NEW YORK (CNN/Money) – Sanofi-Aventis' diabetes drug Lantus has flourished in the lucrative industry for insulin products, and according to analysts, it will continue to do so despite two competing drugs which have recently entered the market.

Lantus, an injectable insulin analogue (a modified version of insulin) on the market since 2000, became a blockbuster last year, when its worldwide sales shot up 80 percent and topped $1 billion. Sales for Lantus, which takes up more than half the U.S. market share for long-acting insulin products, are projected to snowball over the next five years.

"Lantus has been doing extremely well because it's the only once-a-day long-acting analogue," said Bernstein analyst Gbola Amusa. According to Amusa, the drug's once-a-day status makes it superior to its competitors.

As a long-acting insulin analogue, a single injection of Lantus steadily releases insulin into the blood over 24 hours. Insulin is used to control the blood sugar levels in diabetics, who have difficulty producing insulin naturally.

Lantus is used to treat type 2 diabetes, the most common form of the disease affecting more than 90 percent of the 18.2 million diabetics in America. Diabetes is a growing area for health care, with 1.3 Americans diagnosed every year.

Bernstein projected that U.S. sales for Lantus, which totaled $615 million in 2004, would more than double by 2011, to $1.5 billion. Worldwide, Lantus sales are projected to reach $2.6 billion by 2010, according to Merrill Lynch. French drug maker Sanofi (up $0.16 to $41.04, Research) totaled $20 billion in 2004 sales.

But Lantus faces competition from two newly-approved insulin products: Levemir and Byetta.

Levemir, an injectable, long-acting insulin analogue from Danish drugmaker Novo Nordisk (Research), a $5.3 billion company, was approved by the Food and Drug Administration on June 17. It competes directly with Lantus since it treats the same types of diabetic patients. Bernstein projects that Levemir sales will reach $522 million in the U.S. by 2011, about one-third of the projected sales for Lantus that year.

The FDA also approved Byetta, an insulin product from Lilly and San Diego company Amylin Pharmaceuticals, Inc. (up $0.93 to $20.51, Research), on April 29. Byetta, a transition drug mainly for patients moving from mild to severe diabetes indirectly competes with Lantus which treats more serious forms of diabetes. Sales for Byetta, a compound that was discovered in the saliva of the Gila monster, are expected to reach $1.5 billion worldwide by 2011, according to Bernstein.

"In the true sense of insulin analogues, only Levemir is the competition [for Lantus,] but in terms of growth, Sanofi would have to compete against Byetta, as well," said Bernstein analyst Gbola Amusa.

In a recent Merrill Lynch report, analyst Graham Parry called Byetta a "potential competitive threat to Lantus." However, the threat of Byetta would not prevent Lantus from achieving multi-billion Euro sales by the end of the decade.

But Lantus could have a rocky year once Byetta is released but sales of the veteran diabetes treatment are expected to pick up.

"We have already factored in a slowdown in Lantus sales growth in 2005/6 to account for the Byetta launch and despite this promising [clinical] data, our Lantus forecasts are unchanged at Euro 2.1 billion in 2010," wrote Parry.

"Lantus is likely to remain the therapy of choice for difficult to treat type 2 diabetic patients failing on oral therapy." The Merrill Lynch report said.

The analysts interviewed for this story do not own stock in these companies. Merrill Lynch conducts business with a Sanofi subsidiary, but Bernstein does not do business with these companies.

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