Drug Action and Use of Medicine III - Over-the-Counter (OTC) Pharmaceutical Products

Over-the-Counter (OTC) Medicines

• Also known as Non-prescription drugs
• Can be purchased without a prescription
• Provide quick relief for minor health disorders
• Should be used only when needed and for short term, as indicated on the drug Product Information (PI) / label
• Overuse or misuse can lead to serious and potentially life-threatening side effects

Examples of OTC Medications

• Pain relievers and antipyretics:
  • Acetaminophen / paracetamol
  • Ibuprofen
• Anti-flatulent agents (antifoaming agents):
  • Simethicone
• Antihistamines:
  • Chlorpheniramine
• Laxatives:
  • Bisacodyl
  • Dietary fibers
• Cough and Mucolytic drugs:
  • Cocillana Syrup (contains codeine)
  • Acetylcysteine

Classification of Drugs in Hong Kong

Drug Facts Label

The Drug Facts label provides comprehensive information about an OTC medicine.

• A. Active ingredient(s): The therapeutic substance in each dosage unit.
• B. Category or class of medicine: The type of medicine based on the active ingredient.
• C. Approved Use(s) and Condition(s): What the medicine is intended to treat.
• D. Warnings and Precautions: Includes possible side effects.
• F. Dosing Information: How much medicine to take and how often.
• G. Other information: Storage conditions.
• H. Inactive ingredients: Ingredients with no therapeutic effect.
• I. Contact information

Key Sections of Drug Facts

• Active Ingredients (API):
  • Produce the therapeutic effect.
  • Listed first on the label.
  • A product may contain more than one API.
• Warnings:
  • When not to use the product.
  • Advice for pregnant or breastfeeding individuals.
  • Potential drug interactions or side effects.
  • Instructions to stop medication and seek medical advice if side effects/adverse effects appear.
• Inactive Ingredients:
  • Have no therapeutic effect.
  • Examples: preservatives, bulking agents, sweetening agents, coloring agents.
  • Important for individuals with allergies.

Medicine Label Information

• Patient Information:
  • Name of patient
  • Date dispensed
• Medicine Information:
  • Name of drug and dosage
  • Method of administration
  • Function of drug
  • Precautions and side effects
• Clinic Information:
  • Name of the institution
  • Codes for internal use

Proper Use of OTC Medications

• Always read the drug label before taking the medication.
• Do not crush, cut, or chew tablets unless the label permits.
• Take only the recommended dose.
• Do not take medication with alcoholic drinks.
• Use OTC medication for short-term relief only.
• Avoid taking two medications with the same active ingredient (e.g., paracetamol).
• Consult doctors or pharmacists before combining OTC and prescription medications.

Cold vs. Flu

High-Risk Groups for Flu

• People 65 years and older
• People with certain chronic diseases (asthma, diabetes, heart disease)
• Pregnant women
• Children under 5 years old, especially those < 2 years old

OTC Medications for Cold and Flu: Symptom Relief

• Antipyretics
• Antihistamines
• Decongestants (Sympathomimetics)
• Antitussives (Cough suppressants)
• Expectorants and Mucolytics
• Antiseptics

Pharmacological Management of Cold and Flu Symptoms:

Antipyretics and Analgesics

• Examples:
  • Paracetamol (acetaminophen)
  • NSAIDs (e.g., Ibuprofen)
• Indication: Pain and fever
• MOA (Mechanism of Action):
  1. Inhibition of COX1 and COX2 enzymes leads to pain and fever relief.
  2. Paracetamol metabolites may act on cannabinoid receptors in the brain to suppress pain signals.
• Dose:
  • Child: 15mg/kg per dose (max 1 g) every 4-6 hours as needed (PRN)
  • Adult: 500-1000 mg every 4-6 hours as needed (PRN) (max 4000mg per 24 hours)
• Paracetamol overdose can cause direct liver cell damage through its toxic metabolites.

Antihistamines

• First Generation:
  • Chlorpheniramine
  • Diphenhydramine
  • Hydroxyzine
  • Promethazine
• Second Generation:
  • Loratadine
  • Cetirizine
  • Fexofenadine

Antihistamines (Histamine-1 antagonists)

• MOA: Block histamine-1 receptor functions to relieve allergic symptoms
  • Histamines cause vasodilation and increase vascular permeability, leading to inflammation and other allergy symptoms
• Individual response to antihistamines varies widely
  • May need to try different antihistamines to find the best effectiveness and tolerability
• Relief of the symptoms of influenza, common cold, and allergies

Types of Antihistamines

• First Generation (Sedating):
  • Examples: Chlorpheniramine, Diphenhydramine, Hydroxyzine, Promethazine, etc.
  • Slower onset (30-60 min)
  • Shorter duration (4-6 hrs)
  • Able to pass through the blood-brain barrier
  • Sedative side effects (drowsiness)
  • Not for children under 2 for any indication
  • Not for children under 6 for treatment of cough, cold, and flu symptoms
• Second Generation (Non-Sedating):
  • Examples: Loratadine, Cetirizine, Fexofenadine, etc.
  • Faster onset (10-30 mins)
  • Longer duration (12-24 hrs)
  • Less lipid-soluble
  • Do not pass through the blood-brain barrier
  • No sedative side effects
  • Safer for children

Antihistamines - Adverse Events

• Drowsiness (crosses the blood-brain barrier and blocks central nervous system histamine-1 and cholinergic receptors)
• Dryness (eyes/mouth), blurred vision, constipation, urinary retention (due to blockage of cholinergic receptors, anticholinergic activity)
• Do not drive or operate machinery
• Avoid alcohol and other medications that may cause sedation

Antihistamines - Precautions

• Children under the age of 2
  • Avoid use due to increased risk of adverse events (AEs) e.g., sedation, paradoxical CNS stimulation, anticholinergic effects
• Children under the age of 6
  • Do not use sedating antihistamines for the symptomatic relief of coughs and colds
• Pregnancy
  • Considered safe to use
  • Many antihistamines have been used extensively in pregnancy as antiemetics and in treatment of allergic disorders without evidence of fetal adverse effects.
• Elderly
  • Avoid use or use a lower dose due to increased risk of AEs e.g., dizziness, sedation, hypotension, falls

Decongestants

• Oral decongestants:
  • Phenylephrine
  • Pseudoephedrine
• Nasal decongestants:
  • Oxymetazoline
  • Xylometazoline

Decongestants (alpha-1 agonist)

• MOA: Stimulating the α-adrenergic receptors of nasal blood vessels that induce vasoconstriction, decreasing nasal congestion
  • Some alpha-1 agonists could stimulate both alpha and beta receptors (adrenergic receptors)
• Administration route: Oral and nasal
• Examples:
  • Phenylephrine, Pseudoephedrine (oral)
  • Oxymetazoline, Xylometazoline (nasal)
• Decongestants are not effective for relieving nasal congestion in babies and young children

Decongestants - Overuse

• Overuse of nasal decongestants can cause rebound nasal congestion
  • Termed as rhinitis medicamentosa
  • Lead to histological change and/or cause of vasodilation switch to another receptor (beta adrenoreceptor)
  • The congestion becomes worse with continued use of the drug