Four more people accused of prescribing unneeded pain creams to bilk insurers have been indicted on fraud charges in Mississippi.

An indictment unsealed Monday alleges that Dr. Shahjahan Sultan of Madison; Dr. Thomas Edward Sturdavant of Kingsport, Tennessee; Freda Cal Covington of Hattiesburg and Fallon Deenem Page of Soso took part in the scheme. Prosecutors say it improperly reaped $7 million.

The indictment says the scheme targeted federal military insurer Tricare and private insurers Blue Cross & Blue Shield of Mississippi and United Healthcare of Mississippi. The indictment says at least three other unnamed people were involved. It also implicates an unnamed Mississippi Gulf Coast pharmacy.

Sultan and Page pleaded not guilty on Monday in Hattiesburg and are free on bail. Covington and Sturdavant are free on bail and are scheduled to be arraigned on Wednesday.

The charges accuse more people in a wide-ranging scheme that is alleged to have reaped hundreds of millions of dollars. The scheme was centered in Mississippi, but reaches across the country. At least 13 people have been convicted in a series of prosecutions.

The indictment alleges Sultan and Sturdavant wrote bogus prescriptions, including illegally prescribing ketamine, in parts of 2014 and 2015. Covington and Page are nurses accused of recruiting patients.

Sultan is accused of collecting a quarter of all the money the scheme reaped.

Sultan is accused of 15 counts including conspiracy to committee health care fraud, mail fraud, dispensing a controlled substance, conspiracy to pay and receive health care kickbacks and paying health care kickbacks. Studavant is indicted on 10 counts including conspiracy to committee health care fraud, mail fraud, dispensing a controlled substance. Page and Covington are both indicted for conspiracy to commit health care fraud, with Page also accused of four counts of mail fraud.