NEW YORK (Reuters Health) – In a study of a busy coronary care unit in Kuwait, 41.1% of patients treated with unfractionated heparin for 6 hours had a subtherapeutic activated partial thromboplastin time (APTT).

Female gender and an unstable angina diagnosis were among the factors that predicted resistance to unfractionated heparin, according to the report in the Summer issue of Cardiovascular Therapeutics.

“Heparin resistance is a common phenomenon especially in the first period of heparin therapy,” Dr. Shaker A. Mousa, from Albany College of Pharmacy, New York, and co-researchers note. “Evidence based protocols for heparin administration and monitoring must be adopted to prevent the risk of under or over anticoagulation.”

The study, which was conducted at Farwania Hospital, included 146 patients who were admitted to the coronary care unit over a 4-month period. Heparin was given as 5000-unit bolus followed by an infusion at 1000 units/hour. APTT testing was performed every 6 hours with adjustments in the heparin dose to maintain APTT in the therapeutic range.

At 6, 24, and 48 hours, 41.1%, 42.3%, and 46.7% of patients had subtherapeutic APTT values, the report indicates.

In addition to female gender and unstable angina, Arab race and an admission APTT ratio of <1 were both predictive of heparin resistance, the investigators found. No significant differences in complications were noted between patients with therapeutic APTT values and those who were under or overcoagulated, the findings show. Understanding which patients are at risk for heparin resistance is extremely important, the researchers conclude. However, further studies are needed to verify that the predictors identified in the present study are valid, they add. Reference:
Cardiovascular Therapeutics 2009;27:77-82.