Introduction to Antibiotics

Question 1

Answer 1

Question 2

Answer 2

Question 3

Answer 3

Question 4

Answer 4

Question 5

Answer 5

Question 6

Answer 6

Question 7

Resistance

Answer 7

• Intrinsic
• Acquired

Question 8

Ways that Antibiotics are Used

Answer 8

1. Empiric therapy
2. Definitive therapy
3. Prophylactic therapy

Question 9

Empiric Therapy

Answer 9

1. Determine that the patient is (or may be) infected
2. Identify the site(s) of infection
3. Formulate a list of potential pathogens
4. Anticipate the susceptibilities of the presumed pathogens
5. Obtain appropriate specimens for laboratory examination

Question 10

Pharmacokinetics

Answer 10

• absorption
• distribution (e.g., CSF)
• elimination
• metabolism/excretion (e.g. hepatic)
• creatinine clearance

Question 11

Pharmacodynamics

Answer 11

• antimicrobial effect
• toxicity (adverse effects)

Question 12

Pharmacodynamic Factors

Answer 12

• MIC (minimum inhibitory concentration)

• smallest concentration of antibiotic that inhibits growth
• used to define susceptibility
• this is determined based on serum concentration - may not apply to the site of infection

• Post-antibiotic effect (PAE)

• persistent suppression of growth after removal of antibiotic

Question 13

Peak conc./MIC ratio vs. Time Above MIC

Answer 13

Question 14

Host Factors

Answer 14

• Successful treatment of an infection often requires more than just the correct antibiotic
• Immunologic factors: intact innate, humoral, and/or cellular immunity
• Local factors:
• privileged compartments: CSF, bone, prostate, eye
• foreign bodies: catheters, vascular grafts, CNS shunts, prosthetic valves, prosthetic joints
• impaired diffusion: poor diffusion of antibiotics into abscess cavities

Question 15

Mechanisms of Adverse Reactions

Answer 15

1. Direct effects

• aminoglycoside toxicity: ototoxicity, nephrotoxicity
• bone marrow suppression
• drug-induced hepatitis

2. Hypersensitivity

• e.g., anaphylaxis, serum sickness, Stevens-Johnson syndrome

3. Alterations of the microbiota

• e.g. C. difficile-associated colitis

4. Drug interactions

• e.g. warfarin, immunosuppressives

Question 16

Drug interactions: warfarin

Answer 16

• Administration of antibiotic to patient anticoagulated with warfarin may enhance anticoagulant effect
• Antibiotics can alter hepatic vitamin K metabolism or alter absorption by disrupting gut organisms

Question 17

Prevention / Prophylaxis

Answer 17

• Following exposure to a specific infectious agent with risk of serious infection
• Immunocompromised patients at high risk of infection
• post transplantation, advanced HIV, splenectomy
• Following certain surgical procedures
• Prevention of endocarditis in patients with underlying cardiac conditions following dental procedures