Page 1 of 8 Plop Plop, Fizz Fizz, Oh What A Relief It Is (Which Pain Reliever Works Fastest) Learning Objectives: Study the dissolution rate (how quickly the compound dissolves) of common OTC (over the counter) analgesics (pain relievers) Use Ultraviolet (UV) spectroscopy to analyze the samples Plot data to produce a dissolution profile Compare the dissolution profiles to predict which pain reliever work fastest Background: The everyday aches and pains can often be relieved by painkillers that are readily available in supermarkets and pharmacies. When someone is in pain, they want relief as quickly as possible. However, before a drug can begin working to relieve pain, it needs to dissolve (go into solution) so that the body can absorb it. Therefore, how fast a drug dissolves (dissolution rate) is important in predicting how fast pain relief is achieved. Dissolution rate is one of the tests routinely performed on oral drug products such as tablets and capsules by pharmaceutical companies. Dissolution testing is used to guide pharmaceutical companies in developing drug formulations (combination of ingredients in tablets/capsules), identifying critical manufacturing variables, monitoring batch-to-batch variations and stability, and to predict the performance of the drug in the body. In this experiment we will measure the dissolution rates of several types of OTC painkillers and different brands/formulations of painkillers to try and predict which brands will act the fastest in reducing pain. OTC painkiller formulations can be broken down into 4 categories based on the following active ingredients: 1) Aspirin 2) Ibuprofen 3) Naproxen 4) Acetaminophen Each of these active ingredients works differently in relieving pain and has different side effects (action other than pain relief). Remember, the decision to choose one active ingredient over another for pain relief is more complicated than just comparing dissolution rate data..
Page 2 of 8 Experimental Background: The dissolution profiles of Aspirin, Ibuprofen, Naproxen, and Acetaminophen tablets and capsules will be studied using a specialized instrument called USP Dissolution Apparatus 2. It consists of a paddle rotating at 50 rpm in 900 ml of dissolution media (which is supposed to behave like stomach fluid) at a constant temperature bath of 37 C (which is the temperature of the human body). Samples will be withdrawn at 5, 10, and 15 minutes and filtered prior to analysis. The samples will be analyzed using a UV spectrophotometer based on the following principles. The four active ingredients that are contained in OTC painkillers shown below are organic molecules that can absorb UV light. Aspirin Ibuprofen Naproxen Acetaminophen Note that these organic molecules have a common feature of alternating double bonds that are called aromatic systems. These types of bonds absorb UV light strongly. The wavelength range that the molecules absorb is called its UV absorption spectrum. You will measure the absorption spectrum of each of these molecules with an instrument called a UV spectrophotometer. This instrument measures the amount of UV light absorbed by a solution of the molecules over individual wavelengths between 350 nm to 200 nm. The amount of light absorbed by the molecules at a specific wavelength is called the Absorbance, A. The instrument records the absorbance at each wavelength. In addition, the absorbance is also directly related to the concentration (the number of molecules in a given volume) and the path length that light must pass through. Thus, the higher the concentration of molecules, the higher is the absorbance. We will take advantage of this property to measure the amount of drug dissolved at the different sampling time points. In the experiments that follow you will perform the following investigations: 1. Each group will perform dissolution rate profiles on all of the products. Each pair of students will run one of the assigned analgesics and share the results with the group.
Page 3 of 8 2. After all of the data has been plotted, the group will compare results and determine which painkillers have the fastest dissolution profile. Equipment and Materials: 4 USP Apparatus 2 Dissolution Setups including dissolution vessels, paddles, bath, etc. Analgesic tablets and capsules 6-10 ml beakers to hold sample tablet or capsule 6-10 ml plastic syringes 6-Cannulas 2 Stopwatches 10 micron plastic filters ph 4 phosphate buffer Test tube racks 10 ml plastic test tubes Spectrophotometer Quartz cells Beakers for ph4 phosphate buffer and waste Distilled water squeeze bottle Kimwipes Calculators Laptop loaded with Dissolution Excel spreadsheet Set Up: Lab Station Set up and Reagent prep 4 complete USP Apparatus 2 Dissolution Apparatus each consisting of 6 dissolution vessels and paddles, a constant temperature bath with temperature monitor and pump and variable rpm monitor. Before the students arrive, turn on the baths which are pre-set to 37 deg. C and fill up the 4 forward dissolution vessels with 900 ml of 0.2M ph 4 phosphate buffer. (A 5 th vessel is filled in one of the apparatus for the enteric tablet demo). It is advisable to prepare adequate buffer (approximately 20 L for each day) before the day of the lab (see USP for instructions) and to fill the vessels (17 vessels should be filled). Then, you need only turn on the baths the morning of the experiment. Use a 1000 ml graduated cylinder to fill the dissolution vessels. Make sure there is an adequate supply of potassium phosphate monobasic to prepare buffer for upcoming experiments. Phosphate buffer should not be stored longer than 1 week since microbiological growth will quickly form.
Page 4 of 8 Each work station will be set up for one of the 4 analgesics. Each work station should set up with a test tube rack with 4 x 4 labeled test tubes. This is enough test tubes for an entire day of experiments. The labeling for each set should be the Standard, 5 min, 10 min, and 15 min samples for the particular analgesic. The standards are prepared by the instructor the morning of the lab and the standard test tubes are filled by the instructor. Allow at least ½ hour for standard preparation the morning of the lab. (standards are prepared by dissolving one tablet of each analgesic in 900 ml of ph 4 phosphate buffer, shake or ultrasonicate for at least 10 minutes, then filter with a 10 micron cartridge filter into the student s test tubes. Additionally, each work station should have a 10 ml syringe, a metal cannula that fits the syringe and a beaker of 10 micron filters. Each filter is used to take a single sample and then discarded. Students are instructed how to assemble the syringe, cannula, filter assembly and how to take a sample (one inch into the dissolution media to avoid interference with paddle). Two spectrophotometers (and instructors working them) are needed to be able to analyze all the samples in the allotted time. The spectrophotometers and connected computers should be turned on first thing in the morning and a sample scan of an analgesic run to insure they are working correctly. Each spectroscopy work station should be set up with 2 matched quartz cells, a test tube rack, a distilled water squeeze bottle, a beaker of ph 4 phosphate buffer, a waste beaker, and kimwipes. Experimental Procedure for Dissolution Rate: 1. Instructor will place 900 ml of ph 4.0 phosphate buffer into a dissolution vessel and equilibrate to 37 C 2. Start paddle rotating at 50 rpm. 3. Place 1 tablet or capsule of your assigned product into a dissolution vessel and start the stopwatch. 4. Take a 5 ml sample from the dissolution vessel at 5, 10, and 15 minutes using a sampling syringe and 0.45 micron filter. Remove filter and transfer the sample solution into a vial. 5. Dilute sample if necessary with ph 4.0 phosphate buffer (See Table below)
Page 5 of 8 Table 1: Experimental Details Product 1. Kirkland Aspirin safety coated enteric 2. Ecotrin Aspirin safety coated enteric 3. Tri Buffered (Walgreen) Active Ingredient Aspirin 325 mg Aspirin 325 mg Aspirin 325 mg Sample Dilution (into 10 ml) 4. Shop Rite Non-Aspirin 5. Tylenol Rapid Release Gels Acetaminophen 500 mg 200 µl Acetaminophen 500 mg 200 µl 6. Kirkland Ibuprofen 7. Advil Liquid Gel Caps Ibuprofen 200 mg Ibuprofen 200 mg 8. Aleve Naproxen sodium 220 mg Experimental Procedure for UV Analysis 1. Clean the quartz cells by rinsing them with ph 4.0 phosphate buffer 2. Fill both cells with ph 4.0 phosphate buffer and dry the outsides with a Kimwipe 3. Place the cells in the reference and sample cell holders within the spectrometer with the clear sides of each cell facing the open slots of the cell holder 4. Click the grey start button on the computer monitor 5. When the dialog box comes up for the blank, click OK. A background correction is carried out from the maximum to the minimum wavelength range (350 nm 200 nm).
Page 6 of 8 6. Wait for the next dialog box to come up 7. Take out the sample cell (front cell) and place its contents into the waste beaker 8. Fill the sample cell until approximately ¾ full with the 5 minute dissolution sample and wipe the outside of the cell with a Kimwipe. Place the sample cell back into the spectrometer and click OK to record the 5 minute sample spectrum 9. Repeat the process for the 10 minute and 15 minute dissolution samples and the standard solution (theoretical 100% release). After all of the groups have plotted their data, you will compare results and determine which painkillers have the fastest dissolution profile Evaluation of Spectra 1. Evaluate each spectrum for a wavelength where the greatest absorbance occurs (UV max ), the absorbance (A) at UV max. For Aspirin the UV max is 272 nm, Acetaminophen 243 nm, Ibuprofen 221 nm, and Naproxen 330 nm. 2. Record your results for your sample in the table below. Table 2: Results Product Active Ingredient A 5 min. A 10 min. A 15min. A 100% (standard) 3. Convert Absorbances in Table 2 above to % released by dividing the Absorbance at each time interval by the Absorbance of the Standard and multiplying by 100 [(A x min /A 100% ) x 100 = % released], record in Table 3, and plot the data to get a Dissolution Profile for your product. 4. Compare Dissolution Profiles of all of the products to predict which pain reliever will work the fastest. Table 3: % Released Product Active Ingredient % 5 min. % 10 min. % 15 min.
Page 7 of 8 Instructor Notes: Since the acetaminophen analysis requires a dilution, we have been substituting a second aspirin formulation in place of acetaminophen to save time. If you compare a normal uncoated aspirin tablet to a fast release or buffered formulation, you see nice differentiation. You could actually use 4 different aspirin formulations and show differentiation for a different twist on the experiment. Limit the gab when the students arrive. Just give them the basics of what the experiment is about and show them the equipment (no more than 5 minutes) It is important to drop the tablets/capsules into the vessel and get the dissolution experiment going. After the dissolution experiment begins you have 5 minutes before the first sample so now you can show them how to assemble the sampling apparatus, how to take the sample and how they will analyze the samples. Put a piece of red tape in front of the one dissolution vessel each group will use for their experiment. This way they will not take a sample out of the wrong vessel. Place the tablet/capsule each group will be working on in a 10 ml beaker on the lab bench before the students arrive. The instructor (or assistant) starts the timing of the dissolution rate experiment with a stop watch for all groups. Make sure a backup person times the experiment as well. Announce a minute in advance of when samples need to be taken. Make sure the students take at least 5 ml of sample and not air. After the students take the 5 min sample, take 2 of the groups over to the 2 spectrophotometers to analyze their samples. By the time they have analyzed the blank and 5 min sample, usually the 10 min. sample is due. Then they can analyze the 10 min. sample and standard and by that time the 15 minute sample is due. After they have all of their spectra recorded, pass them off to an assistant who can help them with the calculation and entering the data into the Excel spreadsheet. The idea is to get the second pair of students onto the spectrophotometers so they can finish on time. Note that the cells don t need to be rinsed between samples if done in order from lowest to highest concentration. Just tap dry onto a kimwipe. This saves valuable time. At the beginning of the Day 3 series of experiments, place an enteric coated aspirin into the extra dissolution vessel. This tablet will continue stirring for the duration of dissolution experiments to show the students that enteric tablets were designed not to dissolve at acid ph (stomach) but in the basic environment of the intestine to avoid the side effect of stomach irritation. There can be a lot of discussion around this topic. This demo can be done when the students are either waiting to do their spectrophotometric analysis or after the first 2 groups are done entering their data into the spreadsheet.
Page 8 of 8 Wrap Up: If time permits, a separate demonstration can be performed by placing an enteric coated aspirin tablet in a 1000mL Erhlenmeyer flask with ph 4 phosphate buffer, then adding 1 N NaOH dropwise, monitoring the ph with a ph meter and showing that as the ph becomes more basic (usually around 7 8) the enteric coating dissolves and drug is released. Try to allow at least 5 minutes at the end of the experiment for a discussion of the dissolution results using the dissolution curves the students made with the Excel spreadsheet. Discussion topics include: 1. What are some of the factors affecting the Dissolution Rate? 2. Talk about formulations and excipients and the work of pharma scientists in designing formulations. 3. Ask the students about other dosage forms they are familiar with (ie. Chewable vitamins, injections, inhalers, patches, etc.) 4. Based on the dissolution rate, which product would you take for fast pain relief? 5. Talk about how each product is a different drug chemically and that there are other factors besides dissolution rate in picking an analgesic. 6. Which of these products do you take and do they work? 7. Why are the Dissolution curves of the tablets different from the capsules? 8. Would enteric coated tablets be a good choice for quick pain relief?