STUDY OF THE EFFECT OF THE XCIPIENT CROSSCARMELOSE ON METFORMIN INTESTINAL PERMEABILITY BY AN IN SITU INTESTINAL PERFUSION MODEL IN RATS

1
STUDY OF THE EFFECT OF THE XCIPIENT
CROSSCARMELOSE ON METFORMIN INTESTINAL
PERMEABILITY BY AN IN SITU INTESTINAL PERFUSION
MODEL IN RATS
Aceituno, A. PhD1,2, Dibsi, A., Pharm D1,
Gajardo, A., Pharm D.1 Pezoa, R., PhD2 1
Universidad de Valparaíso, 2Instituto de Salud
Pública de Chile This research work was funded
by the University of Valparaiso Research and
Development Division and the Public Health
Institute of Chile
RESULTS The mean calculated permeability values
of Metformin in the whole rat intestinal segment
showed significant differences at lower initial
drug concentrations (50 and 70 ?g/mL). Under the
experimental conditions, the absorption of
Metformin sulfate cannot be described as a
passive process at these concentrations. Metformin
permeability was dependent on the concentration,
therefore the absorption process can be described
as an apparent first order kinetic process
combined with a saturable efflux. The first order
kinetics was used to obtain the first order
apparent constants.

• PURPOSE
• To investigate on the permeability BCS
  classification of the drug Metformin and to study
  the effect of the potential ionic interaction
  between the excipient sodium Crosscarmellose (a
  common tablet disintegrant) and Metformin in
  pharmaceutical formulations by
• an in situ intestinal perfusion model in rats
  (close loop).
• simultaneous perfusion of the drug solution and
  Crosscarmellose in a whole intestinal segment.
• Assessment of the permeability coefficients,
  calculated with and without the excipient
  co-infusion of the drug.
• METHODOLOGY
• In situ infusion model
• An in situ absorption model in rats was used to
  evaluate the intestinal permeability of
  Metformin, a provisional BCS class III drug.
  Three drug concentrations were assayed to
  investigate on the passive or active absorption
  mechanism of the drug 50, 70 and 100 ?g/mL. A
  whole intestinal segment was isolated in
  anesthetized Sprague Dawley rats, washed with an
  electrolyte solution and cannulated at both
  distal ends.
• An isotonic buffered solution of Metformin or
  metformin plus Crosscarmellose was infused into
  the segment with the help of glass syringes, and
  the lumen concentration measured by a validated
  HPLC technique over a period of 30 minutes at 5
  minutes intervals. At the end of this period,
  rats were euthanized following a previously
  approved protocol.
• To investigate the effect of co-infusion of the
  drug and Crosscarmellose, a concentration of the
  disintegrant was chosen to represent the amount
  normally present in conventional tablet
  formulations. The effect on the drug absorption
  and permeability was evaluated by statistical
  comparison of the apparent permeability
  coefficient of Metformin measured when infused
  with and without dissolved Crosscarmellose.

The isolated segment was first washed with 30 mL
of a pH 7,4 solution (solution A) with the
purpose to eliminate the remnant intestinal
content and 30 mL solution B, in order to
condition the intestinal mucosa prior to
experiments Solution
A Solution B Proportion of
Crosscarmellose aded Shown in the next tables are
the volumes of Crosscarmellose added to the
Metformin solution perfunded, keeping in all
cases the drug/excipient ratio close to the one
found in conventional formulations of the
drug The apparent absorption rate constant
(Eq. 1) was calculated by fitting the lumen drug
concentration left versus time data to a first
order kinetics process after correcting the
concentration for the passive water reabsorption.
The intestinal permeability values were
calculated considering the relation between ka
and Peff (Eq. 2) where R is the radius of the
perfused intestinal segment.
Equation 1


Equation 2

Sodium chloride 9,2 g/L 9,2 g/L
Potassium chloride 0,34 g/L
Calcium chloride 0,19 g/L
Monobasic sodium phosphate 0,76 g/L 1/5 M (3,9 mL/L)
Monoacid sodium phosphate 1/5 M (6,1 mL/L)
Figure 4 theoretical ionic interaction between
Metformin and Crosscarmellose

Metformin predicted and experimental
concentrations at different initial drug
concentrations are depicted (Figs. 1, 2, 3). The
determination coefficients of the first order
regression was always higher than 0,95. Results
showed that there was a statistical difference
between the values of Metformin permeability
coefficients when the drug was perfused with or
without Croscarmellose. In the presence of
Croscarmellose, there was a statistically
significant decrease in intestinal permeability
at a concentration of 50 and 70 ?g/mL (5.4 x 10-5
versus 1.9 x 10-5 cm/sec and 2.0 x 10-5 versus
1.5 x 10-5 cm/sec at 70, respectively). No
difference in permeability coefficients was found
at a concentration of 100 ?g/mL (table below).
Likewise, there was dependence between the
concentration of perfused Metformin and the
permeability coefficients measured.
Log concentration
50 µg/mL metformin solution 50 µg/mL metformin
solution Crosscarmellose
time
Figure 1 Average Metformin concentrations in the
luminal intestinal content versus time after
perfusion (50 ?g/mL)
Metformin solution added with Crosscarmellose (50 mL total volume) Metformin solution added with Crosscarmellose (50 mL total volume) Metformin solution added with Crosscarmellose (50 mL total volume)
Metformin concentration (?g/mL) 50 70 100
Added volume (mL) of a 0,1 mg/mL Croscarmellose solution) 0,3 0,4 0,6

Permeability coefficient (cm/seg) (mean SD) Permeability coefficient (cm/seg) (mean SD)
Concentration (?g/mL) Metformin Metformin Crosscarmellose
50 5,4 10-5 (3,2 10-5) 1,9 10-5 (8,7 10-6) ? 0,05 p lt 0,05
70 2,0 10-5 (1,1 10-6) 1,5 10-5 (4,9 10-6) ? 0,05 p lt 0,05
100 2,4 10-5 (7,0 10-6) 1,4 10-5 (1,0 10-5) ? 0,05 p gt0,05
Log concentration
70 µg/mL metformin solution 70 µg/mL metformin
solution Crosscarmellose
time
Figure 2 Average Metformin concentrations in the
luminal intestinal content versus time after
perfusion (70 ?g/mL)

• CONCLUSIONS
• The rat in situ (close loop) absorption model
  proved to be useful to predict potential
  interactions between drug and excipients commonly
  used in tablet formulation
• The simultaneous presence of Croscarmellose and
  Metformin in a formulation might decrease its
  absorbed fraction and probably the
  bioavailability of poorly permeable ionic drug.
• Crosscarmellose produced a concentration
  dependant effect on Metformin intestinal
  permeability that is obscured by the
  concentration dependant permeability of the drug
  itself.

Log concentration
100 µg/mL metformin soluton 100 µg/mL metformin
solution Crosscarmellose
time
Figure 3 Average Metformin concentrations in the
luminal intestinal content versus time after
perfusion (100 ?g/mL)