Thrombocytopenia means a low number of thrombocytes, or platelet cells, in the blood. Made in the bone marrow, platelets help blood to clot when needed; a very low platelet count can cause dangerous bleeding. Thrombocytopenia has many causes. When the cause is obscure or unknown, doctors call it idiopathic thrombocytopenia. Some medications for other conditions can bring on thrombocytopenia in some patients although the mechanism is not entirely clear.
Antibiotics
According to the Mayo Clinic, sulfa-based antibiotics can bring on thrombocytopenia. Many people suffer an allergic response to sulfa-containing antibiotics. Similarly, in some people, these drugs confuse the immune system, causing destruction of the body’s own platelets as if they were foreign invaders. The Merck Manual specifically lists the sulfa antibiotics, trimethoprim (Bactrim) and sulfamethoxazole (Septra) as culprits. Doctors often prescribe these drugs to treat bacterial infections such as urinary tract infections, ear infections, traveler’s diarrhea and chronic bronchitis.
Anticonvulsants
The National Heart, Lung and Blood Institute names some specific anticonvulsant medications that can cause thrombocytopenia. Doctors prescribe dilantin, vancomycin and rifampin to control seizures. The Merck Manual’s monograph for vancomycin lists thrombocytopenia as a known adverse reaction affecting less than one percent of patients who take it. High doses of rifampin are especially likely to cause thrombocytopenia, according to the Merck monograph.
Blood Thinner
Doctors use heparin to reduce the risk of blood clots, to help dissolve clots, or to keep intravenous lines running smoothly. According to the Merck Manual, in about five percent of cases, heparin can cause an abnormal immune reaction that causes platelets to clump together, effectively removing them from the circulation and lowering the platelet count. Ironically, in these cases, heparin actually causes the blood clots that it was meant to prevent. The Merck Manual states that even very low doses of heparin can cause thrombocytopenia, but within seven days of stopping heparin treatment, platelet counts usually return to normal. The National Heart, Lung and Blood Institute notes that heparin-induced thrombocytopenia rarely affects people outside of the hospital.
Antimalaria Medications
Quinidine and quinine, used to prevent and treat malaria, can cause thrombocytopenia. Quinidine might also be used to treat abnormal heart rhythms. The effect on platelets is common enough that the Merck Manual monographs for quinidine and quinine list thrombocytopenia as a contraindication for their use.
Over-the-Counter Medications
The Merck Manual lists acetaminophen (Tylenol) as a drug that can lower platelet count and lead to thrombocytopenia. In addition, the National Heart, Lung and Blood Institute cautions that aspirin and ibuprofen can also affect platelets, thinning the blood.
