61 Questions
Which enzyme is inhibited by fluoroquinolones, leading to their antimicrobial activity?
DNA gyrase
In the context of antimetabolites, what reactive free radicals are formed by the prodrug Metronidazole that are directly toxic to DNA?
Hydroxyl radicals
What is the first-line use of fluoroquinolones like levofloxacin and moxifloxacin?
Osteomyelitis
What condition poses a higher risk of anemia in patients taking Sulfamethoxazole + Trimethoprim (SMX/TMP)?
G6PD deficiency
Which fluoroquinolone is the only active agent against anaerobic infections on its own?
Moxifloxacin
Which type of killing is associated with the statement 'the LONGER the antibiotic concentration stays above MIC, the greater the extent of killing'?
Time dependent killing
Which of the following antibiotics is an example of concentration dependent killing according to the text?
Sulfamethoxazole
What is the mechanism of action of Sulfamethoxazole + Trimethoprim (SMX/TMP)?
Inhibition of folic acid synthesis
What distinguishes Empiric Therapy from Targeted Therapy?
Knowledge of the causative organism
Which unique toxicity is associated with Sulfamethoxazole + Trimethoprim (SMX/TMP)?
Hemolysis
What is the advantage of using Empiric Therapy according to the text?
Rapid initiation of treatment
What is a common indication for Sulfamethoxazole + Trimethoprim (SMX/TMP)?
Urinary tract infections
What does a Loading Dose (LD) refer to in antimicrobial pharmacokinetics?
The amount needed to reach therapeutic levels at once
Which of the following is not a known toxicity associated with SMX/TMP?
Meningitis
What is the mechanism of action of Sulfamethoxazole alone?
Inhibition of folic acid synthesis
What is the significance of the Minimum Inhibitory Concentration (MIC) of an antibiotic?
It inhibits visible bacterial growth
Which statement accurately describes the Minimum Bacteriostatic Concentration (MBC) of an antibiotic?
It results in a 1,000-fold reduction in bacterial density
If the MBC:MIC ratio is 2, how is the antibiotic classified in terms of its effect on the bacteria?
Bactericidal
In terms of antibiotic action, what does it mean if an antibiotic is considered bacteriostatic?
It slows down the growth of bacteria
What does it mean when it is said that increasing the concentration of a bacteriostatic antibiotic high enough will turn it into bactericidal?
The antibiotic will start killing bacteria
How do Sulfamethoxazole and Trimethoprim (SMX/TMP) work synergistically to prevent bacterial DNA synthesis?
Sulfamethoxazole competes with PABA for DHPS, while Trimethoprim competes with folate for DHFR
Which enzyme is targeted by Sulfamethoxazole in bacterial DNA synthesis?
Dihydropteroate synthase (DHPS)
What type of infections are Sulfamethoxazole + Trimethoprim (SMX/TMP) NOT reliably active against?
Pseudomonas infections
Which of the following is an indication for the use of Sulfamethoxazole + Trimethoprim (SMX/TMP)?
Active against Gram-positive and Gram-negative infections
How does Trimethoprim work to inhibit bacterial DNA synthesis in combination with Sulfamethoxazole?
By competing with folate for DHFR
Which class of antibiotic inhibitors targets key steps in nucleic acid synthesis during the replication cycle?
Antimetabolites
What is the mechanism of action of Sulfamethoxazole (SMX) in bacterial DNA synthesis?
Competes with PABA for DHPS
Which antibiotic combination has no reliable coverage against Pseudomonas infections?
Trimethoprim + Sulfamethoxazole (TMP+SMX)
What is the primary target of Trimethoprim (TMP) in bacterial DNA synthesis when combined with Sulfamethoxazole?
DHFR
What distinguishes Minimum Inhibitory Concentration (MIC) from Minimum Bactericidal Concentration (MBC)?
MIC indicates the maximum concentration before bacterial growth; MBC indicates the minimum concentration for killing.
In the context of antibiotics, what does it mean if an antibiotic is considered bacteriostatic?
It only prevents bacterial growth without killing them.
Which antibiotic is no longer used first line to treat uncomplicated C. diff infection?
Metronidazole
What is the unique toxicity associated with Nitrofurantoin use?
Pulmonary fibrosis
What unique toxicity is associated with Mycobacterial Inhibitors?
Hepatotoxicity
Which antibiotic is a DNA synthesis inhibitor and can cause discoloration of body fluids?
Dapsone
In terms of antibiotic action, what does it mean if an antibiotic is considered bacteriostatic?
It prevents bacterial growth without killing them directly
What is the specific combination drug for latent tuberculosis?
Rifampin + Isoniazid
Which antibiotic should be coadministered with vitamin B6 (pyridoxine) to prevent neuropathy?
Dapsone
What is the role of Minimum Inhibitory Concentration (MIC) in determining antibiotic efficacy?
It shows the lowest concentration of antibiotic that inhibits bacterial growth.
What distinguishes concentration dependent killing from time dependent killing of antibiotics?
Concentration dependent killing is associated with higher antibiotic concentrations above MIC, while time dependent killing focuses on longer durations above MIC
Which antibiotics are examples of concentration dependent killing according to the text?
Fluoroquinolones
What is the primary advantage of using targeted therapy over empiric therapy?
Targeted therapy minimizes the risk of resistance development
What is the significance of the Minimum Inhibitory Concentration (MIC) in determining antibiotic efficacy?
MIC indicates the minimum concentration at which an antibiotic inhibits bacterial growth
Which enzyme is targeted by fluoroquinolones to exert their antimicrobial activity?
Topoisomerase
What is the primary difference between empiric therapy and targeted therapy?
Empiric therapy uses broad-spectrum antibiotics, while targeted therapy uses narrow-spectrum antibiotics
What does the term Loading Dose (LD) refer to in antimicrobial pharmacokinetics?
The initial high dose used to rapidly achieve therapeutic levels of the drug
Which statement accurately describes the Minimum Bactericidal Concentration (MBC) of an antibiotic?
MBC is the maximum concentration at which an antibiotic kills all bacteria in a sample
What is the significance of the Minimum Bactericidal Concentration (MBC) of an antibiotic?
It represents an antibiotic that kills bacteria
What distinguishes bacteriostatic antibiotics from bactericidal antibiotics?
Bactericidal antibiotics kill bacteria
Which type of antibiotic action is associated with an MBC:MIC ratio greater than 4?
Bacteriostatic
In terms of antibiotic classification based on MBC:MIC ratio, what does a ratio less than or equal to 4 indicate?
Bactericidal action
What happens theoretically when increasing the concentration of a bacteriostatic antibiotic high enough?
It turns into a bactericidal antibiotic
Which antibiotic action is associated with an MBC:MIC ratio greater than 4 in antimicrobial testing?
Inhibiting bacterial growth
Which antibiotic is a prodrug that forms reactive free radicals directly toxic to bacterial DNA?
Metronidazole
In the context of antibiotics, what does the Minimum Inhibitory Concentration (MIC) measure?
Concentration above which bacterial growth is inhibited
What is the unique toxicity associated with fluoroquinolones like ciprofloxacin and levofloxacin?
Tendon rupture
Which antibiotic is used first-line in osteomyelitis if the bacteria is sensitive to it?
Ciprofloxacin
What does the Minimum Bactericidal Concentration (MBC) of an antibiotic represent?
Concentration below which bacteria are killed
Which antibiotic is mainly active against Gram-negative infections and is used topically as ear drops for otic infections?
Ofloxacin
What is the mechanism of action for nitrofurantoin in inhibiting bacterial growth?
Mixed DNA and ribosomal inhibition
Which antibiotic forms reactive free radicals that are toxic to DNA, functioning as a mycobacterial inhibitor?
Metronidazole
Study Notes
Bacterial DNA Synthesis Inhibitors
- Inhibit bacteria by targeting key steps in nucleic acid synthesis during the replication cycle
- Subdivided into two classes: Antimetabolites (pseudo-analogs) and Direct enzyme inhibitors blocking synthesis of DNA
Antimetabolites
- Sulfamethoxazole + Trimethoprim (SMX/TMP)
- Sulfamethoxazole is a structural analog of para-amino benzoic acid (PABA)
- Competes with PABA for dihydropteroate synthase (DHPS) to stop DNA synthesis
- Trimethoprim is a structural analog of folate
- Competes with folate for dihydrofolate reductase (DHFR) to stop DNA synthesis
- SMX+TMP work synergistically to prevent bacterial DNA synthesis
- Active against Gram positive and Gram negative infections, including MRSA infections
- No reliable pseudomonas coverage
- First line option for E.coli (e.g. urinary tract infections), pneumocystis pneumonia (PCP), and toxoplasmosis in immunocompromised patients (e.g. AIDS)
Direct Enzyme Inhibitors
- Fluoroquinolones (FQ)
- Inhibit bacterial topoisomerase II (aka DNA gyrase)
- Mainly active against Gram negative infections
- Used FIRST LINE in osteomyelitis (only if the bacteria is sensitive)
- "Respiratory FQ" are levofloxacin and moxifloxacin
- Ciprofloxacin is an option to treat urinary tract infections
- Ofloxacin is used topically as ear drops for otic infections
- Only agent active against MRSA is delafloxacin
- Only agent active against anaerobic infection on its own is moxifloxacin
- Metronidazole
- Prodrug, forms reactive free radicals that are directly toxic to DNA
- Mainly active against anaerobic infections (below the diaphragm)
- First line treatment for trichomonas vaginalis infection and bacterial vaginosis (BV)
- Used in combination with FQ to treat intra-abdominal infections (e.g. fistulas in patients with inflammatory bowel disease)
- Nitrofurantoin
- Broad spectrum, active against Gram positive and Gram negative organisms
- Used primarily in urinary tract infections
- Unique toxicity: Pulmonary fibrosis
Mycobacterial Inhibitors
- Rifapentine+isoniazid is for latent TB
- Dapsone is for leprosy (in combo with rifampin)
- All of them cause hepatotoxicity
- Unique toxicity: DNA synthesis inhibitor, Induction of hepatic enzymes, Discoloration of body fluids
Mechanisms of Action
- Isoniazid: Mycolic acid cell wall inhibitor
- Pyrazinamide: Unknown
- Ethambutol: Mycolic acid cell wall inhibitor
- Rifampin/Rifapentine: Rifampin, Isoniazid, Pyrazinamide, and Ethambutol (RIPE) are for active tuberculosis (TB)
Antibiotic Summary
- Concentration dependent killing: The HIGHER the antibiotic concentration is above the MIC, the greater the extent of killing
- Time dependent killing: The LONGER the antibiotic concentration stays above MIC, the greater the extent of killing
- Bacteriostatic: An antibiotic that slows down the growth of bacteria
- Bactericidal: An antibiotic that kills bacteria
- Empiric Tx: Broad spectrum antibiotic used until lab data comes back
- Targeted Tx: Narrow spectrum antibiotic selected based on known identity and sensitivity of the causative organism
Basics of Antimicrobial Pharmacokinetics
- Loading dose (LD): The amount of drug needed to achieve a therapeutic level in the body
- Minimum Inhibitory Concentration (MIC): The concentration of antibiotic that inhibits visible bacterial growth at 24 hours
- Minimum Bactericidal Concentration (MBC): The concentration of antibiotic that results in a 1,000-fold reduction in bacterial density at 24 hours
Test your knowledge on key information about Metronidazole and Nitrofurantoin, including their uses, indications, and toxicities. Explore their roles in treating different infections and understand their clinical significance.
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