Allergy Diagnostics and Treatment

Sub-Lingual Immunotherapy (SLIT)

Although proven to be very effective in the treatment of Inhalant Allergy or Stinging Insect Venom Allergy, the use of SCIT has been limited by the safety factor. Although rare, and even then usually caused by operator error, serious adverse reactions may occur, and the risk of anaphylaxis must always be considered and catered for. This safety factor has lead to the usage of SCIT only for rhinitis and rhino-conjunctivitis cases rather than for cases with a moderate to strong feature of asthma. In addition, many paediatric cases would not consider SCIT due to the discomfort from the injections. Also the inconvenience factor of weekly and then monthly doctor's visits would be a deterrent factor for some patients.

There is however an alternative form of vaccine administration that has been introduced to clinicians in various countries around the world and has become the standard vaccine form in several European countries. In the early 1990s ALK-Abell was the first manufacturer to introduce Sub-Lingual Immuno-Therapy (SLIT).

The early SLIT products were based on the same principle of an Initial Phase of increasing number of drops (1 to 10) and potency of the liquid vaccine under the tongue, followed by daily doses of the Maintenance volume of 10 drops of the highest potency.

More recently, however, after increasing experimentation and experience and documentation, the new single dose product was launched in five European countries in 2005. The product and protocol is more convenient to use than the other SLIT products in the world market as there is no up-dosing; simply 10 drops per day of a single potency, from Day 1 for 3 years.

Due to its great simplicity, compliance is therefore as good as can possibly be achieved for this patient administered treatment.

The clinical effect of SLIT has been shown in an increasing number of studies to be good, the safety profile excellent, compliance good, only mild adverse reactions (such as buccal itching), and in total very acceptable for patients, even including paediatric cases and controlled asthmatic cases.

In many European countries SLIT is now as popular and if not more popular than SCIT amongst Allergists and patients. There is increasing acceptance amongst Specialist Allergists in Australia and New Zealand, mirroring the great acceptance and usage in many parts of Europe.

There are several advantages with Sub-Lingual Immunotherapy in principle.

1. The greater patient acceptance of drops under the tongue compared to injections; so Sub-Lingual Immunotherapy is more acceptable to children in particular.
2. As the drops are dispensed by the patient at home, then the monthly visits to the doctor is not necessary except once every 6 to 12 months for re-assessment. This means far greater convenience, no time off work or school, and less cost for doctor's visits and injection fees.
3. Reduced severity & range of side effects; if present they are most usually only transient and mild such as buccal itching.
4. Vastly improved safety, so that asthmatic patients (lower airway disease), or at least patients with an asthma component to their rhino-conjunctivitis (upper airway disease), can now be considered as candidates for Immunotherapy.
5. It is easier to treat a patient with two different Sub-Lingual Vaccines to treat two different major allergenic sensitivities, (such as Grasses and House Dust Mite), compared to Injection Vaccines which must either be mixed in the vial or the patient must be given two separate injections.

There is however a major disadvantage to Sub-Lingual Immunotherapy; the cost of the Sub-Lingual Vaccine is approximately four times greater than for the Injection Vaccine, for the full three year course of treatment. The reasons for the greater cost are many, but principally because the concentration of the allergen in the Sub-Lingual Vaccine needs to be many times greater due to the less efficient method of buccal absorption compared to injection.

However, the increased cost of the Vaccine product itself is largely offset by the great reduction in costs for the doctor's visits and injection fees, so that the total cost for the three year course of Immunotherapy is indeed not so much more than for Injection Immunotherapy. Further details are available on request.

One other cost factor that should be considered is the fact that as the Immunotherapy becomes increasingly effective as the treatment progresses, then there is a corresponding reduction or even cessation in the use of symptomatic medication such as anti-histamines and bronchodilators and steroids.

Another feature of the Sub-Lingual Vaccine is that a personalised mix of allergens for an individual is usually not possible, so if the patient is highly sensitised to more than one allergen, such as Grass Pollen and House Dust Mite, then the doctor should consider either using two separate Sub-Lingual Vaccines directed against each allergen, or treating only the one major allergen with one Vaccine (and waiting for the other sensitivity to be reduced due to the general suppression of the patient's IgE response), or not choosing Sub-Lingual Immunotherapy at all.

One other important factor with Sub-Lingual iImmunotherapy is Patient Compliance. If the three year course is not completed then the clinical benefit is proportionately reduced. Similarly, a patient must take the daily dose every day regularly, in order to achieve the required stimulation of the immune system. The latest dosage schedule for Sub-Lingual Immunotherapy Vaccines means that the patient starts on Day 1 with the regular dosage of 10 drops from the single-use plastic ampoule, and continues daily with one ampoule per day for the full three years of the treatment course. There is therefore no up-dosing, so there is no need to change the volume of the dose, or to change the strength of the liquid, or any other calculations or manipulations. This great simplicity means minimal errors or missed doses.

The relative advantages and disadvantages of Sub-Lingual immunotherapy Vaccines compared to Injection Vaccines should be discussed with a Specialist Allergist.

In Europe the next generation Immunotherapy Vaccine is already available, the Tablet. However this Immunotherapy Vaccine Tablet (the first allergen being for Timothy Grass, representing the various European grasses) costs more than twice as much as the liquid Sub-Lingual drops of vaccine (and eleven times the cost of the injection vaccine) and so it is not certain if the Immunotherapy Tablet will in the future ever become routinely available in New Zealand.

Last updated 24th October 2007.