PEP is Post-Exposure Prophylaxis, an emergency HIV treatment used when someone has been exposed to HIV and needs treatment to prevent them from becoming infected. PEP is most commonly distributed in cases of sex or shared needles or works with an HIV positive person, or after sexual assault.
If you have been sexually assaulted and are concerned about exposure to HIV, talk to your health care provider or go to an emergency room doctor immediately--every hour of the initial 72 hour period counts. The Rape Crisis Center provides support to sexual assault victims in San Antonio. You can read more information on sexual assault here.
PEP must be started within 72 hours of exposure in order to be effective. It is not 100% effective, and is not a substitute for use of regular HIV prevention methods, such as PrEP. Because of this, condom usage and safe injection practices are always encouraged.