SYNERA
Clinical safety rating: caution
Comprehensive clinical and safety monograph for SYNERA (SYNERA).
Lidocaine is an amide-type local anesthetic that stabilizes neuronal membranes by inhibiting sodium ion influx, thereby blocking nerve impulse initiation and conduction. Tetracaine is an ester-type local anesthetic that similarly inhibits sodium channels. The combination provides local dermal anesthesia.
| Metabolism | Lidocaine: Hepatic metabolism primarily via CYP3A4, also CYP1A2; major metabolite monoethylglycinexylidide (MEGX). Tetracaine: Hydrolysis by plasma pseudocholinesterase to para-aminobenzoic acid (PABA) and diethylaminoethanol. |
| Excretion | Renal excretion of lidocaine and prilocaine metabolites: lidocaine <10% unchanged, prilocaine negligible unchanged. Metabolites primarily renal. |
| Half-life | Lidocaine: 1.5–2 hours; prilocaine: 1–1.5 hours. Terminal half-life similar for both. Note: prolonged in hepatic impairment or neonates. |
| Protein binding | Lidocaine: ~70% bound to alpha-1-acid glycoprotein; prilocaine: ~55% bound to albumin. |
| Volume of Distribution | Lidocaine: 0.7–1.5 L/kg; prilocaine: 0.5–1.0 L/kg. Indicates distribution into peripheral tissues. |
| Bioavailability | Transdermal absorption: ~0.8–3.5% of applied dose systemically absorbed, resulting in low plasma concentrations. |
| Onset of Action | Onset of analgesia: approximately 1 hour after application to intact skin; maximal effect at 2–3 hours. |
| Duration of Action | Duration of analgesia: 1–2 hours after removal of patch; sufficiently long for minor procedures. |
Apply 1 patch (70 mg lidocaine and 70 mg tetracaine) to intact skin over the intended venipuncture site or superficial dermatologic procedure site 20-30 minutes prior to procedure; maximum 1 patch per procedure.
| Dosage form | PATCH |
| Renal impairment | No dose adjustment required for renal impairment. Use with caution in severe renal impairment due to potential accumulation of metabolites. |
| Liver impairment | No dose adjustment required for mild to moderate hepatic impairment. Use with caution in severe hepatic impairment (Child-Pugh class C) due to reduced metabolism of lidocaine and tetracaine. |
| Pediatric use | Children aged 3 years and older: Apply 1 patch to intact skin over the intended site 20-30 minutes prior to procedure. Safety and efficacy not established in children under 3 years. |
| Geriatric use | No specific dose adjustment recommended; use with caution due to potential increased sensitivity to adverse effects such as dizziness or hypotension. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for SYNERA (SYNERA).
| Breastfeeding | Lidocaine and tetracaine are excreted into breast milk in low amounts following systemic administration. The milk-to-plasma (M/P) ratio for lidocaine is approximately 0.4. For tetracaine, M/P ratio is unknown but expected to be low due to high protein binding and rapid metabolism. Topical application of SYNERA results in minimal systemic absorption; therefore, the amount transferred to the infant via milk is negligible. The American Academy of Pediatrics considers lidocaine compatible with breastfeeding. No specific adverse effects in breastfed infants have been reported. Caution if applied to breast area. |
| Teratogenic Risk | SYNERA (lidocaine 70 mg and tetracaine 70 mg topical patch) is classified as FDA Pregnancy Category B. Animal reproduction studies have not demonstrated fetal risk, but no adequate and well-controlled studies in pregnant women. Lidocaine and tetracaine can cross the placenta. In the first trimester, theoretical risk of teratogenicity is considered low due to minimal systemic absorption from topical application. In the second and third trimesters, no specific fetal risks are documented, but caution remains due to potential systemic effects (e.g., maternal hypotension or arrhythmias) that could reduce placental perfusion. Use only if clearly needed. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to lidocaine or tetracaine (or any amide- or ester-type anesthetics)","Hypersensitivity to para-aminobenzoic acid (PABA) or its derivatives"]
| Precautions | ["Methemoglobinemia risk, especially in patients with glucose-6-phosphate dehydrogenase deficiency, congenital or idiopathic methemoglobinemia, or concurrent oxidant exposure.","Use with caution in patients with hepatic impairment, severe renal impairment, or those taking class III antiarrhythmics.","Avoid application to broken skin or mucous membranes.","May cause local skin reactions (erythema, edema, blanching).","Do not use on large body surface areas."] |
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| Fetal Monitoring | Monitor maternal vital signs (heart rate, blood pressure) for signs of systemic toxicity (e.g., CNS excitement, arrhythmias). Assess for local skin reactions (erythema, edema). In pregnancy, monitor fetal heart rate and uterine activity if used during labor. No specific fetal monitoring is mandated for outpatient use, but vigilance for maternal adverse effects that could affect the fetus is recommended. |
| Fertility Effects | No evidence that SYNERA impairs fertility in humans. Animal studies have not shown effects on mating or fertility. Lidocaine and tetracaine are not known to affect reproductive organs or gamete function. |