Duro-Tuss Expectorant Mechanism of Action

Pharmacology: Cough suppressant and mucolytic giving relief over 8 to 10 hours.
Pholcodine: Pholcodine is an opioid chemically related to morphine. Pholcodine is a cough suppressant and has a mild sedative effect which relieves local irritation of the respiratory tract. Pholcodine acts primarily on the CNS causing depression of the cough reflex which is due partly to the direct effect on the cough centre in the medulla.
Pholcodine has little or no analgesic action. Unlike morphine, codeine and dihydrocodeine, therapeutic doses of pholcodine do not cause depression of respiration, CNS excitation, constipation or other side effects associated with narcotics. Pholcodine has a selective effect on the cough centre without affecting the respiratory centre. Pholcodine is not euphorigenic therefore psychological dependence is unlikely to be a problem.
There is no evidence of physical dependence after prolonged administration of pholcodine so it is not likely to be habit forming.
Bromhexine hydrochloride: Bromhexine is an effective oral mucolytic agent with a low level of associated toxicity. Bromhexine is not an expectorant but it has been demonstrated to aid expectoration. Bromhexine alters the structure of bronchial secretions. It has been shown to reduce the viscosity and increase the volume of sputum (or mucus) secretion in chronic chest disease. Bromhexine acts on the mucus at the formative stages in the glands, within the mucus-secreting cells. It has been demonstrated that bromhexine alters the structure of acid mucopolysaccharide fibres (AMPS) which are found in mucoid sputum. It is these fibres which are thought to be responsible for the viscosity of such secretions. By fragmenting the acid mucopolysaccharide fibres bromhexine produces a less viscous mucus, which is thinner, watery, more mobile and hence much easier to expectorant.
Pharmacokinetics: Pholcodine is readily absorbed from the gastrointestinal tract and does cross the blood-brain barrier. It is metabolised in the liver and its action may be prolonged in hepatic insufficiency. Bromhexine is well absorbed from the gastrointestinal tract. Most of the dose is excreted in urine mainly as metabolised; only a small amount is excreted in the faeces.