Results: The focus of this case report are the interesting neuro-otologic signs of central lidocaine toxicity that occurred after a patient fell asleep on a heating pad with his Lidoderm patches in place. Hearing improvement, tinnitus reduction, and severe dizziness and ataxia were present for approximately 48 hours before spontaneous resolution. Based upon his symptoms we estimate an 11-fold increase in plasma concentrations of lidocaine.
Heating Pad Lidoderm Patch
Discussion: Transdermal delivery of medication affords ease of application, ability to provide continuous pharmacological therapy, and ability to supply medication to the affected site. Due to the superficial application of these medications, external environmental factors may influence the pharmacokinetics of drug delivery. This case highlights the complications that can arise from the combination of heating pads and transdermal pain therapies.
Heat can cause the lidocaine in the patch to be absorbed into your body faster. This may increase the chance of serious side effects or an overdose. While you are using this medicine, do not use a heating pad, electric blanket, heat or tanning lamps, sauna, a sunlamp, or a heated water bed. Do not sunbathe. However, you may apply Ztlido patch on the skin after exposure to moderate heat (eg, after 15 minutes of heating pad use on a medium setting).
Prescription lidocaine transdermal comes as a 5% patch (Dermalid, Lidoderm) and as a 1.8% topical system (Ztlido) to apply to the skin. Prescription lidocaine transdermal is applied only once a day as needed for pain. Never apply more than 3 of the lidocaine 5% patch or lidocaine 1.8% topical systems at one time, and never wear them for more than 12 hours per day (12 hours on and 12 hours off). Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Use lidocaine transdermal exactly as directed. Do not apply it more or less often than prescribed by your doctor.
Nonprescription lidocaine transdermal comes as a 4% patch (Absorbine Jr, Aspercreme, Lidocare, Salonpas, others) to apply to the skin. It is applied up to 3 times daily and for no more than 8 hours per application. Use nonprescription lidocaine patches exactly as directed. Do not use more or less of it or use it more often or for a longer period of time than directed by the package instructions.
Your doctor will tell you how many lidocaine patches or topical systems you may use at one time and the length of time you may wear the patches. Applying too many patches or topical systems or leaving them on for too long may cause serious side effects.
Apply the lidocaine patch or topical system to clean, dry, intact skin as directed. Choose an area where the patch will not be rubbed by tight clothing. Do not apply the patch or topical system to an open wound or cut, to skin that is irritated or red, or to skin that is affected by a rash, burn, or other skin problem. If irritation or a burning sensation occurs during lidocaine application, remove the lidocaine patch or system and do not reapply it until the irritation is gone. Prescription patches and topical systems may be cut into smaller sizes with scissors prior to removal of the release liner. Be sure to remove the current patch before you apply a new one.
While you are wearing a lidocaine transdermal patch or system, protect the treated area from direct heat such as heating pads or electric blankets. You can apply the lidocaine 1.8% topical system after moderate heat exposure, such as 15 minutes of heating pad exposure on a medium setting. Do not bandage the affected area tightly.
Do not shower, bathe, or go swimming while you are wearing the prescription lidocaine 5% transdermal patch. If you are using the prescription lidocaine 1.8% topical system, you may shower for up to 10 minutes or wear it while immersed in water for up to 15 minutes. If the lidocaine 1.8% topical system becomes wet, gently pat the skin, but do not rub the skin or lidocaine 1.8% topical system.
This medication is usually used as needed. If your doctor has told you to use lidocaine patches or topical systems regularly, apply the missed patch or topical system as soon as you remember it. However, if it is almost time for the next dose, skip the missed patch and continue your regular dosing schedule. Do not apply a double dose to make up for a missed one.
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Do not store patches and topical systems outside the sealed envelope. Fold used patches or topical systems so that the adhesive side sticks to itself and then safely discard into trash and where children and pets cannot get to them.
If you wear too many lidocaine transdermal patches or topical systems or wear them for too long, too much lidocaine may be absorbed into your blood. In that case, you may experience symptoms of an overdose.
LIDODERM (lidocaine patch 5%) is comprised of an adhesive material containing 5% lidocaine, which is applied to a non-woven polyester felt backing and covered with a polyethylene terephthalate (PET) film release liner. The release liner is removed prior to application to the skin. The size of the patch is 10 cm x 14 cm.
Each adhesive patch contains 700 mg of lidocaine (50 mg per gram adhesive) in an aqueous base. It also contains the following inactive ingredients: dihydroxyaluminum aminoacetate, disodium edetate, gelatin, glycerin, kaolin, methylparaben, polyacrylic acid, polyvinyl alcohol, propylene glycol, propylparaben, sodium carboxymethylcellulose, sodium polyacrylate, Dsorbitol, tartaric acid, and urea.
Apply LIDODERM to intact skin to cover the most painfularea. Apply the prescribed number of patches (maximum of 3), only once for upto 12 hours within a 24 hour period. Patches may be cut into smaller sizes withscissors prior to removal of the release liner. (See Handling And Disposal)Clothing may be worn over the area of application. Smaller areas of treatmentare recommended in a debilitated patient, or a patient with impairedelimination.
Hands should be washed after the handling of LIDODERM,and eye contact with LIDODERM should be avoided. Do not store patch outside thesealed envelope. Apply immediately after removal from the protective envelope.Fold used patches so that the adhesive side sticks to itself and safely discardused patches or pieces of cut patches where children and pets cannot get tothem. LIDODERM should be kept out of the reach of children.
During or immediately after treatment with LIDODERM(lidocaine patch 5%), the skin at the site of application may develop blisters,bruising, burning sensation, depigmentation, dermatitis, discoloration, edema, erythema, exfoliation, irritation, papules, petechia, pruritus, vesicles, ormay be the locus of abnormal sensation. These reactions are generally mild andtransient, resolving spontaneously within a few minutes to hours.
Even a used LIDODERM patch contains a large amountof lidocaine (at least 665 mg). The potential exists for a small child or a petto suffer serious adverse effects from chewing or ingesting a new or usedLIDODERM patch, although the risk with this formulation has not been evaluated.It is important for patients to store and dispose of LIDODERM out of thereach of children, pets and others. (See Handling And Disposal)
Excessive dosing by applying LIDODERM to larger areas orfor longer than the recommended wearing time could result in increasedabsorption of lidocaine and high blood concentrations, leading to seriousadverse effects (see ADVERSE REACTIONS, Systemic Reactions).Lidocaine toxicity could be expected at lidocaine blood concentrations above 5Îg/mL. The blood concentration of lidocaine is determined by the rate ofsystemic absorption and elimination. Longer duration of application, applicationof more than the recommended number of patches, smaller patients, or impairedelimination may all contribute to increasing the blood concentration oflidocaine. With recommended dosing of LIDODERM, the average peak blood concentrationis about 0.13 Îg/mL, but concentrations higher than 0.25 Îg/mL havebeen observed in some individuals.
LIDODERM (lidocaine patch 5%) has not been studied inpregnancy. Reproduction studies with lidocaine have been performed in rats atdoses up to 30 mg/kg subcutaneously and have revealed no evidence of harm tothe fetus due to lidocaine. There are, however, no adequate and well-controlledstudies in pregnant women. Because animal reproduction studies are not alwayspredictive of human response, LIDODERM should be used during pregnancy only ifclearly needed.
The amount of lidocaine systemically absorbed from LIDODERMis directly related to both the duration of application and the surface areaover which it is applied. In a pharmacokinetic study, three LIDODERM patcheswere applied over an area of 420 cm of intact skin on the back ofnormal volunteers for 12 hours. Blood samples were withdrawn for determinationof lidocaine concentration during the application and for 12 hours afterremoval of patches. The results are summarized in Table 1.
When LIDODERM is used according to the recommended dosinginstructions, only 3 Â 2% of the dose applied is expected to be absorbed. Atleast 95% (665 mg) of lidocaine will remain in a used patch. Mean peak bloodconcentration of lidocaine is about 0.13 Îg/mL (about 1/10 of the therapeuticconcentration required to treat cardiac arrhythmias). Repeated application ofthree patches simultaneously for 12 hours (recommended maximum daily dose),once per day for three days, indicated that the lidocaine concentration doesnot increase with daily use. The mean plasma pharmacokinetic profile for the 15healthy volunteers is shown in Figure 1.
It is not known if lidocaine is metabolized in the skin.Lidocaine is metabolized rapidly by the liver to a number of metabolites,including monoethylglycinexylidide (MEGX) and glycinexylidide (GX), both ofwhich have pharmacologic activity similar to, but less potent than that of lidocaine.A minor metabolite, 2, 6-xylidine, has unknown pharmacologic activity but is carcinogenic in rats. The blood concentration of this metabolite is negligiblefollowing application of LIDODERM (lidocaine patch 5%). Following intravenousadministration, MEGX and GX concentrations in serum range from 11 to 36% andfrom 5 to 11% of lidocaine concentrations, respectively.
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