Antibiotics and Their Mechanisms of Action

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Questions and Answers

What is the typical oral dosage range for cephalexin?

0.5–1 g four times daily

0.25–0.5 g four times daily (correct)

1–2 g twice daily

0.1–0.2 g three times daily

Which process is primarily responsible for the excretion of cephalexin?

Hepatic metabolism

Glomerular filtration and tubular secretion (correct)

Passive diffusion

Biliary excretion

How might probenecid affect cephalexin levels?

Increase serum levels substantially (correct)

Decrease serum levels significantly

Alter the metabolism rate

Have no effect on serum levels

What adjustment should be made for patients with impaired renal function when prescribing cephalexin?

Reduce the dosage Signup and view all the answers

Which of the following best describes the molecular structure mentioned in the content?

A 7-aminocephalosporanic acid nucleus Signup and view all the answers

What is the primary mechanism of action of daptomycin?

Covalently binds to cysteine residues in enolpyruvate transferase Signup and view all the answers

Which transport systems are known to transport daptomycin into bacterial cells?

Glycerol phosphate and glucose 6-phosphate transport systems Signup and view all the answers

What type of bacteria does daptomycin primarily target?

Only Gram-positive bacteria Signup and view all the answers

What is a characteristic of the antibiotic fosfomycin?

It requires high concentrations for effectiveness in vitro Signup and view all the answers

Resistance to daptomycin is primarily related to which of the following?

Inadequate transport of the drug into the bacterial cell Signup and view all the answers

What is the primary criterion for classifying cephalosporins into their traditional generations?

Spectrum of antimicrobial activity Signup and view all the answers

Which cephalosporin mentioned has a unique characteristic that may not fit traditional classifications?

Cefotaxime Signup and view all the answers

Which generation of cephalosporins is primarily focused on influencing susceptibility to gram-negative bacteria?

Third generation Signup and view all the answers

How many major groups or generations have cephalosporins traditionally been classified into?

Four Signup and view all the answers

Which of the following cephalosporins is classified as first-generation?

Cefazolin Signup and view all the answers

What is a significant limitation of the traditional classification of cephalosporins?

It does not account for newer cephalosporins. Signup and view all the answers

Which cephalosporin is NOT considered to fit into the traditional classification groups?

Cefotetan Signup and view all the answers

Which feature is commonly associated with second-generation cephalosporins?

Broad spectrum covering both gram-positive and gram-negative bacteria Signup and view all the answers

What is the recommended increase in the daily dose of piperacillin after the first week of life?

33–50% Signup and view all the answers

For neonates weighing less than 2 kg, which dosage range should be used?

Lower dosage range Signup and view all the answers

Why should oral penicillins, except for amoxicillin, not be given with food?

To minimize binding to food proteins and acid inactivation Signup and view all the answers

What effect does probenecid have on blood levels of penicillins?

It raises blood levels by impairing renal tubular secretion Signup and view all the answers

Which condition is benzathine penicillin G effective in treating?

β-hemolytic streptococcal pharyngitis Signup and view all the answers

How often should benzathine penicillin G be administered to prevent reinfection?

Once every 3-4 weeks Signup and view all the answers

Which of the following is a reason why penicillin V is indicated only for minor infections?

Its narrow antibacterial spectrum and poor bioavailability Signup and view all the answers

Which penicillin should be administered without regard to meals?

Amoxicillin Signup and view all the answers

What risk do patients with a history of penicillin anaphylaxis face when receiving cephalosporins?

Increased risk of cephalosporin reaction Signup and view all the answers

What is the route of administration for aztreonam?

Intravenously every 8 hours Signup and view all the answers

Which types of cephalosporins should not be given to patients with penicillin anaphylaxis?

First- and second-generation cephalosporins Signup and view all the answers

What is the primary factor that defines the low frequency of cross-allergenicity between penicillins and cephalosporins?

Different R-1 side chains Signup and view all the answers

How does renal failure affect the pharmacokinetics of aztreonam?

Prolongs its half-life Signup and view all the answers

What percentage represents the cross-allergenicity rate between penicillins and cephalosporins?

Approximately 1% Signup and view all the answers

What serious infections can aztreonam be used to treat in patients with penicillin anaphylaxis?

Pneumonia, meningitis, and sepsis Signup and view all the answers

What type of β-lactamases does cephalosporins show notable exceptions against in terms of stability?

AmpC β-lactamases and extended-spectrum β-lactamases Signup and view all the answers

What is the adjusted dose percentage of Cefazolin for a patient with a creatinine clearance of 10 mL/min?

25% Signup and view all the answers

Which of the following antibiotics has an adjusted dose of 50% at a creatinine clearance of 50 mL/min?

Cephalexin Signup and view all the answers

What is the pediatric dose range for Cefoxitin?

75–150 mg/kg/d Signup and view all the answers

How is the dosing of Daptomycin affected by renal function in terms of creatinine clearance?

No adjustment needed for renal function Signup and view all the answers

For a patient with a creatinine clearance of 50 mL/min, what is the adjusted dose of Meropenem?

66% Signup and view all the answers

What is the adjusted dose percentage of Vancomycin for a patient with a creatinine clearance of 10 mL/min?

10% Signup and view all the answers

Which antibiotic shows a pediatric dose of 50–100 mg/kg/d in 3 or 4 doses?

Cefazolin Signup and view all the answers

What is the adjusted dose of Cefuroxime for a creatinine clearance of 10 mL/min?

33% Signup and view all the answers

Which antibiotic requires a loading dose followed by a maintenance dose based on renal clearance?

Vancomycin Signup and view all the answers

What pediatric dosage is specified for Ertapenem?

100 mg/kg/d Signup and view all the answers

At a creatinine clearance of 50 mL/min, what is required for Ceftolozane-tazobactam?

Not studied Signup and view all the answers

Which of the following requires a dose adjustment of 75% at 50 mL/min creatinine clearance?

Imipenem Signup and view all the answers

What is the typical adult dosing interval for Cefotaxime?

Every 6–12 hours Signup and view all the answers

Which of the following antibiotics does not have an adjusted dosing percentage specified for creatinine clearance of 50 mL/min?

Oritavancin Signup and view all the answers

What role do multidrug resistance-associated protein (MRP) transporters play in the body?

They are involved in the excretion of drugs and metabolites. Signup and view all the answers

Which factor influences the lipid:aqueous partition coefficient of a drug?

The pH of the medium the drug is in. Signup and view all the answers

Which equation is used to express the ratio of lipid-soluble form to water-soluble form for weak acids and bases?

Henderson-Hasselbalch equation. Signup and view all the answers

What type of transport mechanism do some families of transporters utilize to drive transport without binding ATP?

Active transport using ion gradients. Signup and view all the answers

Which characteristic is not associated with the systems discussed for pharmacology in the content?

Dependence on passive diffusion alone. Signup and view all the answers

What is a primary mechanism that drugs utilize to permeate cell membranes?

Active transport via energy expenditure Signup and view all the answers

Which drug characteristic allows it to diffuse passively through lipid membranes?

Lipid solubility Signup and view all the answers

What type of carriers is specialized for transporting drugs out of the cell?

ATP-binding cassette transporters Signup and view all the answers

What influences the movement of charged drug molecules across the membrane?

Electrical fields Signup and view all the answers

Which process is NOT a mechanism of drug permeation mentioned?

Chloride channel facilitation Signup and view all the answers

Which of the following statements is true regarding drug molecules bound to plasma proteins?

They cannot effectively permeate tissues Signup and view all the answers

What type of diffusion of drug molecules is primarily driven by the concentration gradient?

Aqueous diffusion Signup and view all the answers

Which mechanism serves as a key limiting factor for drug permeation in the body?

Lipid diffusion Signup and view all the answers

What does Kd represent in drug-receptor interactions?

The concentration for 50% saturation of the receptors Signup and view all the answers

Which type of bond is important for the selective binding of drugs to their receptors?

Weak bonds Signup and view all the answers

What effect do covalent bonds have on the selectivity of drugs?

They decrease the selectivity due to less specific fitting requirements Signup and view all the answers

What is the primary reason for the varied duration of action between enantiomers of a drug?

Differences in metabolism by drug-metabolizing enzymes Signup and view all the answers

Which statement accurately describes the clinical use of chiral drugs?

Racemic mixtures are commonly used for all chiral drugs. Signup and view all the answers

What is a significant limitation of using racemic mixtures in drug studies?

They complicate the assessment of individual isomer efficacy and safety. Signup and view all the answers

Which inert substance has been noted to have anesthetic effects under certain conditions?

Xenon Signup and view all the answers

What is a structural property of weak bonds in drug-receptor interactions?

They necessitate a highly precise fit for effective binding. Signup and view all the answers

Study Notes

Drug-Receptor Interactions

Hydrophobic bonds are weak bonds important for lipid-soluble drugs interacting with cell membranes and receptor pockets.
Drugs binding through weak bonds are more selective than those with strong bonds, requiring a precise fit to the receptor.
Highly reactive molecules forming covalent bonds are avoided in designing selective, short-acting drugs.
Some substances (e.g., xenon) with negligible chemical reactivity can have significant pharmacologic effects.

Drug Partitioning

The lipid:aqueous partition coefficient influences drug movement between aqueous and lipid environments.
For weak acids and bases, the ability to move between compartments varies with pH due to charge. This is described by the Henderson-Hasselbalch equation.

Drug Permeation Mechanisms

Drugs can diffuse passively through aqueous channels or lipid membranes.
Passive diffusion is often limited by lipid barriers.
Drug permeation can involve carriers, either active transport or facilitated diffusion, which are highly selective, saturable, and inhibitable.
Drugs bound to plasma proteins (e.g., albumin) cannot permeate aqueous pores.
Charged drugs' flux is influenced by electrical fields (membrane potential).
Drugs can be actively transported, engulfed by endocytosis and exocytosed, illustrating complex cell-membrane interactions.

Drug Metabolism and Chirality

Enzyme stereoselectivity affects drug enantiomer duration of action.
Drug transporters can also be stereoselective.
Most clinical studies use racemic mixtures of drugs, resulting in some drugs being inactive or less active.
Some drugs are available as pure enantiomers which decrease adverse effects.

Drug Transport

Special carrier molecules exist for substances vital for cell function, which are too large for passive diffusion.
Carriers like P-glycoprotein (MDR1) and MRP transporters are important in transporting drugs/metabolites into urine and bile.
These transporters can protect tissues (e.g., brain) from drug exposure.
Other transporters (e.g., SLC family) are involved in neurotransmitter uptake.

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Description

This quiz covers key concepts related to antibiotics, focusing on cephalexin, daptomycin, and fosfomycin. It explores their dosage ranges, mechanisms of action, transport systems, and resistance characteristics. Test your knowledge on antibiotic pharmacology and classifications.