Why Tablet Size and Coating Matter in FIP Treatment

What Is FIP and Why It’s a Systemic Disease

Understanding how GS-441524 absorption impacts treatment efficacy.

According to Cornell University (2024), feline infectious peritonitis (FIP) is a viral disease caused by certain strains of feline coronavirus (FCoV). Most of these coronaviruses exist harmlessly in the gastrointestinal tract, particularly in the small intestine.

However, in about 10% of cats, the intestinal FCoV mutates into a more aggressive form — the FIP virus. Once this mutation occurs, the virus infects white blood cells and spreads systemically through the bloodstream and lymphatic system to multiple organs, including the liver, kidneys, and nervous system.

In other words, FIP is a systemic viral disease, not a localized infection. To effectively stop viral replication, antiviral medication must enter the bloodstream and reach all affected tissues throughout the body.

Why Intestinal Absorption Is Essential

An important pharmacological principle is that most oral medications are absorbed in the small intestine, not in the stomach.

This occurs because:

The small intestine has a very large surface area, enhanced by villi and microvilli.
Intestinal epithelial cells contain specialized transport channels that allow drug molecules to pass into the bloodstream.
The stomach’s highly acidic environment can degrade and inactivate many drugs before absorption can occur.

For FIP treatment, this distinction is critical. GS-441524, the active antiviral compound, is a hydrophilic nucleoside analog that is unstable in acidic conditions. If exposed to stomach acid for too long, it may lose part of its biological activity or fail to be absorbed effectively.

Therefore, GS-441524 tablets must have a protective enteric coating to ensure they remain intact as they pass through the stomach and only release their active ingredient once they reach the small intestine. This allows efficient absorption into the bloodstream, where the drug can circulate throughout the body.

As noted by Pedersen et al. (2019, Journal of Feline Medicine and Surgery):

“The drug must reach sufficient plasma concentrations to inhibit systemic viral replication.”

Pharmacokinetic studies have also demonstrated that oral GS-441524 plasma concentration is directly related to treatment efficacy, and that degradation or poor absorption can lead to reduced therapeutic outcomes.

The Scientific Basis of Maxpaw’s Tablet Design

At Maxpaw, we pay close attention to the details that affect both efficacy and safety. Most FIP cases occur in young cats, which often have smaller throats and greater difficulty swallowing tablets.

However, many GS-441524 tablets on the market are relatively large, leading cat owners to split the tablets before administration. This practice, while well-intentioned, damages the enteric coating and reduces both absorption efficiency and treatment effectiveness.

For this reason, Maxpaw’s GS-441524 tablets are designed to:

Be smaller in size, making them easier to swallow.
Feature a protective enteric coating that ensures safe passage through the stomach.
Provide optimized absorption in the intestine for maximum plasma concentration and systemic antiviral action.

How It Works: From Absorption to Action

The pathway of GS-441524 can be summarized in three essential stages:

Intestinal absorption – the drug is absorbed through the intestinal wall and enters the bloodstream.
Systemic distribution – the absorbed compound circulates through the body via the blood and lymphatic systems.
Cellular inhibition – the active metabolite enters infected cells and blocks viral replication.

The therapeutic success of GS-441524 relies entirely on this process: intestinal absorption → systemic distribution → cellular action.

Maxpaw’s Commitment to Scientific Precision

Maxpaw’s research and development are driven by both science and compassion. By focusing on tablet size and coating technology, we aim to ensure that each dose of GS-441524 delivers its full antiviral potential.

Our mission is clear: to help every cat fighting FIP receive treatment that is safe, efficient, and scientifically optimized — enabling faster recovery and a return to a healthy, active life.