The effect of intranasal sodium citrate on olfaction in post-infectious loss: results from a prospective, placebo-controlled trial in 49 patients.

OBJECTIVES: Free calcium plays an integral role in peripheral olfactory processing, including feedback inhibition. It has therefore been suggested that reduction of intranasal free calcium with buffer solutions such as sodium citrate may improve olfactory function in patients with smell impairment. Several previous studies have supported this hypothesis, particularly in post-infectious olfactory loss. We therefore aimed to determine whether treatment with intranasal sodium citrate improves olfactory function in patients with post-infectious impairment.

DESIGN: Prospective, single-blind, placebo-controlled trial.

SETTING: Interdisciplinary Smell and Taste Clinic, TU Dresden (tertiary referral centre).

PARTICIPANTS: Forty-nine adult participants with post-infectious olfactory impairment (M : F = 11 : 38, mean age 58.71 ± 11.03 years).

MAIN OUTCOME MEASURES: Olfactory function (odour threshold and identification) before and after treatment as determined using "Sniffin' Sticks". Patients were treated monorhinally with 1 mL sodium citrate solution. The contralateral nasal cavity was treated with 1 mL physiological sodium chloride solution, which acted as internal control. Clinical improvement was assumed where threshold or identification score increased by ≥2.5 or 3 points, respectively, or ≥5.5 points together.

RESULTS: We demonstrated a statistically significant improvement in composite threshold + identification scores following treatment with sodium citrate, compared with placebo. This was true for all patients (mean improvement 0.87 ± 2.68 points, P = 0.04), and on subgroup analysis in those with hyposmia (mean improvement 1.15 ± 2.37 points, P = 0.02). However, the effect size did not reach clinical significance.

CONCLUSIONS: Further basic and clinical work is required to fully delineate the effect of intranasal sodium citrate in the treatment of post-infectious olfactory loss.