The researchers found that the average cost - adjusted for inflation - of one injection increased from about $36 in 1986 to about $88 in 2011.

The analysis, however, cannot say why the cost is going up.

Dr. Richard Lockey, the analysis's senior author from the University of South Florida College of Medicine in Tampa, told Reuters Health that he and his colleagues decided to track the cost when some patients said they could not afford the autoinjectors.

The autoinjectors - sold by a variety of manufacturers under different brand names, including EpiPen, Twinject and Adrenaclick - are prepackaged and filled with epinephrine, which is used as a fast-acting treatment for severe allergic reactions - known as anaphylactic shock.

The devices allow people to inject themselves soon after being exposed to allergy-causing substances such as peanuts and certain insect bites.

Lockey and his colleagues, who published their work as a letter to the Journal of Allergy and Clinical Immunology, write that a study published last year found only 40 percent of teens and adults and 60 percent of children in California refilled their prescriptions over a six-year period.

The low number of refills, they say, may be from the high cost of the autoinjectors.

GROWING COSTS AND ALTERNATIVES

The new study is not the first to look at the cost of the injections.

One of the most recent cost reports, according to the researchers, was in 2007 when a study found the price of an autoinjector to be between about $55 and $169. That was up from a similar study conducted between 2003 and 2005 that found the price to be between $30 and $110.

To plot the cost of the injectors, Lockey and his colleagues used the average wholesale price for autoinjectors in the U.S. from the 1980s to last year.

The average price for one injector was $35.59 in 1986. The price went up two and a half times to $87.92 by 2011.

While Lockey said he does not know why the price increased, he said it's probably related to increased demand for the autoinjectors around the world.

Mylan Inc, which sells the popular EpiPen in the U.S., did not have a response to the findings at press time.

The researchers said there are alternatives for people who cannot afford autoinjectors.

For example, Lockey told Reuters Health that patients can be given prefilled syringes to carry with them. However, because epinephrine is sensitive to light, they'd have to be wrapped in tinfoil and placed in a container.

Alternatively, he said patients can be given a vial of the drug and taught how to draw it into the syringe. He said the drug also has a longer shelf life in the vial.

"With proper education, proper administration and proper caution, this will work out pretty well for people," said Lockey.

As for price, he said giving patients prefilled syringes costs a few dollars instead of nearly $100 for an autoinjector.

"It's like giving a generic instead of a brand," said Lockey, who consults for several pharmaceutical companies.

SOURCE: bit.ly/MQhIlY Journal of Allergy and Clinical Immunology, online July 24, 2012.

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