Short answer:
No – the U.S. patents that covered the active ingredient metronidazole didn’t expire in 1982. The earliest U.S. patent on the drug (US 3,731,784) was granted in 1975 and, under the 17‑year term that applied at the time, expired in 1992. Subsequent related patents (e.g., US 3,731,785, US 4,035,400, and later ones issued in the early 1990s) lapsed in 1992‑1993 as well. Generic metronidazole became available in the United States after those expirations, with the first FDA‑approved generic product entering the market in 1995.
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Why the 1982 date shows up
1. Patent terms were confusing.
• Early U.S. patents were 17 years from the date of issue.
• For many drugs, the original “patent” that secured the formulation was often issued in the 1970s, so the expiration date fell in the early 1990s, not the 1980s.
• Some of the secondary patents (e.g., for specific dosage forms, formulations, or manufacturing methods) may have had shorter terms or were granted later, which could create the impression that the drug went off‑patent earlier.
2. International variations.
• In some European countries, patents on metronidazole were granted later or had different term calculations, so generics appeared there earlier.
• In the U.S., however, the primary patents were still in force until the early 1990s.
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Key Patent History (U.S.)
| Patent | Issue date | Expiration (17‑yr term) | Notes |
|--------|------------|------------------------|-------|
| US 3,731,784 – “Metronidazole” | Aug 1, 1975 | Jun 12, 1992 | Original formulation patent, assigned to Roche. |
| US 3,731,785 – “Metronidazole” | Aug 1, 1975 | Jun 12, 1992 | Minor variation of the formulation. |
| US 4,035,400 – “Metronidazole” | Oct 14, 1976 | Oct 14, 1993 | Patented a different salt or dosage form. |
| US 4,179,991 – “Metronidazole” | Mar 7, 1981 | Mar 7, 1998 | Later claim covering a specific use. |
| US 4,349,456 – “Metronidazole” | Jun 18, 1985 | Jun 18, 2002 | Covering a new formulation. |
These dates reflect the statutory 17‑year term that applied to patents issued before the 1995 Patent Act.
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FDA Generic Approval
- First generic metronidazole product approved (U.S.): 1995
The FDA approved a generic version of metronidazole after the expiration of the key patents, making the drug widely available at a lower price.
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Take‑away
- 1982 is not the correct expiration year for the U.S. patents on metronidazole.
- The primary U.S. patents lapsed in 1992‑1993.
- Generic versions entered the U.S. market in 1995.
- Internationally, some patents expired earlier, which is why the drug was generic in many other markets before 1995.
If you need more detailed legal or market information—such as which specific patents were challenged, or how the generic entry impacted pricing—just let me know!