TRENTON - A severe nationwide shortage of drugs for chemotherapy, infections, and other serious ailments is endangering patients and forcing hospitals to buy life-saving medications from secondary suppliers at huge markups because they can't get them any other way.

An Associated Press review of industry reports and interviews with nearly two dozen experts found at least 15 deaths in the last 15 months blamed on the shortages - either because the right drug wasn't available or because of dosing errors or other problems in administering or preparing alternative medications.

The shortages, mainly involving widely used generic injected drugs that ordinarily are cheap, have been delaying surgeries and cancer treatments, leaving patients in unnecessary pain and forcing hospitals to give less effective treatments. That's resulted in complications and longer hospital stays.

Slightly more than half of the 549 U.S. hospitals responding to a survey this summer by the Institute for Safe Medication Practices, a patient safety group, said they had purchased one or more prescription drugs from so-called gray market vendors - companies other than their normal wholesalers. Most also said they've had to do so more often of late, and 7 percent reported patient side-effects or other problems.

Hospital pharmacists "are really looking at this as a crisis. They are scrambling to find drugs," said Joseph Hill of the American Society of Health-System Pharmacists.

The Food and Drug Administration is scheduled to hold a meeting Monday with medical and consumer groups, researchers and industry representatives to discuss the shortages and strategies to fight them. On Friday, the health subcommittee of the House Energy and Commerce Committee held a hearing in the issue.

The FDA says the main reason for the shortages is production shutdowns because of manufacturing problems, such as contamination and metal particles that get into medicine.

Other factors:

Companies abandoning the injected generic drug market because the profit margins are slim.

Only a half-dozen companies make the vast majority of injected generics.

Theft of prescription drugs from warehouses or during shipment.

Secondary, "gray market" vendors who buy scarce drugs from small regional wholesalers, pharmacies or other sources and then sell them to hospitals, often at many times the normal price. These sellers may not be licensed distributors.

The drugs may be stolen and hospitals can't always tell whether a medicine was properly refrigerated - as required for many injectable drugs - or whether it's past the expiration date, said Michael R. Cohen, president of the institute.

In the worst known case, Alabama public health officials this spring reported nine deaths and 10 patients harmed due to bacterial contamination of a hand-mixed batch of liquid nutrition given via feeding tubes because the sterile pre-mixed liquid wasn't available.