standardised allergen extract of pollen from white birch (Betula verrucosa): clinical use

Prescribing considerations

• Confirm a compatible clinical history and sensitisation to a member of the birch homologous group using skin-prick testing and/or specific IgE.
• Treatment initiation and first administration require a clinician experienced in allergic disease, facilities to manage systemic reactions and at least 30 minutes of observation.
• Assess asthma control, recent exacerbations, lung function, oral health, immune disease, malignancy, cardiovascular disease and previous systemic reactions to tree-pollen immunotherapy.
• Clinical experience in people aged 65 years or older is limited.
• Review persistent dysphagia, dyspepsia or reflux symptoms for possible eosinophilic oesophagitis and interrupt treatment pending assessment.

Contraindications and cautions

• Hypersensitivity to an excipient
• FEV1 below 70% predicted after adequate pharmacological treatment at initiation
• Severe asthma exacerbation or uncontrolled asthma within the preceding 3 months
• Active systemic autoimmune disease unresponsive to treatment, immune deficiency, immunodeficiency or immunosuppression
• Malignancy with current disease relevance
• Acute severe oral inflammation or oral wounds

Monitoring

• Observe for immediate local or systemic reactions after the first administration.
• Monitor asthma control and advise immediate assessment for sudden deterioration.
• Review the severity and persistence of local mouth, throat and gastrointestinal reactions.
• Assess treatment response, adherence and continuing suitability.
• Temporarily interrupt treatment around significant oral inflammation, wounds or oral surgery until healing.

Clinical pharmacology

The active components are allergenic proteins. Sublingual uptake is thought to involve oral mucosal dendritic cells; material not taken up is expected to be broken down in the gastrointestinal tract. Significant systemic absorption has not been demonstrated. Immunotherapy induces birch-specific IgG4 and reduces IgE binding, although the complete mechanism of clinical benefit remains uncertain.

Formulation and product differences

• The selected UK product is a white to off-white freeze-dried sublingual lyophilisate supplied in moisture-protective aluminium blisters.
• Excipients are fish-source gelatine, mannitol and sodium hydroxide; it is essentially sodium-free.
• No special storage temperature is required, but it must remain in its original blister to protect it from moisture.