Diabetes mellitus is a chronic disease that affects 18.2 million people in the United States.1 Type 2 diabetes is the most commonly diagnosed type; it is frequently caused by peripheral insulin resistance or impaired insulin secretion.2 Combination therapy is often necessary when a single drug fails to control plasma glucose. The FDA has approved Byetta (exenatide), manufactured by Amylin Pharmaceuticals Inc, as an adjunctive therapy for the treatment of type 2 diabetes in patients who cannot achieve blood sugar control on metformin and/or sulfonylurea.3
Byetta is an incretin mimetic agent that is composed of a 39-amino acid peptide. Incretins improve glucose-dependent insulin secretion and inhibit glucagon release. Byetta leads to an increase in insulin secretion, a decrease in glucagon release, a decrease in food intake, delayed gastric emptying, and an elevated beta-cell production.3,4
A triple-blind, placebo-controlled study evaluated the effectiveness of twice-daily subcutaneous injections of Byetta (5 mcg and 10 mcg) with matching placebo. The trial included 377 patients with type 2 diabetes who had been treated with sulfonylurea monotherapy for 3 months prior to initiating the study therapy. All patients continued sulfonylurea therapy throughout the study. After 30 weeks, hemoglobin A1c (HbA1c) changes from baseline were -0.86 + 0.11, -0.46 + 0.12, and 0.12 + 0.09% in the 10-mcg, 5-mcg, and placebo arms, respectively (P <.001). For participants with baseline HbA1c >7%, the 10-mcg and 5-mcg Byetta arms reached an HbA1c ≤7%, significantly greater than the placebo arm (P <.0001). Furthermore, progressive dose-dependent weight loss was observed in the 10-mcg and 5-mcg Byetta arms, compared with baseline.5
Another 28-day, triple-blind, parallel-group, placebo-controlled study examined the efficacy and safety of 3 different subcutaneous Byetta regimens. A total of 109 patients with type 2 diabetes who had been stable on a sulfonylurea and/or metformin regimen for 6 months took part in this study. Patients were enrolled to receive Byetta twice daily at breakfast and dinner, Byetta twice daily at breakfast and bedtime, Byetta 3 times daily (at breakfast, dinner, and bedtime), or placebo. At day 28, patients in the Byetta arms had a statistically significant reduction in serum fructosamine (P <.004) and HbA1c (P <.006), compared with those in the placebo arm. Furthermore, end-of-study HbA1c of <7% was achieved by 15% of all Byetta patients, compared with 4% of placebo-treated patients. Moreover, the beta-cell index for Byetta patients at day 14 and day 28 ranged from 50% to 100% greater than baseline, while the beta-cell index for the placebo group showed no change.6
The most common adverse event reported with Byetta was dose-dependent mild-to-moderate nausea. Other adverse events included vomiting, diarrhea, jitters, dizziness, headache, and dyspepsia.3,4 When Byetta is used with a sulfonylurea, mild-to-moderate hypoglycemia is observed; thus dose reduction is advisable. This effect has not been witnessed with metformin.4 In addition, Byetta is not recommended for patients with severe renal impairment, end-stage renal disease (creatinine clearance <30 mL/min), or severe gastrointestinal disease.3
The delayed gastric emptying that may occur with Byetta may affect some concentration-sensitive drugsfor example, antibiotics and/or oral contraceptives. Patients should be advised to take these medications at least 1 hour before a Byetta injection. Byetta is in Pregnancy Risk Category C.
The appealing side-effect and efficacy profile of Byetta, along with the convenience of prefilled pens, grants health care practitioners another therapeutic option for the control of type 2 diabetes, subsequent to unsuccessful treatment with metformin or a sulfonylurea.
Drs. Faria and Soo are both senior research pharmacists with the Investigational Drug Service at Brigham and Women's Hospital, Boston, Mass. Dr. Faria also is a senior human research specialist at Partners HealthCare System. Diem Chi Tran is a sixth-year PharmD candidate from the Massachusetts College of Pharmacy currently on clinical clerkship in the Investigational Drug Service at Brigham and Women's Hospital.
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