Antibacterial Agents

β-lactams

•    Examples: penicillins, cephalosporins, carbapenems, monobactams

•    Mechanism: inhibit transpeptidase enzyme → block cell wall (peptidoglycan) synthesis

•    Spectrum:

o    Penicillin G: streptococci, syphilis

o    Amoxicillin: broader (e.g., E. coli, H. influenzae), often combined with clavulanate

o    Piperacillin-tazobactam: pseudomonas coverage

•    Resistance: β-lactamases, altered penicillin-binding proteins (e.g., MRSA)

Macrolides

•    Examples: erythromycin, clarithromycin, azithromycin

•    Mechanism: bind 50S ribosomal subunit → inhibit protein synthesis

•    Uses: atypical pneumonia (Mycoplasma, Chlamydia), pertussis, alternative for penicillin allergy

•    Side effects:

o    QT prolongation

o    Cholestatic hepatitis

Fluoroquinolones

•    Examples: ciprofloxacin, levofloxacin, moxifloxacin

•    Mechanism: inhibit DNA gyrase (topoisomerase II) and topoisomerase IV

•    Uses: Gram-negative UTIs, severe GI infections, pseudomonas (cipro)

•    Side effects:

o    QT prolongation

o    Tendonitis, tendon rupture

o    Contraindicated in pregnancy & children (cartilage damage)

Aminoglycosides

•    Examples: gentamicin, amikacin, tobramycin

•    Mechanism: bind 30S ribosomal subunit → misreading of mRNA → defective protein synthesis

•    Uses: severe Gram-negative infections, synergy in endocarditis

•    Side effects:

o    Nephrotoxicity (proximal tubular necrosis)

o    Ototoxicity (vestibular & cochlear damage)

o    Neuromuscular blockade

Tetracyclines

•    Example: doxycycline

•    Mechanism: bind 30S ribosomal subunit → inhibit protein synthesis

•    Uses: Lyme disease, chlamydia, acne, malaria prophylaxis

•    Precautions:

o    Avoid in children <8 years and pregnancy (teeth staining, bone effects)

o    Photosensitivity

Adverse Effects Overview

•    C. difficile colitis: clindamycin, cephalosporins, fluoroquinolones

•    QT prolongation: macrolides, fluoroquinolones

•    β-lactam allergy: consider aztreonam (monobactam) or macrolide

Antituberculous Drugs (RIPE regimen)

•    Rifampicin:

o    Orange secretions

o    Potent CYP450 enzyme inducer → interacts with warfarin, OCP

•    Isoniazid:

o    Peripheral neuropathy (due to B6 deficiency; give pyridoxine)

o    Hepatotoxicity

•    Pyrazinamide:

o    Hyperuricaemia → gout flares

o    Hepatotoxicity

•    Ethambutol:

o    Optic neuritis → red-green colour blindness

o    Visual acuity monitoring

Antiviral Agents

Herpesviruses

•    Aciclovir: HSV, VZV; nephrotoxicity if not adequately hydrated

•    Ganciclovir: CMV; myelosuppression, neutropenia

Influenza

•    Oseltamivir (neuraminidase inhibitor): effective if started within 48 hours

HIV therapy

•    Drug classes:

o    NRTIs (e.g., tenofovir, abacavir)

o    NNRTIs (e.g., efavirenz)

o    Protease inhibitors (e.g., lopinavir, darunavir)

o    Integrase inhibitors (e.g., raltegravir)

•    Key side effects:

o    Lactic acidosis (esp. NRTIs)

o    Lipodystrophy (PIs)

o    Hyperlipidaemia, insulin resistance

o    Hepatotoxicity

Antifungal Agents

•    Azoles (e.g., fluconazole, itraconazole):

o    Inhibit ergosterol synthesis (via CYP inhibition)

o    Side effects: hepatotoxicity, QT prolongation, drug interactions

•    Amphotericin B:

o    Binds ergosterol → pore formation → cell death

o    "Amphoterrible": nephrotoxicity, electrolyte loss (hypokalaemia, hypomagnesaemia), infusion reactions

•    Echinocandins (e.g., caspofungin):

o    Inhibit β-glucan synthesis in fungal cell wall

o    Useful for Candida (esp. fluconazole-resistant), Aspergillus

Antiparasitic and Anthelmintics

Malaria

•    Artemether-lumefantrine: first-line in uncomplicated falciparum malaria

•    Quinine: severe malaria; side effects include cinchonism (tinnitus, headache), hypoglycaemia

•    Mefloquine: neuropsychiatric side effects

Schistosomiasis

•    Praziquantel: increases calcium permeability → spastic paralysis of worms

Helminths

•    Albendazole: inhibits microtubule formation

•    Ivermectin: increases chloride permeability → paralysis (useful in strongyloidiasis, onchocerciasis)

Principles of Antimicrobial Stewardship

•    Select right drug, dose, and duration

•    Empirical therapy guided by local resistance patterns and severity

•    De-escalation once culture results are available

•    Avoid unnecessary broad-spectrum use to reduce Clostridioides difficile risk and resistance

•    Educate patients about adherence and adverse effects

Extra Revision Pearls

•    Penicillin anaphylaxis: cross-reactivity ~1% with first-generation cephalosporins

•    Vancomycin: "red man syndrome" if infused too quickly (histamine-mediated)

•    Linezolid: risk of serotonin syndrome if combined with SSRIs, also causes thrombocytopenia