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Lyophilisation: difference between revisions

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30Values 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.30Values 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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+32Sublimation 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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+34== Freezing ==
+35Cooling 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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+37Because nucleation is stochastic, vials within one batch nucleate at different temperatures and therefore dry at different rates. This is a principal source of vial-to-vial variability in residual moisture and cake appearance, and it is the reason controlled-nucleation techniques — depressurisation, ice fog, or brief pressure cycling — have been developed to force all vials to nucleate within a narrow window.{{r|kasper2011}}
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+39As ice forms, solutes are excluded from the crystal lattice and concentrate in the remaining liquid. This freeze concentration continues until the residual phase either crystallises at a eutectic temperature or becomes so viscous that it vitrifies. The temperature at which the maximally freeze-concentrated amorphous phase undergoes its glass transition is written Tg′ and is a formulation property, not a process setting.
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32== References ==41== References ==
33{{reflist}}42{{reflist}}
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36<ref name="tang2004">Tang X, Pikal MJ. "Design of freeze-drying processes for pharmaceuticals: practical advice." ''Pharmaceutical Research'' 21(2):191–200 (2004).</ref>45<ref name="tang2004">Tang X, Pikal MJ. "Design of freeze-drying processes for pharmaceuticals: practical advice." ''Pharmaceutical Research'' 21(2):191–200 (2004).</ref>
37<ref name="carpenter1997">Carpenter JF, Pikal MJ, Chang BS, Randolph TW. "Rational design of stable lyophilized protein formulations: some practical advice." ''Pharmaceutical Research'' 14(8):969–975 (1997).</ref>46<ref name="carpenter1997">Carpenter JF, Pikal MJ, Chang BS, Randolph TW. "Rational design of stable lyophilized protein formulations: some practical advice." ''Pharmaceutical Research'' 14(8):969–975 (1997).</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>
+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>
38<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>
39<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>
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43[[Category:Fill and finish]]55[[Category:Fill and finish]]
44[[Category:Preparation and handling]]56[[Category:Preparation and handling]]
+57[[Category:Cold chain and stability]]
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