Antimicrobial Therapy and Immune System: Key Vocabulary

Vocabulary-style flashcards covering key terms, definitions, and concepts from the antimicrobial therapy notes.

Goal of anti-infective therapy

To reduce invading organisms to a level at which the human immune response can control and clear the infection.

Spectrum of activity

The range of invading organisms against which an antimicrobial drug is effective.

Narrow spectrum

Antibiotics that are selective for a specific type or small group of bacteria.

Broad spectrum

Antibiotics active against a wide variety of bacteria, including both Gram-positive and Gram-negative species.

Bactericidal

Drugs that kill bacteria, often by causing cell lysis.

Bacteriostatic

Drugs that inhibit bacterial growth and reproduction, allowing the host immune system to eradicate the infection.

Acquiring resistance

The process by which bacteria adapt to survive exposure to an antimicrobial drug, either naturally or through genetic change.

MRSA

Methicillin-resistant Staphylococcus aureus; a strain resistant to methicillin and many other beta-lactam antibiotics.

VRE

Vancomycin-resistant Enterococci; Enterococci resistant to vancomycin.

Prophylaxis

Administration of an antimicrobial to prevent infection, such as around surgery or invasive procedures.

Beta-lactam antibiotics

A major class of antibiotics (penicillins, cephalosporins, carbapenems, monobactams) that inhibit bacterial cell wall synthesis.

Beta-lactamase

Enzyme produced by some bacteria that opens the beta-lactam ring, inactivating many beta-lactam antibiotics.

Beta-lactamase inhibitors

Compounds that block beta-lactamase enzymes, protecting the antibiotic (e.g., clavulanic acid, tazobactam, sulbactam).

Penicillin G

Natural penicillin; narrow-spectrum antibiotic active against certain Gram-positive organisms.

Penicillin V

Natural penicillin for oral use; similar spectrum to Penicillin G.

Aminopenicillins (e.g., amoxicillin)

Penicillin derivatives with expanded spectrum to include some Gram-negative organisms.

Ampicillin

An aminopenicillin with broader spectrum than natural penicillins.

Piperacillin-tazobactam

Extended-spectrum penicillin combined with a beta-lactamase inhibitor to broaden coverage (including Pseudomonas).

Augmentin

Amoxicillin + clavulanic acid; beta-lactamase inhibitor combination.

Timentin

Ticarcillin + clavulanic acid; extended-spectrum penicillin with beta-lactamase inhibitor.

Unasyn

Ampicillin + sulbactam; beta-lactamase inhibitor combination.

Mechanism of penicillins

Inhibit bacterial cell wall synthesis by binding to penicillin-binding proteins, leading to weakened cell walls and bacterial lysis.

Penicillin pharmacokinetics

Absorbed from the GI tract and excreted unchanged in the urine; can enter breast milk.

Penicillin interactions

Tetracyclines can reduce penicillin effectiveness; aminoglycosides can be inactivated by penicillin; estrogens’ effectiveness may be reduced; beta-blockers may increase anaphylaxis risk.

Indications for penicillin

Streptococcal infections (pharyngitis, tonsillitis), endocarditis, syphilis, diphtheria, anthrax, among others.

Cephalosporins (general)

A beta-lactam class with four generations; bactericidal; cross-reactivity with penicillins exists; mainly used for a range of Gram-positive and Gram-negative infections.

1st generation cephalosporins

Examples: cefadroxil, cefazolin, cephalexin; strong against Gram-positive bacteria.

2nd generation cephalosporins

Broader Gram-negative activity than 1st generation (e.g., cefaclor, cefuroxime, cefoxitin).

3rd generation cephalosporins

Less active against Gram-positive but highly active against Gram-negative bacteria (e.g., cefotaxime, ceftriaxone, ceftazidime).

4th generation cephalosporins

Broader spectrum with enhanced Gram-positive activity and increased beta-lactamase resistance (e.g., cefepime).

Cephalosporin cross-reactivity

Patients allergic to penicillin may have cross-sensitivity to cephalosporins; assess history carefully.

Aztreonam (monobactam)

A monobactam antibiotic active mainly against Gram-negative bacteria; minimal cross-reactivity with penicillins.

Carbapenems

Broadest-spectrum beta-lactams (e.g., imipenem, meropenem, ertapenem); often reserved for complicated infections.

Monobactam overview

Aztreonam; a single-structure beta-lactam with activity against Gram-negatives.

Aminoglycosides

Gentamicin, tobramycin, amikacin; bactericidal; inhibit protein synthesis; notable nephrotoxicity and ototoxicity; require monitoring.

Fluoroquinolones

Inhibit bacterial DNA gyrase/topoisomerase IV; broad spectrum especially Gram-negative; risk of tendonitis/rupture; interacts with antacids and iron; not routinely used in children.

Tetracyclines

Inhibit protein synthesis by binding the 30S subunit; avoid in pregnancy and children under 8 due to tooth enamel discoloration; interact with dairy and certain minerals; photosensitivity.

Macrolides

Erythromycin, azithromycin, clarithromycin; inhibit 50S ribosomal subunit; GI upset and hepatotoxicity risk; often taken on an empty stomach.

Lincosamides

Clindamycin and lincomycin; bacteriostatic or bactericidal depending on organism; risk of severe pseudomembranous colitis.

Sulfonamides

Inhibit folic acid synthesis; bacteriostatic; include drugs like sulfamethoxazole; can cause crystalluria, photosensitivity, hematologic effects; numerous drug interactions.

TB RIPES regimen

Rifampin, Isoniazid, Pyrazinamide, Ethambutol, Streptomycin; common combination for TB treatment and prophylaxis.

Directly Observed Therapy (DOT)

Nurse observes patient swallow TB medications to ensure adherence, typically several times a week.

Rifampin (Rifadin)

Inhibits DNA-dependent RNA polymerase; orange-red body fluids; potent inducer of liver enzymes.

Isoniazid (INH)

Inhibits mycolic acid synthesis in Mycobacterium tuberculosis; can cause peripheral neuropathy (prevented with pyridoxine).

Pyrazinamide (PZA)

Converted to pyrazinoic acid; creates acidic environment that inhibits Mycobacteria.

Ethambutol

Inhibits cell wall synthesis; can cause optic neuritis and visual disturbances.

Streptomycin

Aaminoglycoside used in TB regimens; can cause ototoxicity and nephrotoxicity.

Dapsone

Used in leprosy (Hansen’s disease); inhibits dihydropteroate synthesis in folate pathway.

Influenza A antivirals (neuraminidase inhibitors)

Oseltamivir and zanamivir block neuraminidase to prevent viral release and spread.

Influenza A antivirals (adamantanes)

Amantadine and rimantadine block viral uncoating by inhibiting M2 ion channel.

Antivirals for herpes/CMV

Nucleoside analogs (e.g., acyclovir, ganciclovir) inhibit viral DNA polymerase; many require renal monitoring and hydration.

HIV drug classes (overview)

NRTIs, NNRTIs, protease inhibitors, fusion inhibitors, and other agents target different stages of HIV replication.

Hepatitis B antivirals

Nucleos(t)ide reverse transcriptase inhibitors (e.g., tenofovir, entecavir) that inhibit HBV replication.

Neuraminidase inhibitors for influenza A

Drugs that prevent viral release from infected cells, reducing viral spread.

Goal of anti-infective therapy

To reduce invading organisms to a level at which the human immune response can control and clear the infection.

Spectrum of activity

The range of invading organisms against which an antimicrobial drug is effective.

Narrow spectrum

Antibiotics that are selective for a specific type or small group of bacteria.

Broad spectrum

Antibiotics active against a wide variety of bacteria, including both Gram-positive and Gram-negative species.

Bactericidal

Drugs that kill bacteria, often by causing cell lysis.

Bacteriostatic

Drugs that inhibit bacterial growth and reproduction, allowing the host immune system to eradicate the infection.

Acquiring resistance

The process by which bacteria adapt to survive exposure to an antimicrobial drug, either naturally or through genetic change.

MRSA

Methicillin-resistant Staphylococcus aureus; a strain resistant to methicillin and many other beta-lactam antibiotics.

VRE

Vancomycin-resistant Enterococci; Enterococci resistant to vancomycin.

Prophylaxis

Administration of an antimicrobial to prevent infection, such as around surgery or invasive procedures.

Beta-lactam antibiotics

A major class of antibiotics (penicillins, cephalosporins, carbapenems, monobactams) that inhibit bacterial cell wall synthesis. Contraindicated in patients with known severe hypersensitivity (e.g., anaphylaxis) to beta-lactam drugs.

Beta-lactamase

Enzyme produced by some bacteria that opens the beta-lactam ring, inactivating many beta-lactam antibiotics.

Beta-lactamase inhibitors

Compounds that block beta-lactamase enzymes, protecting the antibiotic (e.g., clavulanic acid, tazobactam, sulbactam).

Penicillin G

Natural penicillin; narrow-spectrum antibiotic active against certain Gram-positive organisms (e.g., Streptococcus, some Staphylococcus, Treponema pallidum for syphilis). Generally administered parenterally.

Penicillin V

Natural penicillin for oral use; similar spectrum to Penicillin G, primarily for mild to moderate infections like streptococcal pharyngitis (strep throat).

Aminopenicillins (e.g., amoxicillin)

Penicillin derivatives with expanded spectrum to include some Gram-negative organisms (e.g., H. influenzae, E. coli, Salmonella, Shigella). Commonly used for respiratory tract infections, otitis media, and UTIs.

Ampicillin

An aminopenicillin with broader spectrum than natural penicillins, effective against a range of Gram-positive and Gram-negative bacteria. Indications include urinary tract, respiratory, and gastrointestinal infections; also useful for meningitis and endocarditis.

Piperacillin-tazobactam

Extended-spectrum penicillin combined with a beta-lactamase inhibitor to broaden coverage significantly, including highly resistant Gram-negative bacteria like Pseudomonas aeruginosa. Used for severe hospital-acquired infections, intra-abdominal infections, and febrile neutropenia.

Augmentin

Amoxicillin + clavulanic acid; a beta-lactamase inhibitor combination. Indicated for infections resistant to amoxicillin alone, such as otitis media, sinusitis, lower respiratory tract infections, and skin infections caused by beta-lactamase producing strains.

Timentin

Ticarcillin + clavulanic acid; an extended-spectrum penicillin with beta-lactamase inhibitor. Used for severe infections, especially those caused by Gram-negative bacteria including Pseudomonas.

Unasyn

Ampicillin + sulbactam; a beta-lactamase inhibitor combination. Effective against a broad range of bacteria, including some resistant strains. Indicated for skin and soft tissue infections, intra-abdominal infections, and gynecological infections.

Mechanism of penicillins

Inhibit bacterial cell wall synthesis by irreversibly binding to penicillin-binding proteins (PBPs), which are enzymes involved in peptidoglycan synthesis. This leads to weakened bacterial cell walls and subsequent cell lysis due to osmotic pressure.

Penicillin pharmacokinetics

Absorbed from the GI tract (oral forms) or rapidly distributed (parenteral forms) and primarily excreted unchanged in the urine, requiring dose adjustment in severe renal impairment; can enter breast milk.

Penicillin interactions

Tetracyclines can reduce penicillin effectiveness; aminoglycosides can be inactivated by penicillin (do not mix in the same syringe); estrogens’ effectiveness may be reduced; beta-blockers may increase anaphylaxis risk. Probenecid can increase and prolong penicillin levels. Contraindicated in patients with a history of serious hypersensitivity reactions (e.g., anaphylaxis, Stevens-Johnson syndrome) to penicillins.

Indications for penicillin

Streptococcal infections (pharyngitis, tonsillitis, scarlet fever), endocarditis prophylaxis, syphilis, diphtheria, anthrax, clostridial infections, meningococcal infections, and treatment of other susceptible bacterial infections.

Cephalosporins (general)

A beta-lactam class with four generations; bactericidal by inhibiting cell wall synthesis; cross-reactivity with penicillins exists. Mainly used for a range of Gram-positive and Gram-negative infections, depending on the generation. Contraindications include known severe hypersensitivity (e.g., anaphylaxis) to cephalosporins or a history of severe immediate hypersensitivity to penicillins.

1st generation cephalosporins

Examples: cefadroxil, cefazolin, cephalexin; strong activity against Gram-positive bacteria (e.g., Staphylococcus, Streptococcus) and modest activity against some Gram-negative bacteria (e.g., E. coli, Klebsiella). Used for skin and soft tissue infections, surgical prophylaxis, and urinary tract infections.

2nd generation cephalosporins

Broader Gram-negative activity than 1st generation (e.g., cefaclor, cefuroxime, cefoxitin), including H. influenzae, Neisseria, and some anaerobes (cefoxitin). Indicated for respiratory tract infections, otitis media, sinusitis, UTIs, and abdominal infections.

3rd generation cephalosporins

Less active against Gram-positive but highly active against Gram-negative bacteria (e.g., cefotaxime, ceftriaxone, ceftazidime), including Pseudomonas (ceftazidime). Penetrate the CNS well. Useful for meningitis, pneumonia, complicated UTIs, gonorrhea, and Lyme disease.

4th generation cephalosporins

Broader spectrum with enhanced Gram-positive activity and increased beta-lactamase resistance (e.g., cefepime). Effective against many Gram-negative bacteria, including Pseudomonas, and resistant Gram-positive pathogens. Used for severe nosocomial infections, febrile neutropenia, and complicated intra-abdominal infections.

Cephalosporin cross-reactivity

Patients with a known allergy to penicillin, especially a history of a severe immediate hypersensitivity reaction (e.g., anaphylaxis), may have cross-sensitivity to cephalosporins due to shared beta-lactam ring structure; assess patient history carefully. For mild penicillin allergies, cephalosporins may be used with caution, but they are generally contraindicated in severe penicillin allergy.

Aztreonam (monobactam)

A monobactam antibiotic active mainly against Gram-negative bacteria by inhibiting cell wall synthesis. Unique structure confers minimal cross-reactivity with penicillins, making it a safe alternative for Gram-negative infections in patients with severe penicillin allergy. Indications include UTIs, lower respiratory tract infections, intra-abdominal infections, and gynecologic infections.

Carbapenems

Broadest-spectrum beta-lactams (e.g., imipenem, meropenem, ertapenem); often reserved for complicated infections (e.g., complicated UTIs, intra-abdominal infections, pneumonia, febrile neutropenia), acting similarly to penicillins by inhibiting cell wall synthesis. Contraindicated in patients with documented severe hypersensitivity to carbapenems or other beta-lactam antibiotics. Imipenem is often co-administered with cilastatin to prevent its renal metabolism.

Monobactam overview

Aztreonam; a single-structure beta-lactam with activity primarily against Gram-negative bacteria, including Pseudomonas, but with no activity against Gram-positive bacteria or anaerobes. Its distinct structure makes it suitable for penicillin-allergic patients.

Aminoglycosides

Gentamicin, tobramycin, amikacin; bactericidal; inhibit bacterial protein synthesis by irreversibly binding to the 30S ribosomal subunit. Notable adverse effects include nephrotoxicity and ototoxicity, which can be irreversible. Contraindications include known hypersensitivity, pregnancy (can cause fetal ototoxicity/nephrotoxicity), pre-existing severe renal impairment, and caution in patients with pre-existing hearing loss or neuromuscular disorders. Require therapeutic drug monitoring due to narrow therapeutic index.

Fluoroquinolones

Inhibit bacterial DNA gyrase/topoisomerase IV, essential for DNA replication, repair, and transcription. Broad spectrum, especially Gram-negative bacteria (e.g., ciprofloxacin for UTIs, levofloxacin for respiratory infections). Risk of tendonitis/tendon rupture (especially Achilles tendon), peripheral neuropathy, and CNS effects. Contraindicated in patients with hypersensitivity, history of tendon disorders, Myasthenia Gravis (may exacerbate muscle weakness), pregnancy (potential for cartilage damage in fetus), breastfeeding, and generally not recommended for routine use in children due to risk of cartilage damage. Interacts with antacids, iron, zinc, and dairy products by forming chelates, reducing absorption and effectiveness.

Tetracyclines

Inhibit protein synthesis by binding reversibly to the 30S ribosomal subunit, preventing attachment of tRNA. Broad spectrum, effective against atypical bacteria (e.g., Mycoplasma, Chlamydia), spirochetes (e.g., Borrelia for Lyme disease), Rickettsia, and some protozoa. Contraindicated in pregnancy and children under 8 due to permanent tooth enamel discoloration and potential inhibition of bone growth. Also contraindicated in patients with severe renal impairment (except doxycycline) and hypersensitivity. Interact with dairy products, antacids, iron, calcium, and magnesium supplements by chelation, reducing absorption; photosensitivity is a common side effect.

Macrolides

Erythromycin, azithromycin, clarithromycin; inhibit protein synthesis by binding to the 50S ribosomal subunit. Effective against atypical respiratory pathogens (e.g., Mycoplasma, Legionella, Chlamydia), and some Gram-positive bacteria. Can cause GI upset (especially erythromycin) and hepatotoxicity. Contraindications include known hypersensitivity, severe hepatic dysfunction, history of QT prolongation or concurrent use of other QT-prolonging drugs, and concurrent use of certain statins (e.g., simvastatin, lovastatin) due to increased risk of rhabdomyolysis. Many are potent CYP3A4 inhibitors, leading to increased levels of drugs like warfarin, statins, and digoxin.

Lincosamides

Clindamycin and lincomycin; bacteriostatic or bactericidal depending on organism, inhibit protein synthesis by binding to the 50S ribosomal subunit. Effective against Gram-positive cocci (e.g., Staphylococcus, Streptococcus) and many anaerobes. Important for treating skin and soft tissue infections, intra-abdominal infections, and anaerobic infections. Risk of severe pseudomembranous colitis due to Clostridioides difficile overgrowth (BBW). Contraindicated in patients with hypersensitivity to clindamycin or lincomycin and in patients with a history of C. difficile-associated diarrhea (CDAD).

Sulfonamides

Inhibit bacterial folic acid synthesis by interfering with dihydropteroate synthase; bacteriostatic. Include drugs like sulfamethoxazole (often combined with trimethoprim as Co-trimoxazole/Bactrim). Can cause crystalluria, photosensitivity, and various hematologic effects (e.g., hemolytic anemia, thrombocytopenia) particularly in G6PD deficient individuals. Contraindicated in patients with known hypersensitivity to sulfonamides, severe renal or hepatic impairment, porphyria, megaloblastic anemia due to folate deficiency, infants under 2 months of age (risk of kernicterus), and at term in pregnancy (due to risk of kernicterus in neonates). Numerous drug interactions, including potentiation of warfarin, sulfonylureas, and methotrexate toxicity.

TB RIPES regimen

Rifampin, Isoniazid, Pyrazinamide, Ethambutol, Streptomycin; a common combination for Tuberculosis (TB) treatment and prophylaxis. These drugs are chosen for their synergistic activity and to minimize the development of resistance. Treatment typically involves an intensive phase followed by a continuation phase.

Directly Observed Therapy (DOT)

A strategy for TB treatment where a healthcare worker or designated individual observes the patient swallow their TB medications to ensure adherence. This is typically done several times a week, reducing treatment failure and drug resistance, especially for multidrug-resistant TB.

Rifampin (Rifadin)

Inhibits DNA-dependent RNA polymerase, preventing bacterial RNA synthesis. Causes orange-red discoloration of body fluids (urine, sweat, tears). Is a potent inducer of liver enzymes (e.g., CYP3A4, CYP2C9), significantly reducing the effectiveness of many co-administered drugs like oral contraceptives, warfarin, HIV protease inhibitors, and corticosteroids. Contraindicated in patients with known hypersensitivity, acute liver disease, and should be used with extreme caution or avoided with certain antiretroviral drugs due to severe drug interactions.

Isoniazid (INH)

Inhibits mycolic acid synthesis in Mycobacterium tuberculosis cell walls. Can cause peripheral neuropathy (prevented with pyridoxine/vitamin B6 supplementation) and hepatotoxicity (especially in older adults or those with pre-existing liver disease). Contraindicated in patients with known hypersensitivity, acute liver disease, or a history of INH-induced liver damage. Also inhibits CYP450 enzymes, affecting metabolism of drugs like phenytoin and carbamazepine.

Pyrazinamide (PZA)

Converted to pyrazinoic acid in Mycobacterium tuberculosis, creating an acidic environment that inhibits mycobacterial growth; mechanism is pH-dependent. Can cause hepatotoxicity and hyperuricemia (which can precipitate gout attacks). Contraindicated in patients with known hypersensitivity, acute gout, or severe hepatic damage.

Ethambutol

Inhibits mycobacterial arabinosyl transferases, disrupting cell wall synthesis. Can cause optic neuritis and visual disturbances, including dose-related red-green color blindness. Contraindicated in patients with known hypersensitivity, pre-existing optic neuritis, or in young children (under 6 years) who are unable to reliably report visual changes.