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Abstract

(Letter to Editor )

Dear Editor,
The present letter is focused on the re-classification of Biopharmaceutical Classification System (BCS), which is adopted by United States Food and Drug Administration   (USFDA)¹.  Bioavailability   (BA)   andBioequivalence (BE) studies of drug products not only assure  the  safety  of  drug  products  but  also  assure  the efficacy and allow inter-changeability of drug products, which  is  important  in  cost  reduction  of  drug  therapy. The traditional biopharmaceutical classification system ² , appeared  in  literature  a  decade  before,  is  effectively implemented by pharmaceutical companies for designing BA/BE studies, in-vitro in-vivo correlation (IVIVC),optimization  of  dissolution  media  and  formulation  research³. BCS is based on the two important rate-determining  steps  in  BA  known  as  drug  solubility  and drugpermeability⁴.However, few other parameters like dose,dissolution volume and pH were equally considered for classifying the drugs based on BCS². Even though BCS made a great impact on discovery and development of drugs in pipeline, BCS is mainly focused on bioavailability and IVIVC³.  Moreover,  BCS  serve  as  a  guideline  forformulators in selection of excipients and processes. Onthe other hand, advent of biotechnology, pharmacology,High Through Put (HTP) screening, combinatorial chemistry and drug delivery research encouraged the invention  of  highly  potent  synthetic  drug  substances  as  wellas protein and peptide molecules⁵. The future molecules mayface  conventional  pharmacokinetic  problems  such  as  poor solubility, poor permeability and shorter half life. In addition to  that  unconventional  problems  like  high  first  pass  effect,low in vitro  and  in vivo stability, (Pgp) mediated efflux transport, lack of sensitivity to analyze the drug in biological matrices and lack of sensitivity to detect the polymorphs in dosage forms  will  appear  in  front  of  pharmaceutical  scientist  while developing a drug and/or dosage forms. It is really very difficult  and  most  of  the  time  not  necessary  to  consider  all  the parameters  to  classify  the  drugs.  Our  Proposed Biopharmaceutical Classification System (PBCS) allows classifying  the  drugs  not  only  based  on  drug  solubility  and  permeability  but  also  considering  drug  stability  in  GIT  and  first pass effect. Highly stable drugs should be 90% stable in GIT for  the  time  required  to  absorb  90%  of  unchanged  drug  in GIT.  First  pass  effect  of  more  than  60  %  is  considered  as high  first  pass  effect  of  drugs.  Proposed  biopharmaceutical classification  system  is  presented  in  Table  No  1.  The  main aim of PBCS is to predict the BA of dosage form from the results obtained from Phase I clinical studies. PBCS will give the  clue  for  formulation  scientist  to  optimize  the  BA  by  the addition of enzyme inhibitors, change in micro environmental pH  and  addition  of  buffers  to  improve  the  BA.  PBCS  will also allow addition of some enzymes in dissolution media that will  give  the  trend  of  first  pass  effect  in  in-vivo conditions.BA/BE studies are conducted in healthy human subjects. The unnecessary  exposure  of  drug  in  healthy  human  volunteers needs ethical justification. Moreover, human trails are costly affairs and time consuming process. The main goal of PBCS is to reduce the human trails for BA/BE studies. If at all effective  in vitro  dissolution technologies are invented in future on the basis of PBCS that will serve as surrogate marker in BA and  BE  of  drug  products.  PBCS  conventionally  be  termed as  Modern  Biopharmaceutical  Classification  System (MBCS).

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