Risk Factor: BM
Class: Cardiovascular drugs/ Cardiac drugs

Contents of this page:
Fetal Risk Summary
Breast Feeding Summary
Questions and Answers

Fetal Risk Summary

Lidocaine is a local anesthetic that is also used for the treatment of cardiac ventricular arrhythmias. The majority of the information on the drug in pregnancy derives from its use as a local anesthetic during labor and delivery. Reproduction studies have revealed no evidence of fetal harm in pregnant rats at doses up to 6.6 times the human dose (1).

The drug rapidly crosses the placenta to the fetus, appearing in the fetal circulation within a few minutes after administration to the mother. Cord:maternal serum ratios range between 0.50 and 0.70 after IV and epidural anesthesia (2,3,4,5,6,7,8,9,10,11 and 12). In 25 women just before delivery, a dose of 23 mg/kg was given by IV infusion at a rate of 100 mg/minute (2). The mean cord:maternal serum ratio in 9 patients who received 3 mg/kg was 0.55. A mean ratio of 1.32 was observed in nonacidotic newborns following local infiltration of the perineum for episiotomy (13). A similarly elevated ratio was measured in an acidotic newborn (14). The infant had umbilical venous/arterial pH values of 7.23/7.08 and a lidocaine cord:maternal serum ratio of 1.32 following epidural anesthesia. Because lidocaine is a weak base, the high ratio may have been caused by ion trapping (14).

Both the fetus and the newborn are capable of metabolizing lidocaine (8,9). The elimination half-life of lidocaine in the newborn following maternal epidural anesthesia averaged 3 hours (8). After local perineal infiltration for episiotomy, lidocaine was found in neonatal urine for at least 48 hours after delivery (13).

A number of studies have examined the effect of lidocaine on the newborn. In one report, offspring of mothers receiving continuous lumbar epidural blocks had significantly lower scores on tests of muscle strength and tone than did controls (15). Results of other tests of neurobehavior did not differ from those of controls. In contrast, four other studies failed to find adverse effects on neonatal neurobehavior following lidocaine epidural administration (10,11 and 12,16). Continuous infusion epidural analgesia with lidocaine has been used without effect on the fetus or newborn (17).

Lidocaine may produce central nervous system depression in the newborn with high serum levels. Of eight infants with lidocaine levels greater than 2.5 g/mL, four had Apgar scores of 6 or less (3). Three infants with levels above 3.0 g/mL were mildly depressed at birth (3). A 1973 study observed fetal tachycardia (3 cases) and bradycardia (3 cases) after paracervical block with lidocaine in 12 laboring women (18). The authors were unable to determine whether these effects were a direct effect of the drug. Accidental direct injection into the fetal scalp during local infiltration for episiotomy led to apnea, hypotonia, and fixed, dilated pupils 15 minutes after birth in one infant (19). Lidocaine-induced seizures occurred at 1 hour. The lidocaine concentration in the infant’s serum at 2 hours was 14 g/mL. The heart rate was 180 bpm. Following successful treatment, physical and neurologic examinations at 3 days and again at 7 months were normal.

Lidocaine is the treatment of choice for ventricular arrhythmias (20,21). A 1984 report described the use of therapeutic lidocaine doses (100 mg IV injection followed by 4 mg/minute infusion) in a woman who was successfully resuscitated after a cardiac arrest at 18 weeks’ gestation (22). A normal infant was delivered at 38 weeks’ gestation. Neurologic development was normal at 17 months of age, but growth was below the 10th percentile.

The Collaborative Perinatal Project monitored 50,282 mother-child pairs, 293 of which had exposure to lidocaine during the 1st trimester (23, pp. 358363). No evidence of an association with large classes of malformations was found. Greater than expected risks were found for anomalies of the respiratory tract (3 cases), tumors (2 cases), and inguinal hernias (8 cases), but the statistical significance is unknown and independent confirmation is required (23, pp. 358363, 477). For use anytime during pregnancy, 947 exposures were recorded (23, pp. 440, 493). From these data, no evidence of an association with large categories of major or minor malformations or to individual defects was found.

Breast Feeding Summary

Small amounts of lidocaine are excreted into breast milk (24). A 37-year-old, lactating woman was treated with intravenous lidocaine for acute onset ventricular arrhythmia secondary to chronic mitral valve prolapse. The woman had been nursing her 10-month-old infant up to the time of treatment. She was treated with lidocaine, 75 mg over 1 minute, followed by a continuous infusion of 2 mg/minute (23 g/kg/minute). A second 50-mg dose was given 5 minutes after the first bolus dose. The woman’s serum lidocaine level 5 hours after initiation of therapy was 2 g/mL. The drug concentration in a milk sample, obtained 2 hours later when therapy was stopped, was 0.8 g/mL (40% of maternal serum). Although the infant was not allowed to nurse during and immediately following the mother’s therapy, the potential for harm of the infant from exposure to lidocaine in breast milk is probably very low. The American Academy of Pediatrics considers lidocaine to be compatible with breast feeding (25).



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