Pharmaceutical Microbiology (Note 1)

MCB 525

500 Level

Penicillins:

What is Penicillin? How Do Penicillins Work?

Penicillins are a certain collection ofantibiotics that eliminate infection causing bacteria. Also known in short as pen or PCN, they originate from a type of fungi called Penicillium fungi. They are used in the treatment or prevention of many different bacterial infections, usually caused by Gram-positive organisms. 

They are well known in medicine as they are one of the first types of antibiotic used for major infections and diseases, and are still used regularly in modern medicine. Penicillins are all β-Lactam (Beta-Lactam) antibiotics, which are antibiotic molecules with a β-Lactam nucleus. 

There are a number of penicillin types, that react to bacteria in a variety of degrees, some of these are:

§  ampicillin

§  amoxicillin

§  flucloxacillin

§  phenoxymethylpenicillin

According to Medilexicon's medical dictionary, penicillin is:

1. Originally, an antibiotic substance obtained from cultures of the molds Penicillium notatum or P. chrysogenum; interferes with cell wall synthesis in bacteria.

2. One of a family of natural or synthetic variants of penicillic acid. They are mainly bactericidal, are especially active against gram-positive organisms, and, with the exception of hypersensitivity reactions, show a particularly low toxic action on animal tissue. .

History of Penicillins

Penicillins were originally discovered by Ernest Duchesne (a medical student) in the late 19th Century, and then re-discovered for its antibiotic properties by Alexander Fleming in 1928. He realized this when a sample of a certain bacteria (Staphylococcus) became contaminated by some mold (Penicillium fungi) and that all bacteria cells closest to the mold were dying.

It was with further testing that Fleming realized the mold was actually creating a bacteria destroying substance, which he later named penicillin. This was the catalyst that brought about the future of antibiotic discovery.

Before Fleming's discovery, there were others that came across the bacteriostatic effects of penicillium fungi (such as Duchesne, mentioned above), but at the time knowledge of bacterial and viral infections was not strong enough to support any practical use to this finding.

Mode of action of Penicillin

Our immune system is usually enough to destroy harmful bacteria, as we have white blood cells that attack them before they multiply. Even if symptoms do occur, our immune system can usually fight off the infection itself. Nevertheless there are instances where it is all too much for our bodies, and they need help which is where antibiotics come in.

Bacteria are constantly rebuilding their cell walls (known as peptidoglycan synthesis), which is how they protect themselves and maintain their structure. Penicillins work by damaging and penetrating these cell walls, thus killing the bacteria cells. Bacteria can build a resistance to this by making β-lactamase , which defends the bacterial walls by assaulting the β-lactam ring. This defense can be counteracted by combining the penicillins with β-lactamase inhibitors.

What are Penicillins for?

Penicillins were one of the first drugs used to treat diseases such as syphilis, and are still in great use in modern day medicine. Many kinds of bacteria however are now penicillin resistant.

There are three main instances where penicillins would be used, these are:

§  To help fight off a bacterial infection e.g. tonsillitis

§  To prevent infection for someone with a weakened immune system due to existing illness/condition e.g. someone with sickle cell disease

§  To give someone's immune system help if they are undergoing treatment which could leave them vulnerable to infection.

What are the Side-effects of Penicillins?

Like a lot of drugs, penicillins have adverse effects, there are some common side effects and some rare.

The common side effects can occur in no more than 10% of those that take penicillins, they include:

§  diarrhea

§  feeling and being sick

§  rashes and other types of less serious allergic reactions

The rarer side effects, which occur in less than 1%, can be:

§  dizziness

§  inflammation of the liver (hepatitis)

§  kidney inflammation (nephritis)

§  dermatitis

§  convulsions/fits (especially in epileptics)

§  erythema

§  thrush

§  blood disorders

What can Penicillins be taken with?

When a number of medicines are used in sync, one may prevent or hinder the other(s) from working properly. For instance, some penicillins are known to weaken the effectiveness of oral contraceptives. This is called drug-drug interaction.

The most common medicines or substances that cannot be taken alongside penicillins include:

§  Allopurinol - when taken with ampicillin or amoxicillin, there is risk of developing a non allergic rash.

§  Oral Contraceptives - can impede their effectiveness when used alongside penicillins, thus increasing the chance of getting pregnant.

§  Methotrexate - penicillin decreases the body's ability to rid itself of this methotrexate, this can lead to serious complications.

Substances and medicines that can be taken with penicillins are:

§  Probenecid - this drug can hinder the body's capacity to remove penicillin, however this is not necessarily a problem. Using the two drugs together would increase the amount of penicillins in the bloodstream and improve their effects.

§  Alcohol - there are no complications caused by consuming alcohol while taking penicillins.

How to use Penicillins

Penicillins are normally consumed orally (through the mouth). However, some types can only be injected. Examples of these are:

§  ticarcillin plus clavulanic acid (Timentin)

§  temocillin (Negaban)

§  piperacillin plus tazobactam (Tazocin)

§  benzylpenicillin (Crystapen)

Before taking penicillin there are some factors to consider, such as:

§  Being allergic to penicillin - if this is the case penicillin should definitely not be taken. This applies to all types of penicillin - if you have been allergic to one you will be allergic to them all. If you have been allergic to other β-Lactam antibiotics, you will be allergic to penicillin

§  Having a history of allergies - people with previous allergies, such as eczema orasthma are at greater risk of going into anaphylactic shock if they take penicillins. This risk is still small but don't be afraid to check with your doctor if you have had any allergies in the past or still do.

§  Are pregnant and breastfeeding - only phenoxymethylpenicillin is not guaranteed safe when pregnant so should only be used if completely necessary, most of the other types are fine. When breastfeeding it is important to take note that phenoxymethylpenicillin can pass into the breast milk, this can affect the baby.

Some penicillins are mixed with clavulanic acid and again shouldn't be used when pregnant and breastfeeding unless it is the only option.

§  Suffering from liver or severe kidney problems - penicillins should be taken with care.

It is crucial that the whole course of penicillin is completed to prevent the infection returning. If the course is not completed, the chance of the bacteria becoming more resilient to future treatments is greatly increased. This is due to the bacteria left over from the incomplete course of treatment building up resistance to the penicillin as it has had previous exposure. This shows how important it is to finish the course (even if feeling better) and kill any remaining bacteria.

If a dose is ever missed, you should try to take the dose as soon as possible and then continue back to the normal course. If you haven't realized by the time for the next dose, the forgotten dose should be skipped altogether as it is important a double dose is not taken. If more than one dose has been missed, it is worth contacting your doctor for advice on how to proceed. 

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