PharmPK Discussion - IV bolus and infusion kinetics

• On 9 Jul 2011 at 09:50:50, N A (niviope.-at-.yahoo.co.uk) sent the message
  

  
  Dear all,
   My question relates to Drug A which is administered by an IV infusion.  The terminal half life of Drug A is 30 minutes. In order to reach  immediate therapeutic levels a bolus is administered at the same time as  the infusion is started. At steady state the plasma levels of Drug A is  X, however when modelling the pk data it is apparent that the bolus dose  required equates to an initial plasma concentration of 2 fold higher  than X. It therefore appears that the elimination of the bolus dose is  faster than the elimination of the infusion. Is there an explanation for  this phenomenon?
   Thanks,
   Stuart
  
  

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• On 9 Jul 2011 at 20:40:20, Roger Jelliffe (jelliffe.-at-.usc.edu) sent the message
  

  
  The following message was posted to: PharmPK
  
  Dear Stuart:
  
       The drug probably has at least 2 compartment behavior. After the  bolus it is both distributed aas well as elliminated. Leter on the  exchange between central and peripheral comnpartments has equilibrated,  and only elimination is seen. Common examples are lidocaine and  vancomycin.
  
  Hope this helps,
  
  Roger Jelliffe
  
  

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