The USP performance test is one test in a series of tests that form the dosage form's public specification (tests, procedures for the tests, acceptance criteria). To satisfy the performance test, USP provides three general test chapters Disintegration á701ñ, Dissolution á711ñ, and Drug Release á724ñ. These general chapters specify the conditions of the procedure. For dissolution, these include standards that specify the apparatus/agitation rate, medium, study design, assay, and acceptance criteria. Overall the procedure yields data to allow an accept/reject decision relative to the acceptance criteria. Acceptance criteria are frequently based on a regulatory decision. This general information chapter provides recommendations on how to develop and validate a dissolution procedure.

The dissolution procedure relies on an apparatus, a medium, and a study design chosen to be transferable and rugged and to yield acceptable data. A discriminating procedure yields data that distinguishes important differences in components and composition and/or method of manufacture between dosage forms. The value of dissolution as a quality control tool for predicting in vivo performance of a drug product is significantly enhanced if an in vitro–in vivo relationship (correlation or association) is established; but this relationship is not required (see FDA Guidances). Occasionally the in vitro dissolution test is found to be more sensitive and discriminating than the in vivo test. From a quality assurance point of view, a more discriminating dissolution method is preferred because the test will indicate possible changes in the quality of the product before in vivo performance is affected.

The discriminatory power of the dissolution method depends on the method's ability to detect changes in the drug product. Ideally, the dissolution test conditions would show discrimination for product changes that may affect biopharmaceutical product performance. However, unless an in vitro–in vivo correlation exists for the product, variations in dissolution behavior may or may not reflect variations in the product's in vivo performance. To determine if a dissolution method can show discrimination for product changes, the method should be challenged. There are several ways to challenge the discriminatory power of the method, but the most common approach is to test formulations manufactured with different parameters. Manufacturing variables can come from many sources, e.g., the drug substance, the drug product's formulation, and/or the drug product's manufacturing process. For example, the ability of the method to detect changes in the drug substance can be evaluated by testing products with drug substances having different particle sizes, crystal habits, solvation, surface areas, or synthetic pathways. The method sensitivity to drug product formulation changes can be challenged by testing products with different amounts or ratios of excipients or by testing formulation changes, such as wet granulation versus dry blend, or intra- versus extra-granulation. The method sensitivity to manufacturing process variables such as lubrication blend time, compression force, addition order, drying methods, coating methods, and equipment capability or size can also be evaluated. As different formulations are made using some of the variables just mentioned; the dissolution data are examined. If the data show a measurable difference for the key variables, then the method may be considered a discriminating test for critical manufacturing variables.

With regard to stability, the dissolution test should appropriately reflect relevant changes in the biopharmaceutical performance caused by temperature, aging, humidity, and photosensitivity. A properly designed dissolution test does not generate highly variable dissolution results nor is it associated with significant analytical solution stability problems. If these issues arise, the dissolution test design should be evaluated and appropriately revised.

Apparatus

Basket Mesh Size— A 40-mesh basket screen is used in most cases; however, other mesh sizes (10 and 20 mesh) may be used when the need is clearly documented by supporting data. In countries where available mesh sizes vary from the USP specified mesh value, basket material with the nearest metric dimension should be used. Care must be taken that baskets are uniform and meet the dimensions requirements specified under Dissolution á711ñ. If the basket screens become clogged during dissolution of capsule or tablet formulations, it may be advisable to switch to the paddle method.

Minipaddles— A minipaddle in combination with a 200-mL vessel may be considered for low-dosage products.

Two- or Four-Liter Vessels— The increased volume made possible by using these vessels can assist in meeting sink conditions for poorly soluble drugs.

Other Apparatus— The rotating bottle or static tubes (jacketed stationary tubes enclosed with a water jacket and equipped with a magnetic stirrer) may also have utility for microspheres and implants.

Sinkers

Materials: 316 stainless steel wire, 0.032 inch/20 gauge; one set of cork borers #1 to #15.

Procedure— Cut the specified length of coil length wire around the specified bore of the appropriate size, and use small pliers to curve in the ends. In countries where normal values for wire diameters vary from the tabulated values, use wire with the nearest metric dimension.

Agitation

Physical and chemical data for the drug substance and dosage unit should be determined before selecting the dissolution medium. Two key properties of the drug are the solubility and solution state stability of the drug as a function of the pH value. When adjusting the composition of the medium to generate sink conditions, the influence of surfactants, pH value, and buffers on the solubility and stability of the drug should be evaluated. Key properties of the dosage unit that may affect the dissolution, enteric-coating, modified-release mechanism, and disintegration rate are hardness, friability, presence of solubility enhancers, and the presence of other excipients.

Selection of the dissolution medium is based, in part, on the solubility data and the dose range in order to ensure that sink conditions are met. The term sink conditions is defined as the volume of medium at least greater than three times that required to form a saturated solution of drug substance. A medium that fails to provide sink conditions may be justifiable if it is shown to be more discriminating or if it provides reliable data that otherwise can only be obtained with the addition of surfactants.

Using an aqueous-organic solvent mixture as a dissolution medium is discouraged; however, if an in vitro–in vivo relationship is demonstrated that cannot be accomplished with a pure aqueous medium, this type of medium may be acceptable.

Purified water is often used as the dissolution medium but is not ideal for several reasons: the quality of water can vary depending on the source of water; the pH value is inherently difficult to measure because the pH value can vary from day to day and may also change during the run depending on the active substance and excipients; and finally, the surface tension may also be variable and dependent on the excipients in the formulation. Despite these limitations, water is inexpensive, readily available, disposed of easily, ecologically acceptable, and suitable for products with a release rate independent of the pH value of the medium. Further, if water is named as the medium in an official test, it is not necessary to change to another medium unless there is a compelling reason.

The dissolution characteristics of an oral formulation are evaluated over the physiologic pH range of 1.2 to 6.8 (1.2 to 7.5 for modified-release formulations). During method development, it may be useful to measure the pH before and after a run to see if the pH changes during the test. Selection of the most appropriate conditions for routine testing is then based on discriminatory capability, ruggedness, stability of the analyte in the test medium, and, where possible, relevance to in vivo performance.

Listed below are typical media for a dissolution test. Buffers and acids are prepared as directed for Buffer Solutions and Volumetric Solutions, respectively, under Reagents, Indicators, and Solutions. Simulated gastric fluid and simulated intestinal fluid are prepared as directed for Test Solutions under Reagents, Indicators, and Solutions. The following list is not exhaustive and not in order of preference:

For very poorly soluble compounds, aqueous solutions may contain a percentage of a surfactant (e.g., sodium lauryl sulfate, polysorbate, or lauryldimethylamine oxide) that is used to enhance drug solubility. The need for surfactants and the concentrations used could be justified by showing profiles at several different concentrations. Surfactants can be used as either a wetting agent or, when the critical micelle concentration is reached, to solubilize the drug substance. The molarity of the buffers and acids used can influence the solubilizing effect, and this should be evaluated.

The Biopharmaceutics Classification System describes the classification of compounds according to solubility and permeability.1 “Biorelevant medium” is a term used to describe a medium that has some relevance to the in vivo dissolution conditions for the compound. Choice of a biorelevant medium is based on a mechanistic approach that considers the absorption site, if known, and whether the rate-limiting step to absorption is the dissolution or permeability of the compound. In some cases, the biorelevant medium will be different from the test conditions chosen for the regulatory test, and the time points are also likely to be different. If the compound dissolves quickly in the stomach and is highly permeable, gastric emptying time may be the rate-limiting step to absorption. In this case, the dissolution test is to demonstrate that the drug is released quickly under typical gastric (acidic) conditions. On the other hand, if dissolution occurs primarily in the intestinal tract (e.g., for a poorly soluble, weak acid), a higher pH range (e.g., simulated intestinal fluid with a pH of 6.8) will be more appropriate. The “fed” and “fasted state” may also have significant effects on the absorption or solubility of a compound. Compositions of media that simulate the fed and fasted states can be found in the literature. These media reflect changes in the pH, bile concentrations, and osmolarity after meal intake, and, therefore, have a different composition than that of typical compendial media. They are primarily used to establish in vitro–in vivo correlations during formulation development and to assess potential food effects,but are not intended for quality control purposes. For quality control purposes, the substitution of natural surfactants (bile components) with appropriate synthetic surfactants is permitted and encouraged because of the expense of the natural substances and the labor-intensive preparation of the biorelevant media.

The use of an enzyme in the dissolution medium is permitted (see Dissolution á711ñ) when dissolution failures occur due to pellicle formation with gelatin capsules or gelatin-coated products.

Normally for the basket and paddle apparatus, the volume of the dissolution medium is 500 mL to 1000 mL, with 900 mL as the most common volume. The volume can be raised to between 2 and 4 liters, depending on the concentration and sink conditions of the drug, but proper justification is expected.

The significance of deaeration of the medium may be determined: air bubbles can interfere with the test results, acting as a barrier to dissolution if present on the dosage unit or basket mesh; also, bubbles can cause particles to cling to the apparatus and vessel walls. On the other hand, bubbles on the dosage unit may increase the buoyancy and lead to an increase in the dissolution rate, or, decrease the dissolution rate by decreasing the available surface area. A deaeration method is described as a footnote in Dissolution á711ñ. Typical steps are to heat the medium, filter, and draw a vacuum for a short period of time. Other validated methods of deaeration are available and in routine use throughout the industry. Media containing surfactants are not usually deaerated because of excessive foaming. To determine if deaeration of the medium is necessary, dissolution run in nondeaerated medium versus deaerated medium should be performed.

Time Points

Observations

1. Uneven distribution of particles throughout the vessel, which could occur if particles cling to the sides of the vessels, if there is coning or mounding directly under the apparatus, if particles float at the surface of the medium, if film-coated tablets stick to the vessel, and/or if off-center mounds are formed;
2. Air bubbles on the inside of the vessel or on the apparatus or dosage unit. Sheen on the apparatus is also a sign of air bubbles. This observation would typically be made when assessing the need to deaerate the medium;
3. Dancing or spinning of the dosage unit, or the dosage unit being hit by the paddle;
4. Adhesion of particles to the paddle or inside of the basket, which may be observed upon removal of the stirring device at the end of the run;
5. Pellicles or analogous formations, such as a transparent sacs that are rubbery, swollen masses surrounding the capsule contents;
6. Presence of large floating particles or chunks of the dosage unit;
7. Observation of the disintegration rate (e.g., percent reduction in size of the dosage unit within a certain time frame);
8. For modified or enteric-coated products, complex disintegration of the coating, e.g., the partial opening and splitting apart (like a clamshell) or incomplete opening of the shell accompanied by the release of air bubbles and excipients.

Sampling

Filters

Centrifugation

The usual assay for a dissolution sample is either by spectrophotometry or high-pressure liquid chromatography (HPLC). The preferred method of analysis is spectrophotometry because results can be obtained faster, the analysis is simpler, and fewer solvents are used. HPLC methods are used when there is significant interference from excipients or among drugs in the formulation and/or to improve analytical sensitivity. It may be useful to have data for the drug obtained with a stability-indicating assay (e.g., HPLC chromatograms) in the medium of choice, even if the primary assay is based on a spectrophotometric method.

The validation topics described in this section are typical but not all-inclusive. The acceptance criteria are guidelines only and may differ for some products. Other considerations may be important for special dosage forms. The extent of validation depends on the phase of the product development. Full validation takes place at or just before Phase III clinical studies. For profile testing, validation studies may be necessary at each relevant time point. For products containing more than a single active ingredient, the dissolution method should be validated for each active ingredient.

Specificity/Placebo Interference

100C(AP / AS)(V/L),

NOTE—For extended-release products, a placebo version of the finished dosage form may be more appropriate to use than blends because this placebo formulation will release the various excipients in a manner more nearly reflecting the product than a simple blend of the excipients. The placebo formulation is necessary particularly if one of the released excipients does influence the baseline of the analytical method. For extended-release products, the interference must be determined at each sampling point in the release profile. If the placebo interference exceeds 2%, then HPLC analysis is needed; alternatively, another wavelength, algorithm analysis, or a baseline subtraction (correction factor) may be feasible.

Spectrophotometric Analysis

HPLC

Linearity and Range

Accuracy/Recovery

Precision

Robustness

Standard and Sample Solution Stability

Typical acceptance criteria for the amount of active ingredient dissolved, expressed as a percentage of the labeled content (Q), are in the range of 75% to 80% dissolved. A Q value in excess of 80% is not generally used because allowance should be made for assay and content uniformity ranges. 3 Acceptance criteria including test times are usually established on the basis of an evaluation of the dissolution profile data.

High variability in results can make it difficult to identify trends or effects of formulation changes. Dissolution results may be considered highly variable if the RSD is greater than 20% at timepoints 10 minutes or earlier and greater than 10% RSD in later time points. The source of the variability could be investigated, when practical, and one should strive to reduce variability whenever possible. The two most likely causes are the formulation itself or mechanical artifacts associated with the test procedure (e.g., coning or tablets sticking to the vessel wall).

Occurrences such as those mentioned in the previous section on observations can be a strong indication that the dissolution test itself is creating variability. Any time the dosage contents do not disperse freely throughout the vessel in a uniform fashion, aberrant test results could occur. Depending on the problem, the usual remedies include changing the apparatus type, speed of agitation (flowrate), deaeration, consideration and/or examination of sinker type, or changing the composition of the medium. Modifications to apparatus may be useful, with proper justification and validation.

Many causes of variability can come from the formulation and manufacturing process. For example, poor content uniformity, process inconsistencies, a reaction taking place at different rates during dissolution, excipient interactions or interference, film coating, capsule shell aging, or hardening or softening of the dosage form as it ages may be sources of variability and interferences. During routine testing of the product, variability outside of the expected range should be investigated in terms of both analytical and formulation issues.