T he documented cases of thromboem- bolic disease have risen greatly in the pediatric population, with venous thromboembolism increasing by 70%. 1 Although not completely understood, the growing number of cases is hypothe- sized to be the result of advances in the treatment of critically ill patients, includ- ing the increased use of indwelling catheters. 2-4 Neonates are particularly sus- ceptible to thromboembolic complica- tions. Neonates and adolescents consti- tute the largest groups of pediatric pa- tients diagnosed with thromboembolic disease, with the rate of venous throm- boembolism ranging from 75 to 94 cases per 10,000 hospital admissions, respec- tively. 1,5,6 The coagulation system is immature at birth, resulting in a unique balance be- tween procoagulants and inhibitors. Healthy neonates are considered hemo- dynamically stable because most do not develop spontaneous thrombotic compli- cations. 7 The coagulation system may become hypercoagulable in ill neonates with disease states such as respiratory distress, pulmonary hypertension, and sepsis. 3 Because most patients admitted The Annals of Pharmacotherapy ■ 2012 July/August, Volume 46 ■ 943 Retrospective Evaluation of Enoxaparin Dosing in Patients 48 Weeks’ Postmenstrual Age or Younger in a Neonatal Intensive Care Unit J Kevin Hicks, Chasity M Shelton, Jasmine K Sahni, and Michael L Christensen theannals.com Neonatology Author information provided at end of text. BACKGROUND: Enoxaparin is the anticoagulant of choice in neonates because of the ease of administration, predictable pharmacokinetics, and reduced adverse effects when compared to heparin. The Chest guidelines recommend that therapy in patients younger than 2 months should be initiated with enoxaparin 1.5 mg/kg administered subcutaneously twice daily. This starting dosage may be inadequate, leading to a delay in achieving therapeutic anti-factor Xa plasma concentrations. OBJECTIVE: To determine an enoxaparin dose for neonatal patients that achieves a therapeutic anti-factor Xa plasma concentration and compare that dose to the recommended enoxaparin dose per published guidelines for this patient population. METHODS: The study was designed as a single-center chart review. Eligible patients were identified by pharmacy anticoagulation records or a search of the electronic medical record for enoxaparin orders. Patients must have received enoxaparin subcutaneously twice daily and have had a postmenstrual age of 48 weeks or younger. Patients diagnosed with renal failure and those receiving prophylactic doses of enoxaparin were excluded. RESULTS: The mean (SD) initial dose of enoxaparin was 1.4 (0.3) mg/kg subcutaneously twice daily, resulting in 27 of 33 patients (81.8%) having a subtherapeutic anti-factor Xa concentration. A mean enoxaparin dose of 2.0 (0.5) mg/kg was required to achieve a therapeutic anti-factor Xa plasma concentration (p < 0.001). Patients born prematurely required a higher enoxaparin dose (2.2 [0.5] mg/kg) than did those born at full-term gestation (1.8 [0.4] mg/kg; p < 0.05). CONCLUSIONS: For patients 48 weeks’ postmenstrual age or younger who are treated in a neonatal intensive care unit, a higher initial dose of enoxaparin than that suggested by the Chest guidelines is required to attain a therapeutic anti- factor Xa plasma concentration. Premature neonates require a larger starting dose of enoxaparin than do infants born at full-term gestation. KEY WORDS: anticoagulation, anti-factor Xa, enoxaparin, neonatal intensive care unit, neonate. Ann Pharmacother 2012;46:943-51. Published Online, 24 Jul 2012, theannals.com, doi: 10.1345/aph.1R116 by guest on October 11, 2013 aop.sagepub.com Downloaded from by guest on October 11, 2013 aop.sagepub.com Downloaded from by guest on October 11, 2013 aop.sagepub.com Downloaded from by guest on October 11, 2013 aop.sagepub.com Downloaded from by guest on October 11, 2013 aop.sagepub.com Downloaded from by guest on October 11, 2013 aop.sagepub.com Downloaded from by guest on October 11, 2013 aop.sagepub.com Downloaded from by guest on October 11, 2013 aop.sagepub.com Downloaded from by guest on October 11, 2013 aop.sagepub.com Downloaded from