not usually wet the nasopharynx, tears pass into the nasopharynx as the normal route of drainage from the conjunctival sac.

The pH dependence of partition coefficients of tetracyclines is more complex than for most drugs, as the tetracyclines are amphoteric.

For slightly simpler amphoteric compounds, such as p-aminobenzoic acid and sulfonamides, the apparent partition coefficient is maximal at the isoelectric point. Figure 5.10 illustrates the variation with pH of log Papp for p-aminobenzoic acid and for two sulfonamides.

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