One of the main problems facing the pharmaceutical industry is to optimise the amount of drug available to the body i.e. its “bioavailability”. Inadequacies in bioavailability can mean at best that the treatment is ineffective and at worst potentially dangerous (toxic overdose).
Drug release in the human body can be measured in vivo by measuring the plasma or urine concentrations in the subject concerned. However, there are certain obvious impracticalities involved in employing such techniques on a routine basis.
These difficulties have led to the introduction of official in vitro tests which are now rigorously defined in the respective Pharmacopoeias. Whether or not its numbers have been correlated in vivo, the standard dissolution test is a simple and inexpensive indicator of a products physical consistency.
Initially developed for immediate release (IR) and then later to extended/delayed or modified release (MR) oral dosage forms, the role of the “dissolution test” has now been extended to the “drug release” of various other forms such as semisolids, suppositories, topical and transdermal systems.
The term “dissolution test” is normally used to describe the testing of those forms such as immediate release oral tablets or capsules intended to dissolve rapidly in the test medium.
For non-oral dosage forms such as semisolids, suppositories, topical and transdermal systems, the term “drug release” is normally employed.
In the majority of cases, the effectiveness of tablets or capsules administered orally relies on the drug dissolving in the fluids of the gastrointestinal tract prior to absorption through the walls of the tract into the systemic circulation.
For this reason, the rate at which a tablet or capsule dissolves is critical to its therapeutic efficiency and is a key factor in both the formulation process and final quality control.
The most common apparatus used to measure the dissolution rate of solid dose forms are the basket and the paddle. Both use the same basic configuration, are simple, robust and can be used to test a variety of different products.
The basic apparatus consists of a covered cylindrical vessel having a hemispherical bottom and capable of holding approx. 1000 mL of simulated gastric juice. The vessel is partially immersed in a water bath capable of maintaining the temperature of the vessel contents at 37 degrees C. In the case of the basket method, the tablet or capsule is constrained in a cylindrical mesh basket. In the case of the paddle method, the sample is simply allowed to sink to the bottom of the vessel.
During the test, a motor is used to rotate the drive shafts at the speed specified in the pharmacopoeias. A sample of the dissolution medium is taken at predefined time intervals to determine the percentage of dissolved drug present – this is normally determined by UV/Vis or HPLC.
1) Dissolution Tester DIS 8000
The Dissolution Tester DIS 8000 represents the very latest in tablet testing technology. CNC production techniques combined with modern microprocessor design guarantees the highest standards of performance and reliability.
Efficient and extremely compact, the Tablet Dissolution Tester DIS 8000 is a rugged “no-nonsense” unit having eight stirred test vessels and simple, easy to use controls. It is ideal for both R&D and routine quality control applications.
In common with the rest of the series, the DIS 8000 has been specifically designed to reduce clutter and maximise visibility and access in the critical sampling area above the water bath.
All of the DIS series are equipped with precision ground shafts that will accept any of the baskets, paddles or rotating cylinders described in the Pharmacopoeia and are supplied with USP/Ph.Eur. compliant vessels featuring the unique “Easy-Centre” system to ensure that the vessels are perfectly centred every time.
Individual clutches enable each individual basket/paddle to be raised, lowered or engaged independent of the drive head.
In many laboratories, bench space is at a premium. The Dissolution Tester DIS 6000 has been designed as a direct response to this problem. With a footprint of just 650 x 450 x 640 mm (WxDxH), the DIS 6000 is one of the most compact dissolution testers available on the market today.
The unit has six stirred test vessels arranged in two rows of three.
A common complaint from customers is that their existing dissolution tester is overly complex with unnecessary software functionality for day-to-day use. For this reason, considerable attention was given in the design to ensuring that the number of actions necessary to perform a test was kept to a minimum.
Once the test sequence has been initiated, all that is necessary to start the test is to input the nominal rpm and temperature required, together with the duration of the test and the report interval (the time interval during the test at which the actual rpm and temperature is logged and subsequently reported), introduce the samples and press START.
If you require the ultimate in a Dissolution Tester then the DIS-EMC is the dissolution tester for you.
It goes without saying that the standard DIS 6000 and 8000 units already comply with the new Enhanced Mechanical Calibration (EMC) specifications as laid down by the FDA.
Where the Dissolution Tester DIS-EMC differs from the standard units is the application of the latest state-of-the-art technologies to the manufacture of the Dissolution Vessel which in combination with the precision ground stirring element brings you a new level of standard in terms of dimensions and tolerances.
Traditionally, dissolution vessels have been made individually using manual glass blowing techniques from extruded glass tubing. The solution was to vacuum form the vessel as opposed to extrude it. This method guarantees an inside diameter tolerance and blemish free spherical radius of +/- 0.13 mm together with a flange perpendicularity of 0.50 mm Total Indicated Runout.
This betters the dimensional tolerances specified in the FDA”s Enhanced Mechanical Calibration by a factor of 2.