Chapter 38 Antibiotics Part 1

Question 1

Sulfonamides

Answer 1

• co-trimoxazole (combination of trimethoprim and sulfamethoxazole)
• most drugs begin with “sulfa”
• Inhibit the growth of bacteria (bacteriostatic)
• Prevent the synthesis of folic acid required for the synthesis of nucleic acids
• Broad spectrum used for both gram positive and gram negative
• Take with plenty of fluids to avoid crystaluria or precipitation in the kidneys
• Take with food

Question 2

Sulfonamides contraindications, adverse effects, and interactions

Answer 2

• Contraindications: allergy to chemically similar drugs including sulfonylureas, thiazide and loop diuretics, COX2 inhibitors.
• Also contraindicated in pregnant women and infants younger then 2
• Adverse effects: photosensitivity, GI disturbances
• Interactions: Potentiate sulfonylureas, anticoagulants, and phenytoin (seizure medication).
• Reduces efficacy of oral contraceptives

Question 3

Penicillins

Answer 3

• Bactericidal and they affect cell wall synthesis
• B lactam antibiotic
• Natural (Penicillin G/V), aminopenicillins (amoxicillin), and extended spectrum (piperacillin)
• Bacteria produces enzymes (B-lactamase) that are capable of destroying penicillins. Chemicals (tazobactam and clavulanic acid) bind with the enzyme to prevent it from breaking down penicillin
• Tazocin (piperacillin and tazobactam)
• Mostly used for gram postive

Question 4

Penicillin adverse effects and interactions

Answer 4

• Those allergic to penicillins have a 4-6 times increased risk of allergy to other B-lactam antibiotics.
• Cross reactivity between penicillin and cephalosporins is between 1-18%
• Adverse effects: urticaria, pruritus, angioedema
• Interactions: NSAIDS (compete for protein binding), oral contraceptives, warfarin, potassium supplements, rifampin
• Avoid taking them with caffeine, citrus, fruit juice, tomato juice, cola

Question 5

Cephalosporins

Answer 5

• Cefazolin and carbapenem
• “cef” or “penem”
• Interfere with bacterial cell wall synthesis
• 4 generations
• Same mechanism of action and drug effects as penicillin
• Adverse effects: mild diarrhea, abdominal cramps, rash, pruritis, redness, edema
• Potential cross sensitivity with penicillin’s if allergies exist

Question 6

Macrolides

Answer 6

• Prevent protein synthesis within bacterial cells
• Are considered bacteriostatic (bacteria will eventually die), but in high enough concentrations, may also be bactericidal
• Used for a wide variety of infections (such as upper and lower respiratory infections, STIs)
• Erythomycin
• ends in “mycin”

Question 7

Macrolides adverse effects and interactions

Answer 7

• Adverse effects: nausea, vomiting, diarrhea, hepatotoxicity, jaundice, anorexia, palpitations, rash, headache
• Newer (azithromycin and clarithromycin) have lower incidence of adverse effects
• Interactions: carbamazepine, cyclosporine, digoxin, warfarin, oral contraceptives
• Competes with liver metabolism and protein binding

Question 8

Tetracyclines

Answer 8

• doxycycline hyclate
• Bacteriostatic (inhibit growth)
• Inhibit protein synthesis
• Affect gram positive and gram negative
• May also be used to reduce fluid accumulation related to metastatic tumors that cause pleural and cardiac effusions
• Not used for gonorrhea

Question 9

Tetracyclines adverse effects and interactions

Answer 9

• Adverse effects: superinfection (vaginal candida), diarrhea, photosensitivity, pseudomembranous colitis
• Strong affinity for CA2+ which can cause discoloration of teth in fetuses and children, or nursing infants
• Interactions: Oral contraceptives
• Bind to CA+ and MG+ to form insoluble complexes, this dairy products, antacids, and iron salts reduce the oral absorption of tetracyclines