Short answer: Yes, the label links Qsymia to kidney stones. In 1-year adult trials, stones occurred in 0.2% on the 7.5 mg/46 mg dose and 1.2% on 15 mg/92 mg, against 0.3% on placebo. The topiramate in Qsymia changes urine chemistry in ways that favor stones. The label advises drinking more fluids and avoiding other medicines that work the same way.
Qsymia combines phentermine with extended-release topiramate. The label reports kidney stones (nephrolithiasis) from its 1-year controlled trials in adults (section 6.1):
| Group | Kidney stones |
|---|---|
| Placebo | 0.3% |
| Qsymia 7.5 mg/46 mg | 0.2% |
| Qsymia 15 mg/92 mg | 1.2% |
The rise shows at the top dose. The label does not give a rate for doses below 7.5 mg/46 mg.
Topiramate blocks an enzyme called carbonic anhydrase. The label says this promotes stones by lowering citrate in the urine and raising urine pH (section 5.10). In a year-long study of children on topiramate, urine calcium went up and urine citrate fell sharply, and a higher calcium-to-citrate ratio raises the risk of stones.
The same effect can lower bicarbonate in the blood, a state called metabolic acidosis (section 5.7). In the adult trials, a persistent drop below the normal range (under 21 mEq/L) occurred in 6.4% on 7.5 mg/46 mg and 12.8% on 15 mg/92 mg, against 2.1% on placebo. Markedly low values (under 17 mEq/L) occurred in 0.2%, 0.7% and 0.1%. The drop usually peaked within 4 weeks and corrected in most people by week 56 without a dose change. The label says long-term untreated acidosis may raise the risk of kidney stones and of soft or thin bones.
The label names several things that can add to the effect:
The label also asks for blood tests including bicarbonate, creatinine and potassium before starting and during treatment (section 2.1), and limits the dose to 7.5 mg/46 mg in moderate or severe kidney impairment.
The label advises drinking more fluids to raise urine output, which may dilute the substances that form stones (section 5.10). The Medication Guide tells people to call their provider for severe pain in the side or back, or blood in the urine.
People with past stones, or who take calcium supplements, can ask the prescriber how that history fits with Qsymia. See calcium supplements and kidney stones. Dose Track can hold the dose, lab dates and symptom notes in one place for that visit.
Read more on Dose Track: Qsymia side effects · Qsymia dosing schedule · Phentermine-topiramate · Lomaira vs Qsymia