Microbiology and Pharmacology
Microbiology and Pharmacology tests microbial structure, sterilization, antimicrobial mechanisms, and drug handling relevant to dental prescribing. Questions often combine a drug interaction with a clinical scenario.
Core rules
- Gram-positive bacteria have a thick peptidoglycan layer; Gram-negative bacteria have an outer membrane containing lipopolysaccharide.
- Autoclaving uses 121 degrees C at 15 psi for about 15 minutes to kill spores; alcohol wipes do not sterilize.
- Beta-lactams inhibit cell wall synthesis; macrolides inhibit the 50S ribosome; fluoroquinolones inhibit DNA gyrase; sulfonamides block folate synthesis.
- First-order kinetics means a constant fraction is eliminated per unit time; half-life determines dosing interval.
- Metronidazole inhibits CYP2C9 and can raise warfarin effect.
Worked example
A patient stable on warfarin is prescribed metronidazole for a dental infection. Two days later the INR rises and gum bleeding appears. Metronidazole inhibits CYP2C9, reducing warfarin metabolism, so warfarin concentration and anticoagulant effect increase. The correct reasoning is a pharmacokinetic interaction, not an additive antibacterial effect. Management includes avoiding the combination when possible, checking INR, and adjusting the warfarin dose under medical supervision.
Traps
- Bacteriostatic drugs can still be effective with host immunity; bactericidal does not always mean clinically superior.
- Penicillin allergy can be immediate IgE-mediated or delayed; not every rash is anaphylaxis.
- Epinephrine in local anesthetic prolongs duration and reduces systemic absorption but can cause palpitations.
- Aminoglycosides are ineffective orally and are nephrotoxic and ototoxic.