For many people who have diabetes, insulin can literally mean the difference between life and death. But what if that lifesaving insulin was simply no good?

A new type of insulin called Lantus is causing some confusion. Lantus is a 24-hour insulin that's used along with other fast-acting insulin to help a diabetic maintain a more consistent blood sugar level.

But one Bakersfield, Calif., woman was alarmed when she learned something that neither her doctor nor her pharmacist warned her about: Once the vial is opened, it's only good for 28 days.

Valerie Sumlin has been diabetic since she was 4 years old and she does a good job managing her blood sugar levels.

"You have to know how your insulin works to adjust your lifestyle around it," Sumlin said.

She was happy with the Lantus insulin, but about a month into her prescription, the insulin just stopped working.

Sumlin asked her Walgreen's pharmacist what could be wrong, but he said he didn't know. When Sumlin asked for large-print information on Lantus, he said he couldn't help her.

Sumlin said, "I need something that I can read to get a handle on this insulin, because for four weeks it's working fine -- then all of a sudden -- boom!"

Frustrated, she got the phone number for the manufacturer, Aventis, and spoke to a company representative.

"And he said, 'Ma'am, I'm sorry to tell you, but you took insulin that was no good for over eight days.' I said 'No good? The expiration date said 7-2004. It's highlighted. I'm looking at it,'" said Sumlin.

Walgreen's responded to questions by KERO-TV in Bakersfield about the confusion over the expiration dates by saying that they were "looking into the matter. The written patient information provided for this product is complete and accurate. As with any drug, we encourage patients to become familiar with their prescription medicine and to ask questions, if necessary, at the pharmacy."

Sumlin did ask questions at the pharmacy. She just didn't get any answers.

"And they are so big and they show nationwide they don't care about one person like me, actually maybe going into a coma or dying," said Sumlin.

But the information being provided by the drug company to doctors and pharmacists about the 28-day expiration of lantus is confusing at best. The issue has been brought to both Aventis and the Food and Drug Administration in hopes that other patients like Sumlin don't put their lives at risk.

"Do you realize what eight days can do to a type 1 diabetic like me -- who's right on the verge of dialysis -- who's had two heart attacks -- eight days of high blood sugars?" she said.

As for Sumlin's request for large-print literature on Lantus, Walgreen's corporate office said they don't have the capability of providing it. But Aventis, the manufacturer, has promised to mail the information to Sumlin.

Aventis said they don't provide the 28-day expiration information in their doctor's insert because they say it's common knowledge that insulin expires in one month, once the vial has been used.

But in Sumlin's case, no one but Aventis was aware of that common knowledge.

So, Lantus users, be warned that 28 days after you begin to use your Lantus insulin, it's no longer effective.

To see the patient information online, visit Aventis' site.