Vitamin A-Containing Intranasal Drops Improve Odour Detection Threshold

Retinoic acid, a metabolite of vitamin A (VA), has been shown in animal work to support olfactory receptor neuron regeneration. A limited amount of clinical research has also demonstrated potential therapeutic benefit in patients with olfactory dysfunction (OD). We therefore performed, to our knowledge, the first prospective study investigating whether the intranasal VA-containing "Coldastop" is beneficial in treating patients with non-sinonasal OD.

A non-blinded prospective comparative study was performed, in patients with OD due to post-infectious, post-traumatic, and idiopathic aetiologies. Patients were treated with olfactory training (OT) alone, OT plus intranasal VA (Coldastop, OT+VA), or OT plus intranasal steroids (mometasone furoate, OT+S) for 12 weeks. Full psychophysical olfactory testing was performed before and after treatment using the "Sniffin' Sticks" test battery (with results for odour threshold, discrimination, identification, and composite "TDI").

A total of 144 patients completed the study: 52 OT, 42 OT+S, 50 OT+VA. The majority of patients had post-infective OD. There were no significant differences between groups in age/sex. There were statistically significant improvements in each subtest (T/D/I) and composite scores (TDI) within each treatment regimen. Across groups, there was a significant interaction between treatment and time (controlling for baseline characteristics) for odour threshold, F(2, 139) = 3.2, p = 0.044, with the largest improvement being seen in the OT+VA group. Further, the greatest proportion of patients reached clinically significant improvement within the OT+VA group (T/D/I/TDI), but this did not reach statistical significance.

Intranasal VA may be of benefit in treating OD. Further large-scale randomised trials are required.