Kidney stones 5 times more common in those given 15 mg of phentermine plus 92 mg of Topamax

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Kidney stones 5 times more common in those given 15 mg of phentermine plus 92 mg of Topamax

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Tuesday, April 26, 2011 11:03 am Email this article

Kidney stones were 5 times more common in people given 15 mg of phentermine plus 92 mg of Topamax (topiramate) than those given either a placebo or 7.5 mg of phentermine plus 46 mg of Topamax (topiramate) according to a new study from Duke University in Durham, North Carolina, USA. Kidney Stones

Kidney Stones in 11 out of 994 people given 15 mg of phentermine plus 92 mg of Topamax vs only 2 out of 993 given a placebo

There were 11 cases of kidney stones out of 994 people given 15 mg of phentermine plus 92 mg of Topamax (topiramate) (1%), including three serious adverse events—although they do not say exactly what the serious adverse events were in these patients with kidney stones—compared to only 2 cases of kidney stones out of 993 people given a placebo (0.2%) and only one case out of 498 given 7.5 mg of phentermine plus 46 mg of Topamax (topiramate).

What caused the kidney stones?

Topamax lowers potassium and bicarbonate levels

The increased risk of kidney stones may have been due to the fact that Topamax lowers both potassium, and more importantly, bicarbonate levels in the blood.

They found that potassium levels were below the lower limit of 3·5 mmol per liter in 5.3 percent of patients given 15 mg of phentermine plus 92 mg of Topamax (topiramate) versus 3.6 percent of those given 7.5 mg of phentermine plus 46 mg of Topamax (topiramate) versus 1.1 percent of patients given the placebo.

“Inhibition of carbonic anhydrase by topiramate [Topamax] presumably accounts for the paraesthesia and taste alteration, decreased concentrations of serum bicarbonate and potassium, and risk of nephrolithiasis [kidney stones],” the authors noted.

How to reduce the risk of kidney stones

Potassium Citrate or potassium bicarbonate lowered the risk of kidney stones 12-fold according to 1993 study

A supplement of potassium citrate reduced the number of kidney stones 12-fold over the next 3 years, from 1.2 stones per year to 0.1 stones per year in people who had a history of kidney stones according to a 1993 study (Barcelo et al, 1993).

Forty-two percent (42%) of patients (13 of 31) given potassium citrate had NO kidney stones over the next 3 years.

Potassium citrate is metabolized to potassium bicarbonate in the body, and both reduce urinary excretion of calcium, therefore, I assume potassium bicarbonate would work just as well at reducing kidney stones.

I’ve taken potassium bicarbonate for 11 years, since 2000, to reduce blood pressure. It has lots of benefits.

In 58% of patients (18 of 31) given potassium citrate, kidney stones were reduced 12-fold over the next 3 years, from 1.2 per year to 0.1 per year

Forty-two percent (42%) of patients (13 of 31) given potassium citrate had NO kidney stones over the next 3 years.

This compared to those given a placebo which had
- 1.1 stones per year while receiving the placebo vs 1.1 per year prior to the study, and
- 20% of patients (4 of 20) had no stones over the next 3 years.

Subjects

Subjects: 2487 overweight and obese patients

The study wad done at 93 centers in the US and involved 2487 overweight and obese patients who were 18- to 70-years-old, with an average age of 51.

Seventy percent (70%) of subjects were women.

994 were assigned to placebo
498 were given 7.5 mg of phentermine plus 46 mg of topiramate (Topamax)
995 were given 15 mg of phentermine plus 92 mg of topiramate (Topamax)

Body Weight

Average body weight: 226 lbs; BMI 36-37

The average body weight of the subjects was 226 pounds.

The average body mass index (BMI) was 36-37.

REFERENCE

Gadde K, Allison D, Ryan D, Peterson C, Troupin B, Schwiers M, Day W. Effects of low-dose, controlled-release, phentermine plus topiramate combination on weight and associated comorbidities in overweight and obese adults (conquer): A randomised, placebo-controlled, phase 3 trial. Lancet. 2011 Apr 16, 377(9774):1341-52.

AUTHOR’S CONTACT INFORMATION

Dr Kishore M Gadde
Obesity Clinical Trials Programme
Box 3292
Duke University Medical Center
Durham, NC 27710, USA
.(JavaScript must be enabled to view this email address)

OTHER REFERENCE

Barcelo P, Wuhl O, Servitge E, Rousaud A, Pak C. Randomized double-blind study of potassium citrate in idiopathic hypocitraturic calcium nephrolithiasis. J Urol. 1993 Dec, 150(6):1761-64.

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