Drug Interactions between guanfacine and Steglujan

GENERALLY AVOID: Grapefruit juice may increase the plasma concentrations of guanfacine. The risk of adverse reactions such as hypotension, bradycardia, and sedation may increase. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Ketoconazole, a potent CYP450 3A4 inhibitor, has been reported to increase guanfacine peak plasma concentration (Cmax) and systemic exposure (AUC) by approximately 2- and 3-fold, respectively. A computer simulation suggests that fluconazole, a moderate CYP450 3A4 inhibitor, would increase guanfacine Cmax and AUC by about 1.5- and 2-fold, respectively. In general, the effect of grapefruit juice is concentration-, dose- and preparation-dependent, and can vary widely among brands. Certain preparations of grapefruit juice (e.g., high dose, double strength) have sometimes demonstrated potent inhibition of CYP450 3A4, while other preparations (e.g., low dose, single strength) have typically demonstrated moderate inhibition.

GENERALLY AVOID: Alcohol may enhance the sedative and hypotensive effects of guanfacine.

GENERALLY AVOID: Administration of extended-release guanfacine with a high-fat meal may increase the bioavailability of guanfacine. When a single 4 mg dose of extended-release guanfacine was administered to adult volunteers with a high-fat breakfast, mean guanfacine peak plasma concentration (Cmax) and systemic exposure (AUC) increased by approximately 75% and 40%, respectively, compared to dosing in a fasted state.

MANAGEMENT: Patients treated with guanfacine should avoid consumption of grapefruit and grapefruit juice. In addition, it is preferable to avoid or limit the use of alcohol during treatment. Patients should be advised against driving or operating hazardous machinery until they know how the medication affects them. The extended-release formulation of guanfacine should not be taken together with a high-fat meal.

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GENERALLY AVOID: Alcohol may cause hypoglycemia or hyperglycemia in patients with diabetes. Hypoglycemia most frequently occurs during acute consumption of alcohol. Even modest amounts can lower blood sugar significantly, especially when the alcohol is ingested on an empty stomach or following exercise. The mechanism involves inhibition of both gluconeogenesis as well as the counter-regulatory response to hypoglycemia. Episodes of hypoglycemia may last for 8 to 12 hours after ethanol ingestion. By contrast, chronic alcohol abuse can cause impaired glucose tolerance and hyperglycemia. Moderate alcohol consumption generally does not affect blood glucose levels in patients with well controlled diabetes. A disulfiram-like reaction (e.g., flushing, headache, and nausea) to alcohol has been reported frequently with the use of chlorpropamide and very rarely with other sulfonylureas.

MANAGEMENT: Patients with diabetes should avoid consuming alcohol if their blood glucose is not well controlled, or if they have hypertriglyceridemia, neuropathy, or pancreatitis. Patients with well controlled diabetes should limit their alcohol intake to one drink daily for women and two drinks daily for men (1 drink = 5 oz wine, 12 oz beer, or 1.5 oz distilled spirits) in conjunction with their normal meal plan. Alcohol should not be consumed on an empty stomach or following exercise.

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GENERALLY AVOID: Alcohol may cause hypoglycemia or hyperglycemia in patients with diabetes. Hypoglycemia most frequently occurs during acute consumption of alcohol. Even modest amounts can lower blood sugar significantly, especially when the alcohol is ingested on an empty stomach or following exercise. The mechanism involves inhibition of both gluconeogenesis as well as the counter-regulatory response to hypoglycemia. Episodes of hypoglycemia may last for 8 to 12 hours after ethanol ingestion. By contrast, chronic alcohol abuse can cause impaired glucose tolerance and hyperglycemia. Moderate alcohol consumption generally does not affect blood glucose levels in patients with well controlled diabetes. A disulfiram-like reaction (e.g., flushing, headache, and nausea) to alcohol has been reported frequently with the use of chlorpropamide and very rarely with other sulfonylureas.

MANAGEMENT: Patients with diabetes should avoid consuming alcohol if their blood glucose is not well controlled, or if they have hypertriglyceridemia, neuropathy, or pancreatitis. Patients with well controlled diabetes should limit their alcohol intake to one drink daily for women and two drinks daily for men (1 drink = 5 oz wine, 12 oz beer, or 1.5 oz distilled spirits) in conjunction with their normal meal plan. Alcohol should not be consumed on an empty stomach or following exercise.

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