Pharmacology - Antibiotics

The most frequently asked type of question requires you to be able to compare various penicillin antibiotics in terms of potency against certain bugs, allergenicity, drug of choice against certain conditions, etc. For example:
a. Penicillin V vs. penicillin G: the latter is more sensitive to acid degradation and thus is usually injected rather than taken orally (Certainly no one in dentistry uses Pen G, so I would think they would not use too many of these questions)
b. Which penicillin has the best gram-negative spectrum: ampicillin
c. Which drugs from a list are or are not cross-allergenic with penicillin: most usually asked about ones are: cephalosporins and ampicillin are, erythromycin isn’t
d. Which penicillin is useful against penicillinase-producing bugs such as staphylococcus: dicloxacilline. Which is specific for Pseudomonas infections: an extended spectrum such as carbenicillin
f. Which combination of agents should be used prophylactically for patient with heart valve to prevent bacterial endocarditis: ampicillin and gentamycin (1988- according to latest recommendation of AHA and ADA, although use the latest guidelines that you have heard about)) (here’s a big change obviously, since combinations are no longer used, and neither are doses given before and after treatment – review your latest prophylaxis guidelines)

2. The 2nd largest category expects you to know the mechanism of action of the various antibiotics:
a. Bactericidal agents such as penicillin kill rapidity growing cells by inhibiting cell wall synthesis
b. Bacteriostatic agents such as tetracycline limit population growth, but do not kill bugs by interfering with protein synthesis on bacterial ribosomes
c. Antifungals such as nystatin bind to ergosterol in fungal cell walls to weaken the wall
d. Bacteriostatic agents such as the sulfonamides compete with PABA in folic acid synthesis, thus resulting in folic acid deficiency

3. Many questions are asked regarding side effects or toxicities of penicillins, tetracyclines, clindamycin, etc:
a. What are symptoms seen during allergic reactions to penicillins: dermatitis, stomatitis, bronchoconstriction and cardiovascular collapse
b. What agent produces GI upset and pseudomonas colitis: clindamycin
c. Which agents are most likely or least likely to cause superinfection: most: broad spectrum agents such as tetracyclines; least: narrow spectrum agents such as penicillin G
d. Aplastic anemia is associated with chloramphenicol
e. Liver damage or hepatotoxicity is associated with tetracycline
f. Erythromycin estolate associated with allergic cholestatic hepatitis

4. Questions involving interactions between antibiotics and other drugs:
a. Tetracycline and penicillin (cidal-static interaction)cancel each other out due to opposing mechanisms of action
b. Probenecid alters the rate of renal clearance of penicillin
c. Effectiveness of tetracyclines is reduced by concurrent ingestion of antacids or dairy products
d. Broad spectrum antibiotics enhance the action of coumarin anticoagulants because of the reduction of Vitamin K sources
e. Antibiotics such as ampicillin decrease the effectiveness of oral contraceptives due to suppression of normal Gl flora involved in the recycling of active steroids from bile conjugates, leading to more rapid excretion of the steroids from the body
f. Macrolides such as erythromycin inhibit the metabolism of drugs such as seldane, digoxin, etc.

5. More and more questions these days are being asked about antivirals and antifungals, so review
a. Acyclovir: an antiviral used for various forms of herpes
b. Fluconazole or ketoconazole: systemic-acting antifungals useful for treating candidiasis