Antimicrobial and Antiparasitic Drugs: Mechanisms, Uses, Effects
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🧪 Topic 70: Lincosamides, Amphenicols, Polymyxins
Lincosamides (e.g., Clindamycin)
MOA: Binds to the 50S ribosomal subunit → inhibits peptide translocation → blocks protein synthesis (bacteriostatic).
Use: Anaerobic infections (e.g., Clostridium perfringens, Bacteroides), aspiration pneumonia, oral infections, invasive Streptococcus infections.
Adverse effects: Diarrhea, pseudomembranous colitis (C. difficile), fever.
Contraindication: Pregnancy (first trimester).
Amphenicols (e.g., Chloramphenicol)
MOA: Inhibits peptidyltransferase on the 50S subunit → blocks protein synthesis (bacteriostatic).
Use: Meningitis (H. influenzae, N. meningitidis, S. pneumoniae), Rickettsial infections.
Adverse effects: Bone marrow suppression (aplastic anemia), gray baby syndrome.
Contraindication: Infancy, pregnancy.
Polymyxins (e.g., Polymyxin B, Colistin)
MOA: Acts like a detergent → disrupts Gram-negative (G−) bacterial membranes (bactericidal).
Use: Multidrug-resistant Gram-negative infections (Pseudomonas, Acinetobacter, Enterobacteriaceae).
Adverse effects: Nephrotoxicity, neurotoxicity, respiratory failure.
🧬 Topic 71: Quinolones (Fluoroquinolones)
Generations:
1st: Nalidixic acid
2nd: Ciprofloxacin, Norfloxacin
3rd: Levofloxacin
4th: Moxifloxacin, Gemifloxacin
MOA: Inhibits DNA gyrase (topoisomerase II) & topoisomerase IV → DNA breakage → bactericidal.
Use:
UTIs, GI infections (Gram-negative rods)
Respiratory infections (Levofloxacin, Moxifloxacin)
Atypical bacteria: Mycoplasma, Chlamydia, Legionella
Adverse effects: GI upset, QT prolongation, tendon rupture, photosensitivity, arthropathy in children.
Contraindications: Pregnancy, children <18 years, elderly on steroids, myasthenia gravis.
🧫 Topic 72: Sulfonamides
Examples:
TMP/SMX (co-trimoxazole), Sulfadiazine, Sulfisoxazole
MOA:
Sulfonamides: inhibit dihydropteroate synthase.
Trimethoprim: inhibits dihydrofolate reductase
→ inhibits folic acid synthesis → synergistic bactericidal effect with sulfonamides.
Use:
UTIs, otitis media
Pneumocystis jirovecii (prophylaxis & treatment)
Toxoplasmosis, Nocardia, Shigella, Salmonella
Adverse effects:
Hypersensitivity, Stevens–Johnson syndrome, hemolysis in G6PD deficiency, kernicterus in neonates
Trimethoprim: megaloblastic anemia, hyperkalemia.
Contraindications: Pregnancy, <2 years, breastfeeding
🦠 Topic 73: Antimycobacterial Drugs
TB Therapy (RIPE):
Rifampin: Inhibits DNA-dependent RNA polymerase
SE: Red-orange secretions, hepatotoxicity, CYP inducer.
Isoniazid: Prodrug activated by KatG; inhibits mycolic acid synthesis
SE: Hepatotoxicity, neurotoxicity, vitamin B6 deficiency.
Pyrazinamide: Unclear MOA; active in acidic pH
SE: Hepatotoxicity, hyperuricemia.
Ethambutol: Inhibits arabinosyl transferase → blocks cell wall synthesis
SE: Optic neuritis (decreased vision, red–green color blindness).
Leprosy:
Tuberculoid: Dapsone + Rifampin
Lepromatous: Add Clofazimine
Dapsone:
MOA: Inhibits folic acid synthesis (similar to sulfonamides).
SE: Hemolysis (G6PD), agranulocytosis, methemoglobinemia.
🦠 Topic 74: Antiviral Drugs
General Principles
Antivirals target different stages of the viral life cycle (e.g., entry, uncoating, replication, assembly).
Most used for:
HIV
Herpes viruses
Hepatitis B and C
Influenza
1. Anti-Herpesvirus Drugs
| Drug | MOA | Use | Side Effects |
|---|---|---|---|
| Acyclovir | Guanine analog → inhibits viral DNA polymerase | HSV, VZV | Nephrotoxicity (IV), GI upset |
| Famciclovir | Similar to acyclovir | HSV, VZV | Similar to acyclovir |
| Ganciclovir | Inhibits viral DNA polymerase | CMV | Bone marrow suppression |
| Foscarnet | Inhibits viral DNA/RNA polymerase (no activation required) | CMV, resistant HSV/VZV | Nephrotoxicity, seizures |
2. Antiretroviral Therapy (HIV) – HAART
Regimen:
2 NRTIs + (1 NNRTI / 1 PI / 1 INI)
Classes & Examples:
| Class | MOA | Examples | Notable Side Effects |
|---|---|---|---|
| NRTIs | Block reverse transcriptase → DNA chain termination | Zidovudine, Lamivudine | Bone marrow suppression, lactic acidosis |
| NNRTIs | Bind reverse transcriptase non-competitively | Efavirenz, Nevirapine | CNS effects, hepatotoxicity, rash |
| PIs | Inhibit HIV protease | Lopinavir, Ritonavir | Lipodystrophy, hyperglycemia, nephrolithiasis |
| INIs | Inhibit integrase | Raltegravir, Dolutegravir | Increased creatine kinase |
| Entry Inhibitors | Block gp41 or CCR5 | Enfuvirtide, Maraviroc | Injection site reaction, hepatotoxicity |
3. Anti-Influenza Drugs
| Drug | MOA | Use | Notes |
|---|---|---|---|
| Oseltamivir | Neuraminidase inhibitor | Influenza A & B | Oral, start within 48 hours of onset |
| Zanamivir | Neuraminidase inhibitor | Influenza A & B | Inhaled form |
| Amantadine | M2 ion channel blocker | Influenza A | Resistance common |
| Rimantadine | Similar to amantadine | Influenza A | Less CNS toxicity |
4. Anti-Hepatitis Drugs
| Virus | Drugs |
|---|---|
| HBV | Entecavir, Tenofovir, Peginterferon |
| HCV | Sofosbuvir, Ribavirin, Ledipasvir |
🧫 Topic 75: Antifungal Drugs
Overview of Antifungal Drug Classes
| Class | MOA | Use |
|---|---|---|
| Polyenes | Bind ergosterol → pore formation → cell death | Systemic mycoses (e.g., Amphotericin B) |
| Azoles | Inhibit ergosterol synthesis (CYP450 enzyme) | Candidiasis, dermatophytosis |
| Allylamines | Inhibit squalene epoxidase | Onychomycosis (e.g., Terbinafine) |
| Echinocandins | Inhibit β-glucan synthesis | Invasive candidiasis, aspergillosis |
| Benzofurans | Disrupt mitosis (Griseofulvin) | Dermatophyte infections |
| Antimetabolites | Inhibit DNA/RNA synthesis (Flucytosine) | Cryptococcal meningitis (combo with AmB) |
🦟 Topic 76: Antiprotozoal Drugs
Antimalarial Drugs
Plasmodium species:
P. falciparum: most severe.
P. vivax / P. ovale: relapse due to hypnozoites in the liver.
P. malariae, P. knowlesi.
Drug Classes & Uses
| Drug | Use | Mechanism / Notes |
|---|---|---|
| Chloroquine | Prophylaxis and treatment of malaria (non-resistant areas) | Inhibits heme polymerase → toxic heme buildup in the parasite |
| Quinine | Severe malaria, chloroquine-resistant strains | Used with doxycycline/clindamycin; risk of cinchonism |
| Mefloquine | Chloroquine-resistant malaria | Risk of neuropsychiatric side effects |
| Primaquine | Eradicates liver forms (hypnozoites of P. vivax/ovale) | Causes hemolysis in G6PD deficiency |
| Artemisinin (not in your text) | Modern first-line in severe P. falciparum | Rapid action; short half-life |
| Pyrimethamine | With sulfadiazine for Toxoplasmosis | DHFR inhibitor |
| Proguanil | Prophylaxis & combination therapy | DHFR inhibitor |
| Atovaquone + Proguanil | Prophylaxis and treatment of P. falciparum | Mitochondrial electron transport blocker |
| Doxycycline | Malaria prophylaxis in resistant areas | Often combined with quinine |
🧬 Topic 77: Anthelmintic Drugs
Used to treat helminth infections: nematodes (roundworms), trematodes (flukes), cestodes (tapeworms).
Common Drugs by Worm Type
1. Nematodes (Roundworms)
| Worm | Drug of Choice |
|---|---|
| Enterobius (pinworm) | Mebendazole, Albendazole, Pyrantel pamoate |
| Ascaris (giant roundworm) | Albendazole, Mebendazole |
| Strongyloides | Ivermectin |
| Trichinella | Albendazole |
| Ancylostoma, Necator (hookworms) | Mebendazole, Albendazole |
2. Cestodes (Tapeworms)
| Worm | Drug of Choice |
|---|---|
| Taenia solium (pork tapeworm) | Praziquantel |
| Diphyllobothrium | Praziquantel |
| Echinococcus | Albendazole |
3. Trematodes (Flukes)
| Worm | Drug of Choice |
|---|---|
| Schistosoma | Praziquantel |
| Clonorchis sinensis | Praziquantel |
| Fasciola hepatica | Triclabendazole |