ABSORB THIS!
A medication is given IM rather than SC because the clinician wants faster absorption. What physiologic difference between these sites helps explain the choice?
Greater blood flow/perfusion at the IM site allows more rapid absorption.
Minutes after IV administration, the highest initial drug concentrations occur in the brain, heart, liver, kidneys, and endocrine organs rather than bone and adipose tissue. What characteristic primarily explains this pattern?
Differences in tissue perfusion/blood flow.
A drug's plasma concentration decreases from 80 to 40 to 20 to 10 mg/L over equal time intervals. What elimination pattern does this suggest?
Answer: First-order elimination.
Why: The concentration is decreasing by the same fraction during each interval.
Two spherical bacterial isolates are examined. One consistently forms grape-like clusters while the other forms chains. Which genera do these arrangements suggest?
Staphylococcus forms clusters; Streptococcus forms chains.
A swab from an ear discharge cannot be delivered to the laboratory immediately. What is the most important thing to prevent before it arrives?
Answer: Drying of the specimen.
Why: Swab specimens should be protected from drying and placed in appropriate transport media when needed
Two animals receive the same oral medication. One has delayed gastric emptying and altered intestinal transit time. The dose is identical, but their plasma drug concentrations differ. What part of pharmacokinetics is most directly being altered?
Answer: Absorption.
Why: Gastric emptying and intestinal transit are physiologic factors that influence oral drug absorption.
Two drugs have identical plasma concentrations. Drug X has a much larger apparent volume of distribution than Drug Y. Which drug has distributed more extensively outside the plasma?
Answer: Drug X.
Why: A larger apparent Vd corresponds to lower relative retention in plasma and greater distribution into other body compartments.
Drug A has a 2-hour half-life and Drug B has a 12-hour half-life. Both begin repeated dosing at the same time. Which reaches steady state first?
Answer: Drug A.
Why: Time to steady state depends on half-life, with approximately 4–5 half-lives needed to approach 97% of steady state.
A bacterium reaches a mucosal surface but cannot remain attached long enough to multiply because mucus and other mechanical forces continually remove it. Which stage of pathogenesis is failing?
Adhesion/adherence.
A veterinarian suspects a bacterial infection, but the submitted culture is negative. The sample spent a prolonged period in poor transport conditions. Does the negative result rule out infection?
Answer: No.
Why: Failure to recover bacteria can occur if the organism dies during transport, is overgrown by contaminants, or is no longer being shed when the sample is collected.
A weak acid enters the acidic stomach primarily in its unionized form. After entering the more alkaline plasma, much more of it becomes ionized. Why does the drug tend to remain on the plasma side once this occurs?
The ionized form crosses lipid membranes poorly, producing ion trapping.
A severely hypoalbuminemic patient receives a highly albumin-bound acidic drug. Without changing the dose, why could the patient's risk of an adverse drug effect increase?
Answer: Less albumin can increase the free/unbound fraction of the drug.
Why: Albumin is an important binding protein for acidic drugs, and the unbound fraction is available for distribution and pharmacologic activity.
A drug's volume of distribution remains unchanged, but its whole-body clearance decreases substantially. What happens to its half-life?
Answer: Its half-life increases.
Why: Half-life is related to Vd and inversely related to whole-body clearance.
Bacterium A has a capsule that interferes with engulfment. Bacterium B produces a substance that damages leukocytes. Although their mechanisms differ, both characteristics accomplish what broader pathogenic goal?
Evasion of host immune defenses.
You need a medium that will allow the desired organism to grow while suppressing competing organisms from a contaminated specimen. What type of medium should you choose?
Selective medium.
A drug has excellent lipid solubility and is largely unionized at the intestinal pH. It crosses the intestinal epithelium efficiently, yet only a small amount of unchanged drug reaches systemic circulation. What process best explains this discrepancy?
Answer: Hepatic first-pass metabolism.
Why: Good intestinal absorption does not guarantee high systemic bioavailability if extensive metabolism occurs after portal delivery to the liver.
Drug X is transformed into a metabolite containing a newly exposed functional group. That metabolite is then combined with glucuronic acid and becomes more water soluble. Identify the two sequential metabolic phases.
Answer: Phase I followed by Phase II.
Why: Phase I functionalizes the molecule; Phase II conjugates it with molecules such as glucuronic acid.
A drug normally follows first-order elimination. At a very high concentration, its elimination system becomes saturated. Instead of eliminating the same fraction each hour, the animal begins eliminating approximately the same amount each hour. What kinetic behavior has emerged?
Answer: Zero-order kinetics.
Why: Saturation can change elimination to a constant amount per unit time rather than a constant fraction.
An antimicrobial works against several Gram-positive bacteria but has poor activity against a Gram-negative species that has never previously encountered the drug. No new mutation or acquired resistance gene is detected. What bacterial feature could account for this resistance?
Answer: The Gram-negative outer membrane can prevent adequate antimicrobial penetration.
Why: This is an example of intrinsic resistance, rather than resistance acquired through mutation.
A veterinarian receives a positive bacterial culture from an animal without compatible clinical signs. The organism can also occur as part of normal flora. What additional information is needed before deciding that the organism caused the disease?
Answer: The result must be interpreted with the clinical signs, history, vaccination status, and normal flora.
Why: Isolation alone does not establish causation; animals may also shed organisms that are not responsible for their disease.
Drug A and Drug B are both given orally at the same dose. Drug A crosses intestinal membranes more efficiently, but Drug B ultimately produces the greater systemic exposure to unchanged drug. Give one pharmacokinetic explanation that could allow Drug B to have greater bioavailability despite poorer membrane absorption.
Answer: Drug A could undergo more extensive presystemic/first-pass metabolism.
Why: Bioavailability reflects how much unchanged drug ultimately reaches systemic circulation, not simply how efficiently it crosses the intestinal membrane.
A drug is given orally to two species. Species A has highly efficient glucuronidation, while Species B is deficient in glucuronidation. The drug depends heavily on glucuronide conjugation for elimination. Assuming other factors are similar, predict which species should have the longer drug persistence and why.
Answer: Species B should have longer persistence because deficient glucuronidation reduces an important biotransformation pathway.
Why: Species differences in drug-metabolizing capacity can change elimination and therefore drug persistence.
A drug's half-life becomes substantially longer in a patient, but its apparent volume of distribution has not changed. Using the relationship between half-life, volume of distribution, and clearance, what pharmacokinetic parameter must have decreased?
Answer: Whole-body clearance.
Why: t1/2=0.693×Vd/ClBt_{1/2}=0.693\times V_d/Cl_B. If Vd remains constant while half-life increases, clearance must decrease.
Two bacterial strains colonize the same host tissue. Strain A adheres extremely well but has few mechanisms for avoiding host defenses. Strain B adheres successfully and also inhibits phagocytosis, survives host defenses, and damages host cells. Which strain would be expected to have greater virulence, and why?
Answer: Strain B.
Why: Successful pathogenesis involves more than initial attachment. Multiple virulence determinants that promote establishment, immune evasion, survival, and host damage increase the organism's ability to cause severe disease.
A clinician strongly suspects a bacterial disease, but the first culture is negative. The organism is known to be shed intermittently, and the specimen was collected and transported appropriately. What is the most logical next sampling strategy?
Answer: Collect serial samples at different times.
Why: A correctly collected sample can still be negative if the animal was not shedding the organism at the moment it was obtained.