The patient in this vignette most likely has type II diabetes. Of the given treatments, only metformin is weight neutral in the majority of cases (i.e. it does not cause significant weight gain/loss).
Metformin is a first-line treatment for type II DM in most patients. Although the exact mechanism is unknown, it appears to decrease gluconeogenesis and increase insulin sensitivity. There is no risk of hypoglycemia or weight gain (though some patients even lose weight). The most high yield side effect involves lactic acidosis, particularly in patients with renal insufficiency.
Petznick discusses the management type II DM. The paper reports that insulin therapy is recommended for patients with type 2 diabetes mellitus and an initial A1C level greater than 9 percent, or sugars are still uncontrolled despite optimal oral glycemic therapy. Metformin has been shown to reduce all-cause mortality and cardiovascular events in overweight patients with diabetes.
Mahmood et al. describe the role of metformin in several clinical contexts. They report that the United Kingdom Prospective Diabetic Study (UKPDS) has observed its survival benefits in a large cohort of individuals. Further studies have shown metformin to be beneficial in lipid disorders as it improves markers of metabolic syndrome. Lastly, metformin is also known to improve the fertility in females with Polycystic Ovarian Syndrome (PCOS).
Illustration A exhibits several pathways in which metformin plays a role.
Answer 1: Glargine, a long-acting insulin, can cause weight gain.
Answer 2: Glyburide, a second generation sulfonylurea, can cause weight gain.
Answer 3: Pioglitazone, a thiazolidinedione, can cause weight gain.
Answer 5: Glipizide, a second generation sulfonylurea, can cause weight gain.
Petznick A. Insulin management of type 2 diabetes mellitus. Am Fam Physician. 2011 Jul 15;84(2):183-90.
PMID:21766768 (Link to Abstract)
Mahmood K, Naeem M, Rahimnajjad NA. Metformin: the hidden chronicles of a magic drug. Eur J Intern Med. 2013 Jan;24(1):20-6.
PMID:23177353 (Link to Abstract)