Antibiotic set to wage war on superbugs
1 March 2002
 Golden Staph |
Zyvox, the first new generation antibiotic in more than 30 years, has been released in Australia with claims that it can kill the bugs that have become resistant to other types of antibiotics. |
The active ingredient in Zyvox is linezolid, a specially manufactured synthetic antibiotic that fights Gram-positive bacteria which are among the leading source of infections acquired in hospitals, causing ailments such as skin, blood and urinary tract infections and pneumonia.
These bacteria include Streptococci, Enterococci, and Staphylococci (such as Staphylococcus aureus, also known as Golden Staph because of its colour when examined in a laboratory).
 Vancomycin Resistant Enterococcus (VRE) |
Antibiotic-resistant bacteria — superbugs such as Vancomycin Resistant Enterococcus (VRE) and Methicillin Resistant Staphylococcus aureus (MRSA) — pose one of the greatest challenges facing medical science, with antibiotic resistant infections claiming an estimated 7,000 lives in Australia each year. |
What is antibiotic resistance?
Antibiotic resistance is when bacteria evolve to become resistant to the drugs (antibiotics) that were designed to kill them. Overuse of antibiotics by humans has meant that, over time, the bacteria got used to the antibiotics and evolved so that they could survive attacks from antibiotics.
From the discovery of penicillin by Alexander Fleming in 1928 until the 1950s there were almost no controls on the use of antibiotics, and in the 1970s the first lethal antibacterial resistant strains of bugs emerged.
The hospital environment is where many of these bacteria have evolved and thrive, putting patients who enter hospital for relatively minor conditions at risk of developing major complications — even death — due to infections of the skin, bloodstream, and respiratory and urinary tracts by resistant strains of bacteria.
The development of vancomycin in the late 1950s provided the ability to treat highly resistant bacteria, including Enterococcus and Staphylococcus infections. However, the nature of bacterial evolution has seen the creation of new strains of superbugs resistant even to vancomycin.
 Streptococcus pneumoniae |
Of current concern is the growing incidence of VRE and MRSA. It's estimated that 25 to 40 per cent of Staphylococcus aureus strains are methicillin-resistant. These resistant strains are now emerging as significant problems in Australia with a growing incidence of MRSA on the eastern seaboard and recent outbreaks in Western Australia. For example, in October last year, part of the intensive care unit at the Royal Perth Hospital had to be closed down due to an outbreak of VRE. |
Antibiotic resistance: the facts
- Antibiotic resistant infections kill more people annually than do motor vehicles.
- One in 4 people who develop a bloodstream resistant infection in hospital die.
- Infections acquired in the course of medical treatment contribute to about 150,000 illnesses every year.
- An estimated 14.5 million antibiotic scripts are written by GPs each year.
Why is linezolid useful?
Dr Peter Collignon, Director of the Infectious Diseases Unit and Department of Microbiology at the Canberra Hospital, said: ‘In some Australian hospitals more than half of all Staph that circulate may be resistant to standard antibiotics. Recently we have seen the emergence of resistance to the ‘last line’ drug, vancomycin. The release of linezolid means we now have a new weapon in a rather bare medicine chest.’
Linezolid has been used in Australia, under the Government’s Special Access Scheme, on about 100 seriously ill patients, many of whom would have lost limbs or died due to infections that were resistant to the available antibiotics. Globally, linezolid has been used on about 140,000 patients in many countries throughout Europe, Latin America, the USA and Asia.
‘This unique drug is a powerful new weapon to treat patients with life-threatening infections caused by bacteria that have developed resistance to nearly all other antibiotics. For some patients, this may be the only antibiotic available to treat these superbugs,’ Dr Collignon said.
How does linezolid work?
Linezolid is a synthetic molecule, the first in a new class of antibiotics known as the oxazolidinones, which offer a completely new mechanism of action from other available antibiotics.
Early antibiotics, such as penicillin, were developed after examining natural compounds for antibacterial action. Others were developed by modifying the chemical structure of existing antibiotics. For example, methicillin and flucloxacillin were adapted from penicillin.
Linezolid is a synthetic molecule that kills bacteria by stopping them from producing the vital proteins required to sustain life (protein synthesis). It was specially designed to fight germs at a different point in their life cycle than other drugs.
Linezolid’s manufacturer, Pharmacia, claims that because it is a synthetic medicine it has no natural equivalent, making cross-resistance with other antibiotics (which are usually naturally occurring) unlikely.
How is it used?
Linezolid will be used only as the last line of defence, when other antibiotics have failed or when patients are allergic to other antibiotics, and will be prescribed only through hospitals.
This restriction of its use is intended to help prevent bugs from becoming resistant to it.
Dr Collignon said: ‘It is critical that all antibiotics, whether linezolid or those commonly prescribed by GPs, be used prudently to avoid an unnecessary build-up of resistance.’
It can be taken either intravenously or as a tablet, reducing the risk of other complications — such as further infections — that may be associated with intravenous therapy. And because the tablet delivers as much of the active ingredient to the body as possible (high bioavailability), it may allow patients to be discharged from hospital sooner while still on therapy, instead of relying on intravenous delivery.
The cost is about $200 a day, administered for a maximum of about 28 days. The length of treatment would depend on the site of the infection and its severity. For example, bloodstream poisoning with Golden Staph would need at least 2 weeks’ therapy.
Last Reviewed: 24 May 2002
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