I have a problem with antibiotic guidelines. Okay, I know that’s a controversial statement for a microbiologist to make given all the efforts that have been put in over the last 15-20 years to try and make antibiotic prescribing better, but let me explain.
 
Or better yet, let me ask you a question. How do you choose an antibiotic?
 
Nowadays, when I ask this question, I get a really irritating answer, “I look at the guidelines”.

So basically, people check their brains at the door and just follow what is written down on a piece of paper or on a computer screen, without even thinking about whether it’s the right thing to do. I also suspect that many people think Microbiologists just pluck the names of antibiotics out of the air when giving advice… the ECIC thinks that stat Gentamicin is the answer to every question!
 
But in reality, Gentamicin is not the ONLY answer and guidelines may be the WRONG choice; this leads to mistakes being made every day in the choice of antibiotics to treat patients, and most of these are avoidable.
 
Let me give you some daily scenarios where following a local antibiotic guideline would be the wrong thing to do:

• Patient has frequent urinary tract infections with a Gentamicin resistant E. coli but is treated with Gentamicin because that’s what the antibiotic guidelines say to use for pyelonephritis (Hint, those previous urine results would also have said what the E. coli would actually be sensitive to!) The guideline is NOT applicable in this scenario
• Patient has cellulitis following a dog bite but is treated for cellulitis with Flucloxacillin using the generic cellulitis guidelines, but the prescriber should have looked at the infected bites guideline (Hint, bites often involve Gram-negative bacteria and the generic cellulitis guidelines target Gram-positives) The guideline is NOT applicable in the scenario
• Patient has Clostridium difficile and should be receiving oral Vancomycin, but because someone has decided to make them “nil by mouth” the person has prescribed IV Vancomycin instead even though this will NOT cross into the gut to treat the infection (Hint, making a patient “nil by mouth” doesn’t usually stop them receiving their oral medications)

 
So, how do you avoid making mistakes when choosing what antibiotic to use?
 
First considerations for prescribing
Before deciding whether to prescribe an antibiotic there are a number of things to consider and questions to ask:

• Make sure you know normal flora and the causes of common infections
• Know your speciality’s serious and common infections, the microorganisms that cause these, and the usual treatments for them
• Use the British National Formulary (BNF) for interactions, cautions and contraindications as well as dosing information

Where do "guidelines" come from? 
Empirical antibiotic guidelines are established by answering many of the questions below. It is essential to understand the relevance of these questions and the effect of the answers. Relying on empirical antibiotic guidelines without knowing why or how these guidelines are produced can be dangerous and is poor practice.
 
Important questions to ask when choosing an antibiotic
I have a specific process I follow when choosing what to prescribe. I have been doing this for so long now that much of this is instinctive or I am able to quickly skip the less relevant questions for a given scenario. BUT when you first start prescribing though it is important to be more careful and consider each question IN TURN, all 15 of them!

1. Does the patient have an infection?

There are many non-infectious reasons for “signs of infections”

• Fever caused by drugs, malignancy, connective tissue disorders
• Increased CRP caused by inflammation, malignancy, connective tissue disorders
• Chest crackles caused by heart failure, pulmonary embolus, fibrosis
• Pyuria (white blood cells in urine) caused by appendicitis, connective tissue disorders, malignancy

 
2. If the patient has an infection what is the likely source?

• Urine, respiratory tract, skin, bone, joint, heart, CNS etc.…

 
3. What are the likely causative microorganisms?

• Viruses, bacteria, fungi, parasites

 
4. Does the patient need an antibiotic or is the infection self-limiting?

• Viral infections are usually self-limiting
• Urethral syndrome and gastroenteritis do not usually require antibiotics

 
5. Does the patient need urgent treatment or is there time to make a diagnosis?

There is often time to make a diagnosis before starting treatment HOWEVER certain infections require immediate management without waiting for investigations as delays can lead to serious and permanent harm to the patient:

• Sepsis
• Neutropaenic sepsis
• Meningitis
• Meningococcal sepsis
• Encephalitis
• Epiglottitis
• Spinal epidural abscess
• Necrotising fasciitis
• Toxic shock syndrome

 
6. Is the antibiotic active against the microorganisms?

• See Table of Antibiotic Spectrum of Activity (content from Microbiology N&B)

 
7. Does the antibiotic get into the site of infection?

• See Table of Penetration, content in Microbiology N&B)

 
8. Does the patient need a bactericidal antibiotic or is bacteriostatic adequate?

• Immunodeficient patients require bactericidal antibiotics because they are unable to fight infections themselves

 
9. What route of administration should be used?

• DO NOT use oral antibiotics to treat systemic infections if patients are unable to absorb from the gastrointestinal tract
• Antibiotics with good oral bioavailability rarely need to be given intravenously

 
10. How much antibiotic should be prescribed?

• Patients in renal failure may need doses of antibiotics reducing
• Patients over 60-70kg may need increased doses of antibiotics as normal doses are calculated for previously normal body size (male of 65kg back in the 1950s!)

 
11. Are there any contraindications or cautions for prescribing this antibiotic?

• DO NOT use any Beta-lactam antibiotics if the patient has a history of severe penicillin allergy
• Many antibiotics interact with Methotrexate e.g. Trimethoprim, Ciprofloxacin, Doxycycline
• Many antibiotics are contraindicated in myasthenia gravis e.g. macrolides, quinolones, aminoglycosides, Colistin
• Always check the BNF for interactions, cautions and contraindications as well as dosing information

 
12. What are the side effects of this antibiotic?

• See section Antibiotics, in Microbiology N&B for individual antibiotic agents
• Always check the BNF for side effects

 
13. When should the patient be reviewed?

• Septic patients should be reviewed within 1 hour of starting treatment
• Daily review of ALL patients on antibiotics
• Don’t forget “stop and review” dates as these help prevent over-treatment and CDAD

 
14. When can I switch from IV to oral, and how long should I treat the patient for?
 
15. Do the results of the microbiology investigations identify a specific causative microorganism?

• Once the cause is known, antibiotics should be narrowed down to cover the specific microorganisms identified e.g. CAP caused by Streptococcus pneumoniae can be treated with Penicillin rather than Co-amoxiclav and Clarithromycin

 
So, there it is. When choosing an antibiotic, I run through 15 questions in this order to choose what the right treatment is. It isn’t easy when you start out with prescribing. Like everything it takes time to learn how to do it properly, but it’s worth it. Patients don’t get better on the wrong antibiotic, and prescribers get in trouble when they mess it up, so it’s in everyone’s interest to get it right first time… so give this method a try… it works for me!
 
Don’t forget to order your copy of Microbiology Nuts and Bolts; it’s the perfect size for a stocking filler! Yep that’s a desperate plug for Xmas sales to cover the cost of ECIC’s stocking fillers: a tube of orange smarties, drumstick sweets and refreshers :-)

​Many hospitals rely heavily on aminoglycosides within their antimicrobial regimens. Locally we use Gentamicin as our go-to aminoglycoside of choice for sepsis (combined with Amoxicillin and Metronidazole) as well as for severe pyelonephritis amongst other things. In fact, it was one of my favourite choices for buying time to work out what is wrong with septic patients who cannot afford to wait for a diagnosis before treatment is started. ECIC (a.k.a. my wife) used to tease me that Gentamicin was the only Microbiology oncall advice needed and therefore our cat could do the oncall… how rude!

How do you predict that an antibiotic is going to be able to treat an infection caused by a particular bacterium? Easy… you do the antibiotic sensitivities and if it is susceptible you treat. Right?
 
Well, sometimes it isn’t as simple as that. Sometimes you need more than just a standard laboratory investigation… you need to take your antibiotic testing to another level… do you mean levitation?!

Sunday night is “Antiques Roadshow night” in our house, every Sunday in the UK the BBC1 broadcast an hour of people bringing their various family heirlooms or jumble sale bargains to antique experts for a brief chat about what they are and how much they are worth. I enjoy the social history side of the show although I find the occasional “money-grabbing” a bit depressing.
 
Last Sunday, 20th February, was a bit different as I saw a trailer showing something unusual and medical… queue my curiosity! I was glued to the program in anticipation.
 
It was the last item on the show, and it had been brought in by some school children and their Headmaster and it was this:

There is a change coming to how you will see laboratory culture results reported, but will you know what it means?
 
Within the UK, as well as most of the rest of Europe, laboratories follow a standard procedure for testing whether bacteria are likely to respond to treatment with different antibiotics. You see this on reports where the laboratory says a bacterium is susceptible (or sensitive) to an antibiotic which they mark with an “S” or resistant to an antibiotic which they mark with an “R”.
 
But did you notice that sometimes the laboratory puts an “I” for intermediate? And if you did, did you know what intermediate means?

“We have a septic lady who has just returned from a trip to India. She also has a headache and diarrhoea. We think she might have typhoid but want to cover for meningitis as well as this. What do you suggest?”
 
The Microbiologist listened as the Emergency Department (ED) Consultant expanded on the story with where exactly the patient had been in India, what she had been doing there and what pre-travel vaccinations she had had. It was a great presentation and showed that the Consultant had clearly been listening to the teaching on fever in a returning traveller that the Microbiologist had given the week before!
 
“Okay, she’s been to the North of India, we’d better cover for XDR typhoid as well as meningitis and other potential causes of sepsis. The best thing to do is start IV Meropenem 2g TDS, and if it’s not meningitis then we can reduce the dose to 1g later” replied the Microbiologist.
 
“Isn’t IV Ceftriaxone the normal first line for typhoid?” asked the ED Consultant.
 
“It is” replied the Microbiologist, “unless you have the XDR typhoid which is currently causing mayhem in Pakistan next to India, XDR is Ceftriaxone resistant and so you need Meropenem instead.”
 
“Crikey!” exclaimed the ED Consultant, “long gone are the days when I could treat this with Ampicillin…I’m sure Typhoid Mary would have accepted Ampicillin!”
 
“We all feel a little old these days, I find it’s more about the mileage not so much the years…!” said the Microbiologist.

“Hello Dad, how are you today?” asked Thor, the God of Thunder.
 
“To be honest son, I’m a bit under the weather really. I’ve managed to catch Covid-19 from Hela, your sister, and I’ve just called to let you know you’re a contact and need to test and self-isolate” said Odin.
 
“It’s okay father, I don’t need to worry. I will smite this dastardly virus with my mighty hammer, Mjolnir. No virus is going to get the God of Thunder so easily”

The Microbiologist was doing his daily Critical Care ward round. The next patient to see had been admitted with severe abdominal pain and been diagnosed with a perforated appendix. They had had an urgent laparotomy the night before and had come to the Critical Care Unit as they were a bit unstable after the operation and needed close monitoring. They had improved steadily.
 
The Registrar mentioned that the patient had been on antibiotic prophylaxis since the operation, and they wondered whether it should stop after 24 hours.
 
“It’s not prophylaxis” said the Microbiologist.
 
“Yes, it is” replied the Registrar, “the Surgeons have written that they want the antibiotic prophylaxis to continue, but they haven’t said for how long.”
 
“No, it’s not prophylaxis” said the Microbiologist again, “it’s treatment. They are different things with different purposes”.
 
“Oh, here we go” muttered the Registrar, “pedantics again!”
 
“I heard that!” Exclaimed the Microbiologist, smiling, at least he knew someone had read his blog. “Let me explain…” he said in that manner of, shhh…listen!
 
The Registrar groaned inwardly, knowing a mini-lecture was coming and there was nothing he could now do to stop it…

So we have been let loose and lockdown is being de-escalated slowly but have we gone too soon? We don’t have a vaccine, treatments give only modest benefits and we’re not so good at social distancing on a beach! “Experts” are a little alarmed at the pace of release and I think we’re going to be stuck with Covid-19 for a while yet, so what shall I blog about this week?

One of the stories that keeps grumbling along in the background of Covid-19 is the potential to use antibodies from patients who have survived the infection to treat patients with active infection. It’s known as plasma therapy and it’s not as crazy it might at first sound.

On his way to review a ward patient the Microbiologist was stopped by one of the Consultant Physicians and asked about a different patient. These “corridor consultations” are fairly frequent in medicine and often lead to significant decisions about patient care, it’s important to document them though; remember, “if it isn’t written down then you didn’t do it”.
 
“I have a patient who I have been seeing in clinic who I think might have tuberculosis, but the sputum and bronchoalveolar lavage cultures are negative. Is there anything else that can present in the same way that I might be missing?” the Physician asked.
 
“Why do you think they have TB?” asked the Microbiologist, thinking is this related to those pesky Tabby Cats!?