RxNorm codes indicate the *strength* i.e., the amount of drug in a “unit” of product, rather than the actual dose administered to the patient. For example, Aspirin 500 mg Oral Tablet has a 500mg strength, however the patient can be administered 2 tablets, which would make the dose 1000 mg. In the case of injectable solutions, such as heparin, RxNorm provides the concentration of the solution. For the unfractionated heparin value set, 25000 units in a 500 ML bag would equate to a concentration of 50 UNT/ML. The current value set includes such a concentration (RxNorm code 1361613 | heparin sodium, porcine 50 UNT/ML), and it is appropriate to map any medication with such a concentration, regardless of the total number of units given (dosing), to this code. Since the release of the 2015 Annual Update, RxNorm was revised to retire some heparin codes (including code 136613) and replace them with codes which include heparin concentration as well as volume (e.g. RxNorm code 1659195 | 500 ML heparin sodium, porcine 50 UNT/ML). We plan to revise the unfractionated heparin value set accordingly, and we anticipate these changes will make mapping from your local system to RxNorm more straightforward.