25.11
Oral Hypoglycemic Agents: Biguanides and Glitazones
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Q1: How do biguanides like metformin reduce blood glucose in type 2 diabetes?
Metformin enhances insulin sensitivity by reducing hepatic gluconeogenesis, the primary source of elevated blood glucose in type 2 diabetes. It also slows intestinal sugar absorption and boosts peripheral glucose uptake. Unlike sulfonylureas, metformin does not stimulate insulin secretion, thereby reducing hypoglycemia risk while promoting weight loss through appetite suppression.
Q2: What are the main contraindications and adverse effects of metformin therapy?
Metformin is contraindicated in renal dysfunction, acute myocardial infarction, sepsis, and conditions risking acute renal failure. Common adverse effects are gastrointestinal, including nausea, vomiting, and diarrhea, which can be mitigated by gradual dosage increases and mealtime administration. Long-term use may cause vitamin B12 deficiency, requiring monitoring.
Q3: How do thiazolidinediones work as insulin sensitizers?
Thiazolidinediones function as peroxisome proliferator-activated receptor-gamma (PPARγ) agonists, enhancing insulin sensitivity across various tissues. Unlike sulfonylureas, they do not stimulate insulin release from pancreatic beta cells, avoiding hyperinsulinemia. This mechanism allows them to reduce insulin resistance without triggering excessive insulin secretion.
Q4: What are the differences between pioglitazone and rosiglitazone in clinical use?
Pioglitazone is recommended as a second or third-line agent for type 2 diabetes treatment, while rosiglitazone use is limited due to potential cardiovascular risks. Both drugs are well absorbed orally and bind to serum albumin. Pioglitazone carries increased bladder cancer risk, whereas both agents can cause weight gain and osteopenia.
Q5: Why is metformin considered the drug of choice for initial type 2 diabetes treatment?
Metformin is the American Diabetes Association's recommended initial treatment for type 2 diabetes due to its effectiveness as an insulin sensitizer without stimulating insulin secretion. It can be used alone or combined with other agents or insulin. Its favorable safety profile, weight loss potential, and reduced hypoglycemia risk make it the preferred first-line agent.
Q6: What adverse effects should patients expect from thiazolidinedione therapy?
Thiazolidinediones commonly cause weight gain, edema, and osteopenia with increased fracture risk, particularly in women. Pioglitazone increases bladder cancer risk. Both drugs should be avoided in patients with severe heart failure. These adverse effects require careful patient monitoring and consideration when selecting thiazolidinediones for type 2 diabetes management.
Q7: Can metformin be combined with insulin, and what precautions are necessary?
Metformin can be combined with insulin for enhanced glucose control in type 2 diabetes. However, this combination may increase hypoglycemia risk, requiring careful dose adjustments of both medications. Close monitoring of blood glucose levels and patient education on hypoglycemia recognition are essential when using metformin with insulin therapy.