Risk Factor: C*
Class: Central nervous system drugs/ Narcotic agonist-antagonist analgesics

Contents of this page:
Fetal Risk Summary
Breast Feeding Summary

Fetal Risk Summary

No reports linking the use of pentazocine with congenital defects have been located. As reported by the manufacturer, reproductive studies in animals did not found embryotoxic or teratogenic effects (1). In a 1975 Reference, however, increasing single SC doses of pentazocine (98570 mg/kg) administered to hamsters during the critical period of central nervous system (CNS) organogenesis resulted in a significant increase in the number of offspring with malformations (exencephaly, cranioschisis, and various other CNS lesions) (2). Maternal death was observed in 10% of the mothers at the highest dose, but not with the lower doses.

The drug rapidly crosses the placenta, resulting in cord blood levels of 40%70% of maternal serum (3). Withdrawal has been reported in infants exposed in utero to chronic maternal ingestion of pentazocine (4,5,6,7 and 8) . Symptoms, presenting within 2448 hours of birth, consist of trembling and jitteriness, marked hyperirritability, hyperactivity with hypertonia, high-pitched cry, diaphoresis, diarrhea, vomiting, and opisthotonic posturing.

During labor, increased overall uterine activity has been observed after pentazocine, but without changes in fetal heart rate (9). In equianalgesic doses, most studies report no significant differences between meperidine and pentazocine in pain relief, length of labor, or Apgar scores (10,11,12,13,14 and 15) . However, meperidine in one study was observed to produce significantly lower Apgar scores than pentazocine, especially in repeated doses (16). Severe neonatal respiratory depression may also occur with pentazocine (10,16).

A 1982 report from New Orleans described 24 infants born of mothers using the IV combination of pentazocine/tripelennamine (T’s and blue’s) (17). Doses were unknown, but probably ranged from 200 to 600 mg of pentazocine and 100 to 250 mg of tripelennamine. Six of the newborns were exposed early in pregnancy. Birth weights for 11 of the infants were less than 2500 g; 9 of these were premature (
Three cases of maternal bacterial endocarditis were observed following IV drug abuse, one of which involved the injection of pentazocine/tripelennamine intermittently throughout pregnancy (18). Following satisfactory antibiotic treatment for the infection, the mother gave birth at term to a healthy, male infant.

In a study published in 1983, three groups of pregnant women were evaluated in a perinatal addiction program in the Chicago area (19). One group (N=13) was composed of women addicted to pentazocine/tripelennamine. A second group consisted of women who conceived while self-administering heroin, and who were then converted to low-dose (540 mg/day) methadone (N=46). The third group consisted of drug-free controls (N=27). The three groups were statistically similar as to mean maternal age, educational level, gravidity, cigarette smoking, and mean weight gain during pregnancy. Heavy alcohol users were excluded. All infants were delivered at term. Apgar scores were similar among the three groups of newborns, and no significant perinatal complications were observed. Mean birth weight, length, and head circumference were similar between the two drug groups. Compared with the drug-free controls, the pentazocine/tripelennamine-exposed infants weighed less (2799 vs. 3479 g, p
In 1986, nearly the same data as above were published but with the addition of a group exposed to mixed sedative/stimulant (N=22) and a group exposed to phencyclidine (N=9) (20). The outcome of the pentazocine/tripelennamine group was the same as above.

Another study described the effects of pentazocine/tripelennamine abuse in 50 pregnancies identified retrospectively from a total of 23,779 deliveries occurring between January 1, 1981, and June 30, 1983 (21). Compared with matched controls, users of the combination were more likely to have no prenatal care (p
A study published in 1993 examined the effects on the fetus and newborn of IV pentazocine and methylphenidate abuse during pregnancy (22). During a 2-year (19871988) period, 39 infants (38 pregnancies, 1 set of twins) were identified in the study population as being subjected to the drug abuse during gestation, a minimum incidence of 5 cases per 1,000 live births. Many of the mothers had used cigarettes (34%) or alcohol (71%) or abused other drugs (26%). The median duration of IV pentazocine and methylphenidate abuse was 3 years (range 19 years), with a median frequency of 14 injections/week (range 170 injections/week). Among the infants, 8 were delivered prematurely, 12 were growth-retarded, and 11 had withdrawal symptoms after birth. Four of the infants had birth defects, including twins with fetal alcohol syndrome, one with a ventricular septal defect, and one case of polydactyly. Of the 21 infants that had formal developmental testing, 17 had normal development and 4 had low-normal developmental quotients (22).

In summary, pentazocine does not appear to cause structural malformations in humans, but behavioral teratogenicity, either from the drug itself, the mother’s lifestyle, other drug abuse, or a combination of these factors, is a common finding. Moreover, its abuse during pregnancy is associated with intrauterine growth retardation and withdrawal in the newborn.

[*Risk Factor D if used for prolonged periods or in high doses at term.]

Breast Feeding Summary

No reports describing the use of pentazocine during lactation have been located. The relatively low molecular weight (about 285), however, probably indicates that the drug is excreted into milk. The effects of this predicted exposure on a nursing infant are unknown, but small, infrequent doses most likely present a minimal risk.



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