Slow-release capsules or tablets—often referred to as sustained, controlled, or modified release—are commonly used in humans to reduce dosing frequency or minimize side effects. But can these same formulations be safely used in dogs, cats, or other animals?

Most studies on slow-release formulations have focused on human physiology, and there are significant differences between species that may impact their effectiveness in animals. For example, animals differ from humans in terms of stomach pH, the time it takes for substances to move through the digestive system, their ability to swallow pills as intended, and even the number of stomachs they have.

Slow-release medications can come in different forms, such as solid matrix tablets, where the drug is dispersed in a waxy substance, or in capsule form containing small, coated granules, pellets, or tiny beads. The specific formulation used depends on the type of medication and how best to achieve a controlled release to provide the desired therapeutic effect.

When using human slow-release formulations in animals, there are risks. The capsule may pass through the digestive system without releasing the drug, meaning the animal won’t absorb any of the medication.

Conversely, the drug might be released too quickly, potentially leading to adverse effects or overdose.
In veterinary practice, modified-release capsules are sometimes compounded by pharmacies to suit the needs of individual patients. These preparations typically involve mixing the active drug with a cellulose-based material that swells when it comes into contact with stomach acid. This swelling helps to slow the release of the drug. However, this method requires a sufficiently large capsule size to be effective.

Unfortunately, like most other slow-release formulations, studies on these compounded medications have largely been conducted in humans, with limited data available for animals.
There have been a few small-scale studies exploring the use of human slow-release medications in animals. One such study tested a modified-release human heart medication in cats and found that, with careful monitoring, it was possible to achieve once daily dosing—a significant improvement over the standard three times a day dosing usually required for cats with this drug.

In conclusion, switching an animal to a modified-release medication designed for humans is not straightforward and should never be attempted without thorough research and clinical studies specific to the species in question. Always consult with a veterinarian before making any changes to a pet’s medication regimen