In statehouses around the country, some of the nation’s biggest biotechnology companies are lobbying intensively to limit generic competition to their blockbuster drugs, potentially cutting into the billions of dollars in savings on drug costs contemplated in the federal health care overhaul law.

The complex drugs, made in living cells instead of chemical factories, account for roughly one-quarter of the nation’s $320 billion in spending on drugs, according to IMS Health. And that percentage is growing. They include some of the world’s best-selling drugs, like the rheumatoid arthritis and psoriasis drugs Humira and Enbrel and the cancer treatments Herceptin, Avastin and Rituxan. The drugs now cost patients — or their insurers — tens or even hundreds of thousands of dollars a year.

Two companies, Amgen and Genentech, are proposing bills that would restrict the ability of pharmacists to substitute generic versions of biological drugs for brand name products.

Bills have been introduced in at least eight states since the new legislative sessions began this month. Others are pending.