Synera

Dosage Forms And Strengths

SYNERA topical patch contains 70 mg lidocaine and 70 mg tetracaine, has a total skin contact area of 50 cm², and an active drug-containing area of 10 cm².

SYNERA is available as the following:

NDC 10885-002-01 One individually packaged SYNERA patch
NDC 10885-002-10 Box of 10 individually packaged SYNERA patches

Storage And Handling

Store at 25°C (77°F); excursions permitted to 15 to 30°C (59 to 86°F).

Keep out of reach of children and pets.

Apply SYNERA immediately upon removal from the protective pouch.

Do not cut the patch or otherwise remove the top cover as this could cause the patch to heat to temperatures that could cause thermal injury. Do not cover the holes on the top side of the patch as this could cause the patch not to heat.

Hands should be washed after handling SYNERA, and eye contact with SYNERA should be avoided. The used patch should be disposed of immediately. The adhesive sides of the patch should be folded together and the patch should then be thrown away in a location that is out of the reach of children and pets.

Manufactured for: Galen US Inc. Fretz Road Souderton PA 18964. Revised: March 2014

SYNERA is a combination amide and ester local anesthetic indicated for use on intact skin to provide local dermal analgesia for superficial venous access and superficial dermatological procedures such as excision, electrodessication and shave biopsy of skin lesions.

SYNERA should only be applied to intact skin. Use immediately after opening the pouch.

For adults and children 3 years of age and older

• Venipuncture or Intravenous Cannulation: Prior to venipuncture or intravenous cannulation, apply SYNERA to intact skin for 20 to 30 minutes.
• Superficial Dermatological Procedures: For superficial dermatological procedures such as superficial excision or shave biopsy, apply SYNERA to intact skin for 30 minutes prior to the procedure.

While efficacy has not been established for children less than 3 years of age, safe use of SYNERA in infants 4 to 6 months of age was documented in one study.

Simultaneous or sequential application of multiple SYNERA patches is not recommended. However, application of one additional patch at a new location to facilitate venous access is acceptable after a failed attempt. When SYNERA is used concomitantly with other products containing local anesthetic agents, the amount absorbed from all formulations should be considered, as local anesthetics are thought to have at least additive toxicities. If irritation or a burning sensation occurs during application, remove the patch.

• SYNERA is contraindicated in patients with a known history of sensitivity to lidocaine, tetracaine, or local anesthetics of the amide or ester type.
• SYNERA is also contraindicated in patients with para-aminobenzoic acid (PABA) hypersensitivity and in patients with a known history of sensitivity to any other component of the product.

WARNINGS

Included as part of the PRECAUTIONS section.

PRECAUTIONS

Overexposure

Application of a SYNERA patch for longer duration than recommended, or the simultaneous or sequential application of multiple SYNERA patches, could result in sufficient absorption of lidocaine and tetracaine to result in serious adverse effects.

Storage And Disposal

Used SYNERA patches contain a large amount of lidocaine and tetracaine (at least 90% of the initial amount). The potential exists for a child or pet to suffer serious adverse effects from chewing or ingesting a new or used SYNERA patch. It is important for patients to store and dispose of SYNERA out of the reach of children and pets.

Avoidance Of Exposure To Eyes And Mucous Membranes

• Contact of SYNERA with the eyes should be avoided based on the findings of severe eye irritation with the use of similar products in animals. Also, the loss of protective reflexes may predispose to corneal irritation and potential abrasion. If eye contact occurs, immediately wash out the eye with water or saline and protect the eye until sensation returns.
• SYNERA is not recommended for use on mucous membranes or on areas with a compromised skin barrier because these uses have not been studied. Application to broken or inflamed skin may result in toxic blood concentrations of lidocaine and tetracaine from increased absorption.

Magnetic Resonance Imaging

The integrated heating component contains iron powder; therefore, the SYNERA patch must be removed before a patient undergoes magnetic resonance imaging.

Methemoglobinemia

• Several local anesthetics, including tetracaine, have been associated with methemoglobinemia. The risk of methemoglobinemia is greatest for patients with congenital or idiopathic methemoglobinemia, and infants under the age of twelve months who are receiving treatment with methemoglobin-inducing agents.
• Very young patients or patients with glucose-6-phosphate dehydrogenase deficiencies have an increased risk of methemoglobinemia.
• Patients taking concomitant drugs associated with drug-induced methemoglobinemia such as sulfonamides, acetaminophen, acetanilide, aniline dyes, benzocaine, chloroquine, dapsone, naphthalene, nitrates and nitrites, nitrofurantoin, nitroglycerin, nitroprusside, pamaquine, para-aminosalicylic acid, phenacetin, phenobarbital, phenytoin, primaquine, and quinine are also at greater risk for developing methemoglobinemia.
• There have been no reports of methemoglobinemia with SYNERA. However, providers are cautioned to carefully apply SYNERA to ensure that the areas of application and duration of application are consistent with those recommended for the intended population.

Allergic Reactions

Allergic or anaphylactoid reactions associated with lidocaine, tetracaine, or other components of SYNERA can occur. They are characterized by urticaria, angioedema, bronchospasm, and shock. If an allergic reaction occurs, it should be managed by conventional means.

Special Patient Populations

• SYNERA should be used with caution in patients who may be more sensitive to the systemic effects of lidocaine and tetracaine particularly the acutely ill or debilitated.
• Patients with severe hepatic disease or pseudocholinesterase deficiency, because of their inability to metabolize local anesthetics normally, are at a greater risk of developing toxic plasma concentrations of lidocaine and tetracaine.

Vaccinations

Lidocaine has been shown to inhibit viral and bacterial growth. The effect of SYNERA on intradermal injections of live vaccines has not been determined.

Patient Counseling Information

• Advise patients to read the FDA-approved patient labeling (Instructions for Use).
• Advise patients that SYNERA is a patch containing two medicines (lidocaine and tetracaine) that are known as local anesthetics, and a heating component. These medicines are used to lessen the pain associated with superficial venous access and superficial dermatological procedures such as excision, electrodessication and shave biopsy of skin lesions.
• Advise patients that SYNERA should be applied immediately after opening the pouch. Instruct patients to not cut or remove the top cover of the patch as this could result in thermal injury.
• Advise patients that keeping a patch on longer than recommended or applying multiple patches simultaneously or sequentially could result in systemic absorption sufficient to result in serious adverse effects that are typical of drugs in this class.
• Advise patients that the patch must be removed before magnetic resonance imaging.
• Advise patients that SYNERA is contraindicated in patients with a known history of sensitivity to lidocaine, tetracaine, local anesthetics of the amide or ester type, or any other component of the product and in patients with para-aminobenzoic acid (PABA) hypersensitivity.
• Advise patients that SYNERA should be used with caution in patients who may be more sensitive to the systemic effects of lidocaine and tetracaine, including the acutely ill, the debilitated, and those with compromised hepatic function. Patients with severe hepatic disease or pseudocholinesterase deficiency are at greater risk of developing toxic plasma concentrations.
• Advise patients that SYNERA should be used with caution in patients receiving class I antiarrhythmics and/or other local anesthetics, because the systemic toxic effects may be additive and potentially synergistic with lidocaine and tetracaine.
• Advise patients not to use SYNERA if they have a history of methemoglobinemia.
• Advise patients to avoid contact of SYNERA with the eyes due to potential irritation or abrasion. If contact occurs, immediately wash the eye with water or saline, and protect it until sensation returns.
• Advise patients that SYNERA should only be applied to intact skin. Inform patients that exposure of the skin to SYNERA may result in erythema, blanching and edema; these reactions are generally mild, resolving spontaneously soon after the patch is removed.
• Advise patients that SYNERA is not for use on mucous membranes or on areas with broken skin.
• Advise patients that if skin irritation or a burning sensation occurs during application, the product should be removed.
• Inform patients of the signs of an allergic or anaphylactoid reaction (urticaria, angioedema, bronchospasm, and shock). Instruct patients to seek immediate emergency help if these occur.
• Advise patients that SYNERA may lead to diminished or blocked sensation in the treated skin; therefore, patients should avoid inadvertent trauma (rubbing, scratching, or exposure to heat or cold) before complete sensation returns.
• Advise patients to contact their healthcare professional if they don't recall where to apply the patch.
• Instruct patients to store SYNERA and to discard used patches out of the reach of children and pets.
• The effect of SYNERA on intradermal injections of live vaccines has not been determined.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment Of Fertility

Carcinogenesis

Long-term studies in animals have not been performed to evaluate the carcinogenic potential of either lidocaine or tetracaine.

Mutagenesis

The mutagenic potential of lidocaine base and tetracaine base has been determined in the in vitro Ames Bacterial Reverse Mutation Assay, the in vitro chromosome aberration assay using Chinese hamster ovary cells, and the in vivo mouse micronucleus assay. Lidocaine was negative in all three assays. Tetracaine was negative in the in vitro Ames assay and the in vivo mouse micronucleus assay. In the in vitro chromosome aberration assay, tetracaine was negative in the absence of metabolic activation, and equivocal in the presence of metabolic activation.

Impairment of Fertility

Lidocaine did not affect fertility in female rats when given via continuous subcutaneous infusion via osmotic minipumps up to doses of 250 mg/kg/day (1500 mg/m² or 43-fold higher than the SDA). Although lidocaine treatment of male rats increased the copulatory interval and lead to a dose-related decreased homogenization resistant sperm head count, daily sperm production, and spermatogenic efficiency, the treatment did not affect overall fertility in male rats when given subcutaneous doses up to 60 mg/kg (360 mg/m² or 8-fold the SDA). Tetracaine did not affect fertility in male or female rats when given subcutaneous doses up to 7.5 mg/kg (45 mg/m² or 1-fold the SDA). Multiples of exposure are based on an SDA of 70 mg each of lidocaine and tetracaine in SYNERA patch for 30 minutes to a 60 kg person (43 mg/m²).

Use In Specific Populations

Pregnancy

Pregnancy Category B

Lidocaine was not teratogenic in rats given subcutaneous doses up to 60 mg/kg (360 mg/m² or 8-fold the Single Dermal Administration (SDA)) or in rabbits up to 15 mg/kg (180 mg/m² or 4-fold the SDA). Tetracaine was not teratogenic in rats given subcutaneous doses up to 10 mg/kg (60 mg/m² or 1-fold the SDA) or in rabbits up to 5 mg/kg (60 mg/m² or 1-fold the SDA). SYNERA components (lidocaine and tetracaine) given as a 1:1 eutectic mixture were not teratogenic in rats (60 mg/m² or 1-fold the SDA) or rabbits (120 mg/m² or 3-fold the SDA).

Lidocaine, contained 1:100,000 epinephrine, at a dose of 6 mg/kg (2-fold the SDA) injected into the masseter muscle of the jaw or into the gum of the lower jaw of Long-Evans hooded pregnant rats on Gestation Day 11 led to developmental delays in neonatal behavior among offspring. Developmental delays were observed for negative geotaxis, static righting reflex, visual discrimination response, sensitivity and response to thermal and electrical shock stimuli, and water maze acquisition. The developmental delays of the neonatal animals were transient with responses becoming comparable to untreated animals later in life. The clinical relevance of the animal data is uncertain.

Pre-and postnatal maturational, behavioral, or reproductive development was not affected by maternal subcutaneous administration of tetracaine during gestation and lactation up to doses of 7.5 mg/kg (45 mg/m² or 1-fold the SDA).

No adequate and well-controlled studies have been conducted in pregnant women. Because animal studies are not always predictive of human response, SYNERA should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Labor And Delivery

Neither lidocaine nor tetracaine is contraindicated in labor and delivery. In humans, the use of lidocaine for labor neuraxial analgesia has not been associated with an increased incidence of adverse fetal effects either during delivery or during the neonatal period. Tetracaine has also been used as a neuraxial anesthetic for cesarean section without apparent adverse effects on offspring. Should SYNERA be used concomitantly with other products containing lidocaine and/or tetracaine, total doses contributed by all formulations must be considered.

Nursing Mothers

Lidocaine is excreted into human milk and it is not known if tetracaine is excreted into human milk. Therefore, caution should be exercised when SYNERA is administered to a nursing mother since the milk:plasma ratio of lidocaine is 0.4 and is not determined for tetracaine. In a prior report, when lidocaine was used as an epidural anesthetic for cesarean section in 27 women, a milk:plasma ratio of 1.07 ±0.82 was found by using AUC values. Following single dose administration of 20 mg of lidocaine for a dental procedure, the point value milk: plasma ratio was similarly reported as 1.1 at five to six hours after injection. Thus, the estimated maximum total daily dose of lidocaine delivered to the infant via breast milk would be approximately 36 μg/kg. Based on these data and the low concentrations of lidocaine and tetracaine found in the plasma after topical administration of SYNERA in recommended doses, the small amount of these primary compounds and their metabolites that would be ingested orally by a suckling infant is unlikely to cause adverse effects.

Pediatric Use

The safety and effectiveness of SYNERA have been established in pediatric patients 3 years and older based on adequate and well-controlled studies. While efficacy has not been established for children less than 3 years of age, the safety of SYNERA in infants has been evaluated in one study in which 34 infants 4 to 6 months of age received SYNERA. The recommended application time for the patch for pediatric patients is the same as for adults. Simultaneous or sequential application of more than two SYNERA patches to children is not recommended as it has not been adequately studied.

Use In Geriatric Patients

In the controlled clinical studies, 139 patients over 65 years of age, including 41 patients over 75 years of age, received SYNERA. Visual Analog Scale (VAS) pain score differences between SYNERA and placebo were considerably lower in the geriatric subjects than in the rest of the adult population. No overall differences in safety were observed between geriatric subjects and younger subjects. However, increased sensitivity in individual patients greater than 65 years of age cannot be ruled out. After intravenous dosing, the elimination half-life of lidocaine is significantly longer in elderly patients (2.5 hours) than in younger patients (1.5 hours).

SIDE EFFECTS

Clinical Studies Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.

Three different formulations were studied during clinical development of SYNERA: Developmental A (n=138), Developmental B (n=30), and the SYNERA final formulation (n=1281). The developmental patch formulations each contained the same amount of the active drug (70 mg each of lidocaine and tetracaine) as the final patch formulation, but varying amounts of excipients, principally polyvinyl alcohol and water. Data obtained from studies utilizing the developmental patches have been included in the overall evaluation of SYNERA safety (calculation of adverse event incidence).

Most common adverse events in clinical trials

Localized Reactions

During or immediately after treatment with SYNERA, the skin at the site of treatment may develop erythema, blanching, edema, or abnormal sensation. In clinical studies involving 1449 SYNERA-treated subjects, the most common local reactions were erythema (71%), blanching (12%) and edema (12%). These reactions were generally mild, resolving spontaneously soon after patch removal. There were no treatment-related serious adverse events.

Other application site reactions of various types (contact dermatitis, rash, skin discoloration) occurred in less than 4% of SYNERA-treated patients during clinical trials. Of these adverse events, 75% were mild, resolving spontaneously soon after patch removal.

Application site-related adverse events that occurred in 1% or less of SYNERA-treated subjects included rash, pruritus, pain, contact dermatitis, infection, skin discoloration, allergic reaction, blister, paresthesia, urticaria, and vesiculobullous rash.

Allergic Reactions

Allergic or anaphylactoid reactions can occur with the active or inactive components of SYNERA. They may be characterized by urticaria, angioedema, bronchospasm, and shock. Allergic reactions to the patch should be managed by conventional means.

Systemic (Dose-Related) Reactions

Systemic adverse reactions that occurred in 1% or less of SYNERA-treated subjects included dizziness, headache, nausea, somnolence, and vomiting. Systemic adverse effects of lidocaine and tetracaine are similar in nature to those observed with other amide and ester 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. Signs of CNS toxicity may start at plasma concentrations of lidocaine as low as 1000 ng/mL. The plasma concentrations at which tetracaine toxicity may occur are less well characterized; however, systemic toxicity with tetracaine is thought to occur with much lower plasma concentrations compared with lidocaine. The toxicity of co-administered local anesthetics is thought to be at least additive. Cardiovascular manifestations may include bradycardia, hypotension and cardiovascular collapse leading to arrest.

DRUG INTERACTIONS

Antiarrhythmic Drugs

SYNERA should be used with caution in patients receiving Class I antiarrhythmic drugs (such as tocainide and mexiletine) since the systemic toxic effects are thought to be additive and potentially synergistic with lidocaine and tetracaine.

Local Anesthetics

When SYNERA is used concomitantly with other products containing local anesthetic agents, the amount absorbed from all formulations should be considered since the systemic toxic effects are thought to be additive and potentially synergistic with lidocaine and tetracaine.

Pregnancy Category B

Lidocaine was not teratogenic in rats given subcutaneous doses up to 60 mg/kg (360 mg/m² or 8-fold the Single Dermal Administration (SDA)) or in rabbits up to 15 mg/kg (180 mg/m² or 4-fold the SDA). Tetracaine was not teratogenic in rats given subcutaneous doses up to 10 mg/kg (60 mg/m² or 1-fold the SDA) or in rabbits up to 5 mg/kg (60 mg/m² or 1-fold the SDA). SYNERA components (lidocaine and tetracaine) given as a 1:1 eutectic mixture were not teratogenic in rats (60 mg/m² or 1-fold the SDA) or rabbits (120 mg/m² or 3-fold the SDA).

Lidocaine, contained 1:100,000 epinephrine, at a dose of 6 mg/kg (2-fold the SDA) injected into the masseter muscle of the jaw or into the gum of the lower jaw of Long-Evans hooded pregnant rats on Gestation Day 11 led to developmental delays in neonatal behavior among offspring. Developmental delays were observed for negative geotaxis, static righting reflex, visual discrimination response, sensitivity and response to thermal and electrical shock stimuli, and water maze acquisition. The developmental delays of the neonatal animals were transient with responses becoming comparable to untreated animals later in life. The clinical relevance of the animal data is uncertain.

Pre-and postnatal maturational, behavioral, or reproductive development was not affected by maternal subcutaneous administration of tetracaine during gestation and lactation up to doses of 7.5 mg/kg (45 mg/m² or 1-fold the SDA).

No adequate and well-controlled studies have been conducted in pregnant women. Because animal studies are not always predictive of human response, SYNERA should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Clinical Studies Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in clinical practice.

Three different formulations were studied during clinical development of SYNERA: Developmental A (n=138), Developmental B (n=30), and the SYNERA final formulation (n=1281). The developmental patch formulations each contained the same amount of the active drug (70 mg each of lidocaine and tetracaine) as the final patch formulation, but varying amounts of excipients, principally polyvinyl alcohol and water. Data obtained from studies utilizing the developmental patches have been included in the overall evaluation of SYNERA safety (calculation of adverse event incidence).

Most common adverse events in clinical trials

Localized Reactions

During or immediately after treatment with SYNERA, the skin at the site of treatment may develop erythema, blanching, edema, or abnormal sensation. In clinical studies involving 1449 SYNERA-treated subjects, the most common local reactions were erythema (71%), blanching (12%) and edema (12%). These reactions were generally mild, resolving spontaneously soon after patch removal. There were no treatment-related serious adverse events.

Other application site reactions of various types (contact dermatitis, rash, skin discoloration) occurred in less than 4% of SYNERA-treated patients during clinical trials. Of these adverse events, 75% were mild, resolving spontaneously soon after patch removal.

Application site-related adverse events that occurred in 1% or less of SYNERA-treated subjects included rash, pruritus, pain, contact dermatitis, infection, skin discoloration, allergic reaction, blister, paresthesia, urticaria, and vesiculobullous rash.

Allergic Reactions

Allergic or anaphylactoid reactions can occur with the active or inactive components of SYNERA. They may be characterized by urticaria, angioedema, bronchospasm, and shock. Allergic reactions to the patch should be managed by conventional means.

Systemic (Dose-Related) Reactions

Systemic adverse reactions that occurred in 1% or less of SYNERA-treated subjects included dizziness, headache, nausea, somnolence, and vomiting. Systemic adverse effects of lidocaine and tetracaine are similar in nature to those observed with other amide and ester 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. Signs of CNS toxicity may start at plasma concentrations of lidocaine as low as 1000 ng/mL. The plasma concentrations at which tetracaine toxicity may occur are less well characterized; however, systemic toxicity with tetracaine is thought to occur with much lower plasma concentrations compared with lidocaine. The toxicity of co-administered local anesthetics is thought to be at least additive. Cardiovascular manifestations may include bradycardia, hypotension and cardiovascular collapse leading to arrest.

In adults the maximum peak plasma concentrations of lidocaine and tetracaine following application of two to four SYNERA patches for 30-60 minutes were less than 9 ng/mL and tetracaine levels were not detectable. In children, the maximum observed peak plasma concentrations of lidocaine were 63 ng/mL and 331 ng/mL after the application of one or two SYNERA patches, respectively. Higher maximum concentrations of lidocaine were observed for younger children when compared to older children. The maximum concentration of tetracaine observed in children was 65 ng/mL, and most values obtained were < 0.9 ng/mL. Signs of CNS toxicity may start at plasma concentrations of lidocaine as low as 1000 ng/mL, and the risk of seizures generally increases with increasing plasma levels.

Very high levels of lidocaine can cause respiratory arrest, coma, decreases in cardiac output, total peripheral resistance and mean arterial pressure, ventricular arrhythmias and cardiac arrest. Tetracaine is associated with a profile of systemic CNS and cardiovascular adverse events similar to lidocaine, although toxicity associated with tetracaine is thought to occur at lower doses compared to lidocaine. The toxicity of co-administered local anesthetics is thought to be at least additive. In the absence of massive topical overdose or oral ingestion, other etiologies for the clinical effects or overdosage from other sources of lidocaine, tetracaine or other local anesthetics should be considered. The management of overdosage includes close monitoring, supportive care and symptomatic treatment. Dialysis is of negligible value in the treatment of acute overdosage of lidocaine.

Absorption

Application of one SYNERA patch for 30 minutes in adults produced peak plasma concentrations of lidocaine less than 5 ng/mL while plasma levels of tetracaine were below the limit of quantitation ( < 0.9 ng/mL) in all subjects tested (n = 12, see Table 1). SYNERA application up to 60 minutes did not significantly increase plasma levels of lidocaine or tetracaine compared to a 30-minute application.

Table 1 : Absorption of Lidocaine and Tetracaine from SYNERA in Normal Adult Volunteers (n = 12)

Application of SYNERA to broken or inflamed skin or more than four simultaneous or sequentially applied SYNERA patches could result in higher plasma levels of local anesthetic that carries the risk of systemic toxicity.

Simultaneous or sequential application of multiple SYNERA patches is not recommended. However, plasma levels of lidocaine and tetracaine have been determined in clinical pharmacology studies following multiple successive and simultaneous applications of SYNERA patches on intact skin. Maximum plasma levels of lidocaine after the application of a) four successive SYNERA patches for 30 minutes each with a 30-minute interval between each patch application, and b) three SYNERA patches for 60 minutes each with a 60-minute interval between each application were less than 12 ng/mL and 8 ng/mL, respectively. Tetracaine was not detected in plasma following either treatment. Simultaneous application of two or four SYNERA patches for 60 minutes produced peak plasma concentrations of lidocaine of less than 9 ng/mL, while tetracaine plasma concentrations were not detectable in all subjects (n=22). Sequential 30-minute applications of four SYNERA patches at 60-minute intervals produced peak plasma concentrations of lidocaine of less than 12 ng/mL, while tetracaine plasma concentrations were below the limit of quantitation (n=11).

Distribution

When lidocaine is administered intravenously to healthy volunteers, the steady-state volume of distribution is approximately 0.8 to 1.3 L/kg. At lidocaine concentrations observed following the recommended product application, approximately 75% of lidocaine is 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. CNS toxicity is seen with plasma levels of 5000 ng/mL of lidocaine; however a small number of patients reportedly may show signs of toxicity at approximately 1000 ng/mL. Volume of distribution and protein binding have not been determined for tetracaine due to rapid hydrolysis in plasma.

Metabolism

It is not known if lidocaine or tetracaine 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. The major metabolic pathway of lidocaine, sequential N-deethylation to monoethylglycinexylidide (MEGX) and glycinexylidide (GX), is primarily mediated by CYP1A2 with a minor role of CYP3A4. The metabolite, 2,6-xylidine, has unknown pharmacologic activity. Following intravenous administration of lidocaine, MEGX and GX concentrations in serum range from 11% to 36% and from 5% to 11% of lidocaine concentrations, respectively. Serum concentrations of MEGX were about one-third the serum lidocaine concentrations. Tetracaine undergoes rapid hydrolysis by plasma esterases. Primary metabolites of tetracaine include para-aminobenzoic acid and diethylaminoethanol, both of which have an unspecified activity.

Elimination

The half-life of lidocaine elimination from the plasma following intravenous administration is approximately 1.8 hr. Lidocaine and its metabolites are excreted by the kidneys. More than 98% of an absorbed dose of lidocaine can be recovered in the urine as metabolites or parent drug. Less than 10% of lidocaine is excreted unchanged in adults, and approximately 20% is excreted unchanged in neonates. The systemic clearance is approximately 8-10 mL/min/kg. During intravenous studies, the elimination half-life of lidocaine was statistically significantly longer in elderly patients (2.5 hours) than in younger patients (1.5 hours). The half-life and clearance for tetracaine have not been established for humans, but hydrolysis in the plasma is rapid.

Pediatric Patients

Application of one SYNERA patch for up to 30 minutes in children 4 months to 12 years of age (n=18) produced maximum peak plasma concentrations of lidocaine and tetracaine of 63 ng/mL and 65 ng/mL, respectively. Application of two SYNERA patches for up to 30 minutes to children 4 months to 12 years of age (n=19) produced peak lidocaine levels of up to 331 ng/mL and tetracaine levels of less than 5 ng/mL.

Elderly

After application of one SYNERA patch for 20 minutes, plasma levels of lidocaine and tetracaine were not detectable in elderly subjects (> 65 years of age, mean 72.0 ±4.3 years, n=10). After simultaneous application of two SYNERA patches for 60 minutes to elderly subjects (> 65 years of age, mean 69.5 ±3.7 years, n=12), the maximum peak lidocaine concentration was 6 ng/mL and tetracaine was not detectable. During intravenous studies, the elimination half-life of lidocaine was statistically significantly longer in elderly patients (2.5 hours) than in younger patients (1.5 hours).

Cardiac, Renal and Hepatic Impairment

No specific pharmacokinetic studies were conducted. The half-life of lidocaine may be increased in individuals with cardiac or hepatic dysfunction. There is no established half-life for tetracaine due to rapid hydrolysis in the plasma.