Low dosage promethazine and loratadine negatively affect neuromotor function

Area of Science:

• Pharmacology
• Neuroscience
• Human Physiology

Background:

• Antihistamines are widely used over-the-counter medications.
• Concerns exist regarding potential side effects of both sedating and non-sedating antihistamines.
• Understanding the impact of antihistamines on neuromotor function is crucial for public health.

Purpose of the Study:

• To investigate the effects of promethazine (sedating) and loratadine (non-sedating) on voluntary and involuntary motor processes.
• To assess neuromotor function at various time points, including hours after ingestion and the following morning.
• To compare the effects of these antihistamines against a placebo.

Main Methods:

• A double-blind, placebo-controlled, three-way crossover study involving eight healthy adults.
• Assessment of neuromotor function through reaction time tests, postural tremor analysis, and heart rate variability.
• Neuromotor assessments conducted pre-ingestion, 1 hour post-ingestion, 2 hours post-ingestion, and the next day.

Main Results:

• Promethazine significantly increased self-perceived drowsiness.
• Both promethazine and loratadine negatively impacted simple and choice reaction times.
• Both antihistamines affected postural tremor (RMS and peak power) and autonomic cardiac regulation.

Conclusions:

• Sedating and non-sedating antihistamines can induce selective neuromotor deficits.
• Potential antimuscarinic effects of H(1) antagonists may influence the central dopaminergic system, affecting motor control.
• Non-sedating antihistamines may not prevent motor control side effects, despite avoiding drowsiness.