Prophylactic Use of Enoxaparin in Morbidly Obese Adolescents During Bariatric Surgery
Condition: Obesity
Study type: Observational

Summary: 
      This study is about a drug called enoxaparin which is used to prevent or treat blood clots.
      There are no studies about the use of this drug in obese adolescents and yet the
      investigators use it to prevent clots when they have surgery at Children's National for
      weight loss. The investigators hypothesis is that the obesity leads to increased kidney size
      and faster drug clearance. Therefore the investigators think they might be underdosing these
      adolescents. This study will check the drug levels at different points after the drug dose to
      see whether the investigators are achieving the expected levels for prevention of clots.
    

Detailed description: 
      Enoxaparin is the drug of choice for prevention and treatment of venous thromboembolism (VTE)
      in children and adults. A major concern with any antithrombotic therapy is an increased risk
      of hemorrhage. There are not many concrete data published for enoxaparin use in children and
      adolescents, and absolutely no guidance is available for (morbidly) obese children and
      adolescents as they are not included in clinical trials during the clinical phases of drug
      development. Physicians often find themselves puzzled when selecting a dose for obese
      children. This study aims to find the optimal way to dose enoxaparin in (morbidly) obese
      children and adolescents that will result in a safe and effective use of this drug as
      prophylaxis during bariatric surgery.

      The optimum therapeutic/preventive dose of a drug depends on its pharmacokinetic and
      pharmacodynamic properties. Both these processes can be affected by body composition and the
      physiological changes that occur in obese children. Obesity not only increases the total fat
      amount, but also the lean body mass. However, the percentage of fat tissue increases more
      than the lean body mass. Obesity as a disease state is also associated with changes in plasma
      protein constituents, decreases in tissue perfusion; and increases in adipose tissue mass,
      lean body mass, cardiac output, and splanchnic blood flow, as compared with normal-weight
      individuals.

      High BMI is believed be an independent risk factor for VTE. Therefore, obese adolescents are
      also being prescribed prophylactic doses of enoxaparin in situations where there is risk of
      VTE. The 2008 recommended guidelines by the American College of Chest Physicians does not
      mention any type of dosing considerations of anticoagulants in obese children. However, it
      states that higher than usual doses be used in adult patients undergoing bariatric surgery.
      The use of enoxaparin is not approved for children but is being used widely for the
      prophylaxis and treatment of VTE in a wide variety of settings in children of all age groups.
      There are very limited number of studies that involve enoxaparin use in children. Out of
      these most of the data are available for the use of enoxaparin for the treatment of VTE and
      not prophylaxis of VTE.

      Studies have shown several age related physiologic differences between pediatric and adult
      patients. Neonates exhibit an accelerated clearance rate and a larger volume of distribution
      as compared with adults. Children treated for malignancy required higher doses compared to
      adults. Pharmacokinetic/pharmacodynamic studies that have included children do not provide
      specific data on different age groups. Further more, the sample size is very small and mostly
      involve patients that were treated for VTE or thrombophilia. There is no information
      specifying dosing for prophylactic therapy.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        A total of 12 patients will be enrolled. The population for this study will include both
        male and female adolescent patients from all ethnic backgrounds with BMI greater than or
        equal to 95 percentile. Each patient will receive enoxaparin SC q 12 hours. The blood
        samples for the study would be taken prior to the second dose.
      
Keywords: Pharmacokinetics of enoxaparin