Lyophilisation: difference between revisions
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| 30 | Values follow the standard formulations reviewed by Murphy and Koop.{{r|murphy2005}} The table explains a practical asymmetry of the process: a cycle run with the product at −40 °C rather than −30 °C loses roughly two-thirds of its driving force, and a cycle run 5 °C warmer than intended may dry substantially faster while risking the structural failure described below. | 30 | Values follow the standard formulations reviewed by Murphy and Koop.{{r|murphy2005}} The table explains a practical asymmetry of the process: a cycle run with the product at −40 °C rather than −30 °C loses roughly two-thirds of its driving force, and a cycle run 5 °C warmer than intended may dry substantially faster while risking the structural failure described below. |
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| + | 32 | Sublimation is strongly endothermic. The enthalpy of sublimation of ice is approximately 2.83 MJ·kg⁻¹, about 13% greater than the enthalpy of vaporisation of liquid water, so the shelf must supply a large heat flux for a modest mass flow. That heat must cross a gas gap between shelf and vial base, and the efficiency of that transfer — conventionally expressed as a vial heat transfer coefficient — is itself a function of chamber pressure, because conduction through rarefied gas falls as pressure falls.{{r|rambhatla2003}} | |
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| 32 | == Freezing == | 34 | == Freezing == |
| 33 | Cooling an aqueous solution below 0 °C does not immediately produce ice. Nucleation requires supercooling, and in clean pharmaceutical solutions supercooling of 10–20 °C below the equilibrium freezing point is routine. The temperature at which nucleation happens to occur determines the number and size of the ice crystals formed: nucleation close to 0 °C produces few, large crystals and a coarse, low-resistance dried structure, whereas deep supercooling produces many small crystals and a fine structure that impedes vapour escape.{{r|searles2001,kasper2011}} | 35 | Cooling an aqueous solution below 0 °C does not immediately produce ice. Nucleation requires supercooling, and in clean pharmaceutical solutions supercooling of 10–20 °C below the equilibrium freezing point is routine. The temperature at which nucleation happens to occur determines the number and size of the ice crystals formed: nucleation close to 0 °C produces few, large crystals and a coarse, low-resistance dried structure, whereas deep supercooling produces many small crystals and a fine structure that impedes vapour escape.{{r|searles2001,kasper2011}} |
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| 45 | <ref name="searles2001">Searles JA, Carpenter JF, Randolph TW. "The ice nucleation temperature determines the primary drying rate of lyophilization for samples frozen on a temperature-controlled shelf." ''Journal of Pharmaceutical Sciences'' 90(7):860–871 (2001).</ref> | 47 | <ref name="searles2001">Searles JA, Carpenter JF, Randolph TW. "The ice nucleation temperature determines the primary drying rate of lyophilization for samples frozen on a temperature-controlled shelf." ''Journal of Pharmaceutical Sciences'' 90(7):860–871 (2001).</ref> |
| 46 | <ref name="kasper2011">Kasper JC, Friess W. "The freezing step in lyophilization: physico-chemical fundamentals, freezing methods and consequences on process performance and quality attributes of biopharmaceuticals." ''European Journal of Pharmaceutics and Biopharmaceutics'' 78(2):248–263 (2011).</ref> | 48 | <ref name="kasper2011">Kasper JC, Friess W. "The freezing step in lyophilization: physico-chemical fundamentals, freezing methods and consequences on process performance and quality attributes of biopharmaceuticals." ''European Journal of Pharmaceutics and Biopharmaceutics'' 78(2):248–263 (2011).</ref> |
| + | 49 | <ref name="rambhatla2003">Rambhatla S, Pikal MJ. "Heat and mass transfer scale-up issues during freeze-drying, I: atypical radiation and the edge vial effect." ''AAPS PharmSci'' 5(2):article 14 (2003).</ref> | |
| 47 | <ref name="chang2009">Chang LL, Pikal MJ. "Mechanisms of protein stabilization in the solid state." ''Journal of Pharmaceutical Sciences'' 98(9):2886–2908 (2009).</ref> | 50 | <ref name="chang2009">Chang LL, Pikal MJ. "Mechanisms of protein stabilization in the solid state." ''Journal of Pharmaceutical Sciences'' 98(9):2886–2908 (2009).</ref> |
| 48 | <ref name="murphy2005">Murphy DM, Koop T. "Review of the vapour pressures of ice and supercooled water for atmospheric applications." ''Quarterly Journal of the Royal Meteorological Society'' 131(608):1539–1565 (2005).</ref> | 51 | <ref name="murphy2005">Murphy DM, Koop T. "Review of the vapour pressures of ice and supercooled water for atmospheric applications." ''Quarterly Journal of the Royal Meteorological Society'' 131(608):1539–1565 (2005).</ref> |