Pharmacology and toxicology
Expectorants and mucolytic agents enhance or facilitate the clearance of mucus in the respiratory tract.
Ambroxol is a metabolite of bromhexine, and has been used in the prevention of neonatal respiratory distress syndrome with no reported maternal or fetal/neonatal side effects.
N-acetylcysteine is a derivative of the amino acid L-cysteine, and is used as a mucolytic agent and an antidote in paracetamol (acetaminophen) poisoning. Although the documented data on its use as a mucolytic during pregnancy are scarce, it seems to be safe when used in low doses.
Carbocysteine is a mucus regulator rather than a mucolytic agent.
Guaifenesin and guaiacol stimulate the clearance of viscous mucus via stimulation of the gastropulmonary vagal reflex, but they have no effect on the thickness of the mucus. There is no evidence of an increased risk of congenital malformations or other adverse effects on pregnancy outcome.
Mesna is an expectorant that breaks the disulfide bonds in mucopolysaccharides present in the mucus. Data on human pregnancy outcome are not available.
Potassium iodide also has mucolytic properties. However, it may suppress fetal thyroid function.
Recommendation. N-acetylcysteine, ambroxol and bromhexine are first-choice mucolytics during pregnancy, if (oral) fluid therapy, and other nonmedical treatment is not effective. Iodine-containing mucolytics are contraindicated, especially after the first trimester. Inadvertent short-term use of the other expectorants and mucolytics does not require any intervention.
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