Determination of baseline human nasal pH and the effect of intranasally administered buffers.

Abstract The nose is becoming a common route of drug administration, however, little is known about the pH of the human nasal cavity. Local pH may have a direct effect on the rate and extent of absorption of ionizable compounds and hence this study was performed to investigate normal pH values and whether pH could be manipulated by various buffers. Twelve healthy volunteers participated in a study to measure pH in the anterior and posterior sites of the nasal cavity. Miniature pH electrodes were placed 3 cm apart in the nasal cavity and a baseline was recorded for 30 min once the pH had stabilized. One hundred microlitres of isotonic solution was sprayed into the nostril and the pH was measured for 4 h post-dose. The following five formulations were tested: formulation A — sodium chloride (0.9%) at pH 7.2; formulation B — sodium chloride (0.9%) at pH 5.8; formulation C — Sorensens phosphate buffer (0.06 M) at pH 5.8; formulation D — Sorensens phosphate buffer (0.13 M) at pH 5.8 and formulation E — formulation as (c) but adjusted to pH 5.0. Each formulation also contained saccharin sodium (0.5%) as a taste marker for nasal clearance. The time at which each subject detected the taste of saccharin was noted. The 30-minute baseline recording prior to administration of the nasal spray formulation demonstrates that there was both considerable intersubject and intrasubject variation in nasal pH. The average pH in the anterior of the nose was 6.40 (+0.11, −0.15 S.D.) when calculated from H + values. The pH in the posterior of the nasal cavity was 6.27 (+0.13, −0.18 S.D.). The overall range in pH was 5.17–8.13 for anterior pH and 5.20–8.00 for posterior pH. Formulation A caused the pH in the anterior part of the nasal cavity to reach a maximum of 7.06 in 11.25 min from the baseline of pH 6.14 (P