A shortage of injectable generic drugs for cancer and other serious diseases is putting pressure on hospitals, which are sometimes having to scramble to locate the medicines or search for alternative treatments. The supply of these drugs has tightened in recent years as the generic-drug industry has consolidated, with many of the drugs now made by just one or two companies. In many cases patents have long expired and the original brand-name drug is no longer being produced. Federal regulators have also stepped up enforcement of quality standards, limiting the ability of large manufacturers to ramp up production. The drugs, typically used in hospitals and outpatient clinics, often require complex manufacturing processes with long lead times. Because factories produce many kinds of medicines, companies say they can't easily make more of one without creating a shortage in another.