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Upper Respiratory Tract Infection Treatment (Intranasal decongestants…
Upper Respiratory Tract Infection Treatment
Oral Decongestants
Phenylephrine
Mechanism of action:
Direct alpha-1 agonist causing vasoconstriction --> shrinkage of swollen mucous membranes
Clinical effects:
Decongestion of the nose & eyes
Adverse effects:
Similar to pseudoephedrine but much safer and less side effects
Clinical use:
Much less effective than pseudoephedrine
Studies show over the counter doses are not effective
Pseudoephedrine
Mechanism of action:
Indirect acting sympathomimetic
Structurally related to noradrenaline so it can enter the nerve terminal & synaptic vesicle
Both of these actions release noradrenaline (importantly acts on alpha-1 receptors) causing vasoconstriction --> shrinkage of swollen mucous membranes
Clinical effects:
Non-specific: Increased HR, increased BP, bronchodilation, CNS stimulation (potential for abuse)
Decongestion of the nose & eyes
Adverse effects:
CNS stimulation, nervousness, insomnia, tremor, palpitations, increased BP
Precautions:
Patients with CVD, hyperthyroidism, prostate hypertrophy, diabetes or taking MAO-inhibitor antidepressants
Intranasal decongestants
Drugs:
Oxymetazoline, phenylephrine, tramazoline, xylometazoline
Mechanism of action:
Direct alpha-1 agonist causing vasoconstriction --> shrinkage of swollen mucous membranes
Clinical effects:
Decongestion of the nose & eyes
Adverse effects:
Transient local effects such as stinging & increased discharge
Rebound congestion: This may be due to local ischaemia & receptor down regulation, there is rebound vasodilation in an attempt to overcome ischaemia
Clinical use:
There is rapid tolerance to the drug
Therefore use for 3-5 days at a time
Intranasal antimuscarinics
Drugs:
Ipratropium
Mechanism of action:
Blockade of M3 receptors resulting in an inhibition of nasal glandular secretions
This dries nasal secretions and reduces rhinorrhoea
Clinical effects:
Dries nasal secretions and stops nasal secretions
Clinical use:
Rhinorrhoea with allergic/non-allergic rhinitis
Common cold
Adverse effects:
Nasal dryness, nosebleed, dry mouth
Antihistamines
Drugs:
Sedating antihistamines (First generation): Dexchlorpheniramine, Doxylamine, Promethazine, Cyproheptadine
Non-sedating antihistamine (Second generation): Cetirizine, Fexofenadine, Loratadine
Mechanism of action:
H1-receptor antagonists --> Blocks the effect of histamine on H1 receptors --> Reduces vasodilation, capillary permeability & itch
Sedating vs Non-sedating antihistamines:
Sedating antihistamines are lipid soluble --> Cross the BBB --> Block CNS H1 receptors --> Causing sedation
Non-sedating antihistamines are not lipid soluble
Clinical use:
Sedating antihistamines: Cold, flu, allergic disorders, motion sickness, vertigo, itch associated with skin disorders, nausea, sedation
Non-sedating antihistamines: Allergic reactions
Cough suppressants
Drugs:
Codeine, Dihydrocodeine, Pholcodine, Dextromethorpan
Mechanism of action:
Opioid receptor agonists
These hyperpolarise neurons thus reducing neuronal excitability & inhibiting excitatory neurotransmitter release (substance P)
By reducing substance P release, it is thought to directly depress the cough centre in the medulla
Clinical use:
Dry cough
Adverse effects:
Drowsiness, constipation, dependence