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Figure 9.7. Diurnal variation of nasal pH.

Figure 9.8 Fraction of benzoic acid absorbed in 60 minutes in the rat perfused nasal cavity model

Figure 9.8 Fraction of benzoic acid absorbed in 60 minutes in the rat perfused nasal cavity model

Figure 9.9 Effect of buffers on nasal pH. Anterior pH black line and posterior pH grey line

Figure 9.9 Effect of buffers on nasal pH. Anterior pH black line and posterior pH grey line

Local pH has been demonstrated in vitro and ex-vivo studies to significantly affect the rate and extent of absorption of ionizable compounds (Figure 9.8)78. Buffering a solution to a target pH optimised for a particular drug should in theory, improve the absorption across the nasal epithelia. Reducing the pH of the mucosa enhanced the absorption of vasopressin in rats79, but the rat tracheal cilia model shows that decreased pH has an adverse effect on ciliary beat frequency80. Reduction in nasal pH has also been demonstrated to result in lower blood glucose levels in dogs treated with intranasal insulin81.

Recently, it has been demonstrated that buffers can be used to modify the pH of the human nasal cavity (Figure 9.9)82. Nasal anterior pH can be decreased when buffers of 0.1M and above are used. Mildly acidic solutions produce an increase in pH, presumably due to reflux bicarbonate secretion. It is more difficult to modify the pH in the posterior of the nasal cavity and stronger buffers are required to do this.

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