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Oral Antibiotics


Bacterial Infections

A significant number of human infections are caused by bacteria. However, not all bacteria cause diseases and in fact some naturally reside in our body, e.g. the intestines and skin. Infection occurs when our body is invaded by harmful microorganisms or when our body’s own defence to infections is low and the balance of naturally residing bacteria in our body is disturbed.

  Common Cold

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


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Antibiotics are medicines used in the treatment and prevention of bacterial infections, either by killing the bacteria or stop them from multiplying. They are either derived from microorganisms or synthetically produced and are not effective in treating viral infections such as influenza or the common cold.

There are many different types of antibiotics, targeting at different bacteria. The choice of antibiotics depends on factors such as the infection-causing bacteria, patient’s history of drug allergy and the site of infection. Therefore, it is of utmost importance that medical advice is sought before using any antibiotics.


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Common Used Oral Antibiotics

Antibiotics can only be obtained from pharmacy with a doctor’s prescription in Hong Kong. They are available in many dosage forms, e.g. capsules, tablets, topical creams and ointments and parenteral injections. They should only be used under close supervision by healthcare professionals.

Some of the most commonly used classes of oral antibiotics are :

1. Penicillins and its derivatives;

2. Cephalosporins;

3. Macrolides;

4. Tetracycline and its derivatives;

5. Sulfonamides; and

6. Quinolones.

  Common medication for cough and cold

1. Penicillin and its derivatives

Penicillin was the first antibacterial used therapeutically and was first obtained from a mould. All penicillins have the same beta-lactam ring structure and kill bacteria by interfering with the bacterial cell wall synthesis. Examples of commonly used oral penicillins include amoxicillin, ampicillin, cloxacillin, etc. Penicillins are prescribed for urinary-tract infections, middle ear infections, sinusitis, bronchitis, mouth infections, and pneumonia.

Penicillins are inactivated by an enzyme beta-lactamases. Addition of a beta-lactamase inhibitor to penicillin group (e.g. clavulanic acid to amoxicillin) provides synergistic antibacterial effect.

Between 1 to 10% patients will have a hypersensitivity reaction after taking penicillins. The allergic reactions may range from a skin rash to anaphylaxis (< 0.05%) which can be fatal.

2. Cephalosporins

Cephalosporins are structurally related to penicillins and act similarly as penicillins in killing bacteria by interfering with bacterial cell wall synthesis. They are used orally for the treatment of acute sinusitis, bronchitis, community-acquired pneumonia, acute middle ear infections, sinusitis, urinary tract infections and skin infections.

Commonly used oral cephalosporins include cephalexin, cefadroxil, cefaclor, cefuroxime and cefexime. Since they are structurally related to penicillins, patients who are allergic to penicillins may also be allergic to cephalosporins.

3. Macrolides

Macrolides are antibacterials with a similar ring structure and act by either killing bacteria or inhibiting the growth and multiplication of bacteria. Macrolides have similar but not identical antibacterial activities to penicillins. Hence, they are often used as an alternative for patients who are allergic to penicillins. Examples of orally used macrolides include erythromycin, clarithromycin and azithromycin. Macrolides are useful in middle ear infection, pneumonia, etc.

4. Tetracycline and its derivatives

Tetracyclines are another group of antibiotics which can be used to treat a wide range of infections. However, their clinical use is limited due to emergence of bacterial resistance. Examples of this group include tetratcycline, minocycline, doxycycline, etc. They are commonly used for treatment of severe acne.

5. Sulfonamides

There is increase in bacterial resistance towards sulphonamides group. Their use can be replaced by alternative antibacterials which are generally more active and less toxic. They are used in the treatment of urinary-tract infections and bronchitis. Sulfamethoxazole and trimethoprim are frequently used in combination because of their synergistic activity and has generally replaced the use of sulphonamides alone.

6. Quinolones

Fluoroquinolones are a new group of synthetic antibiotics which can be used to treat wide range of infections such as urinary tract infections and respiratory tract infections. Examples of quinolones include ciprofloxacin, ofloxacin, levofloxacin, nalidixic acid, etc.


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Common Side Effects and Precautions of Oral Antibiotics

Classes of antibiotics
Common side effects
1. Penicillin and its derivatives
  • Hypersensitivity reactions, ranging from maculopapular rash to angioedema
  • Diarrhoea, nausea, vomiting
  • Caution for 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
  • Caution in patients with history of developing diarrhoea after antibiotic use
2. Cephalosporins
  • Hypersensitivity reactions, ranging from maculopapular rash to angioedema
  • Should not be used for patients who are allergic to penicillin as cross-sensitivity may occur
  • Caution in patients with kidney disease
  • Caution for patients with history of allergies including asthma, eczema and hay fever since their risk of developing a serious allergic reaction is higher
  • Caution in patients with history of developing diarrhoea after antibiotic use
3. Macrolides
  • Nausea, vomiting and diarrhoea, abdominal discomfort
  • 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. 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, liver disease
  • Not recommended for children under 12 years of age
  • Not recommended in pregnant/breastfeeding women
  • 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
5. Sulfonamides
  • Nausea and vomiting
  • Headache
  • Hypersensitivity reactions, including rash
  • 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
6. Quinolones
  • Nausea, vomiting and diarrhoea, dyspepsia, abdominal pain
  • Tendinitis, tendon damage
  • May exacerbate muscle weakness in patients with myasthenia gravis
  • Rash
  • QT interval prolongation
  • photosensitivity
  • Avoid in patients with myasthenia gravis
  • Not suitable for children and adolescents
  • Not recommended in pregnant or breastfeeding women

Antibiotics Resistance

Inappropriate use of antibiotics can lead to antibiotics resistance, i.e. the antibiotics no longer kills or work on the bacteria causing the infection. Inappropriate use includes missing doses of treatment, not finishing a course of treatment of antibiotics, using antibiotics when it is not indicated. Bacteria adapt to antibiotics. If they are not completely killed, they will reproduce and the same antibiotics may not work on the same bacteria again. This may lead to fewer treatment options and more severe infections that cannot be treated with available antibiotics.

You should also be aware of personal hygiene, e.g., frequently wash hands, eat or drink only thoroughly cooked or boiled items, disinfect and cover all wounds, and wear mask if you have respiratory symptoms.

Please refer to the following link to learn more about antibiotics resistance:

The Hong Kong Special Administrative Region commits to support World Health Organisation’s global initiative in combatting antimicrobial resistance: No Action today, no cure tomorrow. Since 2012, Antibiotic Awareness Day has been marked annually on November 18 in Hong Kong as a public health initiative to raise awareness about antimicrobial resistance threat and prudent antibiotic use. Please refer to the following link for more details:


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General advice on taking antibiotics

  • It is very important that you follow the directions of use for your medicine.

  • Take your medicines at the same fixed time every day as far as possible. If you miss a dose, take it as soon as possible unless it is almost time for the next scheduled dose. In that case, skip the missed dose and take the next dose as directed. Do not take double doses.

  • Do not stop taking your medicine even if you feel better as you will need to finish the whole course of treatment.

  • 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. (

  • Antibiotics should only be used under medical supervision.

  • Tell your doctor your medical history and the drugs you are also taking because other drugs may interact with the antibiotics and some diseases may warrant special precautions.

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

  • 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 your doctor’s advice on the best treatment option. Different antibiotics may act on your body differently and hence you may encounter varied side effects; your doctor will prescribe the most appropriate drugs for you after considering your condition and your response to the drugs.

  • Seek medical advice as soon as possible if you experience any symptoms or side effects suspected to be related to your antibiotics. Your doctor may review your type of medications.

  • 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 of drugs

Medicines should be stored in a dark, cool and dry place. Unless specified on the label, medicines should not be stored in refrigerators. Furthermore, medicines should be kept properly in places unreachable by children to prevent accidental ingestion.



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

Drug Office
Department of Health
Dec 2012