LIDOCAINE-PRILOCAINE
  • LIDOCAINE-PRILOCAINE

  • (Generic for LIVIXIL PAK)
  • QTY 1 • 2.5 %-2.5% • KIT • Near 77381

LIDOCAINE; PRILOCAINE (LYE doe kane; PRIL oh kane) is a topical anesthetic that causes loss of feeling in the skin and surrounding tissues. It is used to numb the skin before procedures or injections.

LIDOCAINE-PRILOCAINE Pediatric Monographs
  • General Administration Information
    For storage information, see the specific product information within the How Supplied section.

    Route-Specific Administration

    Topical Administration
    -Lidocaine; prilocaine cream is for use on normal, intact skin or genital mucous membranes only.
    -Avoid contact with eyes or open wounds.
    -Strict adherence to the maximum dose, maximum application area, and maximum application time based on the pediatric patient's age and weight is needed to minimize the likelihood of systemic adverse reactions.
    Cream/Ointment/Lotion Formulations
    -Determine the amount to be applied and the application area based on the pediatric patient's age and weight; if a patient greater than 3 months old does not meet the minimum weight requirement, restrict the maximum total dose of the cream to that which corresponds to the patient's weight. To measure 1 g, gently squeeze the cream out of the tube as a narrow strip that is 1.5 inches long and 0.2 inches wide. Use the number of strips that equals your dose. For example, use 2 strips for a 2 g dose. Cover with an occlusive dressing.
    -A secondary protective covering of the cream is not necessary for absorption but may be helpful to keep the cream in place. If a dressing is used, smooth down the dressing edges carefully to ensure it is secure and to avoid leakage. Watch the pediatric patient to make sure that neither the cream nor occlusive dressing is eaten or put into the eyes.
    -Apply the cream to normal, intact skin at least 1 hour before the start of a routine procedure and for 2 hours before the start of a painful procedure (Max application time is 1 hour for pediatric patients < 3 months old OR < 5 kg). Application for 15 minutes to adolescent male genital skin and for 5-10 minutes to adolescent female genital mucous membranes is advised. Prior to the procedure, remove any protective covering, wipe off the cream, and clean the entire area with an antiseptic solution.

    Mild edema of the distal foreskin was a typical reaction after application of 1 gram of lidocaine; prilocaine cream to the penis covered with an occlusive dressing for 2 hours before neonatal circumcision. However, marked edema may occur. Among more than 450 procedures, 2 were associated with loss of anatomical landmarks for circumcision due to marked edema after cream application. Approximately 2 hours after cream application, the foreskin was markedly edematous and no corona was discernable. The cream was removed, and the neonates were not circumcised. No other local or systemic signs of reaction to lidocaine; prilocaine cream were noted in either neonate. Normal uncircumcised external male genitalia were noted on follow-up 24 hours later in 1 baby and 96 hours in the other. Skin irritation and blistering of the foreskin in 2 male neonates who received 1 gram of the cream has been reported. During or immediately after treatment with lidocaine; prilocaine cream on intact skin, local reactions such as erythema (30%), edema (6%), blanching of skin (37%), alteration in temperature sensation (7%), pruritus (2%), and rash (less than 1%) developed. The reactions were generally mild and transient and resolved spontaneously within 1 to 2 hours. Rare cases of discrete purpuric or petechial reactions at the application site and of skin hyperpigmentation have been reported. Purpura that developed within 2 hours after lidocaine; prilocaine cream application and resolved spontaneously within 2 weeks occurred in 2 children. The etiology of purpura related to lidocaine; prilocaine cream exposure is unknown. Toxicity may be due to the direct effect of the cream components on blood vessels, but other factors such as atopic dermatitis, prematurity, subjective predisposition to purpura, trauma, and thrombocytopenia may contribute.

    Case reports of allergic contact dermatitis after topical application of lidocaine; prilocaine cream exist in both pediatric patients and adults. In addition to allergic contact dermatitis, a toxic irritant contact dermatitis may occur. A striking vesico-bullous eruption restricted to the site of cream application was noted 1 hour after the cream was applied under an occlusive dressing for 1 hour to a 9-month old girl with eczema. The diagnosis was toxic irritant contact dermatitis, as the appearance of a vesico-bullous rash within an hour of lidocaine; prilocaine cream application and negative patch test results with lidocaine and prilocaine favor a direct toxic reaction rather than an immune hypersensitivity reaction. To avoid diagnostic confusion, relay that lidocaine; prilocaine cream is used before a skin biopsy.

    Systemic adverse reactions after appropriate use of lidocaine; prilocaine cream are unlikely due to the small dose absorbed. Systemic toxicity (tremors, bradycardia, and hypotension) and an elevated methemoglobin (Met-Hg) concentration developed in a healthy 3 year-old child with eczema who received an appropriate dose (5 grams) applied to 1,140 cm2 of skin (maximum recommended is 100 cm2) under occlusion for 1 hour. The effects of lidocaine; prilocaine are similar to those observed with other amide local anesthetics including CNS excitation and/or depression; excitatory CNS reactions may be brief or nonexistent, and the first manifestation may be drowsiness merging into unconsciousness. Of note, some systemic adverse reactions like dizziness, anxiety, confusion, and seizures are also consistent with an elevated Met-Hg concentration, so evaluation of systemic drug concentrations and of Met-Hg may be warranted. Patients may develop dizziness; hyperacusis; visual impairment (double vision); blurred vision; muscular tremor; generalized seizures; nervousness or anxiety; apprehension; euphoria; confusion; tinnitus; vomiting; sensations of heat, cold, or numbness; twitching; respiratory depression; or respiratory arrest. Cardiovascular manifestations may include sinus bradycardia, hypotension, and cardiovascular collapse leading to cardiac arrest. Decreases in cardiac output, total peripheral resistance, and mean arterial pressure can be caused by toxic concentrations of lidocaine; prilocaine and may be attributable to direct depressant effects of these local anesthetic agents on the cardiovascular system. The concentrations anticipated to give rise to systemic toxicity are approximately 5,000 ng/mL for both lidocaine and prilocaine, but lower concentrations may cause toxicity. Cautious use of lidocaine; prilocaine cream is warranted, especially when applying it over large areas and leaving it on for longer than 2 hours. The incidence of systemic adverse reactions can be expected to be directly proportional to the area and time of exposure. Also, repeated doses may increase blood concentrations of both drugs. To minimize the likelihood of systemic toxicity, apply the cream only to intact skin and do not exceed the FDA-approved maximum dose, application area, or application time, which are for pediatric patients with normal hepatic and renal function. Application of the cream to broken or inflamed skin or use in pediatric patients with impaired elimination could result in higher plasma concentrations that could, in susceptible individuals, produce a systemic pharmacologic response. Instruct patients to immediately report any chest pain (unspecified) or discomfort after administration. Respiratory support, cardiovascular resuscitation, or anticonvulsant drug therapy may be needed in cases of excessive dosage or toxicity.

    Patients may develop urticaria, angioedema, bronchospasm, anaphylactic shock, and anaphylactoid reactions after lidocaine; prilocaine cream. If hypersensitivity occurs, do not reapply the cream, as it is contraindicated in patients with a known history of sensitivity to local anesthetics of the amide type or to any other component of the product. The detection of sensitivity by skin testing is of doubtful value. An adult developed pruritus and generalized urticaria 20 minutes after application of an unknown local anesthetic. She had a positive intradermal test result with lidocaine, mepivacaine, and bupivacaine but not with procaine. The presence of a Type 1 allergic reaction and cross-reactivity with amide-type anesthetics were suspected. In addition to immediate-type reactions, delayed sensitivity reactions have been reported with amide-type local anesthetics. An adult developed intense erythema and pruritus 1 day after subcutaneous mepivacaine receipt. Testing revealed sensitization to lidocaine, which is a local anesthetic that she had previously received. Allergic reactions caused by local anesthetics appear to be rare. Of 177 children and adults with a history of adverse reactions to local anesthetics, 1 had a delayed-type response (Type IV) to mepivacaine and 2 had immediate-type reactions to articaine and lidocaine. Of 205 patients with an alleged history of allergy to local anesthesia, 4 had immediate allergic reactions and 4 had delayed allergic reactions. Thus, 197 patients were determined not to be allergic to local anesthetics.

    Methemoglobinemia has been reported with local anesthetic use. Signs and symptoms of methemoglobinemia may occur immediately or may be delayed some hours after local anesthetic exposure and are characterized by cyanotic skin discoloration and abnormal coloration of the blood. Other symptoms may include headache, rapid heart rate, shortness of breath, dizziness, and drowsiness. Since methemoglobin concentrations may continue to rise, immediately remove lidocaine; prilocaine to avoid serious central nervous system and cardiovascular adverse events including seizures, coma, arrhythmias, and death. Depending on the severity of symptoms, patients may require supportive care, such as oxygen therapy and hydration. More severe symptoms may require treatment with methylene blue, exchange transfusion, or hyperbaric oxygen.

    Lidocaine; prilocaine is contraindicated in patients with amide local anesthetic hypersensitivity or hypersensitivity to any component of the product.

    Conjunctival injection and corneal abrasions were noted in 2 children who got lidocaine; prilocaine cream inadvertently into their eyes. Avoid ocular exposure of lidocaine; prilocaine, as severe eye irritation may occur; the cream is highly alkaline. Symptoms of eye irritation may be initially masked because of local anesthetic effects. Also, a loss of protective reflexes may allow corneal irritation and potential abrasion. Do not apply the cream near the eyes, and carefully observe pediatric patients who have had the cream applied to their skin to help prevent accidental exposure by ingestion or eye contact. If eye contact occurs, immediately wash the eye with water or saline, and protect the eye until normal sensation returns. An ophthalmologist evaluation may be needed. Absorption of the cream in conjunctival tissues has not been determined.

    Animal studies have shown that lidocaine; prilocaine has an ototoxic effect when instilled into the middle ear; no abnormality was noted in animals that were exposed to the cream only in the external auditory canal. Lidocaine; prilocaine should not be used in any situation in which its penetration or migration beyond the tympanic membrane into the middle ear is possible (e.g., tympanic membrane perforation).

    Lidocaine; prilocaine may cause significant methemoglobinemia and, thus, should not be used in premature neonates (defined as a gestational age younger than 37 weeks), in infants younger than 12 months who are receiving treatment with methemoglobin-inducing agents, or in patients with congenital or idiopathic methemoglobinemia. Monitor methemoglobin concentrations in neonates and infants younger than 3 months before, during, and after the application of lidocaine; prilocaine, provided the test results can be obtained quickly. Ensure caregivers understand the need for careful application of lidocaine; prilocaine to pediatric patients. The doses, application time, and application area should not exceed the recommended maximum amounts, especially in infants younger than 3 months. Limit the period of application to the minimum required to achieve the desired anesthesia. Although all patients are at risk for methemoglobinemia, patients with glucose-6-phosphate dehydrogenase deficiency (G6PD deficiency), preexisting (congenital or idiopathic) methemoglobinemia, cardiac or pulmonary compromise (cardiac disease or pulmonary disease), those younger than 6 months, and those with concurrent exposure to oxidizing agents or their metabolites are more susceptible to developing methemoglobinemia. Monitor such patients closely for signs and symptoms of methemoglobinemia if a local anesthetic must be used. Signs of methemoglobinemia may occur immediately or may be delayed hours after exposure. Immediately discontinue the local anesthetic to avoid serious central nervous system and cardiovascular adverse events, as methemoglobin concentrations may continue to rise. Patients may require supportive care such as oxygen therapy and hydration. More severe symptoms may require treatment with methylene blue, exchange transfusion, or hyperbaric oxygen.

    Lidocaine; prilocaine cream is for topical administration to intact skin, and the cream is not recommended for use on open wounds such as wound dehiscence. Cream application to broken or inflamed skin such as skin abrasion could lead to higher plasma concentrations and, thus, potential systemic toxicity. Cautious use in pediatric patients with eczema or psoriasis may be warranted. After cream application to an infant with eczema and extensive vascular malformations, a 6-fold higher serum lidocaine concentration (7,700 ng/mL) than anticipated (1,200 ng/mL) based on an estimated absorption of lidocaine of 0.045 mg/cm2/hour was noted. Systemic toxicity (tremors, bradycardia, and hypotension) and methemoglobinemia developed in a healthy 3 year-old child with eczema who received an appropriate dose (5 grams) applied to 1,140 cm2 of skin (maximum is 100 cm2) under occlusion for 1 hour. In adults, greater systemic absorption of lidocaine and of prilocaine 1 to 2 hours after cream application to either atopic dermatitis sites or psoriatic lesions was noted as compared with data from patients with normal skin. In order to reduce the risk of toxicity due to increased absorption of topical anesthetic, the FDA recommends patients use a topical anesthetic containing the lowest amount of medication needed to relieve pain, apply the medication sparingly, and only treat known or anticipated areas of pain. Further, do not apply the anesthetic to broken or irritated skin, be aware of potential adverse reactions, take steps to reduce the risk of life-threatening side effects, and understand that applying heat to the treated area while the medication is still present and wrapping or covering the skin with any type of material or dressing can increase the chance of serious side effects.

    Pediatric patients with renal impairment, especially renal failure, and/or severe hepatic disease such as hepatic encephalopathy or some cases of hepatitis are at greater risk of developing toxic plasma concentrations of lidocaine and prilocaine. Also, accumulation of glycinexylidide (GX), a renally eliminated and active metabolite of lidocaine, may occur in patients with renal impairment. Patients with hepatic impairment have an inability to metabolize local anesthetics normally. The half-lives of prilocaine and of lidocaine may be increased in patients with hepatic and/or renal impairment. Cautiously use lidocaine; prilocaine cream in acutely ill or debilitated patients. These patient populations may have decreased hepatic function, decreased cardiac function, or be on multiple drugs and thus, be more sensitive to possible systemic effects of lidocaine and prilocaine. Smaller areas of treatment are recommended in a debilitated patient or a patient with impaired elimination. Decreasing the duration of application is likely to decrease the analgesic effect. Repeated doses of lidocaine; prilocaine cream may increase the blood concentrations of lidocaine and prilocaine.

    Use lidocaine; prilocaine cream cautiously in patients with collagen-vascular disease, as adequate analgesia may not be obtained. Increased monitoring to ensure adequate analgesia before and throughout procedures may be necessary. Administration of 5 grams of lidocaine; prilocaine cream to a 10 cm2 area on the upper arm under occlusion for 120 minutes led to significantly less analgesia (lower sensory and pain thresholds) at 30 minutes, 60 minutes, 120 minutes, 135 minutes (15 minutes after cream removal), and 150 minutes (30 minutes after cream removal) in adults with collagen-vascular disease Ehlers Danlos syndrome Type III as compared with controls.

    Description: The combination of lidocaine 2.5% and prilocaine 2.5% provides two amide local anesthetics for topical administration. EMLA, an acronym for Eutectic Mixture of Local Anesthetics, is an emulsion and is available as a cream. Careful consideration of multiple factors are important for the safe use of lidocaine; prilocaine. In pediatric patients, the child's age and weight are needed to determine the maximum dose, maximum application area, and maximum application time. In some patients, the child's weight may restrict the maximum dose. Although an option to reduce the pain associated with circumcision, lidocaine; prilocaine cream is NOT the preferred agent; topical 4% lidocaine is the preferred topical local anesthetic because of a faster onset of action, lower risk of methemoglobinemia, and less risk of minor skin reactions or blistering as compared with lidocaine; prilocaine cream. Lidocaine; prilocaine is FDA-approved for use in patients as young as neonates at least 37 weeks gestation.

    For use as local anesthesia to provide topical anesthesia:
    -application to intact skin before minor (e.g., intravenous cannulation and venipuncture) or major (split thickness skin graft harvesting) dermal procedures:
    Topical dosage:
    Neonates older than 37 weeks gestation: Apply no more than 1 gram/dose over no more than 10 cm2 of skin surface for 1 hour before procedure (Max application time: 1 hour). Cover cream with an occlusive dressing; a secondary dressing may help keep the cream in place. Application of 1 gram/dose 60 to 80 minutes before circumcision led to significantly less facial activity, crying time, and increases in heart rate as compared with data from neonates in the placebo group, but lidocaine; prilocaine cream is NOT the preferred agent; topical 4% lidocaine is the preferred topical local anesthetic because of a faster onset of action, no risk of methemoglobinemia, and less risk of minor skin reactions or blistering as compared with lidocaine; prilocaine cream.
    Infants younger than 3 months and/or weighing less than 5 kg: Apply no more than 1 gram/dose over no more than 10 cm2 of skin surface for 1 hour before procedure (Max application time: 1 hour). Cover cream with an occlusive dressing; a secondary dressing may help keep the cream in place. Application of 1 gram/dose 60 to 80 minutes before circumcision led to significantly less facial activity, crying time, and increases in heart rate as compared with data from neonates in the placebo group, but lidocaine; prilocaine cream is NOT the preferred agent; topical 4% lidocaine is the preferred topical local anesthetic because of a faster onset of action, no risk of methemoglobinemia, and less risk of minor skin reactions or blistering as compared with lidocaine; prilocaine cream.
    Infants 3 months and older weighing 5 kg or more: Apply no more than 2 grams/dose over no more than 20 cm2 of skin surface for 1 hour before a routine procedure and 2 hours before a painful procedure (Max application time: 4 hours). Cover cream with an occlusive dressing; a secondary dressing may help keep the cream in place.
    Children 1 to 6 years weighing less than 10 kg: Apply no more than 2 grams/dose over no more than 20 cm2 of skin surface for 1 hour before a routine procedure and 2 hours before a painful procedure (Max application time: 4 hours). Cover cream with an occlusive dressing; a secondary dressing may help keep the cream in place.
    Children 1 to 6 years weighing 10 kg or more: Apply no more than 10 grams/dose over no more than 100 cm2 of skin surface for 1 hour before a routine procedure and 2 hours before a painful procedure (Max application time: 4 hours). Cover cream with an occlusive dressing; a secondary dressing may help keep the cream in place.
    Children 7 to 12 years weighing less than 20 kg: Apply no more than 10 grams/dose over no more than 100 cm2 of skin surface for 1 hour before a routine procedure and 2 hours before a painful procedure (Max application time: 4 hours). Cover cream with an occlusive dressing; a secondary dressing may help keep the cream in place.
    Children 7 to 12 years weighing 20 kg or more: Apply no more than 20 grams/dose over no more than 200 cm2 of skin surface for 1 hour before a routine procedure and 2 hours before a painful procedure (Max application time: 4 hours). Cover cream with an occlusive dressing; a secondary dressing may help keep the cream in place.
    Adolescents: Apply 2.5 grams/dose over 20 to 25 cm2 of skin surface for at least 1 hour for minor dermal procedures or 2 grams per 10 cm2 for at least 2 hours for more painful dermatological procedures involving a larger skin area such as split thickness skin graft harvesting. Cover cream with an occlusive dressing; a secondary dressing may help keep the cream in place.
    -application to male genital mucous membranes as a pretreatment to local anesthetic infiltration:
    Topical dosage:
    Male Adolescents: 1 gram/10 cm2/dose covered with an occlusive dressing for 15 minutes. Remove the cream and immediately begin local anesthetic infiltration. Of men aged 17 to 59 years, 55 of 57 had sufficient analgesia for cautery of genital warts after lidocaine; prilocaine cream alone. About 1 gram of cream was applied to each area with lesions up to a maximum of 10 grams per patient. Plastic film was applied over the cream. The intended application time of the cream was at least 30 minutes for mucous membranes and 60 minutes for normal skin.
    -application to female external genitalia prior to minor procedures (e.g., removal of condylomata acuminata) or prior to infiltration anesthesia:
    Topical dosage:
    Female Adolescents: Apply a thick layer (5 to 10 grams/dose) for 5 to 10 minutes. Occlusion is not necessary for absorption but may be helpful to keep the cream in place. Patients should be lying down during application of the cream, especially if no occlusion is used. After cream removal, immediately begin the procedure or local anesthetic infiltration. Of women aged 16 to 41 years who had genital warts removed by thermocautery (n = 48), thermocautery and excision (n = 2), or carbon dioxide laser (n = 1), 23 had no pain or only slight pain after lidocaine; prilocaine cream alone. About 1 gram of cream was applied to each area with lesions up to a maximum of 10 grams per patient. Plastic film was applied over the cream if natural occlusion was not present. The intended application time of the cream was at least 30 minutes for mucous membranes and 60 minutes for normal skin. Of the 51 women, 31 went on to have lidocaine hydrochloride infiltration for pain management.

    Maximum Dosage Limits:
    -Neonates
    37 weeks gestation and older: 1 gram applied over 10 cm2 of skin surface for 1 hour.
    -Infants
    1 to 2 months: 1 gram applied over 10 cm2 of skin surface for 1 hour.
    3 to 11 months weighing less than 5 kg: 1 gram applied over 10 cm2 of skin surface for 1 hour.
    3 to 11 months weighing 5 kg or more: 2 grams applied over 20 cm2 of skin surface for 4 hours.
    -Children
    1 to 6 years weighing less than 10 kg: 2 grams applied over 20 cm2 of skin surface for 4 hours.
    1 to 6 years weighing 10 kg or more: 10 grams applied over 100 cm2 of skin surface for 4 hours.
    7 to 12 years weighing less than 20 kg: 10 grams applied over 100 cm2 of skin surface for 4 hours.
    7 to 12 years weighing 20 kg or more: 20 grams applied over 200 cm2 for 4 hours.
    -Adolescents
    Maximum recommended duration of topical exposure is 4 hours.

    Patients with Hepatic Impairment Dosing
    Specific guidelines for dosage adjustments in hepatic impairment are not available, but use of lidocaine; prilocaine cream in pediatric patients with severe hepatic dysfunction may be inadvisable. The half-lives of prilocaine and of lidocaine may be increased in patients with hepatic impairment. Patients with severe hepatic disease, because of their inability to metabolize local anesthetics normally, are at greater risk of developing toxic plasma concentrations of lidocaine and prilocaine.

    Patients with Renal Impairment Dosing
    Specific guidelines for dosage adjustments in renal impairment are not available, but use of lidocaine; prilocaine cream in pediatric patients with severe renal impairment may be inadvisable. The half-lives of prilocaine and of lidocaine may be increased in patients with renal impairment. Patients with severe renal impairment may be at greater risk of developing toxic plasma concentrations of lidocaine and prilocaine. Also, accumulation of glycinexylidide (GX), a renally eliminated and active metabolite of lidocaine, may occur.

    *non-FDA-approved indication

    Monograph content under development

    Mechanism of Action: Lidocaine and prilocaine are amide-type local anesthetics that effect local anesthetic action by stabilization of neuronal membranes. Specifically, lidocaine and prilocaine inhibit the ionic fluxes required for the initiation and conduction of impulses. Dermal analgesia is achieved because the cream releases lidocaine and prilocaine into the epidermal and dermal layers of the skin, and the drugs accumulate in the vicinity of dermal pain receptors and nerve endings.

    Pharmacokinetics: Lidocaine; prilocaine is applied topically.
    -Lidocaine: At concentrations produced by lidocaine; prilocaine cream application, lidocaine is approximately 70% bound to plasma proteins, primarily alpha-1-acid glycoprotein and is rapidly metabolized in the liver to metabolites including monoethylglycinexylidide (MEGX) and glycinexylidide (GX), which both have similar pharmacologic activity but less potency as compared with lidocaine. Metabolism of lidocaine within the skin or mucous membranes is unknown. More than 98% of an absorbed lidocaine dose can be recovered in the urine as metabolites or parent drug; about 10% is excreted renally as unchanged lidocaine. The elimination of GX is renal. After IV administration, the terminal elimination half-life of lidocaine is approximately 65-150 minutes (mean of 110 minutes).
    -Prilocaine: Prilocaine is 55% bound to plasma proteins and is metabolized in both the liver and the kidneys by amidases. Metabolism of prilocaine within the skin or mucous membranes is unknown. The ortho-toluidine metabolite can produce methemoglobinemia after systemic doses of prilocaine approximating 8 mg/kg. After IV administration, the elimination half-life of prilocaine is approximately 10-150 minutes (mean of 70 minutes).

    Affected cytochrome P450 isoenzymes: CYP1A2 and CYP3A4
    The major metabolic pathway, sequential N-deethylation to MEGX and GX, is primarily mediated by CYP1A2 with a minor role of CYP3A4.


    -Route-Specific Pharmacokinetics
    Topical Route
    After lidocaine; prilocaine cream application, the amount of lidocaine and prilocaine systemically absorbed is directly related to both the application duration and application area. Also, greater absorption of both anesthetics may be anticipated if the cream is applied to broken or inflamed skin; increased absorption could result in higher plasma concentrations that could, in susceptible individuals, produce a systemic pharmacologic response. Concentrations anticipated to give rise to systemic toxicity are approximately 5000 ng/ml for lidocaine and prilocaine. However, some patients may show signs of toxicity at approximately 1000 ng/ml. In adults who received 60 g to 400 cm2 applied to intact skin for 3 hours, the Cmax of lidocaine was 120 ng/ml, the Cmax of prilocaine was 70 ng/ml, and the Tmax of both drugs was 4 hours. Low plasma concentrations of lidocaine (2.5-16 ng/ml) and prilocaine (2.5-7 ng/ml) were noted after 0.5-3.3 g of cream applied to adult penile skin for 15 minutes. After application of 10 g of cream for 10-60 minutes in the vaginal fornices, the plasma concentrations ranged from 148 to 641 ng/ml for lidocaine and from 40 to 346 ng/ml for prilocaine. The time to reach maximum concentration was 21-125 minutes for lidocaine and 21-95 minutes for prilocaine. Absorption from the genital mucosa is more rapid than absorption from intact skin.

    The onset, depth, and duration of dermal analgesia on intact skin depend primarily on the duration of application. Satisfactory dermal anesthesia occurs 1 hour after application, reaches a maximum at 2-3 hours, and persists for 1-2 hours after removal. Application to the genital mucosa is associated with a faster onset time (5-10 minutes) as compared with application to intact skin. After a 5-10 minute application to female genital mucosa, the average duration of effective analgesia to an argon laser, which produced a sharp, pricking pain, was 15-20 minutes (range, 5-45 minutes).


    -Special Populations
    Pediatrics
    Neonates
    Among 9 full-term neonates with a mean age of 7 days and a mean gestational age of 38.8 weeks, comparable plasma lidocaine and prilocaine concentrations and blood methemoglobin concentrations were noted after lidocaine; prilocaine cream administration as compared with concentrations noted among infants and children.

    Hepatic Impairment
    Lidocaine; prilocaine administration to pediatric patients with hepatic impairment may lead to an increased half-life of prilocaine and of lidocaine. Patients with severe hepatic disease, because of their inability to metabolize local anesthetics normally, are at greater risk of developing toxic plasma concentrations of both drugs.

    Renal Impairment
    Lidocaine; prilocaine administration to pediatric patients with renal impairment may affect the systemic concentrations of both drugs, and accumulation of glycinexylidide (GX), a renally eliminated and active metabolite of lidocaine, may occur. Among adults who received lidocaine 1 mg/kg IV, increased GX concentrations were noted among adults with a CrCl of 30-60 ml/min (760 +/- 555 ng x hr/ml), those with a CrCl < 30 ml/min (690 +/- 511 ng x hr/ml), and those on hemodialysis (587 +/- 268 ng x hr/ml) as compared with adults with a CrCl > 80 ml/min (274 +/- 150 ng x hr/ml). Also, significantly decreased lidocaine clearance (6.01 +/- 2.54 ml/min x kg vs. 11.87 +/- 2.97 ml/min x kg) and increased half-life (4.55 +/- 1.71 hours vs. 2.24 +/- 0.55 hours) were noted among adults with a CrCl < 30 ml/min who were not receiving hemodialysis as compared with data from patients with a CrCl > 80 ml/min. Of note, lidocaine concentrations were similar among adults undergoing hemodialysis as compared with data from adults with a CrCl > 80 ml/min. Dialyzable uremic toxins may be responsible for inhibition of lidocaine metabolism. In addition to the effect of renal impairment on lidocaine, an increased half-life of prilocaine may occur, as the kidney is involved in the metabolism of prilocaine.

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