11/13/24, 7\:42 PM Guide | Commonly prescribed antibiotics

Commonly prescribed antibiotics

Table of contents

Introduction

The invention of antibiotics had a profound impact on healthcare. In 2021, over 26 million antibiotic prescriptions were
dispensed in the United Kingdom.
1,2
The topic of antimicrobial resistance has been gaining traction. 3
As such, knowledge of antibiotics is essential to improve
antimicrobial stewardship. This article will explore antimicrobial stewardship and commonly prescribed antibiotics by drug
groups. We will also discuss example drugs within groups, common indications, mechanism of action, side e
points.

Antimicrobial stewardship

Key principles of antimicrobial stewardship include\:
1. When prescribing, follow basic prescribing principles
2. Ask for allergies and other medications, including over-the-counter and herbal medicines
3. Write an indication for antibiotics on prescription, especially for in-patient (hospital) prescribed antibiotics
4. Document a clinical review and decision date before commencing hospital antibiotics. Clinical review and decision are made
48-72 hours after starting an antibiotic. Decisions include\: stopping antibiotics, switching from IV to the oral route, changing
antibiotics, continuing antibiotics or discharge with outpatient antibiotic therapy - this guidance is known as ‘Start Smart - Then
Focus’
4
.
Figure 1.
'Start Smart - Then Focus'

Penicillins

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Examples of penicillins include amoxicillin,

Common indications

Community and hospital-acquired pneumonia (amoxicillin), cellulitis (
streptococcal infection and rheumatic fever (phenoxymethylpenicillin).
5
Amoxicillin is used to treat H e l i c o b a c t e r p y l o r i infections in combination with other medications.

Mechanism of action

Penicillins are beta-lactam antibiotics. 6
They inhibit enzymes called penicillin-binding proteins responsible for bacterial cell
wall synthesis. This results in bacterial cell death.
Some bacteria have developed antibiotic resistance by producing beta-lactamase, an enzyme that inhibits the activity of
penicillins. Co-amoxiclav contains amoxicillin and clavulanic acid. Clavulanic acid is a beta-lactamase inhibitor which counters
the impact of beta-lactamase.

Side-e

vomiting).
5
Penicillins are usually well tolerated, although the most common side e
Some patients may have hypersensitivity towards penicillin, resulting in skin rashes or reactions. It is important to let patients
know that mild to moderate reactions can be treated by taking an antihistamine. However, if they develop severe rashes or
breathing dianaphylactic reaction, and they should seek medical attention immediately.
7
Clostridium di
8
Some antibiotics are known to cause C l o s t r i d i u m d i
and causes diarrhoea. The antibiotics that cause C. di
Co-amoxiclav
Clindamycin
Cephalosporins
Cipro
Stool samples should be requested if C. di9
with increased
First-line management is a 10-day course of oral vancomycin

Key points

Consider CURB-65 or CRB65 scoring when prescribing antibiotics for community-acquired pneumonia. 10
These scoring
systems are used to determine pneumonia's severity. A score of 2 or more or 1 or more on CURB-65 or CRB65 may warrant
hospital admission rather than community oral antibiotics.
Infectious mononucleosis, also known as glandular fever or kissing disease, is caused by the Epstein-Barr virus. This infection
is commonly misdiagnosed as it presents similar to tonsillitis, resulting in antibiotics being prescribed (e.g.
phenoxymethylpenicillin).
The use of penicillin in infectious mononucleosis is known to result in a widespread maculopapular rash (Figure 2). 11
mechanism is unknown, and antibiotics should be stopped if this occurs.
The exact
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Figure 2. An example of a maculopapular rash in a patient with infectious mononucleosis who was prescribed penicillin.

Tetracyclines

Examples of tetracyclines include doxycycline, lymecycline and oxytetracycline.

Common indications

Common indications for tetracyclines include\:
5
Acne vulgaris
Chlamydia
Lyme disease
Rosacea
Atypical pneumonia ( m y c o p l a s m a p n e u m o n i a )

Mechanism of action

Tetracyclines are bacterial protein synthesis inhibitors. 6
Their primary mechanism of action is reversible inhibition of bacterial
30S ribosomal subunit. Inhibition e

Side-e

Like other antibiotics, a common side e5
Photosensitivity is increased
when taking tetracyclines, and patients should be advised to reduce exposure to sunlight and UV (e.g. tanning beds).
Tetracyclines cause tooth discolouration, enamel hypoplasia and deposit in growing bones. For these reasons, they are
typically contraindicated in children \<12.

Key points

Tetracyclines should not be prescribed to\:
5
Pregnant women (tetracyclines are teratogenic)
Women are breastfeeding, as they are secreted into breast milk
Children \<12
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Tetracyclines are susceptible to chelation, making them less e12
They commonly interact with antacids that contain
magnesium, aluminium, calcium and sodium bicarbonate. They also interact with calcium and iron supplements. Patients
should be advised to separate taking tetracyclines and antacids or iron supplements by two to three hours.
Some indications, such as chlamydia, have a loading dose of 200mg followed by a maintenance dose of 100mg. Patients
should be counselled speci
100mg capsule once daily). Always check the BNF before prescribing.
A rare but important risk of tetracyclines is idiopathic intracranial hypertension (IIH). 13
Symptoms and signs of IIH include
headache, blurred vision and papilloedema. Tetracyclines should be stopped if IIH is diagnosed.

Macrolides

Examples of macrolides include azithromycin, clarithromycin and erythromycin.

Common indications

Macrolides have similar indications as penicillin antibiotics. 5
Macrolides are typically used as 2nd-line alternatives to penicillin
antibiotics when a patient has an allergy. Macrolides (clarithromycin) are used to treat pertussis (whooping cough).
Clarithromycin is used to treat H . p y l o r i infections with other medications.

Mechanism of action

Macrolides are bacterial protein synthesis inhibitors. 6
Their primary mechanism of action is the reversible inhibition of
bacterial 50S ribosomal subunit. Inhibition e

Side-e

Macrolides are well-tolerated. Patients may complain of gastrointestinal disturbance. 5
interval prolongation.
Macrolides are known to cause QT-

Key points

Clarithromycin and erythromycin inhibit CYP3A4. 5,14
of other medications in the body.
These enzymes metabolise other medications, thereby increasing levels
A common example is warfarin, with clarithromycin and erythromycin leading to increased INR and an increased risk of
bleeding. INR levels should be closely monitored, and the warfarin dose may need to be reduced.
There is an increased risk of rhabdomyolysis when clarithromycin or erythromycin are given with a statin. Concurrent use
should be avoided, and statins should be stopped during treatment with these antibiotics.
Macrolides are useful 2nd line alternatives to penicillin antibiotics if there are allergies or contraindications.
Macrolides are known to cause QT-interval prolongation. Caution and close monitoring are advised when using other
medications with the same e

Quinolones

Examples of quinolones include cipro

Common indications

Ciprobacterial conjunctivitis and corneal
ulcers. 5
Ciproacute otitis externa.
Quinolones are also sometimes used in lower respiratory tract infections (LRTIs). Cipro
a e r u g i n o s a , an infection that can occur in cystic patients.
Quinolones are also used for urinary tract infections (mainly o
C a m p y l o b a c t e r , S a l m o n e l l a ).
Quinolones are the
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Cipromeningococcal meningitis.

Mechanism of action

Quinolones act by inhibiting bacterial DNA synthesis. 6
inhibitors.
They are DNA gyrase (topoisomerase II) and topoisomerase IV
Quinolones are e
tract and gastrointestinal infections.

Side-e

Quinolones commonly cause gastrointestinal disturbances, other side e
5
Neurological\: quinolones are known to lower seizure thresholds and should be used cautiously in patients with or at risk of
seizures
Musculoskeletal\: quinolones damage muscle tendons, putting patients at risk of tendon rupture
Cardiovascular\: quinolones prolong the QT interval and can risk the development of arrhythmias

Key points

The key points of quinolones are related to their side e
Quinolones should be avoided in women who are pregnant or breastfeeding. 5
glucose-6 phosphate dehydrogenase (G6PD) de
They are also contraindicated in patients with
MHRA advice
The Medicines and Healthcare Products Regulatory Agency (MHRA) has released a drug safety update warning about
the risks of quinolones. A patient information sheet has been developed for patients prescribed quinolone antibiotics.
This includes information on the symptoms of rare but serious side e

Trimethoprim and sulphonamides

Co-trimoxazole is trimethoprim and sulfamethoxazole (a sulphonamide).

Common indications

Trimethoprim is a urinary tract infections (UTIs), with alternatives being nitrofurantoin
and amoxicillin. 5
It is also used for catheter-associated UTIs, acute pyelonephritis, acute prostatitis, acute diverticulitis, acne
resistant to other antibiotics, shigellosis and respiratory tract infections.
Co-trimoxazole can be given as treatment and prophylaxis of P n e u m o c y s t i s j i r o v e c i i infections which may occur in
immunosuppressed patients, for example, due to human immunode. It is occasionally used in hospital-
acquired pneumonia, acute exacerbation of COPD, leg ulcer infections and moderate and severe diabetic foot infections.

Mechanism of action

Bacteria require folate for DNA synthesis but cannot use external sources of folate. 6
Trimethoprim is a dihydrofolate reductase
inhibitor. This enzyme is responsible for bacterial folate synthesis. Thereby, trimethoprim reduces bacterial growth.
Trimethoprim has a broad spectrum of activity against gram-positive and gram-negative organisms, particularly E s c h e r i c h i a
c o l i . However, its clinical usefulness is limited to the widespread development of bacterial resistance.
Sulfonamides, such as sulfamethoxazole, also impair bacterial folate synthesis. Combined with trimethoprim, folate synthesis
will be completely inhibited, so they are bactericidal.

Side-e

The most common side e
5
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There is restricted use of sulfonamides due to them commonly causing anaphylactic reactions, erythema multiforme and drug
fever. This rarely occurs with trimethoprim. Due to folate antagonism, they can impair haematopoiesis, resulting in
megaloblastic anaemia, leucopenia, and thrombocytopenia. There is also a risk of hyperkalemia and renal impairment.

Key points

Trimethoprim is teratogenic in the
defects and oral clefts in a foetus. 5
They are generally avoided during pregnancy, with nitrofurantoin used as an alternative
(however, nitrofurantoin is not advised in the third trimester or when breastfeeding).
Trimethoprim combined with potassium-elevating drugs (e.g. aldosterone antagonists, ACE inhibitors and ARBs) can increase
the risk of hyperkalemia.
Avoid using other folate antagonists alongside trimethoprim, such as methotrexate, and medications that increase folate
metabolism, such as phenytoin, due to adverse haematological e

Nitrofurans

The most common example of a nitrofuran is nitrofurantoin.

Common indications

Nitrofurantoin is commonly used as a lower urinary tract infections, with the
alternatives being trimethoprim and amoxicillin. 5
It can also be used for catheter-associated UTIs, severe chronic recurrent
UTIs, pregnancy

Mechanism of action

Nitrofurantoin is reduced to its active form with nitrofuran reductase found in bacterial cell walls. The resultant active
metabolite impairs bacterial DNA, causing cell death.
6
Nitrofurantoin is active against gram-negative organisms such as E s c h e r i c h i a c o l i , and Gram-positive organisms like
S t a p h y l o c o c c u s s a p r o p h y t i c u s , commonly responsible for UTIs. Nitrofurantoin achieves therapeutic levels in the urine via renal
excretion. Its bactericidal e

Side-e

Gastrointestinal upset is the most common side e5
It may also cause hypersensitivity reactions and
discolouration of the urine to dark yellow or brown. Less commonly, prolonged use can cause hepatitis, pneumonitis,
pulmonary

Key points

Nitrofurantoin should be avoided in pregnant women towards term and infants under three months old. 5
in renal impairment due to the risk of toxicity.
It is generally avoided

Nitroimidazoles

The most common example of a nitroimidazole is metronidazole.

Common indications

Metronidazole is commonly used to treat dental abscesses and anaerobic infections. 5
such as trichomoniasis (t r i c h o m o n a s v a g i n a l i s ) and bacterial vaginosis (g a r d n e r e l l a v a g i n a l i s ).
They also treat protozoal infections
Metronidazole is used to treat helicobacter pylori (H. Pylori) infection and pelvic in
other medications.
Topical metronidazole is used in the management of rosacea.

Mechanism of action

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Metronidazole is passively di6
It is then reduced to its active form and
results in the formation of a nitroso-free radical. Subsequently, these metabolites interact with DNA resulting in the inhibition of
DNA synthesis and DNA degradation.
Aerobic bacteria are not susceptible to metronidazole as they cannot reduce metronidazole to its active form.

Side-e

The most common side-e5
taking metronidazole.
Patients may complain of a metallic taste when
Prolonged or high doses of metronidazole can cause optic neuritis, seizures or peripheral neuropathy.

Key points

Patients should not drink alcohol while on a course of metronidazole (oral, rectal or vaginal) or for 48 hours after
course. 5, 15
Metronidazole has a disul
resulting in the accumulation of the toxic metabolite acetaldehyde. 16
Symptoms with concurrent use include
vomiting, abdominal pain, headaches, syncope and tachycardia.

References

1. Mikulic, M. Total consumption of antibiotics in England in 2021, by antibiotic group. Published in 2023. Available from\: [LINK]
2. Mikulic, M. Leading 10 antibacterial drugs dispensed in England in 2022, by number of items. Published in 2023. Available from\:
[LINK]
3. GOV UK. UK 5-year action plan for antimicrobial resistance 2019 to 2024. Published in 2019. Available from\: [LINK]
4. GOV UK. Antimicrobial stewardship\: Start smart- then focus. Published in 2015. Available from\: [LINK]
5. British National Formulary. Published in 2023. Available from\: [LINK]
6. Ritter, JM. Flower, RJ, Henderson, G. Loke, TK. MacEwan D. Rang. H. Rang & Dale’s Pharmacology 9th Edition. 2018.
7. NHS. Side eLINK]
8. Marwick CA. Yu, N. Lockhart, MC. McGuigan CC. Wiu
infection among older people in Tayside, Scotland, is associated with antibiotic exposure and care home residence\: cohort
study with nested case-control. Published in 2013. Available from\: [LINK]
9. NICE CKS. Diarrhoea - antibiotic associated. Published in 2021. Available from\: [LINK]
10. NICE CKS. Chest infections - adult. Published in 2021. Available from\: [LINK]
11. Onodi-Nagy, K. Kinyo A. Meszes, A. Garaczi, E. Kemeny, L. Bata-Csorgo, Z. Amoxicillin rash in patients with infectious
mononucleosis\: evidence of true drug sensitization, Published in 2015. Available from\: [LINK]
12. MedlinePlus. Tetracycline. Published in 2017. Available from\: [LINK]
13. Medsafe. Idiopathic Intracranial Hypertension. Published in 2016. Available from\: [LINK]
14. NHS Greater Glasgow and Clyde. PostScriptAcute. Published in 2013. Available from\: [LINK]
Source\: geekymedics.com
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