Physicochemical drug interactions and incompatibilities

9 Protein binding 419 Summary 425 Appendix 425 References 429 Further reading 430 

This chapter deals with some practical consequences of the physical chemistry of drugs -particularly their interactions with each other, with solvents and with excipients in formulations. Sometimes the interaction is beneficial and sometimes not. In reading this chapter you should appreciate that there are several causes of interactions and incompatibilities which include  

Equations can be written to describe most of these interactions, but these formulae can be applied in vivo only to provide an indication of behaviour because of the complexity of the body. Nevertheless, the equations are important to allow some prediction of the magnitude of effects. 

The chapter discusses the topic of drug interactions from a physicochemical rather than a pharmacological or pharmacodynamic viewpoint. Many drug interactions in vitro are, not surprisingly, readily explained by resorting to the physical chemistry discussed in earlier chapters 

We now discuss, in turn, pH effects in vitro and in vivo, cation-anion interactions, electrolyte effects, formation of complexes, ion-exchange interactions, adsorption and protein binding. 

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