Hypoglycemia or long QT? From Rapa or acarbose?

Got an interesting side effect to report, and hope the hive mind, especially the MDs, might help tease out the likely culprit:

My husband reluctantly hopped on the rapa + acarbose bandwagon a couple of months ago and has experienced more positive results than me — best energy in years, mental sharpness, weight loss. Everything was going great until about two weeks ago:

We had just returned from a cruise where he ate very poorly (i.e., pigged out). And to help go back to normal, he fasted in the morning and drank a lot more water than usual. Around noon all of a sudden he went from normal to nearly passing out: heart felt “weird,” tingling in his feet, swollen feeling in the head, nearly feinted. I called 911 and the paramedics checked his vitals. BP looked great, heart seemed great in the ECG, except the T wave pattern, which they said was suggestive of dehydration or electrolyte imbalance. Since he had been fasting AND drinking a ton of water, the paramedics chalked it up to that. As soon as he drank an electrolyte mix + Gatorade he felt much better and pretty much back to normal after dinner.

Then the day before yesterday it started happening again — this time he recognized the very first seconds of the feeling and nipped it in the bud with Gatorade. He had taken rapa the night before (5 mg + GFJ). Also the night before he had been out drinking with friends and had 6 strong beers (not normal for him, it was a celebration). He’d also had a carb heavy meal that night out, with acarbose. I had explained to him that he can’t take it with alcohol in the mix as it might dangerously lower his glucose levels but he forgot.

Today again mid afternoon, on his way to his doctors for a physical and fasting for eight hours, he started having the slightest hints of a recurrence and as soon as he ate a few pistachios it went away.

Now, I wonder, could the acarbose + intermittent fasting (or just skipping breakfast) lead to hypoglycemia? That itself can lengthen the QTc interval.

I have read that the naringin in the grapefruit juice can significantly lengthen QT intervals and he had had GFJ with the rapa the night before the second occurrence.

Rapa itself can cause hypokalemia and hypomagnesemia which can trigger QT interval lengthening.

Checked this forum for similar symptoms but couldn’t find anything unless I’ve just missed it somehow.

He just saw his physician today, who was agnostic about rapa — though of course wouldn’t dabble with it himself. He seemed to lean toward hypoglycemia being at the root of it as the likeliest explanation.

It would explain why Gatorade made it better right away, and so did the pistachios today. I would agree with him but I don’t understand why the sudden hypoglycemia— rapa if anything tends to increase glucose blood levels. And acarbose doesn’t cause hypoglycemia according to my research. Also a few pistachios don’t bring that much sugar with them. But they pack magnesium and potassium.

He doesn’t want to necessarily stop either medication as he feels great other than this, but is a bit spooked out and wants answers.

Anything you suggest short of biting the bullet on a continuous glucose monitor to see if his levels drop precipitously and coincide with symptom onset?

Looking for food for thought. I understand I’m not soliciting medical advice. Also he just had his physical today. Will report back on his bloodwork—curious what his fasted glucose level was.

And nothing else is new in his life and diet but rapa and acarbose — so pretty sure it’s one or the other or both.

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Might be potassium levels, rapamycin is know to lower potassium. Low potassium might cause you to feel lightheaded or faint.

Side effect frequencies
Very common: may affect more than 1 in 10 people

Increased fat in the blood (cholesterol and/or triglycerides), increased blood sugar, low blood
potassium, low blood phosphorus, increased lactate dehydrogenase in the blood, increased
creatinine in the blood


I believe your husband is not diabetic? In that case alcohol has no real potential to cause hypoglycemia. Alcohol IMO has no adverse effect on blood sugar together with acarbose (since acarbose does not effect absorption or digestion of alcohol). Alcohol can cause hypoglycemia in diabetics on its own.

You’re correct that he doesn’t have diabetes—unless he developed it just recently (he had gone a couple years without a physical, but this is highly unlikely).

He has once had a panic attack, years ago. The doctor said that any similar circumstances—not just stress but even low blood sugar—could precipitate his vagal nerve toward that fainting physiological response. But he seemed to think it was possible to have a hypoglycemia of sorts triggered by diabetic medication.

Would his low potassium show in the blood work he had done within hours of this episode?

It would not show if he supplemented potassium with Getorade or possibly pistachios I would think.
Both contain potassium, pistachios are really good potassium supplement. But I would not know how low potassium level should affect QT interval and how low should it be to feel lightheaded or faint and if potassium is indeed reduced by rapamycin and how well it was substituted. I am just guessing from what you described. I would not lean to hypoglycemia since rapamycin will reduce secretion of insulin and thus elevate glucose. Acarbose would affect only postprandial glucose. And if his EKG showed prolonged QT interval which is also a telltale sign of hypokalemia (low potassium serum levels) and rapamycin may lower potassium this seems more plausible IMO.

Yes I am leaning in the same direction.

Both potassium and magnesium can be lowered by rapa. And either deficiency can cause such a spell. Also the grapefruit juice apparently lengthens QT intervals (though he had only taken grapefruit juice once before an episode).

I have standalone magnesium maleate supplements but nothing for potassium. Easier to get that through nuts / bananas probably. But I wish the blood work showed it clearly so we can narrow it down.

It seems like there’s a lot of discussion here about what might be the cause or how to fix a problem that I can’t discern exists.
What did the ekg show? What was wrong with the T waves? Was the QTc prolonged?
What was his glucose, potassium and magnesium levels?
Was any of this the cause of his symptoms? Or was it something else?

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The QT interval was lengthened. I will find the ekg printout for reference. The paramedics didn’t take his blood glucose when they came so I have no idea what that metric looked like during any of these spells. Also he just had his blood work done at the doctor’s but the results aren’t in yet. I’ll post once I have the lab results but since they weren’t taken exactly during the feinting spell it’s not a given that they’ll reveal exactly what was happening in those moments.

That’s exactly what I’m trying to find out, with imperfect data — as the magnesium / potassium / glucose levels were unknown during his near feinting spells.