Dissolution apparatus Flow-through cell

The USP Apparatus 4, also known as the flow-through cell, was introduced and extensively studied by Langenbucher (22). In the open loop configuration, this system offers the advantage of unlimited medium supply, which is of particular interest for the dissolution of poorly soluble drugs. The idea to develop a flow-through cell method dates back more than 45 years. As early as 1957, a flow-through cell method with a... 

The flow-through cell is especially useful for dissolution rate-limited products, where sink conditions may be hard to obtain (18,19). The operation of the flow-through cell is illustrated in Figure 12. A closer look at the tablet holders is shown in Figure 13. This particular apparatus can be utilized as either a closed or open system. In Figure 14, the closed system mode,... 

When using USP 23 Apparatus 3 (reciprocating cylinder), USP 23 Apparatus 4 (flow- through cell), or USP 23 Apparatus 7 (reciprocating disk) the above dissolution testing conditions should be modified accordingly. 

The preferred dissolution apparatus is 1 ISP apparatus 1 (basket) or 11 (paddle), used at compendially recognized rotation speeds (e.g., 100 rpm for the basket and 50-75 rpm for the paddle). In other cases, the dissolution properties of some ER formulations may be detennined with USP apparatus 111 (reciprocating cylinder) or IV (flow through cell). 

Singh I, Aboul-Enein HY. 2006. Advantage of USP apparatus IV (flow-through cell apparatus) in dissolution studies. J. Iran. Chem. Soc. 3(3) 220-222. 

Numerous dissolution methods (not limited to those officially prescribed) must be available to ensure proper discrimination as well as the use of various media. The preferred dissolution apparatus is USP I (basket), II (paddle), or IV (flow through cell). USP apparatus III (reciprocating cylinder) could be considered in some cases. An aqueous medium, either water or a buffered solution preferably not exceeding pH 6.8 (or 7.2), is recommended, other pH must be justified. For poorly soluble drugs, the addition of a surfactant may be necessary. 

Correlation of the in vitro dissolution to the in vivo dissolution is a crucial property of a dissolution test. The major difference in this respect between different apparatus is the hydrodynamic conditions. It has been argued for some of the methods, such as the USP IV flow-through cell or a rotating flask with baffles, that an in vzvo-like situation is created in the... 

A dissolution testing apparams consists of a set of six or eight thermostatted, stirred vessels of an established geometry and volume from the USP guidelines. The dissolution apparatus provides a means to dissolve each sample, but does not provide a means to determine the concentration of the aetive ingredient in the bath. In the most well-established scheme, sipper tubes withdraw samples from each dissolution vessel and send them through a multiport valve to a flow cell sitting in the sample chamber of a UV-vis spectrophotometer. In recent years, moves have been made to make in situ measurements in the dissolution baths by means of fiber-optic probes. There are three possible probe implementations in situ, down shaft, and removable in situ (see Table 4.2). 

Consequently, the flow-through apparatus has been developed, which features a dissolution cell of low volume (often <30 ml) and a reservoir to provide fresh solvent. This is official in USP 28 as USP Apparatus 4 (Fig. 6) where it is prescribed for testing extended-release articles. 

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