# How to Make Pill Coatings That Keep Medicine Stable Over Time

> A method for coating pills with a specific plasticized acrylic polymer that ensures the medicine releases at a steady, predictable rate, even after sitting on a shelf for months.

- **Patent:** US 5639476
- **Original title:** Controlled release formulations coated with aqueous dispersions of acrylic polymers
- **Owner:** Euro Celtique SA
- **Granted:** 1997
- **Status:** Public domain (expired)
- **Times cited:** 1,092
- **Field:** pharmaceutical, mechanical

## What it does

This patent describes a way to coat medicine-filled substrates, like beads or tablets, with a special acrylic polymer dispersion. The core mechanism involves curing the coated pill at a temperature above the polymer's glass transition temperature for 24 to 60 hours. This process stabilizes the coating, ensuring that the rate at which the medicine dissolves in the body remains consistent even after the pill has been stored in hot and humid conditions. By achieving this stability, the manufacturer guarantees that the drug release profile does not shift by more than 15% after a month of accelerated storage.

## What it does NOT cover

- Does not cover coatings made from polymers other than ammonio-methacrylate copolymers.
- Does not cover formulations that are not cured at a temperature above the polymer's glass transition temperature.
- Does not cover coatings that do not include a permeability-enhancing agent or pore-former.
- Does not cover immediate-release medications that do not require a controlled release profile.

## The clever bit

The innovation is the specific curing process—heating the coated pill above its glass transition temperature for a long duration—which forces the polymer particles to fuse into a stable, uniform film that resists environmental degradation.

## Real-world examples

1. OxyContin extended-release tablets
2. Various 12-hour and 24-hour controlled-release opioid medications
3. Extended-release analgesic beads in capsules

## Why it matters

This technology was essential for the commercial success of long-acting opioid analgesics, such as OxyContin. By ensuring that the drug release rate remained stable during storage, manufacturers could reliably market pills intended to provide pain relief over 12 or 24 hours. The patent became a cornerstone of the pharmaceutical industry's ability to produce consistent, extended-release oral dosage forms.

## Frequently asked questions

### What does How to Make Pill Coatings That Keep Medicine Stable Over Time cover?

A method for coating pills with a specific plasticized acrylic polymer that ensures the medicine releases at a steady, predictable rate, even after sitting on a shelf for months.

### Who owns patent US 5639476?

Euro Celtique SA owns this patent, granted in 1997.

### When does this patent expire?

This patent has expired and is now in the public domain — anyone can use the invention freely.

### What is patent US 5639476 cited by?

This patent has been cited by 1092 later patents that build on its ideas.

### What problem does this patent solve?

This technology was essential for the commercial success of long-acting opioid analgesics, such as OxyContin. By ensuring that the drug release rate remained stable during storage, manufacturers could reliably market pills intended to provide pain relief over 12 or 24 hours. The patent became a cornerstone of the pharmaceutical industry's ability to produce consistent, extended-release oral dosage forms.

### What does this patent NOT cover?

Does not cover coatings made from polymers other than ammonio-methacrylate copolymers.

**Full plain-English explainer:** https://patentbrief.org/patent/us/5639476/nicoderm-nicotine-patch

**Original patent:** https://patents.google.com/patent/US5639476

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_Source: PatentBrief — https://patentbrief.org. Patent facts are from public records; the plain-English explanation is PatentBrief's._