(Reuters) - U.S. Democratic Senator Claire McCaskill sought on Tuesday details from the nation's top opioid drugmakers on their sales and marketing practices, as lawmakers step up efforts to tackle the country's deadly opioid crisis.

The Missouri senator's investigation comes amid an epidemic of opioid addiction, with 91 Americans dying everyday as a result of overdose, according to the U.S. Centers for Disease Control and Prevention.

"This epidemic is the direct result of a calculated sales and marketing strategy major opioid manufacturers have allegedly pursued over the past 20 years to expand their market share," McCaskill, the top Democrat on the Senate Homeland Security and Governmental Affairs Committee, wrote in a letter to the drugmakers. (http://bit.ly/2o7pa4p)

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McCaskill asked Johnson & Johnson, Mylan NV, Purdue Pharma, Insys Therapeutics Inc and Depomed Inc for internal estimates of the risk of abuse, addiction and overdose of opioids.

The companies are the top five U.S. prescription opioid drugmakers by 2015 sales, according to McCaskill's letter.

Depomed and Purdue Pharma said they were reviewing the letter and would respond accordingly.

Purdue also said its OxyContin painkiller made up just 2 percent of the U.S. opioid analgesic prescription market.

Johnson & Johnson said it had received the letter and would address the senator's request.

"We believe that we have acted appropriately, responsibly and in the best interests of patients regarding our opioid pain medications," said Jessica Castles Smith, a spokeswoman for Johnson & Johnson unit Janssen.

Mylan said it is committed to helping find solutions to the issue of opioid abuse and misuse.

"We welcome the senator's interest in this important matter and we share her concerns regarding the misuse of prescription opioids," a Mylan spokeswoman told Reuters in an email.

(Reporting by Ankur Banerjee and Nikhil Subba in Bengaluru; Editing by Sai Sachin Ravikumar)