If urine is collected within 24 hours of a dose of guaifenesin a metabolite of guaifenesin may cause a colour interference with laboratory determinations of urinary 5-hydroxyindoleacetic acid (5-HIAA) and vanillylmandelic acid (VMA).

4.6 Pregnancy and lactation
The safety of this medicine during pregnancy and lactation has not been established, but in view of a possible association of foetal abnormalities with first trimester exposure to pseudoephedrine, the use of the product during pregnancy should be avoided. The amounts of pseudoephedrine and guaifenesin secreted into breast milk are considered too small to be harmful.

4.7 Effects on ability to drive and use machines
No adverse effects known.

4.8 Undesirable effects
Guaifenesin

The following side effects may be associated with the use of guaifenesin:

Gastrointestinal disorders: Nausea, vomiting, gastrointestinal discomfort.

Immune system disorders: Hypersensitivity reactions.

Pseudoephedrine

Cardiovascular disorders: Tachycardia, palpitations, other cardiac dysrhythmias.

Gastrointestinal disorders: Nausea and/or vomiting, dry mouth.

General disorders and administration site conditions: Irritability.

Immune system disorders: Hypersensitivity reactions, including cross-sensitivity that may occur with other sympathomimetics.

Metabolism and nutrition disorders: Anorexia.

Nervous system disorders: Headache, tremor, anxiety, restlessness, excitability, insomnia, hallucinations (particularly in children) and paranoid delusions.

Psychiatric disorders: Sleep disturbance.

Renal and urinary disorders: Urinary retention.

Skin and subcutaneous tissue disorders: Skin reactions including rash.

Vascular disorders: Hypertension, impaired circulation to the extremities.

4.9 Overdose
Symptoms of overdosage include irritability, restlessness, palpitations, hypertension, difficulty in micturition, nausea, vomiting, thirst and convulsions. In severe overdosage gastric lavage and aspiration should be performed. Symptomatic and supportive measures should be undertaken, particularly with regard to the cardiovascular and respiratory systems. Convulsions should be controlled with intravenous diazepam. Chlorpromazine may be used to control marked excitement and hallucinations. Severe hypertension may need to be treated with an alpha-adrenoreceptor blocking drug, such as phentolamine. A beta blocker may be required to control cardiac arrhythmias.

5. Pharmacological properties
5.1 Pharmacodynamic properties
Pseudoephedrine is a sympathomimetic agent with direct and indirect effects on adrenergic receptors. It has alpha and beta adrenergic activity and some stimulant effect on the central nervous system. The sympathomimetic effect of pseudoephedrine produces vasoconstriction which in turn relieves nasal congestion.

Guaifenesin reduces the viscosity of tenacious sputum and is used as an expectorant.

5.2 Pharmacokinetic properties
Pseudoephedrine is readily and completely absorbed from the gastrointestinal tract. It is resistant to metabolism by monoamine oxidase and is largely excreted in the urine unchanged. It has an elimination half-life of 5 to 8 hours but its urinary elimination and hence half life is pH dependent. Pseudoephedrine is rapidly distributed throughout the body, its volume of distributi