The best replacement for extended release is sustained release.

The best alternatives to extended release are rated as following:
★★★★★  sustained release
★★★  delayed release
★★  immediate release
★★  controlled release
★★  instant release
★  time release
★  instant release adderall
★  slow release
★  metformin
★  delayed release depakote
★  enteric coated
★  long acting
  modified release
  sustained
  timed release
  sustained release tablets
  rapid release

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Speaking about extended release, one probably shouldn't forget about no extended release.

Other search terms related to extended release and their ratings are:
★★★★★ no extended release
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Google Trends

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extended release
sustained release
delayed release