The manufacturers of Dalteparin recommend a capped dose of 18,000 units subcutaneously daily for patients with body weight >83 kg, yet other low molecular weight heparin (LMWH) brands such as Enoxaparin and Tinzaparin recommend non-capped weight-based dosing in obese patients.

In NHS England some Exemplar centres are advising a similar weight-based dosing approach for Dalteparin for patients with body weight >120 kg and the suggested doses are given in Tables 1.4 and 1.5. These doses are off-label and are intended to be used by haematology only to recommend starting doses of Dalteparin when clinical situations arise, for example a patient with a life[1]threatening acute venous thrombosis, when immediate full anticoagulation is necessary. It is advised that LMWH anti-Xa monitoring is performed to monitor the response in this setting. In general, this approach should not be used in the peri-operative setting, when the manufacturer's recommended capped dose should be given, but this is at the discretion of the advising and attending clinicians.

LMWH anti-Xa levels are ordered on TRAK as "heparin assay" and click on LMWH; samples are sent in a green citrated tube filled adequately to the level marked on the tube. Samples must be couriered to the RIE haematology laboratory if the patient is being managed at other NHS Lothian sites. A 24-hour service is available for this automated test and all requests should be discussed with the duty laboratory haematology biomedical scientist (laboratory): extension 26093 or page 6550/via switchboard out of hours.

A peak LMWH anti-Xa level should be taken after the third dose of LMWH has been administered, and taken 3-4 hours following the administration of the drug.

Interpretation:

For patients on once daily dosing, the expected peak plasma concentration is about 1.0 anti-Xa unit per mL with a range of 0.5 to 1.5 (and 0.5 to 1.0 anti-Xa units per mL for twice daily dosing). The duty haematologist can assist with dose adjustment if the level is subtherapeutic, low or supratherapeutic.

Single doses should not exceed 18,000 units

*The use of CrCl is preferred over eGFR in obese patients with renal impairment. Creatinine clearance could be calculated by using the CrCl calculator on the Intranet (see link below).

http://intranet.lothian.scot.nhs.uk/Pages/Search-Results.aspx?k=creatinine%20clearance%20calculator

The alternative is to use intravenous (IV) unfractionated heparin (UFH) and monitor the APTT appropriately.

• The advantage of UFH is that it can be easily stopped if necessary and its effects wear off rapidly. It can also be easily reversed with protamine.
• The disadvantage is that achieving adequate anticoagulation is unpredictable and dosage adjustments based on appropriately timed APTT measurements require careful management. Venous access may also be problematic in patients with obesity.