March 18 (Reuters) - Drugmaker AstraZeneca said on Monday it would cap out-of-pocket costs for its inhaled respiratory products at $35 per month in the United States, following a similar move by rival Boehringer Ingelheim earlier in the month.

High drug prices in the United States have been the subject of growing political scrutiny for years. Senator Bernie Sanders and other lawmakers in January criticized the top four manufacturers of inhalers sold in the U.S. — AstraZeneca, Boehringer, Teva Pharmaceuticals and GlaxoSmithKline — over the product's high prices.

In letters sent to these companies, the lawmakers said they were launching an investigation into what they termed "extremely high prices" for inhalers for asthma and chronic obstructive pulmonary disease in the U.S. versus other countries.

UK-based AstraZeneca's cap, effective June 1, would apply to its entire respiratory products portfolio, including inhalers such as Airsupra, Bevespi Aerosphere and Breztri Aerosphere, and would be applicable for patients who are uninsured or underinsured.

Breztri Aerosphere costs $645 in the U.S. but $49 in the UK, according to the letter by Sanders and other lawmakers.

"We remain dedicated to addressing the need for affordability of our medicines, but the system is complex and we cannot do it alone," AstraZeneca CEO Pascal Soriot said. "It is critical that Congress bring together key stakeholders to help reform the healthcare system so patients can afford the medicines they need."

Boehringer had also said it would cap out-of-pocket costs for its inhaler products for chronic lung disease and asthma to $35 per month, starting June 1.

The letter said Boehringer's Combivent Respimat costs $489 in the U.S. but just $7 in France.

Sanofi and Eli Lilly had also announced last year that they would cap insulin prices at $35 a month. (Reporting by Puyaan Singh in Bengaluru; Editing by Shilpi Majumdar)