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724 DRUG RELEASE
This test is provided to determine compliance with drug-release requirements where specified in individual monographs. Use the apparatus specified in the individual monograph. Replace the aliquots withdrawn for analysis with equal volumes of fresh Dissolution Medium at 37 or, where it can be shown that replacement of the medium is not necessary, correct for the volume change in the calculation. [NOTE—Medium replacement is not necessary for Apparatus 4, which is a continuous-flow system.] Keep the vessel covered for the duration of the test, and verify the temperature of the mixture under test at suitable times.

EXTENDED-RELEASE ARTICLES—GENERAL DRUG RELEASE STANDARD
Apparatus 1 and Apparatus 2
Apparatus— Proceed as directed under Dissolution 711.
Apparatus Suitability Test, Dissolution Medium, and Procedure— Proceed as directed under Dissolution 711.
Time— The test-time points, generally three, are expressed in hours. Specimens are to be withdrawn within a tolerance of ±2% of the stated time.
Interpretation— Unless otherwise specified in the individual monograph, the requirements are met if the quantities of active ingredient dissolved from the units tested conform to Acceptance Table 1. Continue testing through the three levels unless the results conform at either L1 or L2. Limits on the amounts of active ingredient dissolved are expressed in terms of the percentage of labeled content. The limits embrace each value of Qi, the amount dissolved at each specified fractional dosing interval. Where more than one range is specified in the individual monograph, the acceptance criteria apply individually to each range.
Acceptance Table 1
Level Number Tested Criteria
L1 6 No individual value lies outside each of the stated ranges and no individual value is less than the stated amount at the final test time.
L2 6 The average value of the 12 units (L1 + L2) lies within each of the stated ranges and is not less than the stated amount at the final test time; none is more than 10% of labeled content outside each of the stated ranges; and none is more than 10% of labeled content below the stated amount at the final test time.
L3 12 The average value of the 24 units (L1 + L2 + L3) lies within each of the stated ranges, and is not less than the stated amount at the final test time; not more than 2 of the 24 units are more than 10% of labeled content outside each of the stated ranges; not more than 2 of the 24 units are more than 10% of labeled content below the stated amount at the final test time; and none of the units is more than 20% of labeled content outside each of the stated ranges or more than 20% of labeled content below the stated amount at the final test time.
Apparatus 3 (Reciprocating Cylinder)
Apparatus— The assembly consists of a set of cylindrical, flat-bottomed glass vessels; a set of glass reciprocating cylinders; stainless steel fittings (type 316 or equivalent) and screens that are made of suitable nonsorbing and nonreactive material and that are designed to fit the tops and bottoms of the reciprocating cylinders; and a motor and drive assembly to reciprocate the cylinders vertically inside the vessels and, if desired, index the reciprocating cylinders horizontally to a different row of vessels. The vessels are partially immersed in a suitable water bath of any convenient size that permits holding the temperature at 37 ± 0.5 during the test. No part of the assembly, including the environment in which the assembly is placed, contributes significant motion, agitation, or vibration beyond that due to the smooth, vertically reciprocating cylinder. A device is used that allows the reciprocation rate to be selected and maintained at the dip rate specified in the individual monograph, within ± 5%. An apparatus that permits observation of the specimens and reciprocating cylinders is preferable. The components conform to the dimensions shown in Figure 1 unless otherwise specified in the individual monograph.
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Fig. 1. Apparatus 3. (All measurements are expressed in mm unless noted otherwise.)
USP Reference Standards 11 USP Chlorpheniramine Extended-Release Tablets RS (Drug Release Calibrator, Single Unit).
Apparatus Suitability Test— Individually test 1 tablet of the USP Drug Release Calibrator Tablets (Single Unit) according to the operation conditions specified. The apparatus is suitable if the results obtained are within the acceptable range stated in the certificate for that calibrator in the apparatus tested.
Dissolution Medium— Proceed as directed under Dissolution 711.
Procedure— Place the stated volume of the Dissolution Medium in each vessel of the apparatus, assemble the apparatus, equilibrate the Dissolution Medium to 37 ± 0.5, and remove the thermometer. Place 1 dosage-form unit in each of the six reciprocating cylinders, taking care to exclude air bubbles from the surface of each dosage-form unit, and immediately operate the apparatus as specified in the individual monograph. During the upward and downward stroke, the reciprocating cylinder moves through a total distance of 9.9 to 10.1 cm. Within the time interval specified, or at each of the times stated, raise the reciprocating cylinders and withdraw a portion of the solution under test from a zone midway between the surface of the Dissolution Medium and the bottom of each vessel. Perform the analysis as directed in the individual monograph. If necessary, repeat the test with additional dosage-form units.
Where capsule shells interfere with the analysis, remove the contents of not fewer than 6 capsules as completely as possible, and dissolve the empty capsule shells in the specified volume of Dissolution Medium. Perform the analysis as directed in the individual monograph. Make any necessary correction. Correction factors greater than 25% of the labeled content are unacceptable.
Time and Interpretation— Proceed as directed under Apparatus 1 and Apparatus 2.
Apparatus 4 (Flow-Through Cell)
Apparatus— The assembly consists of a reservoir and a pump for the Dissolution Medium; a flow-through cell; a water bath that maintains the Dissolution Medium at 37 ± 0.5 (see Figures 2 and 3). The cell size is specified in the individual monograph.
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Fig. 2. Large cell for tablets and capsules.(All measurements are expressed in mm unless noted otherwise.)
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Fig. 2a. Tablet holder for the large cell.(All measurements are expressed in mm unless noted otherwise.)
The pump forces the Dissolution Medium upwards through the flow-through cell. The pump has a delivery range between 240 and 960 mL per hour, with standard flow rates of 4, 8, and 16 mL per minute. It must be volumetric to deliver constant flow independent of flow resistance in the filter device; the flow profile is sinusoidal with a pulsation of 120 ± 10 pulses per minute.
The flow-through cell (see Figures 2 and 3), of transparent and inert material, is mounted vertically with a filter system (specified in the individual monograph) that prevents escape of undissolved particles from the top of the cell; standard cell diameters are 12 and 22.6 mm; the bottom cone is usually filled with small glass beads of about 1-mm diameter with one bead of about 5 mm positioned at the apex to protect the fluid entry tube; a tablet holder (see Figures 2a and 3a) is available for positioning of special dosage forms, for example, inlay tablets. The cell is immersed in a water bath, and the temperature is maintained at 37 ± 0.5.
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Fig. 3. Small cell for tablets and capsules.(All measurements are expressed in mm unless noted otherwise.)
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Fig. 3a. Tablet holder for the small cell. (All measurements are expressed in mm unless noted otherwise.)
The apparatus uses a clamp mechanism and two O-rings for the fixation of the cell assembly. The pump is separated from the dissolution unit in order to shield the latter against any vibrations originating from the pump. The position of the pump should not be on a level higher than the reservoir flasks. Tube connections are as short as possible. Use polytef tubing with a 1.6-mm inner diameter and chemically inert flanged-end connections.
Apparatus Suitability Test and Dissolution Medium— Proceed as directed under Dissolution 711.
Procedure— Place the glass beads into the cell specified in the monograph. Place 1 dosage-form unit on top of the beads or, if specified in the monograph, on a wire carrier. Assemble the filter head and fix the parts together by means of a suitable clamping device. Introduce by the pump the Dissolution Medium warmed to 37 ± 0.5 through the bottom of the cell to obtain the flow rate specified in the individual monograph and measured with an accuracy of 5%. Collect the eluate by fractions at each of the times stated. Perform the analysis as directed in the individual monograph. Repeat the test with additional dosage-form units.
Where capsule shells interfere with the analysis, remove the contents of not less than 6 capsules as completely as possible, and dissolve the empty capsule shells in the specified volume of Dissolution Medium. Perform the analysis as directed in the individual monograph. Make any necessary correction. Correction factors greater than 25% of the labeled content are unacceptable.
Time and Interpretation— Proceed as directed under Apparatus 1 and Apparatus 2.

DELAYED-RELEASE (ENTERIC-COATED) ARTICLES—GENERAL DRUG RELEASE STANDARD
Use Method A or Method B and the apparatus specified in the individual monograph. Conduct the Apparatus Suitability Test as directed under Dissolution 711. All test times stated are to be observed within a tolerance of ±2%, unless otherwise specified.
Method A
Procedure (unless otherwise directed in the individual monograph)—
Acid Stage— Place 750 mL of 0.1 N hydrochloric acid in the vessel, and assemble the apparatus. Allow the medium to equilibrate to a temperature of 37 ± 0.5. Place 1 tablet or 1 capsule in the apparatus, cover the vessel, and operate the apparatus for 2 hours at the rate specified in the monograph.
After 2 hours of operation in 0.1 N hydrochloric acid, withdraw an aliquot of the fluid, and proceed immediately as directed for Buffer Stage.
Perform an analysis of the aliquot using the Procedure specified in the test for Drug release in the individual monograph.
Unless otherwise specified in the individual monograph, the requirements of this portion of the test are met if the quantities, based on the percentage of the labeled content, of active ingredient dissolved from the units tested conform to Acceptance Table 2. Continue testing through all levels unless the results of both acid and buffer stages conform at an earlier level.
Acceptance Table 2
Level Number Tested Criteria
A1 6 No individual value exceeds 10% dissolved.
A2 6 Average of the 12 units (A1 + A2) is not more than 10% dissolved, and no individual unit is greater than 25% dissolved.
A3 12 Average of the 24 units (A1 + A2 + A3) is not more than 10% dissolved, and no individual unit is greater than 25% dissolved.
Buffer Stage— [NOTE—Complete the operations of adding the buffer, and adjusting the pH within 5 minutes.] With the apparatus operating at the rate specified in the monograph, add to the fluid in the vessel 250 mL of 0.20 M tribasic sodium phosphate that has been equilibrated to 37 ± 0.5. Adjust, if necessary, with 2 N hydrochloric acid or 2 N sodium hydroxide to a pH of 6.8 ± 0.05. Continue to operate the apparatus for 45 minutes, or for the time specified in the individual monograph. At the end of the time period, withdraw an aliquot of the fluid, and perform the analysis using the Procedure specified in the test for Drug release in the individual monograph. The test may be concluded in a shorter time period than that specified for the Buffer Stage if the requirement for minimum amount dissolved is met at an earlier time.
Interpretation— Unless otherwise specified in the individual monograph, the requirements are met if the quantities of active ingredient dissolved from the units tested conform to Acceptance Table 3. Continue testing through the three levels unless the results of both stages conform at an earlier level. The value of Q in Acceptance Table 3 is 75% dissolved unless otherwise specified in the individual monograph. The quantity, Q, specified in the individual monograph, is the total amount of active ingredient dissolved in both the acid and buffer stages, expressed as a percentage of the labeled content. The 5% and 15% values in Acceptance Table 3 are percentages of the labeled content so that these values and Q are in the same terms.
Acceptance Table 3
Level Number Tested Criteria
B1 6 Each unit is not less than Q + 5%.
B2 6 Average of 12 units (B1 + B2) is equal to or greater than Q, and no unit is less than Q 15%.
B3 12 Average of 24 units (B1 + B2 + B3) is equal to or greater than Q, not more than 2 units are less than Q 15%, and no unit is less than Q 25%.
Method B
Procedure (unless otherwise directed in the individual monograph)—
Acid Stage— Place 1000 mL of 0.1 N hydrochloric acid in the vessel, and assemble the apparatus. Allow the medium to equilibrate to a temperature of 37 ± 0.5. Place 1 tablet or 1 capsule in the apparatus, cover the vessel, and operate the apparatus for 2 hours at the rate specified in the monograph. After 2 hours of operation in 0.1 N hydrochloric acid, withdraw an aliquot of the fluid, and proceed immediately as directed under Buffer Stage.
Perform an analysis of the aliquot using the Procedure specified in the test for Drug release in the individual monograph.
Unless otherwise specified in the individual monograph, the requirements of this portion of the test are met if the quantities, based on the percentage of the labeled content, of active ingredient dissolved from the units tested conform to Acceptance Table 2 under Method A. Continue testing through all levels unless the results of both acid and buffer stages conform at an earlier level.
Buffer Stage— [NOTE—For this stage of the procedure, use buffer that previously has been equilibrated to a temperature of 37 ± 0.5.] Drain the acid from the vessel, and add to the vessel 1000 mL of pH 6.8 phosphate buffer, prepared by mixing 0.1 N hydrochloric acid with 0.20 M tribasic sodium phosphate (3:1) and adjusting, if necessary, with 2 N hydrochloric acid or 2 N sodium hydroxide to a pH of 6.8 ± 0.05. [NOTE—This may be accomplished also by removing from the apparatus the vessel containing the acid and replacing it with another vessel containing the buffer and transferring the dosage unit to the vessel containing the buffer.] Continue to operate the apparatus for 45 minutes, or for the time specified in the individual monograph. At the end of the time period, withdraw an aliquot of the fluid, and perform the analysis using the Procedure specified in the test for Drug release in the individual monograph. The test may be concluded in a shorter time period than that specified for the Buffer Stage if the requirement for minimum amount dissolved is met at an earlier time.
Interpretation— Proceed as directed for Interpretation under Method A.

TRANSDERMAL DELIVERY SYSTEMS—GENERAL DRUG RELEASE STANDARDS
Apparatus 5 (Paddle over Disk)
Apparatus— Use the paddle and vessel assembly from Apparatus 2 as described under Dissolution 711, with the addition of a stainless steel disk assembly 1 designed for holding the transdermal system at the bottom of the vessel. Other appropriate devices may be used, provided they do not sorb, react with, or interfere with the specimen being tested 2 . The temperature is maintained at 32 ± 0.5. A distance of 25 ± 2 mm between the paddle blade and the surface of the disk assembly is maintained during the test. The vessel may be covered during the test to minimize evaporation. The disk assembly for holding the transdermal system is designed to minimize any “dead” volume between the disk assembly and the bottom of the vessel. The disk assembly holds the system flat and is positioned such that the release surface is parallel with the bottom of the paddle blade (see Figure 4).
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Fig. 4. Paddle Over Disk.(All measurements are expressed in mm unless noted otherwise.)
Apparatus Suitability Test and Dissolution Medium— Proceed as directed for Apparatus 2 under Dissolution 711.
Procedure— Place the stated volume of the Dissolution Medium in the vessel, assemble the apparatus without the disk assembly, and equilibrate the medium to 32 ± 0.5. Apply the transdermal system to the disk assembly, assuring that the release surface of the system is as flat as possible. The system may be attached to the disk by applying a suitable adhesive3 to the disk assembly. Dry for 1 minute. Press the system, release surface side up, onto the adhesive-coated side of the disk assembly. If a membrane4 is used to support the system, it is applied so that no air bubbles occur between the membrane and the release surface. Place the disk assembly flat at the bottom of the vessel with the release surface facing up and parallel to the edge of the paddle blade and surface of the Dissolution Medium. The bottom edge of the paddle is 25 ± 2 mm from the surface of the disk assembly. Immediately operate the apparatus at the rate specified in the monograph. At each sampling time interval, withdraw a specimen from a zone midway between the surface of the Dissolution Medium and the top of the blade, not less than 1 cm from the vessel wall. Perform the analysis on each sampled aliquot as directed in the individual monograph, correcting for any volume losses, as necessary. Repeat the test with additional transdermal systems.
Time— The test time points, generally three, are expressed in hours. Specimens are to be withdrawn within a tolerance of ±15 minutes or ±2% of the stated time, the tolerance that results in the narrowest time interval being selected.
Interpretation— Unless otherwise specified in the individual monograph, the requirements are met if the quantities of active ingredient released from the system conform to Acceptance Table 4 for transdermal drug delivery systems. Continue testing through the three levels unless the results conform at either L1 or L2.
Acceptance Table 4
Level Number Tested Criteria
L1 6 No individual value lies outside the stated range.
L2 6 The average value of the 12 units (L1 + L2) lies within the stated range. No individual value is outside the stated range by more than 10% of the average of the stated range.
L3 12 The average value of the 24 units (L1 + L2 + L3) lies within the stated range. Not more than 2 of the 24 units are outside the stated range by more than 10% of the average of the stated range; and none of the units is outside the stated range by more than 20% of the average of the stated range.
Apparatus 6 (Cylinder)
Apparatus— Use the vessel assembly from Apparatus 1 as described under Dissolution 711, except to replace the basket and shaft with a stainless steel cylinder stirring element and to maintain the temperature at 32 ± 0.5 during the test. The shaft and cylinder components of the stirring element are fabricated of stainless steel to the specifications shown in Figure 5. The dosage unit is placed on the cylinder at the beginning of each test. The distance between the inside bottom of the vessel and the cylinder is maintained at 25 ± 2 mm during the test.
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Fig. 5. Cylinder Stirring Element.5 (All measurements are expressed in cm unless noted otherwise.)
Dissolution Medium— Use the medium specified in the individual monograph (see Dissolution 711).
Procedure— Place the stated volume of the Dissolution Medium in the vessel of the apparatus specified in the individual monograph, assemble the apparatus, and equilibrate the Dissolution Medium to 32 ± 0.5. Unless otherwise directed in the individual monograph, prepare the test system prior to test as follows. Remove the protective liner from the system, and place the adhesive side on a piece of Cuprophan4 that is not less than 1 cm larger on all sides than the system. Place the system, Cuprophan covered side down, on a clean surface, and apply a suitable adhesive 3 to the exposed Cuprophan borders. If necessary, apply additional adhesive to the back of the system. Dry for 1 minute. Carefully apply the adhesive-coated side of the system to the exterior of the cylinder such that the long axis of the system fits around the circumference of the cylinder. Press the Cuprophan covering to remove trapped air bubbles. Place the cylinder in the apparatus, and immediately rotate at the rate specified in the individual monograph. Within the time interval specified, or at each of the times stated, withdraw a quantity of Dissolution Medium for analysis from a zone midway between the surface of the Dissolution Medium and the top of the rotating cylinder, not less than 1 cm from the vessel wall. Perform the analysis as directed in the individual monograph, correcting for any volume losses as necessary. Repeat the test with additional transdermal drug delivery systems.
Time— Proceed as directed under Apparatus 5.
Interpretation— Unless otherwise specified in the individual monograph, the requirements are met if the quantities of active ingredient released from the system conform to Acceptance Table 4 for transdermal drug delivery systems. Continue testing through the three levels unless the results conform at either L1 or L2.
Apparatus 7 (Reciprocating Holder)
NOTE—This apparatus may also be specified for use with a variety of dosage forms.
Apparatus— The assembly consists of a set of volumetrically calibrated or tared solution containers made of glass or other suitable inert material6, a motor and drive assembly to reciprocate the system vertically and to index the system horizontally to a different row of vessels automatically if desired, and a set of suitable sample holders (see Figure 67 and Figures 7a7d). The solution containers are partially immersed in a suitable water bath of any convenient size that permits maintaining the temperature, T, inside the containers at 32 ± 0.5 or within the allowable range, as specified in the individual monograph, during the test. No part of the assembly, including the environment in which the assembly is placed, contributes significant motion, agitation, or vibration beyond that due to the smooth, vertically reciprocating sample holder. Apparatus that permits observation of the system and holder during the test is preferable. Use the size container and sample holder as specified in the individual monograph.
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Fig. 6. Reciprocating Disk Sample Holder.7
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Fig. 7a. Transdermal system holder—angled disk.
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Fig. 7b. Transdermal system holder—cylinder.
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Fig. 7c. Oral extended-release tablet holder—rod, pointed for gluing.
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Fig. 7d. Oral extended-release tablet holder—spring holder.
Dissolution Medium— Use the Dissolution Medium specified in the individual monograph (see Dissolution 711).
Sample Preparation A (Coated tablet drug delivery system)— Attach each system to be tested to a suitable sample holder (e.g., by gluing system edge with 2-cyano acrylate glue onto the end of a plastic rod or by placing the system into a small nylon net bag at the end of a plastic rod or within a metal coil attached to a metal rod).
Sample Preparation B (Transdermal drug delivery system)— Press the system onto a dry, unused piece of Cuprophan4, nylon netting, or equivalent with the adhesive side against the selected substrate, taking care to eliminate air bubbles between the substrate and the release surface. Attach the system to a suitable sized sample holder with a suitable O-ring such that the back of the system is adjacent to and centered on the bottom of the disk-shaped sample holder or centered around the circumference of the cylindrical-shaped sample holder. Trim the excess substrate with a sharp blade.
Sample Preparation C (Other drug delivery systems)— Attach each system to be tested to a suitable holder as described in the individual monograph.
Procedure— Suspend each sample holder from a vertically reciprocating shaker such that each system is continuously immersed in an accurately measured volume of Dissolution Medium within a calibrated container pre-equilibrated to temperature, T. Reciprocate at a frequency of about 30 cycles per minute with an amplitude of about 2 cm, or as specified in the individual monograph, for the specified time in the medium specified for each time point. Remove the solution containers from the bath, cool to room temperature, and add sufficient solution (i.e., water in most cases) to correct for evaporative losses. Perform the analysis as directed in the individual monograph. Repeat the test with additional drug delivery systems as required in the individual monograph.
Interpretation— Unless otherwise specified in the individual monograph, the requirements are met if the quantities of the active ingredients released from the system conform to Acceptance Table 1 for coated tablet drug delivery systems, to Acceptance Table 4 for transdermal drug delivery systems, or as specified in the individual monograph. Continue testing through the three levels unless the results conform at either L1 or L2.

1  Disk assembly (stainless support disk) may be obtained from Millipore Corp., Ashley Rd., Bedford, MA 01730.
2  A suitable device is the watchglass-patch-polytef mesh sandwich assembly available as the Transdermal SandwichTM from Hanson Research Corp., 9810 Variel Ave., Chatsworth, CA 91311.
3  Use Dow Corning, MD7-4502 Silicone Adhesive 65% in ethyl acetate, or the equivalent.
4  Use Cuprophan, Type 150 pm, 11 ± 0.5-µm thick, an inert, porous cellulosic material, which is available from Medicell International Ltd., 239 Liverpool Road, London NI ILX, England.
5  The cylinder stirring element is available from Accurate Tool, Inc., 25 Diaz St., Stamford, CT 06907, or from VanKel Technology Group, 13000 Weston Parkway, Cary, NC 27513.
6  The materials should not sorb, react with, or interfere with the specimen being tested.
7  The reciprocating disk sample holder may be purchased from ALZA Corp., 1900 Charleston Road, P.O. Box 7210, Mt. View, CA 94039–7210 or VanKel Technology Group.

Auxiliary Information—
Staff Liaison : William E. Brown, Scientist
Expert Committee : (BPC05) Biopharmaceutics05
USP29–NF24 Page 2682
Pharmacopeial Forum : Volume No. 31(1) Page 213
Phone Number : 1-301-816-8380