WASHINGTON (AP) — Medicare's "Part B" outpatient premium will jump by $21.60 next year, one of the largest increases ever. Officials said Friday a new Alzheimer's drug is responsible for about half of that.

The increase guarantees that health care will gobble up a big chunk of the recently announced Social Security cost-of-living allowance, a boost that had worked out to $92 a month for the average retired worker, intended to help cover rising prices for gas and food that are pinching seniors.

Medicare officials told reporters on Friday that about half the increase is due to contingency planni...