Antidote
PREGNANCY RECOMMENDATION: Limited Human Data—Probably Compatible
BREASTFEEDING RECOMMENDATION: No Human Data—Probably Compatible
PREGNANCY SUMMARY
Only three reports describing the use of black widow spider antivenin in pregnancy have been located. In each case, the maternal symptoms did not respond to other therapies but did within 1 hour to the antivenin. No fetal harm was observed in these cases. Although there is a risk of immediate hypersensitivity reaction, the risk can be reduced by sensitivity testing before administration (1). Because the maternal symptoms can be severe and do not always respond to other therapies, the antivenin should not be withheld because of pregnancy if the test for sensitivity is negative (2).
FETAL RISK SUMMARY
Black widow spider antivenin is used to treat patients with symptoms due to bites by the black widow spider (Latrodectus mactans). It is a sterile, nonpyrogenic preparation of specific venom-neutralizing globulins obtained from the blood serum of healthy horses immunized against the venom, a neurotoxin, of black widow spiders. It is given either IM or IV. A skin or conjunctival test should be preformed before administration of the antivenin to rule out sensitivity to horse serum (3).
Reproduction studies in animals have not been conducted, nor have studies for carcinogenesis, mutagenesis, and impairment of fertility (3).
It is not known if the globulins cross the human placenta. However, globulins are a family of proteins with high molecular weight. As such, it is doubtful if clinically significant amounts will cross to the embryo–fetus, although exposure in the 3rd trimester might occur.
The first published case of a black widow spider bite in pregnancy was in 1979 (4). A 20-year-old woman in her 16th week of pregnancy was bitten below the right breast. She experienced severe pain accompanied by abdominal and generalized muscle cramps. There was no cervical dilation, vaginal bleeding, or evidence of active labor. Fetal heart tones were 144 beats/minute. After skin testing, she was given an IV dose of antivenin and within 20 minutes was almost asymptomatic. She was discharged home the next day. About 18 weeks later, she gave birth by cesarean section to a healthy 3.7-kg male infant (4).
A 1994 case report described the pregnancy outcome of a 36-year-old woman at 22 weeks’ gestation who was bitten by a black widow spider (5). There was no vaginal bleeding and her cervix was long and closed. She experienced restlessness, pain, and muscle cramping and was treated with calcium gluconate, diazepam, and morphine. She had some relief but her symptoms soon returned. After a negative skin test, one 2.5-mL vial of the antivenin was administered IV over 15 minutes. Within 1 hour her symptoms resolved and she was discharged home the following day. No further details on her pregnancy were provided (5).
In a 2000 case report, a 27-year-old woman at 38 1/7 weeks was bitten by a black widow spider (6). Her symptoms included anxiety and severe abdominal, chest, and back pain. She had irregular uterine contractions and her cervix was dilated 1 cm, 50% effaced. She was initially treated with calcium gluconate, morphine, diazepam, and midazolam, but these agents were not effective in relieving her symptoms. After a negative conjunctival test, she was given the antivenin (dose and route not specified) and within 1 hour her symptoms had markedly decreased. She still had uterine contractions and her cervix was now 2 cm, 75% effaced. However, she was discharged home the next day after her contractions stopped and with no further changes in her cervix. One week later, she had a spontaneous vaginal birth of a healthy male infant (6).
BREASTFEEDING SUMMARY
No reports describing the use of black widow spider antivenin during breastfeeding have been located. It is doubtful if such reports will appear because the symptoms of the bites can be quite severe and would probably hinder any attempt to breastfeed. In addition, the antivenin is composed of globulins (i.e., proteins). Even if they were excreted into breast milk, they would probably be digested in the nursing infant’s gut. Thus, the limited data suggest that administration of the antivenin to the mother is compatible with breastfeeding.
References
1.Miller JR. Treatment of black widow spider bite. J Am Board Fam Pract 1994;7:183–4.
2.Bailey B. Are there teratogenic risks associated with antidotes used in the acute management of poisoned pregnant women? Birth Defects Res A Clin Mol Teratol 2003;67:133–40.
3.Product information. Antivenin—Latrodectus mactans. Merck Sharp & Dohme, 2010.
4.Russell FE, Marcus P, Streng JA. Black widow envenomation during pregnancy. Report of a case. Toxicon 1979;17:188–9.
5.Handel CC, Izquierdo LA, Curet LB. Black widow spider (Latrodectus mactans) bite during pregnancy. West J Med 1994;160:261–2.
6.Sherman RP, Groll JM, Gonzalez DI, Aerts MA. Black widow spider (Latrodectus mactans) envenomation in a term pregnancy. Curr Surg 2000;57:346–8.