What are patch tests?Patch tests are used in patients with, to find out whether their skin condition may be caused or aggravated by a. Patch tests are not the same as, which are used to diagnose hay fever allergy (house dust mite, grass pollens and cat dander). Skin prick tests have very limited value for patients with skin rashes.The patch testing described here is as it is undertaken in Hamilton, New Zealand. There may be slight differences in methods used at other centres - if you are having patch tests done, ask your to explain.A range of substances can be used for patch testing. A baseline series such as the European (or similar) is applied to nearly every patient, together with specific tests appropriate to the individual. Each substance (known as an allergen) has been tested to find the best concentration to demonstrate an allergic reaction without causing irritation to those who are not allergic to the material.Sometimes the results can be inconclusive or misleading.
Instead of one or two positive reactions, sometimes nearly all test areas become red and itchy. This is known as ‘angry back’ and is most likely to occur in those with very active dermatitis (false positive result). At other times, there may be little or no apparent reaction to a substance that regularly causes dermatitis in that person (false negative result).Further testing may be necessary. Patch tests do not always explain the cause of a dermatitis. Patch testing.
The appointmentsThe first appointment will take about half an hour. Tiny quantities of 25 to 150 materials in individual square plastic or round aluminium chambers are applied to the upper back. They are kept in place with special hypoallergenic adhesive tape. The patches stay in place undisturbed for 48 hours.At the second appointment, usually two days later, the patches will be removed. Sometimes further patches are applied. The back is marked with an indelible black felt tip pen or other suitable marker to identify the test sites.These marks must still be visible at the third appointment, usually two days later (4 days after application). The back should be checked and if necessary remarked on several occasions between the 2nd and 3rd appointments.
The resultsThe dermatologist will complete a record form at the second and third appointments (usually 48 and 96 hour readings). The result for each test site is recorded. The system we use is as follows:. Negative (-). Irritant reaction (IR).
Equivocal / uncertain (+/-). Weak positive (+). Strong positive. Extreme reaction Irritant reactions include sweat rash, follicular pustules and burn-like reactions. Uncertain reactions refer to a pink area under the test chamber. Weak positives are slightly elevated pink or red plaques. Strong positives are ‘ papulovesicles’ and extreme reactions are blisters or ulcers.
The relevance depends on the site and type of dermatitis and the specific allergen. The interpretation of the results requires considerable experience and training. Essentially negative patch test reactions. Photopatch testsSome patients have photopatch tests because their dermatitis develops on skin exposed to the sun. Two sets of perfumes, antiseptics, plant materials and sunscreens may be applied. After removal, one set is exposed to a small dose of ultraviolet radiation (UVA).
This is not enough to cause a photosensitivity reaction on its own. Adverse reactions to patch testsPositive patch test results are small areas of active eczema / dermatitis.
They will be itchy and may require treatment with. Occasionally patch test reactions persist for several weeks. Patch tests may provoke other areas of dermatitis to recur or to appear for the first time.
Although hypoallergenic tape is used, occasionally people react to all areas in contact with the tape. An 'angry back' reaction may arise, particularly in a patient with active dermatitis at the time of testing, or in someone who has multiple positive reactions. 'Angry back' refers to false positives to many or all of the tested allergens.
Rarely, sensitisation to a new allergen may occur as a result of the test – this is revealed as a reaction occurring around 10 days after the test was applied. Re-testing may be required, sometimes one allergen at a time, to confirm or clarify a reaction.Adverse reactions to patch testing.
DESCRIPTIONLIDODERM (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 × 14 cm.Lidocaine is chemically designated as acetamide, 2-(diethylamino)-N-(2,6-dimethylphenyl), has an octanol: water partition ratio of 43 at pH 7.4, and has the following structure. AbsorptionThe amount of lidocaine systemically absorbed from LIDODERM is directly related to both the duration of application and the surface area over which it is applied. In a pharmacokinetic study, three LIDODERM patches were applied over an area of 420 cm 2 of intact skin on the back of normal volunteers for 12 hours.
Blood samples were withdrawn for determination of lidocaine concentration during the application and for 12 hours after removal of patches. The results are summarized in Table 1. Table 1Absorption of lidocaine from LIDODERMNormal volunteers (n = 15, 12-hour wearing time)LIDODERM PatchApplication SiteArea(cm 2)Dose Absorbed (mg)C maxmcg/mL)T max(hr)3 patches(2100 mg)Back42064 ± 320.13 ± 0.0611 hrWhen LIDODERM is used according to the recommended dosing instructions, only 3 ± 2% of the dose applied is expected to be absorbed.
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At least 95% (665 mg) of lidocaine will remain in a used patch. Mean peak blood concentration of lidocaine is about 0.13 mcg/mL (about 1/10 of the therapeutic concentration required to treat cardiac arrhythmias). Repeated application of three patches simultaneously for 12 hours (recommended maximum daily dose), once per day for three days, indicated that the lidocaine concentration does not increase with daily use. The mean plasma pharmacokinetic profile for the 15 healthy volunteers is shown in Figure 1.Figure 1Mean lidocaine blood concentrations after three consecutive daily applications of three LIDODERM patches simultaneously for 12 hours per day in healthy volunteers (n = 15). DistributionWhen lidocaine is administered intravenously to healthy volunteers, the volume of distribution is 0.7 to 2.7 L/kg (mean 1.5 ± 0.6 SD, n = 15). At concentrations produced by application of LIDODERM, lidocaine is approximately 70% bound to plasma proteins, primarily alpha-1-acid glycoprotein.
At much higher plasma concentrations (1 to 4 mcg/mL of free base), the plasma protein binding of lidocaine is concentration dependent. Lidocaine crosses the placental and blood brain barriers, presumably by passive diffusion. MetabolismIt 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 of which 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 negligible following application of LIDODERM (lidocaine patch 5%).
Following intravenous administration, MEGX and GX concentrations in serum range from 11 to 36% and from 5 to 11% of lidocaine concentrations, respectively. CLINICAL STUDIESSingle-dose treatment with LIDODERM was compared to treatment with vehicle patch (without lidocaine), and to no treatment (observation only) in a double-blind, crossover clinical trial with 35 post-herpetic neuralgia patients. Pain intensity and pain relief scores were evaluated periodically for 12 hours. LIDODERM performed statistically better than vehicle patch in terms of pain intensity from 4 to 12 hours.Multiple-dose, two-week treatment with LIDODERM was compared to vehicle patch (without lidocaine) in a double-blind, crossover clinical trial of withdrawal-type design conducted in 32 patients, who were considered as responders to the open-label use of LIDODERM prior to the study. The constant type of pain was evaluated but not the pain induced by sensory stimuli (dysesthesia).
Statistically significant differences favoring LIDODERM were observed in terms of time to exit from the trial (14 versus 3.8 days at p-value. Risk of MethemoglobinemiaCases of methemoglobinemia have been reported in association with local anesthetic use. Although all patients are at risk for methemoglobinemia, patients with glucose-6-phosphate dehydrogenase deficiency, congenital or idiopathic methemoglobinemia, cardiac or pulmonary compromise, infants under 6 months of age, and concurrent exposure to oxidizing agents or their metabolites are more susceptible to developing clinical manifestations of the condition.
If local anesthetics must be used in these patients, close monitoring for symptoms and signs of methemoglobinemia is recommended.Signs of methemoglobinemia may occur immediately or may be delayed some hours after exposure, and are characterized by a cyanotic skin discoloration and/or abnormal coloration of the blood. Methemoglobin levels may continue to rise; therefore, immediate treatment is required to avert more serious central nervous system and cardiovascular adverse effects, including seizures, coma, arrhythmias, and death. Discontinue LIDODERM and any other oxidizing agents.
Depending on the severity of the signs and symptoms, patients may respond to supportive care, i.e., oxygen therapy, hydration. A more severe clinical presentation may require treatment with methylene blue, exchange transfusion, or hyperbaric oxygen. Excessive DosingExcessive dosing by applying LIDODERM to larger areas or for longer than the recommended wearing time could result in increased absorption of lidocaine and high blood concentrations, leading to serious adverse effects (see ). Lidocaine toxicity could be expected at lidocaine blood concentrations above 5 mcg/mL. The blood concentration of lidocaine is determined by the rate of systemic absorption and elimination. Longer duration of application, application of more than the recommended number of patches, smaller patients, or impaired elimination may all contribute to increasing the blood concentration of lidocaine.
With recommended dosing of LIDODERM, the average peak blood concentration is about 0.13 mcg/mL, but concentrations higher than 0.25 mcg/mL have been observed in some individuals. GeneralHepatic DiseasePatients with severe hepatic disease are at greater risk of developing toxic blood concentrations of lidocaine, because of their inability to metabolize lidocaine normally.Allergic ReactionsPatients allergic to para-aminobenzoic acid derivatives (procaine, tetracaine, benzocaine, etc.) have not shown cross sensitivity to lidocaine.
However, LIDODERM should be used with caution in patients with a history of drug sensitivities, especially if the etiologic agent is uncertain.Non-intact SkinApplication to broken or inflamed skin, although not tested, may result in higher blood concentrations of lidocaine from increased absorption. LIDODERM is only recommended for use on intact skin.External Heat SourcesPlacement of external heat sources, such as heating pads or electric blankets, over LIDODERM patches is not recommended as this has not been evaluated and may increase plasma lidocaine levels.Eye ExposureThe contact of LIDODERM with eyes, although not studied, should be avoided based on the findings of severe eye irritation with the use of similar products in animals. If eye contact occurs, immediately wash out the eye with water or saline and protect the eye until sensation returns. PregnancyTeratogenic EffectsPregnancy Category B.LIDODERM (lidocaine patch 5%) has not been studied in pregnancy. Reproduction studies with lidocaine have been performed in rats at doses up to 30 mg/kg subcutaneously and have revealed no evidence of harm to the fetus due to lidocaine.
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There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, LIDODERM should be used during pregnancy only if clearly needed. Systemic (Dose-Related) ReactionsSystemic adverse reactions following appropriate use of LIDODERM are unlikely, due to the small dose absorbed (see ). Systemic adverse effects of lidocaine are similar in nature to those observed with other amide local anesthetic agents, including CNS excitation and/or depression (light headedness, nervousness, apprehension, euphoria, confusion, dizziness, drowsiness, tinnitus, blurred or double vision, vomiting, sensations of heat, cold or numbness, twitching, tremors, convulsions, unconsciousness, respiratory depression and arrest). Excitatory CNS reactions may be brief or not occur at all, in which case the first manifestation may be drowsiness merging into unconsciousness. Cardiovascular manifestations may include bradycardia, hypotension and cardiovascular collapse leading to arrest. OVERDOSAGELidocaine overdose from cutaneous absorption is rare, but could occur.
If there is any suspicion of lidocaine overdose (see ), drug blood concentration should be checked. The management of overdose includes close monitoring, supportive care, and symptomatic treatment. DOSAGE AND ADMINISTRATIONApply LIDODERM to intact skin to cover the most painful area. Apply the prescribed number of patches (maximum of 3), only once for up to 12 hours within a 24 hour period.
Patches may be cut into smaller sizes with scissors prior to removal of the release liner. (See ) Clothing may be worn over the area of application. Smaller areas of treatment are recommended in a debilitated patient, or a patient with impaired elimination.If irritation or a burning sensation occurs during application, remove the patch(es) and do not reapply until the irritation subsides.When LIDODERM is used concomitantly with other products containing local anesthetic agents, the amount absorbed from all formulations must be considered.LIDODERM may not stick if it gets wet.
Avoid contact with water, such as bathing, swimming or showering. HOW SUPPLIEDLIDODERM (lidocaine patch 5%) is available as the following:Carton of 30 patches, packaged into individual child-resistant envelopesNDC 63481-687-06Store at 25°C (77°F); excursions permitted to 15°-30°C (59°-86°F). See USP Controlled Room Temperature.For more information, call Endo Pharmaceuticals at 1-800-462-3636.Manufactured for:Endo Pharmaceuticals Inc.Malvern, PA 19355LIDODERM ® is a registered trademark of Hind Health Care, Inc.© 2018 Endo Pharmaceuticals Inc. All rights reserved.Printed in the U.S.A.Revised: November 2018.