Indications:
● Coughs and upper respiratory tract symptoms
● Nasal congestion
● Allergy or common cold
Mechanism:
Dextromethorphan:
suppresses medullary cough center and is an NMDA receptor antagonist (receptors, N-methyl-D-aspartate). It acts as a non-competitive channel blocker and is one of the widely used antitussives. It is also used to study the involvement of glutamate receptors in neurotoxicity. Dextromethorphan is categorized as an opioid drug that acts as antagonist to the NMDA glutamatergic receptor, it is an agonist to the opioid sigma 1 and sigma 2 receptors. It is also an alpha3/beta4 nicotinic receptor antagonist and targets the serotonin reuptake pump.
It is rapidly absorbed from GIT and is extensively metabolised to dextrorphan (active metabolite) in liver. The half-life is 3-6 hours.
Chlorphenamine Maleate:
is a H1 receptor antagonist used in allergic reactions, hay fever, rhinitis, urticaria, and asthma. This blocks the action of endogenous histamine, which subsequently leads to temporary relief of the negative symptoms brought on by histamine.
It is well orally absorbed with a plasma protein binding of 72%. It is metabolised in liver with a half-life of 21-27 hours.
Phenylephrine: is categorized as sympathomimetic drug and mimics the actions of epinephrine (commonly known as adrenaline) or norepinephrine. Phenylephrine selectively binds to alpha-1 receptors which cause blood vessels to constrict leads to nasal decongestant action.
When orally administered, the bioavailability was found to be 38%. Peak concentration reaches between 0.5 and 2 hours after administration. No protein‐binding data in humans are available. It undergoes extensive biotransformation in the gut wall and the liver. Half‐lives is relatively short, approximately 2.5 hours. Reduced metabolism of Phenylephrine occurs with concurrent administration of monoamine oxidase inhibitors.
Side Effects:
● Blurred vision
● Dry mouth
● Nausea
● Stomach pain
● Constipation
● Skin rash or itching
Interactions:
● Chlorpheniramine can interact with tranylcypromine, isocarboxazid, sodium oxybate and ivacaftor
● Dextromethorphan can interact with isocarboxazid, phenelzine, rasagiline, selegiline and tranylcypromine
● Phenylephrine may interact with heart or blood pressure medications, antidepressants, diabetes medications, migraine headache medications, and other decongestants.
Contraindications:
● Severe hypertension
● Ventricular tachycardia
● Severe coronary artery disease
● Chronic bronchitis