

Serious Side Effects Seek Emergency Help Immediately

Seizures or convulsions
Severe confusion or incoherent speech
Rapid or irregular heartbeat
Dangerously low blood pressure
Difficulty breathing or respiratory depression
Cardiovascular collapse or cardiac arrest
Anaphylactic reaction (hives, swelling of face/lips/throat)

Signs of Overdose / Toxicity

Toxicity progresses in stages CNS effects appear before cardiovascular effects:

Drowsiness, inebriation-like behavior, restlessness
Twitching, tremors, seizures
Circulatory depression, cardiovascular collapse

Emergency: If overdose is suspected, call emergency services immediately. Prioritize maintaining the airway and breathing.

Warnings & Precautions

Locain is a powerful medication. Certain conditions require extra caution or make it unsafe to use.

Allergy: Do not use if you are allergic to lidocaine or any amide-type local anesthetic.
Heart conditions: Contraindicated in complete heart block, Stokes-Adams syndrome, Wolff-Parkinson-White Syndrome, and cardiogenic shock.
Liver disease: Locain is processed by the liver. Patients with moderate to severe hepatic impairment need reduced doses and closer monitoring.
Broken skin: Never apply gel or plasters to cut, infected, or inflamed skin.
Long-term use: A lidocaine metabolite called 2,6-xylidine has shown genotoxic effects in animal studies. Long-term treatment is only justified when there is a clear therapeutic benefit.
MAOIs & antidepressants: When lidocaine is combined with epinephrine, using it alongside MAOIs or tricyclic antidepressants can cause severe, prolonged high blood pressure.
Post-procedure awareness: After dental treatment, you may accidentally bite the inside of your mouth or have trouble swallowing while still numb. Avoid solid food until sensation fully returns.

Drug Interactions

Locain has moderate interactions with at least 62 drugs and mild interactions with at least 28 more. Always inform your doctor of everything you are taking.

Drug / Drug Class	Effect
Beta-blockers	Increased risk of bradycardia and low blood pressure
MAOIs / Tricyclic Antidepressants	Severe hypertension when combined with epinephrine
Cimetidine, Fluvoxamine, Nefazodone	May affect lidocaine metabolism
Norepinephrine	Reduces clearance, increasing toxicity risk
Other lidocaine-containing products	Combined dose must not exceed safe limits
Sedatives / Opioids / Tranquilizers	Additive CNS depression
St. John’s Wort	May interfere with lidocaine metabolism

Use in Special Populations

Pregnancy

Locain is Category B. Animal studies show no fetal risk, but no adequate human studies exist. In obstetrical procedures, unintended fetal injection has caused neonatal seizures within 6 hours. Use only when clearly necessary and after discussing risks with your doctor.

Breastfeeding

Lidocaine passes into breast milk in low amounts with poor absorption in infants. Apply topical forms to the smallest area for the shortest time possible. Consult your doctor before use.

Elderly Patients

Older adults are more likely to have liver, kidney, or heart problems that slow Locain’s processing. Dose adjustments and careful monitoring are usually required.

Children

Children absorb more lidocaine through the skin relative to their body weight, raising the risk of toxicity. Use is not recommended for children under 3 years unless other options have been exhausted.

Contraindications

Do not use Locain if you have any of the following:

Allergy to lidocaine or any amide-type local anesthetic
Complete heart block (without a pacemaker present)
Stokes-Adams syndrome or Wolff-Parkinson-White Syndrome
Cardiogenic shock or severe hypovolemia (low blood volume)
History of porphyria (a blood/liver disorder)
Infected, cut, or inflamed skin at the intended application site

Drug Onset, Duration & Key Pharmacokinetics

Understanding how fast Locain works and how long it lasts helps patients and caregivers use it safely and effectively.

Onset of Action

IV injection: within 90 seconds
Topical gel or ointment: 3–5 minutes
Medicated plaster: gradual onset over several minutes to hours

Duration of Action

Standard injection: 30 minutes to 3 hours depending on site and dose
With epinephrine: significantly longer due to reduced local blood flow
Topical forms: typically 30–60 minutes

How the Body Processes It

Metabolized primarily by the liver (CYP3A4 pathway)
Excreted through the kidneys
Half-life: approximately 1.5–2 hours in healthy adults; prolonged in liver disease or heart failure
Plaster absorption: only about 3% of the total dose enters the bloodstream when used correctly making it very safe for long-term topical pain management

Safe Use Tips & Patient Guidance

This practical guidance helps patients use Locain safely, whether at home or after a procedure.

Before Using Locain

Disclose your full medical history especially liver disease, heart conditions, epilepsy, and drug allergies
Tell your doctor about all medications, supplements, and herbal products you take
If you have ever had a reaction to any local anesthetic, do not use Locain without direct medical supervision

During Use

Never apply more plasters than prescribed or leave them on longer than 12 hours
Do not apply gel or plasters to broken, burned, or inflamed skin
Avoid eye contact with the plaster; rinse immediately with water if contact occurs
Do not drive or operate heavy machinery until the numbing effects have completely worn off

After a Dental or Oral Procedure

Avoid solid foods until sensation fully returns
Be careful not to bite your cheek or tongue while still numb
Difficulty swallowing may occur temporarily wait until numbness resolves

Warning Signs Contact Your Doctor Immediately If You Notice:

Unusual drowsiness or confusion after applying Locain
Skin rash, hives, or facial swelling (signs of allergic reaction)
Irregular heartbeat or chest tightness
Seizure or muscle twitching
Persistent redness or rash at the patch site beyond 24 hours

Storage

Store below 25°C (77°F)
Protect injectable solutions from light and heat
Keep all forms out of reach of children

Medical Disclaimer: This article is for informational purposes only and does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting, stopping, or changing any medication.