Understanding The Enteric Coating Process and Its Role in Gastric Acid Resistance

During the manufacture of solid oral medication, pharmacologists make critical decisions to ensure the medication works as intended. One of these design decisions is making sure the medicine distentgates in the small intestines rather than in the stomach. The enteric coating process is used to make this happen. Let us learn more about this process.

The Enteric Coating Process

The Enteric Coating Process

If this is the first time you have come across this process, keep reading to understand everything there is to know about it. 

Tablets and capsules have active ingredients with the pharmacology properties required by the body. These ingredients are supposed to be absorbed by the blood after the medication disintegrates in the appropriate part of the body.

In most cases, these tablets are designed to disintegrate in an environment that has an alkaline pH level. The pH state of the environment is crucial since it affects the stability of the drug, release time, and its resorption. If these conditions are not met, the drug could end up not disintegrating and therefore ending up as waste.

After ingesting oral solid medication, it first settles in the stomach. The stomach is a highly acidic environment, which means that it is not suitable for drugs. This is where the enteric coating process comes in. 

The enteric coating process involves adding a special coating on tablets to help them sustain the acidic nature of the stomach. In other words, the drugs can stay in the stomach without disintegrating before they are transported to the small intestines.

One of the main advantages of this process is to aid gastric acid resistance. To clarify, if drugs are broken down in the stomach, you are likely to experience acid reflux which is quite uncomfortable.

Tablets and capsules are coated with special polymer compounds that are resistant to dissolution by acids. We will learn more about these polymers in another section of this article.

Methods of Enteric Coating Process

There is one major technique used to apply the enteric coat on drugs. This method, known as dry coating, is quite effective and reliable. Let us learn more about what it entails.

Dry coating in the enteric coating process

Dry coating seeks to create a uniform coat of polymer on the tablet. While the specific steps in the process may vary depending on the coating polymer and the drug, the basic process remains universal across the board.

As the name suggests, dry coating does not involve any solutions. Essentially, it involves spraying the polymer on the surface of the tablets and subsequently spraying the plasticizing agent onto them for coaring. 

The enteric coating process is carried out in either of the following machines;

  • Centrifugal granulator
  • Fluidized bed
  • Tablet coating machine

Each of these equipment has a particular mode of function but they all have one major goal — to apply a protective coating on the surface of the oral solid dosages (OSDs).

The approach used to create the enteric coat on OSD medication will depend on several factors. On one hand, many plasticizers and coating polymers can be used. 

Equipment Used in the Enteric Coating Process

Typically, the enteric coating process can either be done in dry or wet conditions. This gives us a dry or wet coating. Each of these methods has a particular equipment that is used. Let us discuss these equipment and how they work.

Pan Coater

The pan coater is the equipment used for dry coating in the enteric coating process. As the name suggests, this coating machine is tasked with applying the coat onto the surface of the tablets. These machines are engineered specifically for this process.

Pan coaters can further be divided into 

  • Standard pan coater
  • Perforated pan coater 

The standard pan coater is the original equipment that pioneered the enteric coating process. This pan is titled at a certain angle and has an electrified rotating mechanism that facilitates the uniform coating. 

As the pan rotates, the air-automized pray system sprays every individual tablet or capsule with the polymer. Subsequently, hot air is blown inside the pan to dry the coating powder and create a firm coating on the OSDs.

To create more efficient enteric coating equipment, engineers developed the perforated pan coater. It is a more advanced coater that improves on the original design of the standard coating equipment.

The difference between the standard and the perforated coating pan is that the latter has a more efficient drying mechanism and high yield. This is aided by the numerous spray guns inside the enclosed drum and the advanced air inlet systems.

Fluidized Bed

The fluid bed uses a fluidized compound to apply an even coat on the surface of the tablets and/or capsules. This technique is also known as the air suspension system.

The fluidized bed has a vertical cylinder that holds the tablets that are to be coated. The cylinder also serves as the enclosure that keeps the tablets and air from escaping the system. This is because the air being blown in the cylinder can eject the tablets easily.

One of the main advantages of the fluidized bed is that it sprays the polymer and at the same time dries it. In other words, the two processes occur simultaneously, thereby increasing the efficiency of the system.

The classification of fluidized beds is based on the spraying patterns and approaches used to achieve the coating. They are;

  • Top spray. Here, the spraying nozzle is located on the top of the cylinder. The heated air then comes from the bottom of the cylinder.
  • Bottom spray. For this mechanism, the spraying liquid emanates from the bottom of the cylinder while the heated air comes from the top. This technique is also known as the Wurster Process.
  • Tangential spray. The tangential spray applies a thick layer of polymer and plasticizer on the tablets. This process happens in a spiral movement and the spraying solution typically comes from the bottom of the cylinder.

Factors Affecting Enteric Coating Process

The effectiveness of the enteric coating process is dependent on several factors. This means that the outcome of the process can be altered either positively or negatively by external and internal factors.

Some of the factors that influence this process include;

  • Environmental factors

The environment around us is highly volatile and prone to change. Elements such as temperature and humidity can have negative implications on the enteric coating process. They can affect the quality of the coat as well as the productivity of the coating machines.

  • Coating equipment used

In a previous section, we saw that not all equipment has the same functionality. As such, the equipment used has a major impact on the enteric coating process. For instance, if you chose the fluidized bed over the pan coater, you could end up with more productivity. This shows that the latter is a less effective method than the former.

Polymers Used for the Enteric Coating Process

In chemistry, polymers are compounds made up of repeating units of individual elements known as monomers. These compounds are known to have properties such as resistance to corrosion, durability, and more. 

The polymers used in the enteric coating process are organic. This is crucial to ensure that the body can effectively break down the polymer to access the active ingredients of the oral dosage. The following are some of the common polymers used in this process.

  • Cellulose acetate phthalate (CAP)
  • Hydroxypropyl methylcellulose phthalate (HPMCP)
  • Polyvinyl acetate phthalate (PVAP)

Pros and Cons of the Enteric Coating Process

Like most technical approaches, the enteric coating process has its fair share of advantages and disadvantages. Some of them are;

Advantages of the enteric coating process

The common advantages of the enteric coating process include;

Protects drugs from stomach acids

We started by saying that the stomach has quite strong acids such as hydrochloric acid. Provided that one of the characteristics of acids is to dissolve virtually any material, this acid has the potential to ‘eat up’ the medicine, which then prevents its absorption in the bloodstream. The main function of the enteric coating is to ensure that these acids do not affect the drugs.

Improves gastric resistance 

The situation where the drugs in the stomach are stopped from disintegrating in the stomach for them to reach the distal ileum and the small intestines is described as gastric resistance. It is essential since it prevents gut discomforts such as acid reflux. This is a result of the polymer and plasticizers that make up the enteric coating substances.

Helps deliver acid-sensitive drugs

Generally, the whole idea of the enteric process is to help administer oral drugs that are sensitive to acid found in the stomach. This means that not all drugs need to undergo this coating since they can withstand harsh acids such as concentrated hydrochloric acid. Those that cannot have to be coated properly to ensure the safe delivery of the drugs’ active ingredients to the limbic system.

Disadvantages 

While this method is considered highly effective and reliable, it has some disadvantages that could make it an option. Some of these drawbacks include;

Generally more expensive than other methods

The cost of operating a pan coater or fluidized bed is considerably high. For one, the polymers and plasticizers need to be manufactured with high precision for them to work. Also, these equipment require a lot of resources to work. This becomes an economic challenge, especially for small-scale drug manufacturers.

Tablets cannot be crushed before swallowing

Crushing the tablets that are coated with a polymer means exposing the contents of the drugs to the stomach, which results in a lack of absorption in the bloodstream. This could be a challenge, especially for kids who cannot swallow whole tablets. The alternative here is other types of medication such as syringe drugs.

Drug release might be delayed 

There is a range of times that contents in the stomach take when you swallow them. Typically, this period could be anywhere between 40 minutes to two hours. In situations where you need fast relief, for instance with painkillers, this delay can be a challenge. 

Conclusion

Methods of gastric resistance such as the enteric coating process are inevitable in the pharmaceutical industry. They not only help administer OSD correctly but also create a safe environment for all medication users. This article has taught us how essential this process is, alongside its mechanism of action and its significance.

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