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Oral Antibiotics

  
 
 

Bacterial Infections


A bacterial infection is an infection caused by harmful bacteria. However, not all bacteria are harmful, in fact some naturally reside in the body, e.g. those found in the intestines and on the skin. Infection occurs when the body is invaded by pathogenic microorganisms or when the immune system is weakened, leading to a disruption in the balance of the body’s normal bacterial flora.

   Common Cold

Examples of bacterial infections include urinary tract infections, middle ear infections, acne, meningitis, and certain types of pneumonia.
 

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Treatment


Antibiotics are medicines that fight infections caused by bacteria in humans and animals, and they work by either killing the bacteria or making it difficult for the bacteria to grow and multiply. But, they do not work against viral infections such as influenza or the common cold.

Antibiotics come in many different types, each targeting specific bacteria. The choice of antibiotics depends on factors such as the infection-causing bacteria, patient’s medical history of drug allergy and the site of infection. Therefore, antibiotics must be prescribed by a doctor after proper diagnosis and used according to doctor’s instruction.

 

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Commonly Used Oral Antibiotics

Antibiotics are available in many dosage forms, e.g. capsules, tablets, topical creams/ointments, and parenteral injections. They should only be prescribed and used under close supervision by a doctor.

Some of the commonly used classes of oral antibiotics include:

1. Penicillins and its derivatives;

2. Cephalosporins;

3. Macrolides;

4. Aminoglycosides;

5. Lincosamides;

6. Tetracyclines;

7. Sulfonamides; and

8. Quinolones and Fluoroquinolones

  Common medication for cough and cold

1. Penicillins and its derivatives

Penicillin was the first antibiotic used therapeutically, and was first obtained from mould. All penicillins share a beta-lactam ring structure and kill bacteria by inhibiting the bacterial cell wall synthesis. Examples of commonly used oral penicillins include amoxicillin, ampicillin, cloxacillin, etc. Penicillins are used to treat a variety of bacterial infections, such as urinary-tract infections, middle ear infections, sinusitis, bronchitis, and pneumonia.

2. Cephalosporins

Cephalosporins are structurally related to penicillins and kill bacteria similarly by inhibiting bacterial cell wall synthesis. They are used orally to treat acute sinusitis, bronchitis, community-acquired pneumonia, acute middle ear infections, urinary tract infections and skin infections.

Common oral cephalosporins include cephalexin, cefadroxil, cefaclor, cefuroxime, etc. Since they are structurally related to penicillins, patients who are allergic to penicillins may also be allergic to cephalosporins.

3. Macrolides

Macrolides are a class of antibiotics that work by inhibiting bacterial protein synthesis. They have an antibacterial spectrum similar but not identical to that of penicillin, making them an alternative for penicillin-allergic patients. Examples of orally used macrolides include erythromycin, clarithromycin and azithromycin. Macrolides are used in the treatment of pneumonia, whooping cough, skin infections, etc.

4. Aminoglycosides

Aminoglycosides are a class of antibiotics that work by inhibiting bacterial protein synthesis. Aminoglycosides should in general only be used for the treatment of serious infections because of their potential toxicity and antimicrobial spectrum. An example of orally used aminoglycoside is neomycin. Neomycin can be administered orally for bowel preparation before abdominal surgery.

5. Lincosamides

Lincosamides are a class of antibiotics that work by inhibiting bacterial protein synthesis. Examples of orally used lincosamides include clindamycin and lincomycin. Because of more potent antibacterial activity as compared to lincomycin, clindamycin is usually the preferred lincosamide antibiotic for susceptible infections. Clindamycin can be administered orally for the treatment of intra-abdominal sepsis, peritonitis, moderate or severe diabetic foot infection, etc.

6. Tetracyclines

Tetracyclines are a class of antibiotics which can be used to treat various infections, including pelvic and skin infections. They work by inhibiting bacterial protein synthesis. However, their clinical use is limited due to the emergence of bacterial resistance. Examples of this group include tetracycline, minocycline, doxycycline, etc. They are commonly used to treat severe acne.

7. Sulfonamides

Sulfonamides are a class of antibiotics that work by inhibiting folic acid synthesis in susceptible organisms. However, the emergence of bacterial resistance has limited their clinical usefulness. Their use can be replaced by alternative antibacterials which are generally more active and less toxic. Sulfamethoxazole and trimethoprim are frequently used in combination because of their synergistic activity, and has generally replaced the use of sulphonamides alone. Sulfonamides are used in the treatment of urinary tract infections, inflammatory bowel disease, malaria, etc.

8. Quinolones and Fluoroquinolones

Fluoroquinolones are derived from quinolones through the addition of a fluorine atom to the original quinolone compound. They were once used to treat a wide range of infections, including urinary tract and respiratory tract infections. Examples of fluoroquinolones include ciprofloxacin, ofloxacin, levofloxacin, etc. As fluoroquinolones have been associated with serious adverse reactions, they should be reserved for use in patients who have no alternative treatment options for certain indications, such as acute sinusitis, acute bronchitis, or uncomplicated urinary tract infections.

 

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Common Side Effects and Precautions of Oral Antibiotics*
Classes of antibiotics
 		 Common side effects
 		 Precautions
 
1. Penicillins and its derivatives
  • Hypersensitivity reactions, ranging from maculopapular rash to angioedema
  • Diarrhoea, nausea, vomiting
  • Use with caution in patients with history of allergies including asthma, eczema and hay fever since their risk of developing a serious allergic reaction is higher
  • Patients with kidney disease may need reduced dosages
  • patients allergic to cephalosporins may also be allergic to penicillins
  • Use with caution in patients with history of developing diarrhoea after antibiotic use
2. Cephalosporins
  • Hypersensitivity reactions, ranging from maculopapular rash to angioedema
  • Abdominal pain
  • Diarrhoea, nausea, vomiting
  • Headache
  • Dizziness
  • Should not be used for patients who are allergic to penicillin as cross-sensitivity may occur
  • Use with caution in patients with kidney disease
  • Use with caution in patients with history of allergies including asthma, eczema and hay fever since their risk of developing a serious allergic reaction is higher
  • Use with caution in patients with history of developing diarrhoea after antibiotic use
3. Macrolides
  • Nausea, vomiting and diarrhoea, abdominal discomfort
  • Appetite decreased
  • Headache
  • Hearing impairment
  • Vision disorders
  • Pancreatitis
  • Use with caution in patients who might be predisposed to Long QT Syndrome, e.g. taking medicines that may prolong QT interval
  • Stevens-Johnson syndrome, antibiotic-associated colitis, and QT prolongation have been reported very rarely
  • May aggravate myasthenia gravis (a condition with muscle fatigue and weakness)
4. Aminoglycosides
  • Nausea, vomiting, diarrhoea
  • Hearing loss
  • Kidney damage
  • Electrolyte imbalance
  • Contraindicated in adult patients with intestinal obstruction, myasthenia gravis and in patients with a history of allergy to aminoglycosides
5. Lincosamides
  • Skin reactions
  • Abdominal pain
  • Pseudomembranous enterocolitis
  • Diarrhoea
  • Allergic reactions
  • For Clindamycin: For patients with pre-existing renal dysfunction or taking concomitant nephrotoxic drugs, monitoring of renal function should be considered. Acute kidney injury, including acute renal failure, has been reported infrequently.
6. Tetracyclines
  • Nausea, vomiting and diarrhoea
  • Difficulty in swallowing and oesophageal irritation
  • Cause yellow teeth and teeth disfigurement if taken during teeth development
  • Not recommended for patients with kidney or liver disease
  • To avoid dental disfigurement and discolouration, tetracycline should not be given to children under 12 years
  • Tablets or capsules should be swallowed whole with plenty of fluid and patients should not lie down for about half an hour afterwards
  • Avoid taking with antacids, milk, calcium/magnesium salts
  • Photosensitivity may occur rarely. Avoid prolonged sunlight exposure and use appropriate sunscreen
7. Sulfonamides
  • Nausea and vomiting
  • Headache
  • Hypersensitivity reactions, including rash
  • Severe reactions including Stevens-Johnson Syndrome and toxic epidermal necrolysis have been reported rarely
  • May need to monitor blood count with prolonged treatment due to possible risk of blood dyscrasia
  • Use with caution in patients with impaired liver or kidney function
  • Contraindicated in acute porphyria
8. Quinolones and Fluoroquinolones
  • Nausea, vomiting, diarrhoea, dyspepsia, abdominal pain
  • Tendinitis, tendon rupture
  • May exacerbate muscle weakness in patients with myasthenia gravis
  • Rash
  • QT interval prolongation
  • Photosensitivity
  • Peripheral Neuropathy
  • Avoid in patients with myasthenia gravis
  • Fluoroquinolones have been associated with an increased risk of peripheral neuropathy. Avoid in patients who have previously experienced peripheral neuropathy.
  • Not suitable for children and adolescents
  • Fluoroquinolones have been associated with disabling and potentially irreversible serious adverse reactions from different body systems that can occur together in the same patient. Commonly seen adverse reactions include tendinitis, tendon rupture, arthralgia, myalgia, peripheral neuropathy, and central nervous system effects (hallucinations, anxiety, depression, insomnia, severe headaches, and confusion).
 
 

Antibiotics Resistance (AMR)

What is an antimicrobial? The World Health Organization (WHO) defines antimicrobials (including antibiotics, antivirals, antifungals, and antiparasitics) as medicines used to prevent and treat infectious diseases in humans, animals and plants. Antimicrobial resistance (AMR) occurs when microorganisms (e.g., bacteria, viruses, fungi) evolve resistance to antimicrobial drugs that were previously effective. Antimicrobial resistance is accelerated by the overuse and misuse of antimicrobials (including antibiotics).

Antimicrobial resistance is affecting everyone. Members of the public can help to combat antimicrobial resistance through responsible practices, such as:

  • Proper use of antibiotics*:
    • Always follow the dosage and administration instructions as prescribed by your doctor
    • If you are prescribed antibiotics, it is essential to complete the full course of treatment, even if your symptoms improve. Do not discontinue the medicine without your doctor’s guidance
    • Do not take leftover antibiotics
    • Do not share your antibiotics with others
    • Do not self-medicate with antibiotics without a prescription
  • Practise frequent hand hygiene, especially before eating and taking medicine, and after going to the toilet
  • Ensure your vaccination is up-to-date
  • Maintain cough etiquette, wear a surgical mask if you have respiratory symptoms
The Government of the Hong Kong Special Administrative Region has been placing great importance on combating antimicrobial resistance (AMR). In 2022, the Government published the second Hong Kong Strategy and Action Plan on Antimicrobial Resistance, outlining strategies to tackle the threat of AMR from 2023 to 2027. The Government will continue to implement the Action Plan comprehensively to integrate human, animal, and environmental health efforts under the One Health framework.

Please refer to the following link to learn more information about antimicrobial resistance:
https://www.chp.gov.hk/en/features/47850.html

 

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General Advice on Taking Antibiotics*

  • It is crucial to follow the prescribed dosage and administration instructions strictly.

  • It is essential to complete the full course of antibiotic treatment, even if your symptoms improve. Do not discontinue the medicine without your doctor’s guidance.

  • Do not drink alcohol as it may affect the effectiveness or increase the risk of side effects of your antibiotics.

  


 

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Communication with Your Doctor*

  • The Centre for Health Protection (CHP) strongly advises the public to ask the right questions and use antibiotics smartly. (http://www.chp.gov.hk/files/jpg/poster_Final_170211.jpg)

  • Antibiotics should only be used under medical supervision.

  • Inform your doctor about your current medications and medical history as some drugs may interact with your antibiotics and some medical conditions may require special precautionary measures.

  • Inform your doctor if you are or have been found to be allergic to any medicines. Some antibiotics may share cross-sensitivities and you may need to avoid certain antibiotics even if you have never taken them before.

  • Inform your doctor if you are taking oral contraceptives as some antibiotics may affect the effectiveness of your pills and you may need additional method of contraception.

  • Seek medical advice as soon as possible if you experience any side effects suspected to be related to your antibiotics

  • Inform your doctor if you are pregnant as some antibiotics may affect fetus and should not be used during pregnancy.

 

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Storage Guidelines

Oral antibiotics should be stored in a cool dry place. Do not refrigerate unless specified. Always keep medications out of reach and sight of children to prevent accidental ingestion.

 


* This information may not cover all possible side effects, precautions, or medical advice. Always consult your healthcare professional for guidance.
 

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Acknowledgement : The Drug Office would like to thank the Professional Development and Quality Assurance Service (PD&QA) and the Infection Control Branch (ICB) for their valuable contribution to the preparation of this article.
  



Drug Office
Department of Health
January 2026

 

 

 

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