[LONGITUDINAL]
input = {ka, V, Cl, IC50, kin, kout, a1, a2}  

EQUATION:
C     = pkmodel(ka, V, Cl)
t0    = 0
E_0   = kin/kout
ddt_E = kin*(1 - C/(IC50+C)) - kout*E

DEFINITION:
Concentration = {distribution = lognormal, 
                 prediction   = C, 
                 sd           = a1}

Effect = {distribution = normal, 
          prediction   = E, 
          sd           = a2}
