Eli Lilly's (LLY 0.47%) mealtime insulin product Humalog brought in a whopping $2.4 billion last year. This drug comprises more than 10% of the drugmaker's total revenue, but Humalog's longevity could be compromised by an upcoming patent expiration, stiff competition by diabetes specialist Novo Nodisk (NVO -2.60%), and more competition in the future if MannKind (MNKD 2.91%) can get Afrezza, an ultra-rapid and inhalable insulin, on the market. In this video, health-care analyst Max Macaluso dives into this drug's sales, and breaks down the competitive landscape for investors.