Freeze drying is an important technique to formulate PI because it enhances the solubility and stability of the final product (48). High moisture content in the end product adversely affects not only the stability but also the reconstitution properties. Excipients used during freeze drying also have an impact on reconstitution time. Use of (SBE)7m-β-CD as a freeze-drying excipient in melphalan formulation improved the formulation's reconstitution behavior (47). The chemically modified cyclodextrins such as 2-hydroxypropyl-β-cyclodextrin (HPβCD), 2-hydroxypropyl-γ-cyclodextrin (HPγCD) and γ-cyclodextrin (γCD) enhanced the rate of dissolution of prototype lyophilized formulations of doxorubicin. It has been reported that HPγCD, present in five-fold excess relative to doxorubicin, decreased the reconstitution time from 26 min to less than 9 min (49). Using organic-aqueous mixtures instead of only aqueous solution during freeze-drying generates amorphous cakes with a large surface area, resulting in enhanced reconstitutability. Freeze drying of sucrose and lactose solutions from a tert-butanol and water mixture demonstrated rapid reconstitution, which was attributed to higher cake porosity (48, 50).

Degradation products. The presence of excess moisture in the formulation can sometimes accelerate chemical and physical degradation, which results in the formation of less-soluble degradation products that slow the reconstitution process. A lyophilized bovine serum albumin formulation when stored at elevated temperature (37 °C) and high relative humidity exhibited a loss of solubility that was attributed to protein aggregation occurring in the wet solid. Similar observations were made for recombinant human albumin, insulin, and tetanus toxoid (51). In such cases, special attention should be given to the choice of rubber plugs because it is the most potential source of ingress of moisture to the product (50).

Foaming. Foaming during reconstitution is a serious problem for biopharmaceutical drugs because it may lead to protein denaturation and a consequent loss in their activity. This situation necessitates determination of the protein activity that is lost as a result of shaking, which may further assist in setting specifications for reconstitution time. Kanavage et al. reported that the usual reconstitution time for lyophilized antivenom preparations by gentle swirling is approximately 45 min. Minimal changes observed in activity of the antivenom formulation, even with severe intentional foaming, obviated the need for any special reconstitution specifications (52). Apart from product stability, foaming also causes problems during administration, requiring it to be dissipated before use. In case of lyophilized palivizumab (Synagis, MedImmune), a rapid spurt of water into the vial may cause immediate and prolonged foaming that will require up to 2 h to dissipate (53).

Extrinsic parameters affecting reconstitution time

Extrinsic parameters include variables related to the container of the product and the conditions used on the product in storage and during the reconstitution process.

Method of reconstitution. Reconstitution of ziprasidone (Geodon), an antipsychotic drug, was found to be quick and more effective when carried out by hand shaking rather than using a commercially available agitation machine (56). Stogniew made a comparison between shaking and hand swirling for anidulafungin, an antifungal drug, and found that swirling generally resulted in longer reconstitution times, although with reduced foaming. With shaking, reconstitution times were shortened, but foaming was invariably observed (46).