Bacterial Groups and Infection Sites

Bacterial Meningitis: Common causative agents include Streptococcus pneumoniae, Neisseria meningitidis, Haemophilus influenzae, Streptococcus agalactiae, and Listeria monocytogenes.
Otitis Media: Streptococcus pneumoniae is a frequent cause.
Pneumonia (Community-Acquired): Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus are frequently implicated. Atypical causes include Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella pneumophila.
Sexually Transmitted Diseases: Chlamydia trachomatis, Neisseria gonorrhoeae, Treponema pallidum, Ureaplasma urealyticum are commonly encountered.
Upper Respiratory Tract Infections (RTIs): Streptococcus pyogenes and Haemophilus influenzae are common causative agents.
Eye Infections: Staphylococcus aureus, Neisseria gonorrhoeae, and Chlamydia trachomatis are all possible offenders.
Sinusitis: Streptococcus pneumoniae and Haemophilus influenzae are important pathogens.
Gastritis: Helicobacter pylori is a key factor.
Food Poisoning: Salmonella, Shigella, and Clostridium are implicated.
Urinary Tract Infections (UTIs): Escherichia coli and other Enterobacteriaceae are common.
Skin Infections: Staphylococcus aureus, Streptococcus pyogenes, and Pseudomonas aeruginosa cause skin conditions like cellulitis, folliculitis, and impetigo.
GI Gram +ve and -ve, and Anaerobes: Campylobacter jejuni and various Enterobacteriacea.

Mechanisms of Action of Antibiotics

Cell Wall Synthesis Inhibitors: Cycloserine, vancomycin, bacitracin, penicillins, cephalosporins, monobactams, carbapenems.
DNA Gyrase Inhibitors: Quinolones.
RNA Synthesis Inhibitors: Actinomycin.
DNA-directed RNA Polymerase Inhibitors: Rifampin, Streptovaricins.
Protein Synthesis 50S Inhibitors: Erythromycin (macrolides), chloramphenicol, clindamycin, lincomycin.
Protein Synthesis 30S Inhibitors: Tetracyclines, spectinomycin, streptomycin, gentamicin, kanamycin, amikacin, nitrofurans.
Folic Acid Metabolism Inhibitors: Trimethoprim, sulfonamides.
Cytoplasmic Membrane Inhibitors: Polymyxins, daptomycin.

Antimicrobial Stewardship: Start Smart then Focus Clinical Management Algorithm

Start Smart: Assess evidence of infection, patient risk, and severity. Prescribe medications based on urgency, guidelines, allergies, and contraindications.
Investigate: Take appropriate cultures or laboratory investigations, assess organ function and immunology, and conduct source control to determine working diagnosis.
Document: Create a working diagnosis, consider possible treatment regimens, and create a plan for review.
Focus (48-72 hours): Review the post-prescription outcome with different options including discontinuation, amendment, referral, or switching.

Mechanisms of Resistance

Penetration Resistance: Bacteria limit antibiotic entry.
Efflux Pumps: Active transport of antibiotics out of the cell.
Hydrolysis: Enzymatic degradation of antibiotics.
Mutation of the Binding Site: Changes in the antibiotic-target protein render the antibiotic ineffective.

Selection of Appropriate Antimicrobials

Blood Infections/Septicemia: Broad-spectrum beta-lactams, vancomycin.
Eye Infections: Chloramphenicol, usually for very serious cases.
Dental Infections: Amoxicillin, metronidazole.
Ear Infections: Flucloxacillin, clarithromycin, erythromycin, amoxicillin, co-amoxiclav.
Cardiovascular Infections: Amoxicillin, low-dose gentamicin, vancomycin, flucloxacillin.
Genital System Infections: Metronidazole, topical clindamycin, azithromycin, doxycycline, ceftriaxone.
Gastrointestinal Infections: Clarithromycin, erythromycin, amoxicillin, clarithromycin/erythromycin, triple therapy.
Nose Infections: Phenoxymethylpenicillin, co-amoxiclav, or doxycycline/clarithromycin.
Skin Infections: Hydrogen peroxide, fusidic acid, mupirocin, flucloxacillin (if not penicillin allergic), clarithromycin, or erythromycin.
Leg Ulcers: Flucloxacillin (if not penicillin allergic), doxycycline, clarithromycin, or erythromycin.

Other Antimicrobials

Penicillins: beta-lactamase sensitive/resistant, adverse reactions.
Cephalosporins: different generations, cross-sensitivity to penicillins, side-effects.
Aminoglycosides: Serum concentration monitoring, side-effects, warnings for use, and cautions for nephrotoxicity and ototoxicity.
Glycopeptides: Warnings, side effects, and cautions concerning use in elderly patients.
Macrolides: Side-effects and warnings, Important information about food and interactions.
Quinolones: potential prolongation of QT interval, side-effects, including but not limited to seizing, gastrointestinal disorders, decreased appetite, headache, ophthalmic issues.
Tetracyclines: side-effects, warnings, and contraindications.
Trimethoprim: cautions and contraindications, including blood dyscrasias in certain patient populations, warnings about acute prophylaxis, and elderly/neonate use.
Nitrofurantoin: side-effects, warnings, and interactions with other drugs. Monitoring includes renal function.
Clindamycin: Warnings concerning inappropriate administration, reactions, and interactions with other drugs.
Metronidazole: Warnings about potential interactions with alcohol, and side effects, especially for use in topical medications.
Linezolid: Side effects, warnings (including optic neuropathy), and contraindications.

Summary-Principles of Antibiotic Prescribing

Initiate antibiotics rapidly in severe infections.
Adjust dosage and duration for different patient populations.
Increase the dose or length of treatment in severe or recurrent cases.
Confirm appropriate dosing and potential interactions in patients with complex conditions.
Ensure appropriate allergy checks.
Consider lower prescribing thresholds in patients with multiple morbidities and underlying conditions.
Suspect and address neutropenic sepsis promptly in immunocompromised patients.
Prescribe only when a clear clinical benefit is expected.