Alaska ? The mother of Bristol Palin’s boyfriend sent text messages to two police informants discussing drug transactions before her arrest on felony drug charges, authorities say.

An affidavit filed Monday says Sherry L. Johnston sent text messages referring to “coffee” as a code for the drug OxyContin.

The 42-year-old Johnston was arrested last week after state troopers served a search warrant at her Wasilla home. She is out on bail.

Johnston is the mother of 18-year-old Levi Johnston. Gov. Sarah Palin announced in September that her 18-year-old daughter Bristol was pregnant and Johnston was the father.

Authorities say the case began in the second week of September — a couple of weeks into Palin’s campaign as Republican vice presidential candidate — when drug investigators intercepted a package containing 179 OxyContin pills. That led to the arrest of the suspects, who agreed to be informants.