WASHINGTON – Medication mistakes injure well over 1.5 million Americans every year, a toll too often unrecognized and unfought, says a sobering call to action.

At least a quarter of the errors are preventable, the Institute of Medicine said Thursday in urging major steps by the government, health providers and patients alike.

Topping the list: All prescriptions should be written electronically by 2010, a move one specialist called as crucial to safe care as X-ray machines.

Perhaps the report’s most stunning finding was that, on average, a hospitalized patient is subject to at least one medication error a day.

A serious drug error can add more than $5,800 to the hospital bill of a single patient. Assuming that hospitals commit 400,000 preventable drug errors each year, that’s $3.5 billion – not counting lost productivity and other costs – from hospitals alone, the report concluded.

“I’m a patient-safety researcher [yet] I was surprised and shocked at just how common and how serious a problem this is,” said Dr. Albert Wu of Johns Hopkins University, co-author of Thursday’s report.

Worse, there’s too little incentive for health providers to invest in technology that could prevent some errors today, added Dr. J. Lyle Bootman, the University of Arizona’s pharmacy dean and co-chairman of the IOM probe.

“We’re paid whether these errors occur or not,” lamented Bootman, who recently experienced the threat firsthand as his son-in-law dodged some drug near-misses while in intensive care in a reputable hospital.

The new probe couldn’t say how many of the injuries are serious, or how many victims die. A 1999 estimate put deaths, conservatively, at 7,000 a year.

Even the total injury estimate is conservative, Bootman stressed. It includes drug errors in hospitals, nursing homes and among Medicare outpatients, but it doesn’t attempt to count mix-ups in most doctors’ offices or by patients themselves.

There have been efforts to improve patient safety in the six years since the IOM first spotlighted medical mistakes of all kinds, including recent bar-coding of drugs to minimize mix-ups in hospitals and pharmacies.

Clearly more are needed, and the new report highlights how the nation’s fragmented health care system is conducive to drug errors, said Dr. Donald Berwick, a Harvard professor who heads the nonprofit Institute for Healthcare Improvement.

“This isn’t a matter of doctors and nurses trying harder not to harm people,” Berwick cautioned. “Safety isn’t automatic. It has to be designed into the system.”

Medications’ sheer volume and complexity illustrate the difficulty. There are more than 10,000 prescription drugs on the market and 300,000 over-the-counter products. It’s impossible to memorize their different usage and dosage instructions, which may vary according to the patient’s age, weight and other risk factors, such as bad kidneys.

Plus, four of every five U.S. adults take at least one medication or dietary supplement every day; almost a third take at least five. The more you use, the greater your risk of bad interactions, especially if multiple doctors prescribe different drugs without knowing what you already take.

Add doctors’ notoriously bad handwriting and sound-alike drug names: Was that order for 10 milligrams or 10 migrams? The hormone Premarin or the antibiotic Primaxin?

Moreover, consumer instructions are woefully inadequate, the report concludes. One study found parents gave their children the wrong dose of over-the-counter fever medicines 47 percent of the time.

Then there was the newly diagnosed asthmatic wondering why his inhaler didn’t work. Asked how he used it, the middle-age man squirted two puffs into the air and tried to breathe the mist. His original doctor had demonstrated the inhaler without telling him to spray it inside his mouth.

Among the report’s recommendations:

. The government should speed electronic prescribing, including fostering technology improvements so that the myriad computer programs used by doctors, hospitals and drugstores are compatible.

Fewer than about 20 percent of prescriptions are electronic, said report co-author Michael Cohen, president of the Institute for Safe Medication Practices.