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  Absorption Model

• First-Order

  Volume of Distribution

• Full PBPK (Method 2)

Note: Kp scalar used

  Route of Elimination

• UGT1A9 (50%); UGT2B7(50%)

  Perpetrator DDI

• CYP1A2 Inhibitor

  Validation

• One clinical study describing single dose exposure of DHA was used to verify the PBPK model.  100% of studies were within 2-fold, of which 100% were within 1.5-fold. 

  Limitations

• The absorption model does not consider the formation of ‘DHA from artesunate’ mechanistically. Instead, an optimized ka and fa were applied to the DHA model to describe the observed plasma concentration-time curve of DHA. The remainder of the DHA model was identical to the DHA model which is described above.
• The model does not account for the differences in plasma fraction unbound observed in patients compared to healthy volunteers.
• Verification needed for perpetrator DDI assessment as literature data is unavailable at this time.

  Updates in V19

• Updated in vitro data
  • Propranolol Papp: 30 cm/s x 106
• Converted model to full PBPK with Vss predicted through Method 2
• Updated retrograde clearance

  Absorption Model

First-Order

  Volume of Distribution

• Full PBPK (Method 2)

Note: A Kp scalar (0.5) was used in the model along with optimized partitioning into adipose tissue (Kp,adipose = 0.5) to recover the clinical observed data. 

  Route of Elimination

• CYP2B6 and CYP3A4 (non-linear kinetics); incorporates autoinduction of CYP2B6

  Perpetrator DDI

• Induction of CYP2B6

  Validation

• Two clinical studies describing single dose exposure and two describing multiple dose exposure of artemether were used to verify the PBPK model.  The single dose exposures were within 1.5-fold of observed for both studies. The multiple dose exposures were slightly over-predicted at 2.02 and 2.63-fold for the two studies.  Clinical DDI studies with ketoconazole, rifampicin and efavirenz where artemether was the victim of CYP3A4 (and CYP2B6 for efavirenz)-mediated DDIs were accurately recovered (within 1.25-fold) using the PBPK model.  A clinical DDI study with efavirenz, where artemether was the perpetrator of a CYP2B6-mediated DDI was accurately recovered (within 1.25-fold) using the PBPK model. 

  Limitations

• The tendency towards over-prediction of artemether exposure upon multiple dosing could indicate a greater extent of induction is required. However, any increase in induction potency resulted in under-prediction of single dose exposure, which is of greater importance for the therapeutic effect of artemether.

  Updates in V19

• Updated in vitro­ data
  • fu: 0.083 -> 0.038
  • B:P: 1.7 -> 1.1
• Optimized ka and t_lag
• Converted from minimal PBPK model to full PBPK model
  • Optimized CYP2B6 IndC₅₀