CYCLOBENZAPRINE

Fetal Risk Summary

Cyclobenzaprine is a centrally acting skeletal muscle relaxant that is closely related to the tricyclic antidepressants (e.g., imipramine). The agent is not teratogenic or embryotoxic in mice, rats, and rabbits given doses up to 20 times the human dose (1). No published reports of its use in human pregnancy have been located.

In a surveillance study of Michigan Medicaid recipients involving 229,101 completed pregnancies conducted between 1985 and 1992, 545 newborns had been exposed to cyclobenzaprine during the 1st trimester (F. Rosa, personal communication, FDA, 1993). A total of 24 (4.4%) major birth defects were observed (23 expected), including (observed/expected) 5/5 cardiovascular defects, 1/1 oral clefts, and 2/2 polydactyly. No anomalies were observed in three other categories of defects (spina bifida, limb reduction defects, and hypospadias) for which data were available. Earlier data, obtained from the same source between 1980 and 1983, totaled 168 1st trimester exposures with 12 defects observed (10 expected). These combined data do not support an association between the drug and congenital defects.

Breast Feeding Summary

No reports are available on the excretion of cyclobenzaprine into milk. The molecular weight (about 312 for the hydrochloride salt), however, is low enough that excretion into milk should be expected. In addition, the closely related tricyclic antidepressants (e.g., see Imipramine) are excreted into milk and this should be considered before cyclobenzaprine is used during lactation.

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