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Drying: Problems and Remedies

Nonuniform Drying

Causes: Remedies
  • Poor air circulation (tray dryer): Have oven air circulation checked and corrected
  • Dryer overload:
  1. Reduce the number of trays.
  2. Reduce the thickness of wet mass on the trays (tray load).
  3. Try a fluid bed dryer.

Granule case hardening (hard crust forms with incomplete drying inside granule)

Causes: Remedies
  • Too rapid evaporation of water / Oven drying conditions too efficient:
  1. Try recirculating oven air (damper closed) for an initial 15 to 30 minutes, then open the damper partially for a short period, and finally open the damper fully.
  2. Reduce drying temperature
  3. Add Avicel PH-101 to formulation (gives more even water evaporation and uniform granule moisture content).
  4. Use a fluid bed dryer

Color Migration

Causes: Remedies
  • Colors migrate to granule surfaces (wet granulation); tablets have a mottled appearance:
  1. Use lakes instead of soluble dyes (will minimize but not eliminate).
  2. Decrease the size of the wet granules
  3. Decrease thickness of granulation bed; stir granulation bed frequently during drying to expose fresh surfaces at the top of the wet mass
  4. Use Avicel PH-101- reduces or eliminates dye migration in wet granulation.

Drug Migration

Causes: Remedies
  • Drug migrates to granule surfaces; content uniformity problems may result as the drug becomes part of “fines” after dry screening or there is a loss of drug with subsequent low tablet assays
  • Use lakes instead of soluble dyes (will minimize but not eliminate).
  • Decrease the size of the wet granules
  • Decrease thickness of granulation bed; stir granulation bed frequently during drying to expose fresh surfaces at the top of the wet mass
  • Use Avicel PH-101- reduces or eliminates dye migration in wet granulation.

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