Measuring Drug Release
This sample experiment was conducted in water and showed that after 2.5 hours,
release was still continuing from the controlled release capsule.
| Conventional Capsule |
|
Controlled Release Capsule |
| Clock Time |
Run Time |
Absorb. |
Conc. |
Cum. Amt. Released |
|
Clock Time |
Run Time |
Absorb. |
Conc. |
Cum. Amt. Released |
| 2:40 |
0 |
0.000 |
0.0 |
0.0 |
|
2:35 |
0 |
0.000 |
0.0 |
0.0 |
| 2:55 |
15 |
0.005 |
0.0010 |
0.10 |
|
2:50 |
15 |
0.012 |
0.001 |
0.15 |
| 3:10 |
30 |
0.016 |
0.0017 |
0.17 |
|
3:05 |
30 |
0.031 |
0.003 |
0.27 |
| 3:25 |
45 |
0.031 |
0.0027 |
0.27 |
|
3:20 |
45 |
0.059 |
0.004 |
0.44 |
| 3:40 |
60 |
0.048 |
0.0037 |
0.37 |
|
3:35 |
60 |
0.089 |
0.006 |
0.63 |
| 3:55 |
75 |
0.065 |
0.0048 |
0.48 |
|
3:50 |
75 |
0.123 |
0.008 |
0.84 |
| 4:10 |
90 |
0.592 |
0.037 |
3.75 |
|
4:05 |
90 |
0.160 |
0.011 |
1.07 |
| 4:25 |
105 |
0.609 |
0.039 |
3.85 |
|
4:20 |
105 |
0.194 |
0.013 |
1.28 |
| 4:40 |
120 |
0.610 |
0.039 |
3.86 |
|
4:35 |
120 |
0.240 |
0.016 |
1.56 |
| 4:55 |
135 |
0.614 |
0.039 |
3.88 |
|
4:50 |
135 |
0.287 |
0.019 |
1.85 |
| 5:10 |
150 |
0.612 |
0.039 |
3.87 |
|
5:05 |
150 |
0.302 |
0.019 |
1.95 |
The same experiment was repeated in 0.01N
HCl.
| Conventional Capsule |
|
Controlled Release Capsule |
| Clock Time |
Run Time |
Absorb. |
Conc. |
Cum. Amt. Released |
|
Clock Time |
Run Time |
Absorb. |
Conc. |
Cum. Amt. Released |
| 2:20 |
0 |
0.000 |
0.0 |
0.0 |
|
2:15 |
0 |
0.000 |
0.0 |
0.0 |
| 2:35 |
15 |
0.301 |
0.014 |
1.38 |
|
2:30 |
15 |
0.030 |
0.00044 |
0.044 |
| 2:50 |
30 |
0.808 |
0.039 |
3.87 |
|
2:45 |
30 |
0.176 |
0.0076 |
0.76 |
| 3:05 |
45 |
0.815 |
0.039 |
3.90 |
|
3:00 |
45 |
0.368 |
0.017 |
1.71 |
| 3:20 |
60 |
0.822 |
0.039 |
3.94 |
|
3:15 |
60 |
0.516 |
0.024 |
2.48 |
| 3:35 |
75 |
0.800 |
0.038 |
3.83 |
|
3:30 |
75 |
0.637 |
0.030 |
3.03 |
| 3:50 |
90 |
0.800 |
0.038 |
3.83 |
|
3:45 |
90 |
0.740 |
0.035 |
3.54 |
| 4:05 |
105 |
0.804 |
0.039 |
3.85 |
|
4:00 |
105 |
0.814 |
0.039 |
3.90 |
The "rate of
release" is determined by plotting the Cumulative Amount Released versus some
function of time. For matrix diffusion controlled release, adaptations of the
Higuchi equation are used; time is expressed as the square root of time and
has units of minutes1/2. A linear trendline is fit through the points that occur
after a lag time or before any asymptotic values are reached. The release of
salicylic acid in 0.01N HCl is shown in the plot below. The conventional capsule
apparently released all of its contents by 30 minutes, since after that time
the amount released remained constant. The release rate was 1.55 mg/minutes1/2
which is almost three times as fast as seen with the controlled release capsule.
But more importantly, the controlled release capsule continuously releases drug
for hours, where the conventional capsule released all the drug within 30 minutes.