A case study of a 62-year-old man in the US provides a prime example of why it's so important to keep a close eye on rapid weight loss while juggling medications.
At 132 kg (291 lbs), the man qualified as obese, a factor that may have contributed to his development of type 2 diabetes and may have been linked closely with another of his conditions, an underactive thyroid gland.
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Consequently his family doctor prescribed him with daily insulin injections, as well as a daily dose of a thyroid hormone replacement drug called levothyroxine. He was also told to take a weekly dose of the diabetes and weight loss drug tirzepatide (sold under the brand name Zepbound).
Tirzepatide is one of a growing number of popular weight loss drugs that mimic the hormones GLP-1 (glucagon-like peptide-1) and GIP (gastric inhibitory polypeptide) to manage blood sugar levels and appetite.
The treatment was so effective the man's weight dropped by 39 kg (86 lbs), or almost 30 percent of his body weight, in just six months.
Unfortunately, his weight loss came with a sting in the tail. Shortly after, the man presented himself to an emergency department suffering from "palpitations, excessive sweating, confusion, fever, and hand tremors", according to the case study written up by a team from the University of Colorado.
After getting checked out, it was revealed that the palpitations were a sign of atrial fibrillation; an irregular heartbeat condition that can trigger strokes and heart attacks. Further tests showed this had been brought on by thyrotoxicosis, which is an overabundance of a hormone produced by the thyroid.
Or, in this case, a medication designed to look just like it.
Dosages for many medications are weight based. So as the man lost weight, the relative dosage of levothyroxine crept higher. At his initial weight he was takening 1.5 μg per kilogram of his weight. By the end that had inadvertantly jumped to 2.15 μg per kilogram.
All of this could have been prevented if the man had adjusted his other medications in relation to his changing weight. The levothyroxine should have been adjusted as his weight changed to avoid the thyrotoxicosis and atrial fibrillation, according to the case study authors.
The man also missed a scheduled follow-up appointment with his doctor due to traveling, which may have played a part in this lapse in monitoring.
Losing a lot of weight quickly does come with potential risks, as well as all the health benefits, and previous studies have shown it's important to maintain good health in other areas while trying to shed the pounds.
Tirzepatide has proved very effective in tackling obesity – but when it comes to any extreme weight loss strategy, patients (and their existing medications) need to be closely monitored to prevent other health problems from arising.
"With the increasing use of tirzepatide and other GLP-1 analogues for the treatment of patients with obesity, we recommend evaluating patients using tirzepatide closely (every 4 to 6 weeks initially) for assessment of therapy response, adverse events, and possible dose adjustment of other concomitant medications," write the case study authors.
The research has been published in JAMA Internal Medicine.
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