Local Anesthesia and Breastfeeding

Topical Anesthetics

Topical anesthetics are generally not a serious concern for use during breastfeeding as long as they are not applied to the breast, nipple, or other parts of the body where the infant may ingest them directly. When ingested, topical anesthetics vary in their toxic potential from minor gastrointestinal symptoms to seizures, arrhythmias, and death. Topical anesthetics can also cause allergic contact dermatitis, so they are best kept away from the infant's skin. Most local anesthetics fall into one of two classes: esters and amides. Topical esters are more sensitizing than amides, but individual drugs vary in their sensitizing potential.

Cocaine is the prototype local anesthetic, having both anesthetic and vasoconstrictive properties. It is converted to inactive metabolites by plasma pseudocholinesterase after absorption into the bloodstream. Infants have low levels of pseudocholinesterase, making cocaine a particularly dangerous drug in infants. No data are available on the medical use of cocaine in nursing mothers, but it is available as a nasal solution for local anesthesia when performing procedures on or through the nasal cavities in a maximum dose of 160 mg. The manufacturer recommends not breastfeeding for 48 hours after use of cocaine nasal solution.

All of the information on cocaine during breastfeeding derives from cocaine abuse. For example, a mother used about 500 mg of cocaine intranasally over a 4-hour period and breastfed her 2-week-old infant five times during this period. The infant's urine had measurable cocaine at 4 and 12 hours, and it was detectable up to 60 hours after the mother's last dose. Another mother of an 11-day-old infant applied cocaine powder to her nipples for pain relief and then breastfed her infant. Three hours later, she found the infant gasping, choking and blue. On arrival at the emergency room, the infant was ashen and cyanotic. He had hypertension, tachycardia, shallow breathing, hypothermia, and was in status epilepticus. Seizures resolved in a few hours after treatment and the infant was discharged at 16 days of age with no apparent sequelae.

Benzocaine, which can cause methemoglobinemia, is found in many topical preparations, including some oral products for mouth and sore throat pain. Signs and symptoms of methemoglobinemia may appear within minutes to 1–2 hours after using benzocaine and may occur after using benzocaine for the first time or after several uses. Benzocaine gels and liquids should be used sparingly and only when needed, but not more than four times a day. The U.S. Food and Drug Administration recommends that benzocaine products are not to be used on children <2 years of age. ² Topical benzocaine has not been studied during breastfeeding, but it is unlikely to affect the breastfed infant if it is applied away from the breast. Because of its toxicity, it is particularly important not to apply benzocaine to the nipples.

Topical dibucaine has not been studied during breastfeeding but is unlikely to affect the breastfed infant if it is applied away from the breast. Direct ingestion of dibucaine products by toddlers has caused seizures, arrhythmias, cardiovascular collapse, and death.^3,4 There are also many reports of allergic skin reactions, including photosensitivity with dibucaine. Although dibucaine is an amide, its structure is somewhat different from other amides, and it appears not to cross-react in those sensitized to other amides.

Dyclonine is readily absorbed through the skin and mucous membranes. Its onset is rapid, and it has a short duration of action. Dyclonine is an active ingredient in many over-the-counter medications, including sore throat lozenges and topical solutions for minor wounds. A prescription strength topical solution is also available. Topical use is relatively safe, but allergic contact dermatitis has been reported after dyclonine use, so it is best kept away from the infant's skin.

Pramoxine is a topical anesthetic with a distinct chemical structure that does not cause cross-reactions in patients allergic to other local anesthetics. Direct ingestion of pramoxine has resulted mostly in nausea and vomiting, with no serious toxicity. ⁵ No adverse reactions have been reported in nursing women using pramoxine for the symptomatic relief of hemorrhoids or other anorectal conditions.

Tetracaine is available as topical and injectable solutions. If the solution is not applied to a part of the body where the infant might directly ingest it, the infant should not be adversely affected.

Injectable Anesthetics

Procaine was among the first synthetic local anesthetics, indicated by its U.S. brand name, Novocaine. Consequently, the term “Novocaine” has become synonymous with local anesthesia in the minds of many lay persons, much like “Scotch tape” has become synonymous with cellophane adhesive tape. Procaine is no longer marketed in the United States, so if a mother asks about “Novocaine” during breastfeeding, the exact local anesthetic should be determined.

Procaine, chloroprocaine, articaine, and tetracaine are all esters. No measurements have been made of any of these ester-type local anesthetics in breast milk. After absorption from the injection site, they are inactivated rapidly by plasma pseudocholinesterase and are unlikely to be found in milk in clinically relevant amounts. Injected tetracaine is inactivated more slowly than the other esters and has a longer duration of action.

The most commonly used injectable local anesthetics are the amides bupivacaine, lidocaine, mepivacaine, ropivacaine, and prilocaine. Levobupivacaine is no longer available in the United States. No information is available on the amounts of mepivacaine or prilocaine excreted into breast milk, but prilocaine can produce methemoglobinemia so it should probably not be used in nursing mothers. All of the amide local anesthetics have poor oral bioavailability; the low amounts that reach the infant's gastrointestinal tract in breast milk usually will not reach the infant's systemic circulation.

The most experience is with lidocaine. Two articles reported eight women undergoing dental anesthesia who received lidocaine with or without epinephrine. Milk lidocaine concentrations were all <150 mcg/L, or <1% of the maternal weight-adjusted dosage. Another woman undergoing tumescent liposuction received a large dose of 4.2 g of lidocaine into her body fat. Seventeen hours after the procedure, a milk lidocaine level was 550 mcg/L. Lidocaine is also used intravenously as an antiarrhythmic. One nursing mother who was 10 months postpartum received intravenous lidocaine 75 mg, then 50 mg 5 minutes later, concurrent with starting a continuous lidocaine infusion at a rate of 2 mg/minute. After 7 hours, the infusion was stopped, and a milk sample contained 800 mcg/L of lidocaine. Even with these higher dosages, milk levels were not a concern. Twenty-eight infants whose mothers received dosages of lidocaine by injection up to 500 mg have reportedly had no adverse effects from ingesting their mothers' milk.

One woman who was 10 months postpartum received bupivacaine 50 mg intrapleurally, followed in 1 hour by a continuous intrapleural infusion of 25 mg/hour for 5 days for operative and postoperative analgesia. Breastfeeding resumed postoperatively 22 hours after the start of the infusion. A serum sample taken from the infant 5 hours after the morning feeding on day 3 postoperatively (52.5 hours after the bolus dose) contained undetectable amounts of bupivacaine.

Information on ropivacaine is limited to epidural use during cesarean section. During maternal patient-controlled epidural analgesia in 25 women, the cumulative maternal dosages of ropivacaine at 18 and 24 hours averaged 188 and 248 mg, respectively. Colostrum ropivacaine concentrations at these times averaged 246 and 301 mcg/L, respectively. A neonate who ingests about 40 mL of colostrum would receive only 10–12 mcg of ropivacaine during the first 24 hours of life.

Summary

Lidocaine and bupivacaine have extensive documented use in nursing mothers and are the preferred injectable local anesthetics during breastfeeding. Topical anesthetics known to cause systemic toxicity after oral ingestion, such as benzocaine, cocaine, and dibucaine, should not be applied to the breast. In addition, many topical anesthetics can cause allergic contact dermatitis, so they should not be applied where the nursing infant can contact them.