title: Measured density and calculated baricity of custom-compounded drugs for chronic intrathecal infusion.
abstract: OBJECTIVE
  To minimize the frequency that intrathecal pumps require refilling, drugs are custom compounded at very high concentrations. Unfortunately, the baricity of these custom solutions is unknown, which is problematic, given baricity's importance in determining the spread of intrathecally administered drugs. Consequently, we measured the density and calculated the baricity of clinically relevant concentrations of multiple drugs used for intrathecal infusion.
  
  
  METHODS
  Morphine, clonidine, bupivacaine, and baclofen were weighed to within 0.0001 g and diluted in volumetric flasks to produce solutions of known concentrations (morphine 1, 10, 25, and 50 mg/mL; clonidine 0.05, 0.5, 1, and 3 mg/mL; bupivacaine 2.5, 5, 10, and 20 mg/mL; baclofen 1, 1.5, 2, and 4 mg/mL). The densities of the solutions were measured at 37°C using the mechanical oscillation method. A "best-fit" curve was calculated for plots of concentration versus density for each drug.
  
  
  RESULTS
  All prepared solutions of clonidine and baclofen were hypobaric. Higher concentrations of morphine and bupivacaine were hyperbaric, whereas lower concentrations were hypobaric. The relationship between concentration and density is linear for morphine (r > 0.99) and bupivacaine (r > 0.99) and logarithmic for baclofen (r = 0.96) and clonidine (r = 0.98).
  
  
  CONCLUSIONS
  This is the first study to examine the relationship between concentration and density for custom drug concentrations commonly used in implanted intrathecal pumps. We calculated an equation that defines the relationship between concentration and density for each drug. Using these equations, clinicians can calculate the density of any solution made from the drugs studied here.
authors: Department of Anesthesiology, Virginia Mason Medical Center, University of Washington, 1100 Ninth Avenue, Seattle, WA 98101, USA.
authors: Michael R
authors: MR
authors: Hejtmanek
authors: Tracy D
authors: TD
authors: Harvey
authors: Christopher M
authors: CM
authors: Bernards
mesh_terms: D001418:Baclofen / Q000008:administration & dosage / Q000737:chemistry*; D002045:Bupivacaine / Q000008:administration & dosage / Q000737:chemistry*; D002626:Chemistry, Pharmaceutical; D003000:Clonidine / Q000008:administration & dosage / Q000737:chemistry*; D004334:Drug Administration Schedule; D004339:Drug Compounding; D015918:Infusion Pumps, Implantable; D007263:Infusions, Parenteral; D016014:Linear Models; D008956:Models, Chemical; D009020:Morphine / Q000008:administration & dosage / Q000737:chemistry*; D009991:Oscillometry; D019999:Pharmaceutical Solutions; D013997:Time Factors
chemical_list: D019999:Pharmaceutical Solutions; D009020:Morphine; D001418:Baclofen; D003000:Clonidine; D002045:Bupivacaine