PEP involves taking medicine to help prevent infection after a situation where you may have come into contact with HIV. For... morePEP involves taking medicine to help prevent infection after a situation where you may have come into contact with HIV. For example, a person may choose to use PEP after sex in which a condom has broken. To be effective, PEP must be initiated as soon as possible – and certainly within 72 hours – after exposure. You must take PEP daily for 28 days after exposure. If PEP is taken as prescribed, the likelihood of contracting HIV is very low. The price of PEP can be high. However, it is covered by some public and private drug insurance plans. less