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Objective:The critically ill, premature patients of neonatal intensive care units are susceptible to venous thrombosis, an adverse event associated with short- and long-term morbidity. Venous thrombosis is frequently treated with low-molecular-weight heparins (LMWHs) such as enoxaparin, but optimal dosing of LMWH must balance the morbidity of venous thrombosis with the potential adverse affects of anticoagulation. The optimal dosing of enoxaparin for premature infants is unclear. The objective of this study was to describe enoxaparin therapy and follow-up in critically ill neonates diagnosed with venous thrombosis.Study Design:Retrospective medical record review in the neonatal intensive care unit (NICU) in a single tertiary care institution. Infants with venous thrombosis diagnosed in the NICU were identified using preexisting quality improvement lists and medical records.Results:Twenty-six infants with 30 venous thromboses were identified with a median gestational age of 31 weeks at birth. Eighteen (69%) infants received enoxaparin for venous thrombosis during their hospitalization, beginning with a median dose of 1.5 mg kg−1every 12 h. This dose was increased to a median of 2.1 mg kg−1every 12 h to achieve target anti-factor Xa levels. The target dose was significantly higher in patients with a postmenstrual age of <37 weeks. Enoxaparin treatment was documented after discharge in 12 patients, continuing for a median of 99 days. Four patients died during hospitalization and their deaths were not attributable to venous thrombosis or anticoagulation complication. Follow-up documentation between 6 and 24 months after venous thrombosis diagnosis revealed no major morbidity of venous thrombosis or enoxaparin therapy.Conclusion:Our data reinforce the relative safety and necessity of enoxaparin doses above 1.5 mg kg−1per 12 h in most neonates. This was particularly true for infants at lower postmenstrual age.