Old-fashioned asthma inhalers that contain environment-harming chemicals will no longer be sold at year’s end _ and the government is urging patients not to wait until the last minute to switch to newer alternatives.

Patients use inhalers to dispense airway-relaxing albuterol during asthma attacks.

Chemicals called chlorofluorocarbons, or CFCs, once were widely used to propel the drug into the lungs. But CFC-containing consumer products are being phased out because CFCs damage the Earth’s protective ozone layer. As of Dec. 31, asthma inhalers with CFCs can no longer be made or sold in the U.S. Inhalers instead will be powered by ozone-friendly HFAs, or hydrofluoroalkanes.

The ozone layer shields the planet from harmful ultraviolet radiation.

Patients have been warned of the change for several years, but the Food and Drug Administration issued an advisory Friday saying anyone still using CFC inhalers should ask their doctor about switching now.

The FDA warns that patients will face a learning curve: HFA inhalers may taste and feel different. The spray may feel softer. Each must be primed and cleaned in a specific way to prevent clogs. And they tend to cost more.

CFC-free albuterol inhaler options include GlaxoSmithKline’s Ventolin HFA, Schering Plough’s Proventil HFA and Teva Specialty Pharmaceuticals’ ProAir HFA. Sepracor’s Xopenex HFA is also CFC-free, but it contains levalbuterol, a similar medication.

The FDA said Armstrong Pharmaceuticals is the sole remaining maker of CFC inhalers and is expected to stop production even before the deadline. A spokesman for Armstrong’s parent company wouldn’t say when production would stop, but sales of remaining inventory will continue until Dec. 31.

(This version CORRECTS 6th graf to ProAir maker.)