Bone Mineral Density 

Effects of multiple courses of Zenatane on the developing musculoskeletal system are unknown. There is some evidence that long-term, high-dose, or multiple courses of therapy with isotretinoin have more of an effect than a single course of therapy on the musculoskeletal system. In an open-label clinical trial (N=217) of a single course of therapy with Zenatane for severe recalcitrant nodular acne, bone density measurements at several skeletal sites were not significantly decreased (lumbar spine change >-4% and total hip change >-5%) or were increased in the majority of patients. One patient had a decrease in lumbar spine bone mineral density >4% based on unadjusted data. Sixteen (7.9%) patients had decreases in lumbar spine bone mineral density >4%, and all the other patients (92%) did not have significant decreases or had increases (adjusted for body mass index). Nine patients (4.5%) had a decrease in total hip bone mineral density >5% based on unadjusted data. Twenty-one (10.6%) patients had decreases in total hip bone mineral density >5%, and all the other patients (89%) did not have significant decreases or had increases (adjusted for body mass index). Follow-up studies performed in eight of the patients with decreased bone mineral density for up to 11 months thereafter demonstrated increasing bone density in five patients at the lumbar spine, while the other three patients had lumbar spine bone density measurements below baseline values. Total hip bone mineral densities remained below baseline (range –1.6% to –7.6%) in five of eight patients (62.5%).

In a separate open-label extension study of ten patients, ages 13-18 years, who started a second course of Zenatane four months after the first course, two patients showed a decrease in mean lumbar spine bone mineral density up to 3.25% (see PRECAUTIONS: Pediatric Use). 

Spontaneous reports of osteoporosis, osteopenia, bone fractures, and delayed healing of bone fractures have been seen in the Zenatane population. While causality to Zenatane has not been established, an effect cannot be ruled out. Longer term effects have not been studied. It is important that Zenatane be given at the recommended doses for no longer than the recommended duration. 

Hyperostosis 

A high prevalence of skeletal hyperostosis was noted in clinical trials for disorders of keratinization with a mean dose of 2.24 mg/kg/day. Additionally, skeletal hyperostosis was noted in 6 of 8 patients in a prospective study of disorders of keratinization.6 Minimal skeletal hyperostosis and calcification of ligaments and tendons have also been observed by x-ray in prospective studies of nodular acne patients treated with a single course of therapy at recommended doses. The skeletal effects of multiple Zenatane treatment courses for acne are unknown. 

In a clinical study of 217 pediatric patients (12 to 17 years) with severe recalcitrant nodular acne, hyperostosis was not observed after 16 to 20 weeks of treatment with approximately 1 mg/kg/day of Zenatane given in two divided doses. Hyperostosis may require a longer time frame to appear. The clinical course and significance remain unknown. 

Premature Epiphyseal Closure 

There are spontaneous reports of premature epiphyseal closure in acne patients receiving recommended doses of Zenatane. The effect of multiple courses of Zenatane on epiphyseal closure is unknown.