Patients taking the meglitinide repaglinide (Prandin, GlucoNorm, NovoNorm) should not start taking a cholesterol-controlling drug called gemfibrozil (Lopid), and vice versa, because the combination may prolong repaglinide's glucose-lowering effect, according to the U.S. Food and Drug Administration (FDA).

Nor should people take repaglinide in combination with NPH insulin (an intermediate-acting insulin no longer available in the United States) because of risk of myocardial ischemia (inadequate oxygen supply to heart tissue), the FDA advises.

Physicians may instruct patients not to take meglitinides with sulfonylureas. Patients should consult a physician before taking any additional prescriptions, over-the-counter medications, nutritional supplements or herbal medications. Alcohol lowers glucose (blood sugar), and any use of alcohol should be first discussed with and cleared by a physician.

Meglitinides are eliminated from the body (metabolized) in the liver by enzymes called cytochrome P450 enzymes 2C8 and 3A4. There are several drugs that may affect this enzyme, thereby affecting the ability of meglitinides to lower glucose levels. These drugs include:

• Antifungal medications such as fluconazole, ketoconazole and itraconazole, which are used to treat conditions that include yeast infections
  
  
• Antibiotics such as clarithromycin and erythromycin

Other medications can cause meglitinides to be eliminated too quickly from the body. This can result in high blood glucose (hyperglycemia). Drugs that may trigger this condition include:

• Barbiturates (central nervous system depressant)
• Carbamazepine (epilepsy and trigeminal neuralgia drug)
• Rifampin (antibiotic)

Medications that may increase the risk of hypoglycemia when combined with meglitinides include:

• Anabolic steroids
• Androgens (male sex hormones)

Medications that may increase the risk of hyperglycemia include:

• Corticosteroids, an anti-inflammatory class of immunosuppressives
• Calcium channel blockers
• Diuretics
• Estrogens (female hormones) and oral contraceptives
• Sympathomimetics (e.g., amphetamines, epinephrine)
• Thyroid drugs
• Isoniazid (tuberculosis treatment)
• Nicotinic acid (niacin)
• Phenothiazines (drugs used to treat mental disorders)
• Phenytoin (anticonvulsant)

Certain medications may affect the body’s response to meglitinides. A dosage adjustment may be necessary for patients using these medications. They include:

• Antibiotics including sulfonamides and chloramphenicol
• Beta blockers (a class of antihypertensives)
• Coumarins (anticoagulants)
• Monoamine oxidase inhibitors (class of antidepressants)
• Nonsteroidal anti-inflammatory agents (NSAIDs) such as aspirin
• Albuterol (asthma drug)
• Probenecid (gout drug)