Conditioning Antihistamine

In the present study, the effects of behavioural conditioning on self-reported itch are studied in a closed versus open label conditioning paradigm. In a randomized controlled trial, participants will be screened and following inclusion allocated to one of four study groups. The conditioning paradigm consists of two phases. In the acquisition phase – consisting of 3 sessions on 3 consecutive days – an association between an unconditioned stimulus (UCS, levocetirizine) and a conditioned stimulus (CS, a distinctive-tasting drink) will be made. In the evocation phase – 3 consecutive days in the following week – it will be tested whether presenting the CS alone will evoke the conditioned effect. It is expected that conditioning will lead to a reduction in reported itch following a short-term validated histamine test. Secondary outcomes include effects on psychophysiological measurements, for example pulmonary functioning, wheal size, flare response, and scratching behaviour.

The aim of the study is to investigate the effect of behavioural conditioning on self-reported itch in response to a short-term validated histamine test in healthy participants. Additionally, the study will explore the efficacy of open label conditioning (i.e. being told about the conditioning procedure) in a closed vs. open label design, the latter of which is more related to clinical practice. It is expected that conditioning will lead to a reduction in self-reported itch following a short-term validated histamine test.

The study consists of 7 sessions during the course of 3 weeks. In the first week, participants will be screened for medical and psychological conditions. In the second week, the acquisition phase - consisting of 3 sessions on 3 consecutive days - takes place and in the final week during the evocation phase - again consisting of 3 consecutive sessions - the conditioned response will be tested.

In line with previous conditioning studies, a randomised placebo-controlled conditioning paradigm consisting of 2 phases will be applied. In the acquisition phase - consisting of 3 sessions on 3 consecutive days - an association between an unconditioned stimulus (UCS, levocetirizine diHCl) and a conditioned stimulus (CS, a distinctive-tasting drink) will be made. In the evocation phase - 3 consecutive days in the following week - the conditioned effect will be tested.
Participants will be randomly assigned to 1) the experimental closed label group (acquisition: CS+UCS; evocation: CS+placebo pill), 2) the experimental open label group (acquisition: CS+UCS; evocation: CS+placebo pill), 3) the placebo group (acquisition: CS+placebo pill; evocation: CS+placebo pill), or 4) the conditioned not evoked group (acquisition: CS+UCS; evocation: water+placebo pill).
In the experimental closed label group, participants will be conditioned through repeated pairing of the administration of the distinctive-tasting drink (CS) and levocetirizine diHCl (UCS)in the acquisition phase. In the evocation phase, the conditioned effect will be tested by receiving the distinctive-tasting drink in combination with a placebo pill. In the experimental open label group, the same procedure will be applied as in the experimental closed label group, but participants will receive additional information about their group allocation and the conditioning procedure. The placebo group will receive the CS and a placebo pill throughout the acquisition and evocation sessions. To control for residual effects of levocetirizine diHCl during the evocation phase, participants in the conditioned not evoked group will receive the CS and levocetirizine diHCl in the acquisition sessions and, in the evocation sessions, will receive water and a placebo pill to prevent invoking conditioned responses through re-exposure to the CS.