Dissolution apparatus Rotating basket

Table 2 Recommended Dissolution Medium Composition and Volume for Rotating Basket or Rotating Paddle Apparatus...

The requirements for the basket and paddle apparatus described by the three major pharmacopoeias is generally similar but do have some unique differences. These general requirements are summarized in Table 4.2. It is important to know these differences at the time of method development and dissolution. Some of these characteristics are utilized as a system check in the regular performance verification of the dissolution apparatus (e.g., shaft position, shaft rotation variation, and distance of bottom of apparatus to inside bottom of vessel). 

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). 

USP Apparatus 1 (rotating basket) and 2 (paddle) are the first choices when developing a dissolution method for solid oral dosage forms. Even though the compendial equipment may not be suitable for all low-dose drug products, a brief discussion of these apparatuses is necessary in order to understand the basic operation of dissolution testing. 

As a general guideline in the choice of dissolution test apparatus, the simplest and most well-established method should be chosen, with respect to both in-house know-how and regulatory aspects. In most cases, this is the USP II paddle method or the USP I rotating basket method. However, if satisfactory performance cannot be obtained by these methods, others should be considered. Primarily, the USP III and USP IV methods, and non-compendial methods could also provide relevant advantages. 

Standard USP or BP dissolution apparatus has been used to study in vitro release profiles using rotating elements, paddle, and basket. Dissolution medium used for the study varied from 100 to 500 nd and speed of rotation from 50 to 100 rpm. 

Visual Observation Method Each sample of microspheres is placed into 500 ml of simulated gastric fluid (SGF, pH 1.2, without enzymes) filled in basket-type dissolution apparatus. Paddle rotation speed is set at 100 rpm, temperature is to be maintained at 37°C 0.5°C. The number of floating microspheres has to be counted visually after 24 h. The percentage of floating microspheres was calculated according to the following equation ... 

For some products the USP/EP/JP rotating basket apparatus (Figure 2) may be more appropriate for example, in the case of floating capsules and granules. Operation of the basket apparatus is similar to that of the paddle apparatus, except that the basket containing the dosage form is immersed in the dissolution medium prior to starting the rotation. 

The dissolution behavior of the SAS generated powder is measured, using a dissolution apparatus in accordance to the U.S. Pharmacopeial (USP) convention. The apparatus is equipped with rotating baskets and allows the measurement in... 

A Shah, C Peot, J Ochs. Design and evaluation of a rotating filter-stationary basket in vitro dissolution test apparatus I Fixed fluid volume system. J Pharm Sci 64 671, 1973. 

In the paddle method, bulk Reynolds numbers range from Re = 2292 (25 rpm, 900 mL) up to Re = 31025 (200 rpm, 500 mL). In contrast, Reynolds numbers employing the basket apparatus range from Re = 231 to Re = 4541. These Reynolds numbers are derived from dissolution experiments in which oxygen was the solute [(10), Chapter 13.4.8] and illustrate that turbulent flow patterns may occur within the bulk medium, namely for flow close to the liquid surface of the dissolution medium. The numbers are valid provided that the whole liquid surface rotates. According to Levich (9), the onset of turbulent bulk flow under these conditions can then be assumed at Re 1500. 

The release tests were performed using the USP dissolution method (apparatus I) and utilized 1000 ml of pH 1.2 simulated gastric fluid (USP XXI) or pH 6.8 simulated intestinal fluid (USP XXI) without enzymes, equilibrated to 37°C and stirred with the basket rotating at 50 or 150 rev/ min. Drug concentrations were assayed by UV spectrophotometry at 255 nm. The experiments were continued until 100% dissolution was achieved. The release data were analysed to zero order, calculating the slope and intercept of the line. Each data point is the average of six individual determinations. In all cases the standard deviation was less than 9%. 

Rotational Speed. The rotational speed of a basket or paddle is an important consideration in the development and validation of the dissolution test. A speed of 100 rpm is commonly used with the basket apparatus and a speed of 50 rpm is used with paddles. In method validation, one needs to ensure that slight variations in rotational speed will not affect the outcome of the dissolution test. The compendial limit for variations in rotational speed is 4%, but a wider variation (e.g., 10%) may be considered in testing the robustness of the method. 

Basket Apparatus. This method is very similar to the one described above except that the inverted T-shape stirrer is replaced with a cylindrical metallic-wire basket (Fig. 4). The tablet product is placed in the basket that is attached to the spindle, which provides rotation to the basket. The dissolved drug comes out of the basket and mixes with the bulk medium. In this apparatus, it is possible that when the product is disintegrated and particles drop and settle at the bottom of the vessel without dissolving thus providing limited dissolution. Therefore, one may anticipate erratic dissolution results using such an apparatus, at least for some products. 

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