If indeed you have developed a rash due to medications, contact your doctor, who may tell you to stop taking the prescription.
You may not notice a drug rash right away; it could take a few days to develop, but usually occurs in the first week or so. After you stop taking the medicine, the rash will gradually disappear [source: Mayo Clinic].
In rare cases, an allergic reaction to medication can be life threatening, affecting the respiratory and other systems [source: Mayo Clinic]. This is why it's important to discuss all the details with your health care provider.