Topical application of medication provides beneficial relief of pain via dermal application and local absorption with minimal systemic effects. By inhibiting the ionic fluxes (charged sodium and potassium) lidocaine prohibits the initiation and transmission of pain impulses and stabilizes the nerve membranes. Topically, lidocaine, an amide anesthetic, produces a local analgesic effect without complete sensory block. Since only 1-3% of the applied dose is absorbed there are essentially no significant side effects on the cardiovascular system as this is approximately less than 1/10 of the dosage for cardiac arrhythmias.

The recommended daily dose of the 5% lidocaine path (LIDODERM PATH) is up to 3 patches for 12 hours daily for 3 days. Lidocaine is metabolized (broken down) by the liver to active metabolites (chemical byproducts which also produce a pharmacologic effect) and is excreted by the kidneys, approximately 90% is changed to its metabolites. The patch should only be applied to INTACT skin, not to any cuts, scrapes, or ulcerations.

Lidocaine topical patch is approved for the treatment of post herpetic neuralgia(the lingering pain of herpes (shingles), but is often also used for topical relief of local pain to the skin or skin structures, joint pain, pain of neuropathy due to diabetes, alcoholism, vitamin malabsorption syndromes, trauma, for superficial relief . Patients with allergies to lidocaine or various anesthetics or the components of the patch itself (polyethylene, glycerin, kaolin, propylene glycol, and various preservative agents -components of the patch) should avoid use of the product. It is important to note that even a used patch, after 12 hour application, still contains a large mount (AT LEAST 665mg) of lidocaine and should be disposed of properly , as a small child or pet may suffer serious effects. As with all medication, whether topical, rectal, buccal (in the cheek), sublingual (under the tongue) or oral, the recommendation dosage should not be exceeded. The excessive application of the lidocaine patch could cause toxicity(serious even, life threatening events) depending on the size of the application, longer than 12 hour application, smaller surface area of patients(very small stature patients), and usually seen at blood levels greater than 5mcg/cc blood.

Since lidocaine is metabolized in the liver, patient with liver disease should be carefully monitored by blood tests while using this medication. Patient who have demonstrated sensitivities to procaine, tetracaine, benzocaine(a common medication found in sore throat sprays, lozenges, cold sore preparations) can use lidocaine since cross sensitivity has not been noted, but still prescribed with caution. Upon using the patch, the patient should wash hands and avoid any eye contact of the medication, as severe eye irritation may occur and should be constantly flushed with saline or water till normal eye sensation returns.

Drug interactions may also occur with topical lidocaine. Antiarrhythmic heart medication such as tocainide and mexiletine and lidocaine are additive (synergistic) and will induce toxic levels for the patient. Other topical anesthetics (i.e. benzocaine, etc) and lidocaine will be cumulative in effect and also elevate blood levels to possibly toxic. Studies to date reveal no contraindications to pregnant women, however it should be used cautiously, and only when the benefits outweigh possible risks to the fetus. Lidocaine is excreted in human milk.

Adverse reactions include possible localized reactions such as erythematous hives and rash which are generally mild, transient, and are spontaneously self resolving. Rare systemic reactions can occur and are characterized by urticaria (well defined band of raised rash lesions about the body midline) angioedema (facial vascular swelling), bronchospasm, and shock. Dose related reactions include CNS stimulation and/or depression manifest as confusion, light-headedness, nervousness, apprehension, drowsiness, tinnitus (ringing in the ears), blurred or double vision, nausea, vomiting, feelings of hot, cold, numbness, or twitching. These CNS symptoms maybe brief or not occur with the first manifestation being unconsciousness with cardiovascular responses of bradycardia (abnormal slow heart beat) hypotension leading to cardiac arrest.

Cutaneous (topical) Lidocaine overdose is rare and when suspect blood levels should be evaluated with treatment of supportive care, symptomatic treatment.

AKTEN

- a local anesthetic consisting of Lidocaine 3.5% an ophthalmic gel used as a surface anesthetic for eye surgical procedures.

ANESTAFOAM and LMX 4%

- are two topical anesthetic products consisting of 4% Lidocaine in foam spray used for burns, cuts, sunburns, abrasions, and insect bites.

EMILA

- is a topical product consisting of 2.5% Lidocaine and 2.5% prilocaine used on the skin prior to injections or superficial minor surgery? (For example warts, skin tag removal).

SYNERA

- a topical anesthetic consisting of 70mg Lidocaine and 70mg of tetracaine also for topical skin analgesic for superficial procedure such as shave biopsies of skin lesion, excisions or electrodessications –warts etc.

XYLOCAINE JELLY or OINTMENT

- a 2% aqueous product of endotracheal lubrication prior to intubation for surgical general anesthesia,

XYLOCAINE VISCOUS

- a 2% viscous product of Lidocaine for anesthesia of the oral mucosa for the treatment of severe sore throats

References

PDR, Physician’s Desk Reference, 64th edition, 2010.

MPR, Monthly Prescribing Reference, Pain Management Pocket Reference, 2011 edition.

My personal experience for pain relief has been very favorable. Local pain relief for lower extremity soft tissue injury responds favorably, applied in small cut patches or with the viscous gel applied to non-stick pads and applied to the skin of diabetics during hours of sleep under the occlusion of socks, provides improved sleep with reduced neuropathy wakening pain.

ADDITIONAL REFERENCES

Drugs.com

National Institutes of Health

MedlinePlus

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