Cocrystal hydrate formation

Another approach that is fast gaining popularity is the formation of cocrystals to alter the pharmacokinetics of a drug. The tendency of the system to salt or co-crystal formation is governed by the pA a difference, steric and electrostatic properties of the molecules involved. The rule of thumb widely accepted is that there is salt formation if ApA a > 2, while ApATg < 0, results in co-crystal formation. For 0 < Ap.Ka < 2, the system could swing either way resulting in the formation of a salt or co-crystal or a complex with partial proton transfer. Other approaches include formation of solvates, hydrates or variation in the crystal lattice through the formation of polymorphs. 

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