Skeleton Pirate

Skeleton Pirate
Artist: LindaB


Have you experienced, or read about, negative, and even dangerous, side effects from Fosamax (alendronate), Boniva (ibandronate), Actonel (risedronate), and other bisphosphonates prescribed for osteoporosis? If you have, then rest assured there is a safe, effective treatment for this condition. Strontium, primarily in the form of strontium citrate, is taken orally once a day.

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Monday, March 28, 2016

Strontium Interaction with Calcium and Food and Antacids

Most of us taking strontium know that for maximum absorption strontium must be taken at least two hours away from calcium supplements and dairy foods. Actually, strontium is best absorbed on an empty stomach, defined as at least two hours after eating. Food, milk and derivative products, and medicinal products containing calcium may reduce the bioavailability of strontium by about 60-70%.

Many are unaware that antacids should be taken at least two hours AFTER strontium. A study has shown that taking antacids containing magnesium hydroxide or aluminum hydroxide either together with strontium or two hours before strontium causes a 20-25% decrease in strontium absorption.

Here is a direct quote from Servier’s Summary of Product Characteristics (SPC) for Protelos (strontium ranelate):

“An in vivo clinical interaction study showed that the administration of aluminium and magnesium hydroxides either two hours before or together with strontium ranelate caused a slight decrease in the absorption of strontium ranelate (20-25% AUC decrease), while absorption was almost unaffected when the antacid was given two hours after strontium ranelate. It is therefore preferable to take antacids at least two hours after Protelos. However, when this dosing regimen is impractical due to the recommended administration of Protelos at bedtime, concomitant intake remains acceptable.”


Jane B. said...

The Servier warning was specifically about magnesium hydroxide, which is used as an antacid. Was there any clue as to the mechanism by which it interferes with absorption of strontium? I've been taking magnesium citrate at bedtime for its magnesium content, at the same time as my strontium. This makes me think I should reschedule something...

BoneLady said...

Dear Jane B.,

The Servier caution was specifically about antacids containing aluminum and magnesium hydroxide. I found out the company’s interaction studies used the antacid Maalox® and strontium ranelate (SR). The active ingredients in each 5-ml teaspoon of Maalox® are 200 mg aluminum hydroxide, 200 mg magnesium hydroxide, and 20 mg simethicone. Each teaspoon contains 25 mg calcium and 85 mg magnesium. The inactive ingredients are butylparaben, carboxymethylcellulose sodium, flavor, hypromellose, microcrystalline cellulose, propylparaben, purified water, saccharin sodium, simethicone emulsion, and sorbitol.

Servier does not give the mechanism by which antacids reduce the absorption of strontium, only that they do reduce it—but to a lesser extent than calcium does. When calcium competes with strontium for absorption, calcium wins. My educated guess is that magnesium also competes with strontium for absorption, although to a lesser degree. If you look at the Periodic Table, under column 2, you’ll see the following elements from top to bottom: Be, Mg, Ca, Sr, Ba, and Ra. See how close magnesium, calcium and strontium are on the table. That means they are closely related chemically. That is why they compete for absorption.

Servier recommends taking SR at bedtime at least two hours after eating. Food also reduces strontium absorption. I’ve always taken my SC near bedtime and several hours away from food and supplements.

I found the initial scientific discussion for the approval of Protelos. Here are some excerpts on interaction studies found on page 13 of the report:

“In vivo interaction studies have been performed with the antacid Maalox® and with Vitamin D supplementation. In addition, interactions with co-administered drugs were investigated in a Phase III population pharmacokinetic analysis. Vitamin D supplementation had no effect on the pharmacokinetics of Sr. Administration of Maalox® 2 hours after S12911 caused a 14% decrease in AUC (90% CIs within 80-125%), while administration 2 hours before or together with S12911 caused 20-25% decreases. When S12911 and an antacid like Maalox® are co-prescribed, the preferred dosing regimen would be to administer the antacid 2 hours after S12911 to achieve the highest bioavailability. However, when this dosing regimen is impractical due to the recommended administration of Protelos at bedtime, concomitant intake remains acceptable.”

“It can be concluded that few interaction studies have been performed with S12911 and other drugs. Since Sr and RA are not metabolised and no in vitro inhibitory potential was observed for Sr on CYP isoenzymes, interactions involving absorption are most likely to occur. Food, Ca and the antacid Maalox® reduced the bioavailability of Sr to different extents.”

BoneLady said...

Dear Jane B.

I have one more thought about the possible mechanisms by which antacids reduce strontium absorption. Because antacids raise stomach pH, they may make it more difficult to absorb strontium. Magnesium citrate would not have that alkalizing effect. However, magnesium could still compete for absorption with strontium because of its chemical similarity, as mentioned in my earlier comment.

Jane B. said...

I really appreciate your detailed response. That's very helpful! I'll change the timing of my strontium to make sure I get maximum benefit.

Wandering Skeleton

Wandering Skeleton
Artist: Joel Hoekstra

Osteoporotic Bone

Osteoporotic Bone

How Strontium Builds Bones

Strontium is a mineral that tends to accumulate in bone. Studies have shown that oral doses of strontium are a safe and effective way to prevent and reverse osteoporosis. Doses of 680 mg per day appear to be optimal. See my "For More Information About Strontium" links section.

Osteoporosis is caused by changes in bone production. In healthy young bones there is a constant cycle of new bone growth and bone removal. With age, more bone is removed and less new bone is produced. The bones become less dense and thus more fragile.

Scientists believe that strontium works in two ways. It may stimulate the replication of pre-osteoblasts, leading to an increase in osteoblasts (cells that build bone). Strontium also directly inhibits the activity of osteoclasts (cells that break down bone). The result is stronger bones.

When taking strontium, be sure to take 1200 mg calcium, 1000 IU vitamin D3, and 500 mg magnesium daily. It is best to take strontium late at night on an empty stomach. Calcium and strontium may compete with each other for absorption if taken together.