Monday, January 12, 2009

Help! My Bone Density Is Decreasing On Forteo...

I recently received a question from an out-of-state patient whose bone mineral density did not improve after the first year of Forteo. It's uncommon for bone density to not improve on Forteo, however, in this post, I'll list some common reasons we see in our patient population. This is meant to clear up confusion rather to provide medical advice--always speak with your physician.

Common Causes
Here are a couple of common causes of this problem, from my experience.

1. Unknown cause (idiopathic): First of all, sometimes we can't identify a reason. Despite appropriate evaluation and follow-up, bone density doesn't increase on teriparatide (Forteo).

2. Secondary osteoporosis: When we do identify a cause, however, one of the most common reasons we see patients who don't improve with teriparatide (Forteo) therapy is an underlying medical disorder, usually severe vitamin D deficiency. There are upwards of twenty other medical causes--anything from hormonal imbalance to idiopathic hypercalcuria.

3. Other Medications: Another commonly identified cause is a drug interaction or side effect. Some diuretics can directly cause calcium loss through the kidneys. This is very common with loop diuretics, such as furosemide (Lasix), and bisphosphonates, such as Fosamax and Actonel, basically kill off osteoclasts--the cells that take up old bone (by contrast, osteoblasts are the cells that lay down new bone). In this case, it can take a while for the osteoclasts to be replaced after the bisphosphonate is stopped. From a biological standpoint, different people seem to react to the above issues differently.

4. Nutrition/Absorbtion Causes: Sometimes the cause is basic nutrition--patients may not have adequate calcium or vitamin D in their diets to lay down new bone. Some medications can decrease absorbtion of these nutrients. In addition, certain inflammatory gastrointestinal conditions, such as Celiac disease or nontropical sprue can cause malabsorption, leading to deficiency of vitamin D (among other things). This can also be a problem after gastric bypass, although this is not commonly seen (most bypass patients are younger than osteoporosis patients).

What Can You Do To Help
It's important to at least check a vitamin D level before STARTING Forteo, but this guideline isn't always followed. Unfortunately, I have seen two patients in the last year who continued to lose or didn't improve after even two years. Both patients had vitamin D deficiency--apparently their doctor (not me) didn't check the level before they started.

In summary, though it's common to not change or continue to lose measured bone density after other therapy, it's uncommon to not improve in after the first year of Forteo. If this should occur, it should definitely prompt an investigation by your physician.

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