Good Evening, Thanks for given information,carefully I have checked both medicine combinations,but Anastrazole create osteoporosis back pain anastrozole had a mean decrease in both lumbar spine and total hip bone mineral density (BMD) compared to baseline. Caution should exercised when prescribing this agent to patients with a risk of fractures, such as the elderly and patients with osteoporosis. Consider bone mineral density monitoring in patients treated with anastrozole. I think if you stop Anastrazole you will be safe from back pain Gabapentin you can take for pain, further if you want to take Anastrazole you need to check your Essential minerals level from laboratory