One class of medicines that has been shown to raise glucose levels is called the glucocorticoids. This includes such drugs as prednisone, dexamethasone, and triamcinolone. These drugs are called glucocorticoids because they have a profound effect on carbohydrate metabolism. They also have very powerful anti-inflammatory effects and are usually reserved for serious medical conditions that require a substantial reduction in inflammation, such as rheumatoid arthritis, severe asthma, or inflammatory bowel disease.
Glucocorticoids counteract the effect of insulin on the liver and stimulate the production of glucose. They also block the entry of glucose into the muscles and fat tissue by preventing glucose-transport proteins in the cells of those tissues from reaching the cell membrane, where they normally serve to remove glucose from the blood. These drugs have many other serious side effects, including osteoporosis, suppression of the adrenal glands, and cataracts. For these reasons, they are only used when the possible benefits outweigh the risks. Many of these drugs are now available in an inhaled form for asthma or an intranasal form for allergies. These forms of delivery are associated with far fewer side effects than oral forms, including those related to the body’s use of glucose.
High blood pressure is itself a significant risk factor for Type 2 diabetes, but some of the drugs used to treat it also appear to raise the risk of developing diabetes.
Thiazide diuretics are a class of drugs that treat high blood pressure by blocking the reabsorption of sodium in the kidneys. As part of this process, potassium is also lost in the urine. This results in a lower level of potassium in the blood, a condition known as hypokalemia. Many people who take this type of blood-pressure-lowering drug also need to take potassium supplements to keep their blood levels of potassium in the normal range. As noted earlier, potassium levels are closely linked with both insulin secretion and glucose uptake into muscle and fat tissue.
Multiple studies have looked at the effect of thiazide diuretics on blood glucose levels, and the majority suggest that these drugs tend to raise blood glucose. The most recent study was ALLHAT (Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial). In this trial, whose results were published in 2006, participants were given one of several different types of medicine to treat their high blood pressure, to try to determine the best type of therapy. Based on a subgroup analysis of approximately 18,000 people without diabetes who were treated and followed for an average of five years, the risk of developing diabetes was slightly higher in those who took a thiazide diuretic (14%) compared to those who took two other types of blood-pressure-lowering drugs, a calcium channel blocker (11.1%) or an angiotensin-converting enzyme (ACE) inhibitor (9.5%).
While this difference may seem small, when these percentages are applied to the millions of people with high blood pressure, many more will develop diabetes on a thiazide diuretic than on a different type of drug. However, choosing a drug to treat high blood pressure is not a simple issue, since ALLHAT also showed that thiazide diuretics were superior to or equally as effective as other classes of blood-pressure-lowering drugs in people with diabetes.
When ALLHAT investigators specifically looked at study participants who had diabetes, they found that these people tended to do well on thiazide diuretics but also had, on average, a small increase in blood glucose (5 mg/dl). Many other large studies have also noted this effect.