Design a Delayed-Release Tablet

Medication comes in many forms such as liquids, capsules, tablets, creams, drops, sprays, or injections (Figure 1). The main purpose of medication is to treat, cure, or prevent a disease in an individual. This is achieved by a chemical inside the drug, called the active ingredient, which interacts with the drug's target inside the body and thus has a certain effect on a person. For a drug to be effective, it has to be inside the body at the site of action for the correct time and duration. For example, a drug that is injected goes directly into the bloodstream whereas oral tablets pass through the digestive system and the active ingredient is then absorbed into the bloodstream. The active ingredient not only has to be at the right place at the right time, but it also has to have the right dosage. If the dosage of the drug is too low, it won't have the desired effect. If the dosage is too high, it could have harmful consequences and even be fatal!

Figure 1. Medicine can take the form of capsules, tablets, or injections.

This is where drug delivery systems come in. A drug delivery system is a specific form of medication or a medical device that is able to control the rate, time, and place at which a certain drug is introduced into the body. A drug delivery system allows to specifically target where and when a drug is released inside the body. Many different drug delivery techniques have been developed. Among these are controlled-release drugs. These types of drugs release their active ingredient at a prespecified time.

One specific type of controlled-release drug is a delayed-release drug. Delayed-release drugs are medications, such as capsules or tablets, which do not immediately disintegrate when taken. Because of this, the active ingredient is released slowly in smaller portions, rather than immediately after being administered. This includes, for example, enteric-coated drugs that are designed to delay the release of the medication until the tablet has passed through the stomach. This prevents the active ingredient from being destroyed or inactivated by stomach fluids. The delayed release of the active ingredient is often achieved by coating or encapsulating the active ingredient in a polymer film that gradually dissolves over time, as shown in Figure 2.

Figure 2. Delayed-release drugs are often encapsulated in polymers that dissolve over time.

Choosing the right encapsulation polymers with the right physical and chemical properties is crucial for designing delayed-release drugs. Polymers, which are large chains of many repeating subunits, can have very different properties depending on their molecular composition. This is why their properties have to be carefully tested. This includes testing not only the way in which the polymers dissolve in different solutions but also their toxicity in the human body as well as their interaction with the active drug ingredient.

In this lesson, students are challenged to design and build a delayed-release tablet, which will be made from different colored bath tablets and a variety of water-soluble plastics. Their task will be to create a tablet that releases each color from the bath tablets at a pre-determined time after it has been submerged in water. Before students start making their tablets, they will have to test the properties of each of the different materials they have been given, such as their dissolution behavior in water as well as other characteristics. As students design and build their delayed-release tablets, they will realize how the structure and properties of each of their materials influence their results. At the same time, students will get insight and exposure to drug formulation and development procedures.