Over the past few weeks, Sheri Colberg, Ph.D., FACSM, has focused on insulin and oral medications and their relationship to exercise and many of you asked about Byetta and Symlin. This week she covers them in Diabetic Medications and Exercise, Part 2: Use of Byetta and Symlin.
Diabetic Medications and Exercise, Part 2: Use of Symlin and Byetta
By Sheri Colberg, Ph.D., FACSM
In Part 1, we discussed the use of oral diabetic medications, such as sulfonylureas, TZDs, and others. In this column, newer medication choices like Symlin and Byetta are discussed.
The turn of the millennium brought the first new drug to treat Type 1 diabetes in over 80 years since the discovery of insulin in 1921. The medication is called Symlin (generic name: pramlintide). It is a synthetic form of the body’s natural hormone, amylin, normally released along with insulin from pancreatic beta cells. Its main action is to improve the action of insulin after meals by slowing down how quickly the glucose coming from the food that you’ve eaten shows up in your circulation. If you normally take or pump insulin to control your postmeal highs, then your body likely is not releasing enough of this hormone naturally. Replacing it will likely even out your blood sugars after eating, make you feel full sooner while eating, and potentially cause weight loss. As an added benefit, Symlin may also reduce oxidative stress and prevent you from developing diabetic complications, although this potential effect needs further study. Its potential side effects are severe hypoglycemia (blood glucose levels below 55 mg/dl, or 3.1 mmol/L, more common in insulin users), nausea, vomiting, abdominal pain, headache, fatigue and dizziness. Another drawback is that it must be injected.
Many Type 1 diabetic exercisers have tried Symlin. Bill King, a marathon runner from Aston, Pennsylvania, has found that using Symlin, taken at the same time as his insulin boluses, helps him correct his blood sugars more rapidly when he becomes hyperglycemic following a big meal. To deal with the nausea that it often causes, some people have tried pumping basal doses of Symlin (using an insulin pump filled with Symlin) instead of giving premeal injections with higher doses and found that this off-label delivery method works better for them. You may need to be careful about taking Symlin before exercising, however, because it can make hypoglycemia harder to treat by slowing the absorption of anything that you eat to raise low blood sugars. Some athletes have complained about getting Symlin lows that they can’t easily treat during and following exercise. In addition, if you have gastroparesis (delayed emptying of the contents of your stomach because of damage to the central nerves by diabetes), you may not want to use Symlin at all because it can cause more frequent, severe hypoglycemia by further slowing your already less-rapid absorption of food.
Another new medication made by the Symlin manufacturers is called Byetta (exenatide), which is an injectable medication mainly intended for the treatment of Type 2 diabetes, although some people with slow-onset Type 1 in adulthood have used it to try to regenerate their beta cells. Like Symlin, Byetta causes food to empty from the stomach more slowly and blood glucose levels to stay more stable after meals. Byetta also stimulates the pancreas to make more insulin (which will obviously not work in most Type 1s), keeps the liver from overproducing glucose, and in most users results in weight loss. This new class of medications effectively replaces natural hormones released by the digestive tract (gut hormones) after meals to spur insulin release and provides another choice for diabetes treatment, particularly if your treatment with oral medications is no longer working effectively. Byetta does have to be injected (rather than ingested) twice a day, which may not appeal to you if you’ve shied away from insulin therapy to avoid taking shots. Recent studies, however, have suggested that Byetta therapy may be as effective as insulin.
Another potential drawback of Byetta is that it may negatively affect your ability to exercise. Janis Eggleston, a Type 2 diabetic athlete from Berkeley, California, reported the following: “I have never been able to cycle with Byetta on board without throwing up, feeling weak, losing steam, and having ‘no legs’ to pedal with. I learned to drop that med early in my training season.” In fact, she never takes Byetta when cycling over 65 miles (105 kilometers) in one day because she gets major low blood sugars if she does. Also, she can’t take her usual dose of metformin either because it impedes her liver from producing enough glucose to keep her blood sugars stable. When riding long distances, she only takes her evening dose of metformin. Similarly, Tom Seabourne, a Type 1.5 diabetic cyclist from Mt. Pleasant, Texas, says, “I have had extreme lows with Byetta, so I dropped to a single dose of 10 units before dinner. I tried Byetta before breakfast for a while, but it turned me into a vegetable until lunchtime. I would never consider taking Byetta before a workout!”
In conclusion, the more you know about your diabetic medications, their actions, and how they may be affected by exercise, the easier it will be for you to make adjustments to have as normal a physiological response to your physical activities as possible. You will undoubtedly have to suffer through some trial and error to figure out how best to manage all these variables, but many diabetic athletes do it successfully, and so can you. The key things to remember are the following: (1) if you don’t have diabetes, your insulin levels go down while the levels of other glucose-raising hormones rise during exercise, more so when you’re working out hard; (2) how much insulin you have in your bloodstream during exercise affects whether your blood sugars stay normal, go down too much, or even rise; and (3) other diabetic medications like certain sulfonylureas, Symlin, and Byetta also increase your risk for hypoglycemia during exercise and may need to be adjusted for your physical activity.
This column is excerpted from Diabetic Athlete’s Handbook (released November 2008 from Human Kinetics), which contains essential exercise-related information and examples for Type 1 and Type 2 diabetic exercisers. Look for it in stores or find links to places to buy it online at www.shericolberg.com, along with additional information.