Experience with heparin dosing at Christchurch Hospital

To assess the effectiveness of the conventional dosing regimen for unfractionated heparin as it is used at Christchurch Hospital.

Dosage regimens and activated partial thromboplastin times (APTTs) were collected prospectively for 100 consecutive patients who received heparin at Christchurch Hospital, the majority being treated for ischaemic heart disease. All patients received the conventional dosing regimen. Parametric and non-parametric descriptive statistics were used to describe the time to therapeutic APTTs (50 to 70 s).

The arithmetic and geometric mean time to first therapeutic APTTs were 26.6 and 16 hours respectively, with one patient taking up to 126.5 hours to reach the therapeutic range. After 24 hours of therapy, 20% of patients were below the therapeutic range, 42% were within, and 38% of patients were above the therapeutic range. Similarly, at the end of treatment with heparin or after seven days of treatment, only 44% of patients were within the therapeutic range, with ten patients consistently below the therapeutic range throughout therapy.

This study shows that the conventional dosing regimen for heparin at Christchurch Hospital was similar in effectiveness to other studies employing the conventional dosing regimen. In addition, this study and those of others suggest that the conventional dosing strategy is not an effective method of dosing heparin with a significant number of patients undertreated at 24 hours. As a result of this research, weight-based dosing guidelines have been introduced at Christchurch hospital. Validation of this new dosing regimen will be performed subsequently.