PharmPK Discussion - Carrier mediated absorption

• On 26 Jan 2011 at 15:09:31, rahul vats (rahulvats1983.aaa.gmail.com) sent the message
  

  
  Dear All,
   I have one question regarding carrier mediated absorption.
   If a drug absorption is carrier mediated . Administration of such drug  at high dose (above saturation) follows zero order absorption (because  of capacity limited transportation) but what about drug concentration  which is below transporter saturation level?.
   Will absorption be depend on X (amount of drug) at sub saturation case  or transporter will transport all the molecule inside (in to the  circulation) post to release from formulation and again zero order  kinetics (absorption) will be followed (As no. of transporters are more  than no of drug molecule released and all molecules will be transported  at a time and again will be ready to transport new released molecules  and so on.As a result transportation of drug inside is controlled.
  Can we say zero order absorption again even at sub saturation levels?
  
  -- Regards,
  
  Rahul Vats
  BITS-Pilani, Hyderabad Campus
  
  

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• On 27 Jan 2011 at 18:49:03, kanchan soni (kanchansoni.-a-.gmail.com) sent the message
  

  
  Hi Sir,
  Since the number of carriers is limited, the system is capacity-limited  i.e. at higher concentration, the system becomes saturated and  approaches an asymptote.
  It is important to note that for a drug absorbed by passive diffusion,  the rate of absorption increases linearly with the concentration but in  case of carrier-mediated process, the drug absorption increases linearly  with concentration until the carriers become saturated after which it  become curvilinear and approach a constant value at higher doses.
  Such capacity-limited process are called mixed order kinetics, because  it is first order at sub-saturation drug concentration and apparent zero  order at and above saturation level.
  Hope it may help u.
  Regards
  kanchan Soni
  Sr Research Associate-Bioanalytical
  Veeda Clinical Research
  
  

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