How lidocaine works
Lidocaine is an active ingredient of the Ib antiarrhythmic class, i.e. it suppresses the influx of sodium ions via their channels in the heart. Applied locally, lidocaine also blocks sodium channels and in this way inhibits the sensation and transmission of pain (local anesthetic effect).
Antiarrhythmic effect
In order to trigger a single heartbeat, many individual steps are required in the heart muscles and the associated nerve pathways. Mainly involved in this are so-called sodium channels in the cell membranes, which become permeable to small, charged sodium particles (sodium ions) when excited. In this way, excitation is transmitted along the nerve pathways. At the end of this transmission is the tensing of the heart muscles (contraction).
It may then be necessary to treat the arrhythmias with medication. So-called antiarrhythmic drugs such as lidocaine are used. It blocks the sodium channels, which can normalize the heartbeat.
Local anesthetic effect
Sodium channels are also needed for the transmission of pain. They allow the stimulus to be transmitted along the nerve pathways to the spinal cord and brain so that one can respond to the stimulus (for example, by quickly pulling one’s hand away from a hot stove top).
Targeted blockade of sodium channels by lidocaine, such as in conduction or infiltration anesthesia, inhibits the transmission of painful stimuli – the treated area is anesthetized for a short time.
Absorption, degradation and excretion
When used as an anesthetic, lidocaine is applied externally to the corresponding skin site (e.g., as an ointment) or injected into the vicinity of a supplying nerve. Depending on the chosen administration, the effect occurs after about 20 minutes (ointment) or immediately (injection).
The active substance is broken down in the liver by certain enzymes. The degradation products are excreted by the kidneys.
When is lidocaine used?
The indications for use (indications) of lidocaine include:
- certain forms of cardiac arrhythmia
- Anesthesia of the mucous membrane in cases of pain and mild inflammation (e.g., inflammation of the mouth and throat, hemorrhoids)
- Infiltration, conduction and epidural anesthesia for nerve blockade
- neural therapy (only certain lidocaine preparations are approved for this purpose)
- premature ejaculation (lidocaine ointment or lidocaine spray)
How lidocaine is used
The active ingredient must be applied differently depending on the therapeutic objective.
Lidocaine ointment is used to anesthetize the skin.
Relief from pain in the mucous membranes is achieved with lidocaine gel, lidocaine suppositories or lidocaine spray. The dosage depends on the area to be anesthetized. Children and elderly patients receive a lower dose.
For cardiac arrhythmias, the active substance must be injected directly into the blood in the form of a solution.
For neuropathic pain, a lidocaine patch is applied to the affected area for a maximum of 12 hours.
What are the side effects of lidocaine?
Local application to skin and mucous membranes
Often (that is, one to ten percent of those treated), local application of lidocaine causes side effects such as temporary skin irritation or redness. Rarely (in less than 0.1 percent of those treated), allergic reactions occur.
Intravenous use
What should be considered when using lidocaine?
Contraindications
Medicines containing lidocaine must not be injected in:
- severe cardiac dysfunction (blockade of impulse conduction, weak performance of the heart)
- heart attack in the last three months
- volume deficiency or shock
- severe hypotension (low blood pressure <90/50mmgHg)
- certain neurological diseases (e.g. multiple sclerosis)
Restrictions
Lidocaine should be used with caution in cases of mild cardiac dysfunction, excessively slow heartbeat (bradycardia), hepatic and renal dysfunction, low blood pressure, and low blood salt levels (potassium).
In case of prolonged use of the active substance, blood values must be checked regularly.
Plasters containing the active substance may only be applied to uninjured skin areas without skin irritation.
Drug interactions
Interactions with other drugs occur mainly with intravenous use.
In contrast, the following drugs may potentiate lidocaine effects and side effects:
- cimetidine (used to treat heartburn and stomach ulcers)
- Norepinephrine (for cardiac dysfunction)
Age restriction
Approval is preparation-specific. Generally, lidocaine-containing injectable solutions, gels, ointments, and suppositories are intended for use from the first year of life. Lozenges and sprays containing lidocaine are approved for use from six years of age.
Combination preparations (e.g., suppositories with other active ingredients) and patches containing lidocaine must not be used in children and adolescents under 18 years of age.
Pregnancy and lactation
Medicines containing lidocaine should be used during pregnancy and lactation only if absolutely necessary.
Use as a local anesthetic is possible during pregnancy. As an antiarrhythmic agent, lidocaine is administered to pregnant women only in cases of severe cardiac arrhythmias.
Trafficability and operation of machines
The use of lidocaine may impair the ability to react. The treating physician therefore decides on a case-by-case basis whether a patient may nevertheless actively participate in road traffic or operate heavy machinery.
How to obtain medicines containing lidocaine
Medicines intended for application to the skin and mucous membranes are available over-the-counter in pharmacies in Germany, Austria and Switzerland. Lidocaine solutions for intravenous use are only available from pharmacies with a doctor’s prescription.
How long has lidocaine been known?
The active ingredient has been known for a long time. First, its anesthetic effect was discovered. Shortly thereafter, the antiarrhythmic effect of lidocaine was also discovered.