Thrombocytopenia is a medical condition that occurs when a patient does not have enough platelets in his or her blood, resulting in a high risk for bleeding. Thrombocytopenia can be inherited or can be caused as a result of several conditions or medications. Circulating platelets can be reduced by decreased platelet production, increased destruction, or being trapped in the spleen. Sometimes a drug confuses the immune system and makes it destroy platelets. Examples include heparin, quinine, sulfa-containing antibiotics, and anticonvulsants.