PTCB Pharmacology #2 3 — Questions and Answers
Question 1: Which of the following best describes a drug's "half-life"?
- Time for the drug to reach maximum concentration
- Time required for the plasma drug concentration to decrease by 50% (Correct answer)
- Duration of drug effect after a single dose
- Time for the drug to begin working
Correct answer: Time required for the plasma drug concentration to decrease by 50%
Half-life (t½) is the time required for the plasma concentration of a drug to decrease by 50%. It determines dosing frequency — drugs with short half-lives require more frequent dosing.
Question 2: Fluoroquinolone antibiotics (e.g., ciprofloxacin) work by:
- Inhibiting cell wall synthesis
- Inhibiting DNA gyrase and topoisomerase IV (Correct answer)
- Inhibiting protein synthesis at the 30S ribosome
- Disrupting bacterial cell membrane integrity
Correct answer: Inhibiting DNA gyrase and topoisomerase IV
Fluoroquinolones inhibit DNA gyrase (topoisomerase II) and topoisomerase IV, enzymes essential for bacterial DNA replication, repair, and transcription.
Question 3: A drug's "volume of distribution" (Vd) indicates:
- How quickly the drug is eliminated from the body
- The extent to which the drug distributes throughout the body relative to plasma (Correct answer)
- The rate at which the drug crosses the blood-brain barrier
- The percentage of drug bound to plasma proteins
Correct answer: The extent to which the drug distributes throughout the body relative to plasma
Volume of distribution (Vd) is a theoretical volume that relates plasma concentration to total drug in the body. A high Vd indicates extensive tissue distribution (lipophilic drugs); a low Vd indicates drug stays in plasma.
Question 4: Which of the following is a tetracycline antibiotic?
- Azithromycin
- Amoxicillin
- Doxycycline (Correct answer)
- Clindamycin
Correct answer: Doxycycline
Doxycycline is a tetracycline antibiotic that inhibits protein synthesis by binding to the 30S ribosomal subunit. It is used for atypical pneumonia, Lyme disease, acne, and malaria prophylaxis.
Question 5: Which of the following drug classes are typically used as "rescue" medications for acute asthma attacks?
- Inhaled corticosteroids (ICS)
- Long-acting beta-agonists (LABA)
- Short-acting beta-agonists (SABA) (Correct answer)
- Leukotriene receptor antagonists
Correct answer: Short-acting beta-agonists (SABA)
Short-acting beta-agonists (SABAs) like albuterol are quick-relief/rescue medications for acute asthma. Inhaled corticosteroids are controller/maintenance therapy; LABAs are never used as monotherapy or rescue.
Question 6: Macrolide antibiotics (e.g., azithromycin) work by:
- Inhibiting cell wall synthesis
- Disrupting the bacterial cell membrane
- Inhibiting protein synthesis by binding the 50S ribosomal subunit (Correct answer)
- Inhibiting DNA gyrase
Correct answer: Inhibiting protein synthesis by binding the 50S ribosomal subunit
Macrolides bind the 50S ribosomal subunit, blocking translocation and inhibiting bacterial protein synthesis. They are used for atypical pneumonia, community-acquired pneumonia, and STIs.
PTCB Pharmacology #2 3
Which of the following best describes a drug's "half-life"?