Oral Drug Administration in Livestock: Pros & Cons

The oral route of drug administration involves delivering medications through the mouth, and it is one of the most common and convenient methods used in both human and veterinary medicine. Various forms of medications can be administered orally, including suspensions, tablets, pills, capsules, powders, mixtures, and boluses, also known as pessaries and premixes.

1. Suspensions: These medications consist of solid particles dispersed in a liquid medium. The particles are not fully dissolved and can settle over time, requiring shaking before administration. After swallowing, the suspension enters the stomach and intestines, where the drug is absorbed.
2. Tablets: Tablets are solid dosage forms that contain compressed drugs and other excipients. They are designed to melt and disintegrate when consumed. The tablet dissolves in the stomach or intestines, releasing the medication for absorption.
3. Pills: Pills are round, solid dosage forms similar to tablets. They break down and dissolve in the stomach or intestines for absorption.
4. Capsules: Capsules are solid dosage forms that enclose the drug in a gelatin shell. They can be either hard or soft capsules. Upon ingestion, the capsule shell dissolves in the stomach or intestines, releasing the drug for absorption.
5. Powders: Medications in powdered form can be mixed with liquids or food for administration. Once ingested, the powder particles dissolve in the stomach or intestines, allowing absorption of the drug.
6. Mixtures: Mixtures consist of medications dissolved in a liquid medium, such as syrups or solutions. The drug is already fully dissolved and readily available for absorption upon ingestion.
7. Boluses (Pessaries): Boluses are large, solid dose forms typically used in veterinary medicine. They are usually inserted at the rear of the animal's throat and given orally. In the stomach, boluses disintegrate, releasing the medication for absorption.
8. Premixes: Premixes are formulations that combine drugs with animal feed or feed ingredients. They are often used in animal husbandry, where the medicated feed is consumed by the animals, leading to systemic drug absorption.

Note:

After being taken, drugs travel through the gastrointestinal tract (GIT), where they are exposed to various physiological conditions that may alter their absorption. The stomach plays a vital role in drug absorption as it aids in breaking down solid dosage forms, combining medications with gastric fluids, and starting drug dissolution.

However, the main location for medication absorption is the intestines, especially the small intestine. The intestinal lining contains many blood vessels and specialized transport systems that allow medications to enter the bloodstream and reach their intended targets.

The following factors may affect drug absorption after administration:

a). State of GIT mucosa:

The condition of the gastrointestinal (GIT) mucosa can significantly impact drug absorption. Ulceration or inflammation of the mucosal lining can enhance drug absorption by creating disruptions in the mucosal barrier, allowing drugs to pass more readily into the bloodstream. This can lead to increased drug absorption and potentially higher systemic exposure to the medication.

b). Nature of GIT contents:

Food in the gastrointestinal system can affect the absorption of orally taken medications. Food can postpone the drug's interactions with the mucosal lining, slowing down absorption.

Additionally, certain food ingredients, such as dietary fiber or lipids, can bind to medications and create complexes that are less easily absorbed. This may further delay or decrease drug absorption. Some medications may need to be taken on an empty stomach to achieve optimal absorption.

c). Chelation:

Chelation refers to the process of a medicine interacting or forming complexes with other molecules in the gastrointestinal tract, particularly heavy metals like zinc or lead. When medications form chelates with these metals, the availability of the metals for absorption may decrease. Chelation can decrease drug absorption, resulting in less systemic exposure and potentially reducing the therapeutic efficacy of the medicine.

Note:

Some medications may be more vulnerable to the impact of these factors than others. Healthcare professionals consider these factors when prescribing medications and may provide special recommendations to improve drug absorption, such as taking medications on an empty stomach or avoiding particular foods or substances that may interfere with absorption.

Advantages of using oral routes to administer drugs to livestock:

a). Local effect in the gastrointestinal tract (GIT):

The oral route allows for targeted drug delivery to the GIT itself. When medications are administered orally, they can directly act on the affected area of the GIT, providing local relief and treatment in cases of gastroenteritis or other inflammatory conditions.

b). Large absorption area:

The gastrointestinal system provides an extensive absorption surface for drug absorption. The abundance of blood vessels and highly vascularized tissue in the GIT makes it easier for drugs to enter the bloodstream effectively. When medications are taken orally, this vast absorption area enables efficient systemic distribution.

c). Ease of administration:

Administering medications orally to animals is typically considered an easy and practical way to provide medications. It can be easily done by combining medications with food or water, or by administering tablets or boluses orally. This method's simplicity lessens the tension and discomfort associated with other drug delivery routes.

d). Accuracy in dosing with tablets and boluses:

Tablets and boluses are solid dosage forms designed for oral administration. These forms often have defined doses, making it easier to ensure accurate dosing and maintain proper medication records. Tablets and boluses can be conveniently administered to livestock, allowing for efficient and controlled drug delivery.

e). Cost-effectiveness:

Compared to alternative medication delivery methods like injections, the oral route is usually more economical. Oral drugs are often sold in larger quantities, allowing treatment for multiple animals at once. This can result in cost savings for animal owners and reduce overall treatment costs.

Disadvantages of using oral routes to administer drugs to livestock:

i). The large size of the rumen and its low pH:

In ruminant animals such as cattle and sheep, the rumen is the largest compartment of the stomach and has a relatively low pH of around 6. This acidic environment can affect the absorption of orally administered drugs.

Acidic drugs may be effectively absorbed in the rumen, but basic drugs can ionize and become less available for absorption. This phenomenon, known as ion trapping, can cause basic drugs to remain in the rumen and be expelled in the feces, leading to reduced efficacy.

ii). The fermentative activity of rumen microflora:

The rumen contains a complex ecosystem of microflora responsible for the fermentation of feed. Some of these microflora can affect the stability of certain drugs. Enzymatic activity in the rumen can degrade or modify the structure of drugs, leading to decreased efficacy.

Additionally, some orally administered drugs, such as antibiotics, may disrupt the balance of microflora in the rumen, potentially affecting digestion and overall rumen function.

iii). Delayed absorption due to the presence of feed:

The presence of feed in the gastrointestinal tract can delay the absorption of orally administered drugs. The physical presence of feed particles can slow down the dissolution and absorption of drugs, resulting in a delayed onset of action. To optimize absorption, it may be necessary to fast the animal prior to drug administration.

iv). Vomiting caused by irritant medications:

Certain orally taken medications may have irritating effects on the gastrointestinal mucosa. This can cause the medicine to be expelled from the body before complete absorption, decreasing its potency.

v). Risk of aspiration pneumonia during drenching:

Drenching, which involves administering liquids orally using a syringe or drenching gun, carries a risk, especially if performed by an inexperienced person. Improper drenching techniques can lead to the drug entering the respiratory tract instead of the gastrointestinal tract, resulting in aspiration pneumonia.

Conclusion

In conclusion, the oral route of drug administration is a widely utilized and convenient method in both human and veterinary medicine. It offers various advantages, including targeted drug delivery to the gastrointestinal tract, a large absorption area for efficient systemic distribution, ease of administration, accuracy in dosing with tablets and boluses, and cost-effectiveness compared to other delivery methods.

However, there are also disadvantages to consider, such as the impact of the rumen environment on drug absorption, the potential for microflora interactions in the rumen, delayed absorption due to the presence of feed, the risk of vomiting with certain medications, and the possibility of aspiration pneumonia during drenching.

Understanding these factors and their effects on drug absorption is crucial for healthcare professionals and livestock owners when choosing the appropriate route of administration and optimizing treatment outcomes. By considering the state of the gastrointestinal mucosa, the nature of gastrointestinal contents, and the potential for chelation, healthcare professionals can provide tailored recommendations to enhance drug absorption.