Most people believe – and have been told by health professionals –
that it’s essential to finish a course of antibiotics to prevent
antibiotic resistance. But this advice is not only wrong, it could
actually be harmful.
The idea that you have to take all the
antibiotics you’re prescribed is based on the assumption that all the
bacteria causing the infection have to be killed, so the surviving
minority don’t become resistant. In fact, for most otherwise healthy
people, significantly reducing, but not necessarily totally eliminating,
the bacteria causing the infection allows the body’s natural defences
to take over and mop up the remaining few.
Some important caveats
are some special circumstances when it’s important to kill all the
bacteria – when the patient’s normal defences are damaged for any
reason, for instance, or when the infection is in a site that’s
relatively inaccessible to antibiotics and the white blood cells that
kill bacteria. This can be in the middle of an abscess or cavity filled
with pus (as in tuberculosis infection), on a foreign body, such as a
prosthetic heart valve, or in dead tissue that can’t be removed (as in
osteomyelitis or infection of the bone).
Obviously, stopping antibiotics before a serious infection
is cured will risk a relapse. That’s what happened to Albert Alexander,
the London policeman who was one of the first people to be treated with penicillin by Howard Florey in 1941.
had a terrible infection that started with a scratch on his face. He
developed abscesses all over his head and had already had an eye
removed, but he was dying.
Within 24 hours of being given a small
dose of penicillin, his fever fell, his appetite returned and the
abscesses started to heal. But when the penicillin supply ran out after
five days, the infection flared up again. Alexander died four weeks
We now know that severe staphylococcal infection
with multiple abscesses, which is what Alexander had, is a type of
infection that needs antibiotic treatment for weeks to prevent relapse.
But there’s a lot we still don’t know about the best way to treat some
types of infection. It has recently become clear that some of the conventions around antibiotic prescribing are neither based on evidence nor harmless.
Antibiotics are generally benign but they all cause allergies and other rare side effects in a small proportion of people. And there’s a universal effect that’s less well known – even a very short course will kill many of the friendly bacteria in the gut.
effect lasts for weeks, and the longer the antibiotic course, the
greater the risk that antibiotic-resistant bacteria will take their
place and cause harm. What’s more, they can spread to other people and
add to the pool of antibiotic resistance in the community.
can do worse damage too. Antibiotic-resistant bacteria include
Clostridium difficile, which can be carried harmlessly in the bowel
until a course of antibiotics kills off its competition. This allows it to multiply and produce toxins, potentially causing life-threatening diarrhoea.
in turn, increases the risk of the bug spreading to other people,
especially in hospitals and nursing homes where serious outbreaks often
occur. Again, the longer the antibiotic course, the greater the risk of
The right dose
The rate of antibiotic resistance (in a community, a hospital or a whole country) is proportional to the total amount of antibiotics
used. The relationship is complex but the dangerous increase in
multidrug-resistant bacteria has led some experts to predict the “end of
the antibiotic era”. This is the downside of 75 years of antibiotic
Antibiotics have saved countless millions of lives, but
have been often misused because of the misguided belief that they are
The most important – but hardly novel – message for
doctors is “don’t prescribe antibiotics unnecessarily, especially for
colds and flu, which are nearly always viral”. Antibiotics simply don’t
work in acute upper respiratory infections. We all know from experience
that a cough will often last for around ten days and there’s not a lot
we can do to change that.
The problem is that it’s not always
obvious whether some illnesses are due to infection and whether they are
bacterial – and so might need treatment – or viral. Tests might help,
but the patient would have to wait for results. So the decision to treat
is usually based on clinical judgement – often influenced by the
patient’s anxiety and the doctor’s (in)tolerance of risk.
challenge for doctors and patients is to weigh the risks and benefits of
treatment. Unless there are compelling reasons to start immediately, we
should wait for test results or to see how symptoms develop. Equally
importantly, we should stop the treatment immediately if, in hindsight,
the diagnosis was wrong or symptoms disappear quickly.
serious bacterial infections, of course, need urgent and quite prolonged
treatment. How long depends on the type of infection, how serious it
is, the patient’s underlying condition and response to treatment.
recommended antibiotic courses are often arbitrary; they may reflect
long-standing convention or be based on a manufacturer’s decision during
an initial drug trial. Recent clinical trials show that even for some serious infections, shorter antibiotic courses can be as effective as conventional, longer ones.
general rule is: the shorter the course, the lower the risk of side
effects or resistance. More trials are needed to determine the shortest
courses that can be recommended without increasing the risk of relapse.
But ultimately, it will still depend on clinical judgement not arbitrary
rules, conventions or package inserts.