Alendronate-induced auditory hallucinations and visual disturbances.

A 79-year-old Caucasian woman who had been taking alendronate 10 mg/day for over 2 years to prevent osteoporosis reported hearing "voices in her head" along with red-colored visual disturbances. These auditory hallucinations and visual disturbances began shortly after her regimen was changed from alendronate 10 mg/day to 70 mg once/week. Assessment of causality using the Naranjo and Jones algorithms revealed a "probable" and "highly probable" relationship, respectively, between this adverse drug event and the switch from daily to weekly alendronate therapy. Other bisphosphonates, such as etidronate and pamidronate, have caused both reversible and irreversible auditory, visual, and olfactory hallucinations beginning 2 hours--1 week after drug administration. The mechanism behind these adverse effects is unknown but is thought to be independent of calcium homeostasis. Clinicians should be aware of central nervous system toxicity as a rare but potential adverse effect associated with bisphosphonates.