Topical Nasal Antihistamines

Topical nasal antihistamines (azelastine, olopatadine, levocabastine) relieve sneezing, itch, discharge and blockage in allergic and vasomotor rhinitis. They act faster than intranasal steroids but are less effective on blockage, and are used alone for intermittent symptoms or as an add-on to a steroid spray.

Mechanism. Selective blockade of histamine H1 receptors, with additional mast cell stabilising and anti-inflammatory effects (reduced leukotrienes and cytokines). Azelastine also reduces neurogenic inflammation, which may explain benefit in vasomotor rhinitis.

Pharmacokinetics. Onset within 15 minutes, duration about 12 hours. Systemic absorption of azelastine is about 40 percent (swallowed fraction), with an active metabolite and half-life of about 20 hours; olopatadine has low absorption.

• Azelastine 0.1 percent (137 micrograms/spray) and 0.15 percent (205.5 micrograms/spray): best-evidenced agent; bitter taste in a proportion of patients.
• Olopatadine 0.6 percent (665 micrograms/spray): less bitter taste.
• Levocabastine 0.05 percent: short-term seasonal use.
• Fixed combination: azelastine 137 micrograms with fluticasone propionate 50 micrograms/spray.

Regimens.

• Azelastine 0.1 percent: 1 or 2 sprays in each nostril twice daily (adults and children from 5 years: 1 spray).
• Azelastine 0.15 percent: 1 or 2 sprays in each nostril twice daily, or 2 sprays once daily (adults and children from 6 years).
• Olopatadine 0.6 percent: 2 sprays in each nostril twice daily (from 12 years; 1 spray from 6 years).
• Levocabastine 0.05 percent: 2 sprays in each nostril twice daily, increased to three or four times daily if needed.
• Fixed azelastine with fluticasone: 1 spray in each nostril twice daily.
• Technique: tilt the head forward and avoid sniffing hard, to reduce taste and drip.

Selection. Intermittent or episodic allergic rhinitis when an immediate effect is needed, patients who dislike steroid sprays, and when oral antihistamine fails; add-on to intranasal steroid for incomplete control. Use daily for 2 weeks to judge effect.

Contraindications. Hypersensitivity; use with caution in the first trimester of pregnancy.

Effects. Bitter taste (up to 20 percent), drowsiness (about 5 percent), headache, nasal irritation, epistaxis, nausea; rarely weight gain with olopatadine.

Interactions. Alcohol and other central nervous system depressants increase sedation; cimetidine raises azelastine levels.

Monitoring. Review at 2 weeks; warn patients about driving if drowsy.

Special groups. Pregnancy: avoid in the first trimester unless needed; use intranasal steroid and saline irrigation first. Breastfeeding: use with caution. Children: azelastine from 5 or 6 years depending on strength. Older adults: sedation risk. Region: oral sedating antihistamines (chlorphenamine) are the usual choice, and nasal antihistamines are costly and often unavailable, so an intranasal steroid is the practical first option.