Antibacterial Drugs

Question 1

Define bactericidal drugs

Answer 1

Those antibacterial drugs that work by killing bacteria

Question 2

Define bacteriostatic drugs

Answer 2

Those antibacterial drugs that work by preventing bacterial replication/growth but do not kill bacteria.

This will allow their numbers to be kept low enough for the immune system (complement system, macrophages, monocytes and other inflammatory mediators) to fight against them and completely eradicate their presence.

Question 3

How do bacteriostatic drugs treat bacterial infections?

Answer 3

Although these drugs don’t kill bacteria, they stop them from replicating or growing. This keeps the number of bacteria (infection) low enough for the immune system (complement system, macrophages, monocytes and other inflammatory mediators) to fight against them and completely eradicate their presence.

Question 4

Why are broad spectrum antibiotics not usually the gold standard treatment for most bacterial infections?

Answer 4

Most infections are caused by a singular bacterial species that is causing harm. Therefore, we would only want to target the pathogenic bacteria causing the disease. But broad spectrum antibiotics target a wider range of bacterial species, many outside of the pathogenic species causing the disease.

We do not want to kill all the bacteria within the body because many of these other bacterial species are needed for the body e.g. those on the skin, in the gut and those around us etc. which aid in forming part of the body’s natural defence as well as aiding with the metabolism of vitamins and other nutrients.

Question 5

When would a broad spectrum antibiotic be better than a narrow spectrum antibiotic?

Answer 5

Multiple bacterial species involved in the infection. All of these need to be eradicated in order to limit or prevent the disease process.

Patient requiring emergency intervention with no time to send a bacterial specimen to the labs in order to identify the causative pathogen and its subsequent sensitivity to varying antibiotics

Question 6

Describe the mechanism of action of Metronidazole

Answer 6

Bactericidal, broad spectrum antibiotic.

Kills bacteria by inhibiting DNA synthesis and degrading existing DNA

Particularly useful against anaerobic infections.

Question 7

Why are patients told to AVOID alcohol when prescribed with a course of Metronidazole?

Answer 7

Metronidazole interferes with the metabolism of alcohol. Alcohol and its harmful metabolites cannot be destroyed in the presence of Metronidazole.

Their accumulation can therefore cause severe nausea, flushing and vomiting

Question 8

List some macrolide antibiotics

Answer 8

Erythromycin
Azithromycin
Clarithromycin

Question 9

Describe the mechanism of action of macrolide antibiotics

Answer 9

Bacteriostatic, broad spectrum antibiotic

Binds the 50s subunit of ribosomes, preventing protein synthesis. Essential proteins that allow the bacteria to survive can no longer be produced.

Question 10

A patient presents to your clinic with severe nausea and flushing. Just as you are about to initiate treatment, the patient begins to vomit. He apologises and says he had been drinking the night before and the sickness is likely because of this. On further inquiry, he informs you that he did just complete a 1-week antibiotic course for an infection as well. What antibiotic course was he likely on? How could the antibiotic relate to his presenting symptoms/signs?

Answer 10

Metronidazole

When taken in conjunction with alcohol, it can cause alcohol poisoning as Metronidazole prevents the metabolism of alcohol

Question 11

A patient calls your clinic to complain of severe nausea and stomach upset/diarrhoea following the antibiotics you’ve prescribed him for a submandibular space infection. What antibiotic course did you likely prescribe to result in these symptoms?

Answer 11

Macrolide antibiotics

Question 12

List some tetracycline antibiotics

Answer 12

Tetracycline
Doxycycline
Oxytetracycline

Question 13

Describe the mechanism of action of tetracycline antibiotics

Answer 13

Mixed bacteriostatic and bactericidal broad spectrum antibiotics

Binds the 30s subunit of ribosomes, preventing protein synthesis. Essential proteins that allow the bacteria to survive can no longer be produced.

Question 14

Which antibiotic should not be prescribed to children with a developing dentition? Explain your answer

Answer 14

Tetracyclines

Can discolour the permanent teeth as they erupt due to their ability to deposit themselves in growing bones and teeth.

Question 15

Describe the mechanism of action of aminoglycoside antibiotics

Answer 15

Bactericidal, broad spectrum antibiotics.

Especially active against gram - bacteria

Binds the 30s subunit of ribosomes, preventing protein synthesis. Essential proteins that allow the bacteria to survive can no longer be produced.

Question 16

Which antibiotic can cause nephrotoxicity or ototoxicity?

Answer 16

Aminoglycoside antibiotics. E.g. Gentamicin

Question 17

Describe the mechanism of action of Trimethoprim

Answer 17

Bacteriostatic antibiotic

Interferes with DNA replication by impairing folate synthesis. Folate is required for the continuation of DNA synthesis

Question 18

How does bacteria develop resistance to penicillin and cephalosporins?

Answer 18

Able to cleave a fixed structural component of all penicillin/cephalosporin antibiotics known as the beta lactam ring.

Bacteria use an enzyme known as beta lactamase to split this beta lactam ring and render the antibiotic ineffective and non-functional

Question 19

Describe the mechanism of action of Penicillins and Cephalosporins

Answer 19

Bactericidal antibiotics
Penicillin = narrow spectrum
Amoxicillin = broad spectrum
Cefalexin = broad spectrum

Inhibit peptidoglycan (murein) cross linking in the cell wall which destroys the cell wall. The cell wall is essential to protect the internal contents of the cell and fend off adverse host immune responses. If it is destroyed, the bacteria will not survive.

Question 20

How can we counteract Penicillin/Cephalosporin resistance?

Answer 20

Via the use of clavulanic acid/co-amoxiclav which is a beta lactamase inhibitor.

The beta lactamase enzyme that cleaves the beta lactam ring of these antibiotics is inhibited from doing so. This means the bacteria is no longer resistant to the antibiotics

Question 21

An inpatient is given Cephalosporins to treat an infection. The next day, the patient has watery and bloody diarrhoea, stomach cramps, nausea, a high temperature and loss of appetite. What could have caused the patient’s symptoms?

Answer 21

Cephalosporins are a broad spectrum antibiotic which can kill almost all the bacteria within the gut apart from C. Difficile.

As a result, C. Difficile thrives in the environment due to lack of competition (for nutrients and space) leading to the manifestation of pseudomembranous colitis- a disease which would otherwise have not manifested

Question 22

What are 2 issues with Penicillins and Cephalosporins antibiotics?

Answer 22

Antibiotic resistance

Hypersensitivity. There is a particular shared structure (R1 side chain, BZD ring with amine group) between cephalosporins and penicillins, that cause the allergy.

Question 23

If a patient has a penicillin allergy, what antibiotics should they not be prescribed?

Answer 23

Any other penicillin antibiotic (amoxicillin etc.)

Cephalosporins

Question 24

Briefly describe the ways in which bacteria can develop antibiotic resistance

Answer 24

Preventing entry of antibiotics into the bacterial cell will allow DNA replication/protein synthesis/folate metabolism to remain intact with the antibiotics unable to enter to have their effects on these processes

Cleavage of the antibiotic structure e.g. beta lactamases can split the beta lactam ring of the antibiotics making them non-functional

Altering the antibiotic structure so that is no longer able to enter the cell or bind to the target site that allows it to impart its activity

Altering the site of action of the antibiotic e.g. if the antibiotic targets the bacterial ribosomes, the bacteria can develop resistance by altering the shape of their ribosomes so that the antibiotic can no longer bind to them to have their effects

Question 25

Bacterial resistance can spread through species . Briefly describe the methods in which the bacteria can spread resistance

Answer 25

Resistance can be transferred to non-resistant bacterium within a colony. These recipients do not need to be from the same species.

Conjugation (mating)
Plasmids
Transposons

Question 26

List some general issues with antibiotics, especially broad spectrum forms

Answer 26

All antibiotics interfere with gut flora. Broad spectrum antibiotics have a greater interference with gut flora posing a risk of C. Difficile overgrowth that can cause pseudomembranous colitis.

Can interact with warfarin to make it act more or less potently.

Potential ototoxicity which can lead to a loss of hearing or a reduction in hearing (aminoglycosides)

Potential hepatotoxicity as antibiotics are often metabolised in the liver and therefore they alongside their metabolites can accumulate in the liver to cause liver damage

Potential nephrotoxicity as antibiotics are often excreted from the kidneys, therefore the kidneys are a very vulnerable organ which is particularly susceptible to damage from antibiotics (aminoglycosides)

Can cause permanent discolouration of the teeth (tetracyclines can become deposited in the teeth/bones if given to a child with a developing dentition)

Question 27

What is the mechanism of interaction of antibiotics with warfarin?

Answer 27

There are shared metabolic pathways between antibiotics and warfarin. Interfering with these metabolic processes will inevitably impact the action of warfarin, either increasing bleeding risk (more potent) or making blood clots more likely (less potent)

Question 28

How would you treat a patient with a tooth abscess if they have a penicillin allergy?

Answer 28

If the patient is allergic to penicillin, they will also be allergic to amoxicillin and ampicillin. And due to the shared common structure between penicillin and cephalosporins, they may also be allergic to cephalosporin.

Need to completely avoid prescriptions of these antibiotics as they could induce an anaphylactic reaction which can be lethal.

Prescribe macrolide antibiotics such as erythromycin instead

Question 29

In what situation would you administer IV antibiotics as opposed to tablets/solution?

Answer 29

If a patient presents with a severe swelling that would impedes his ability to swallow (floor of the mouth swelling, that pushes the tongue upwards and back)