Antibiotics and Drug Interactions Quiz

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Questions and Answers

What was the mean increase in theophylline AUC due to oral administration with theophylline?

113%

45% (correct)

20%

30%

Which antibiotic is noted for its ability to decrease theophylline clearance?

Ciprofloxacin

Moxifloxacin

Levofloxacin

Erythromycin (correct)

What is one of the serious manifestations of theophylline toxicity?

Dry skin

Dizziness

Nausea/vomiting (correct)

Blurred vision

Which of the following quinolones has no significant interaction with theophylline disposition?

Levofloxacin Signup and view all the answers

What percentage of theophylline clearance reduction has been observed in several studies?

30% to 113% Signup and view all the answers

What condition can occur in severe cases of theophylline toxicity?

Metabolic acidosis Signup and view all the answers

What is required when adding agents that interact with theophylline therapy?

Pharmacokinetic monitoring Signup and view all the answers

Which agent has not been shown to have a significant effect on theophylline disposition?

Azithromycin Signup and view all the answers

What should be closely monitored during antibiotic therapy when a patient is on warfarin?

INR levels Signup and view all the answers

Which cephalosporin is noted for its potential to potentiate warfarin?

Cefotetan Signup and view all the answers

What clinical condition may gradually appear due to the depletion of vitamin K stores?

Hypoprothrombinemia Signup and view all the answers

What is the proposed mechanism through which infections may amplify the effects of warfarin?

Inhibition of hepatic drug metabolism Signup and view all the answers

Which antibiotic was mentioned as potentially resulting in clinically significant hypoprothrombinemia in a patient on warfarin?

Amoxicillin-clavulanate Signup and view all the answers

What is a potential impact of adding antibiotics to a medical regimen involving narrow-therapeutic-window medications?

Both potentiation and antagonism of the clinical effects Signup and view all the answers

Which medication is NOT mentioned as having interactions with antibiotics?

Insulin Signup and view all the answers

In addition to influencing anticoagulation, what other factors may lead to significant hypoprothrombinemia with cefotetan?

Malnutrition and debility Signup and view all the answers

What is the INR level that indicated hypoprothrombinemia in the reported case?

6.2 Signup and view all the answers

What is the significance of the cytochrome P450 system in relation to warfarin?

It metabolizes warfarin Signup and view all the answers

What pharmacological effect does the N-methylthiotetrazole side chain of certain cephalosporins exert?

Inhibits vitamin K metabolism Signup and view all the answers

What is the role of awareness in managing drug interactions?

It helps identify and monitor potential drug interactions. Signup and view all the answers

Which statement about narrow-therapeutic-window medications is correct?

They require careful monitoring due to potential side effects. Signup and view all the answers

What is one of the purposes of understanding drug-drug interactions?

To prevent or minimize unwanted iatrogenic effects. Signup and view all the answers

What does the abbreviation INR stand for in relation to drug interactions?

International Normalized Ratio Signup and view all the answers

Which of the following medications is a calcineurin inhibitor mentioned in the content?

Tacrolimus Signup and view all the answers

What effect do azole antifungals have on tacrolimus requirements in pediatric heart/lung transplant patients?

Decrease requirements markedly Signup and view all the answers

Which cephalosporin is mentioned as having effects on hemostasis in the literature?

Cefotetan Signup and view all the answers

How long does it take for the effects of CSA and tacrolimus to plateau after starting treatment with azoles?

5-7 days Signup and view all the answers

What is the proposed mechanism of interaction between azole antifungals and other medications like CBZ?

Inhibition of 2C and 3A4 isozymes Signup and view all the answers

What percentage decrease in requirements is recommended upon initiation of reversible interactions with azoles?

50% Signup and view all the answers

What is the approximate increase in CBZ levels observed after 10 days of fluconazole administration?

From 6 mcg/mL to 18 mcg/mL Signup and view all the answers

What should be monitored when azoles are started to manage drug interactions effectively?

Serum concentrations of CSA and tacrolimus Signup and view all the answers

What effect does erythromycin have when used in combination with azole antifungals?

It potentiates the effects of azoles Signup and view all the answers

What effect does ciprofloxacin have on warfarin metabolism?

Decreased metabolism of warfarin Signup and view all the answers

Which mechanism is primarily responsible for the interaction between erythromycin and theophylline?

Inhibition of theophylline metabolism Signup and view all the answers

What is the potential consequence of the interaction between metronidazole and phenytoin?

Increased risk of phenytoin toxicity Signup and view all the answers

Which of the following antibiotics is known to decrease metabolism of cyclosporine?

Azole antifungals Signup and view all the answers

How should warfarin therapy be managed when starting antibiotic treatment with clarithromycin?

Decrease warfarin dosage Signup and view all the answers

What common side effects could occur due to phenytoin toxicity influenced by sulfamethoxazole/trimethoprim?

Tremors and dizziness Signup and view all the answers

What should be monitored closely during and after treatment with azole antifungals in patients on tacrolimus?

Serum tacrolimus concentrations Signup and view all the answers

Which of the following antibiotics has no significant interaction with warfarin?

Doxycycline Signup and view all the answers

If a patient on phenytoin starts treatment with azole antifungals, what might be necessary?

Monitor serum phenytoin levels Signup and view all the answers

What type of interactions do macrolide antibiotics have with warfarin?

Decrease warfarin metabolism Signup and view all the answers

Which patient management action is recommended when prescribing ciprofloxacin alongside warfarin?

Increase INR testing frequency Signup and view all the answers

What is the potential risk when both clarithromycin and theophylline are used together?

Increased theophylline toxicity Signup and view all the answers

What effect do azole antifungals have on the metabolism of tacrolimus?

Decrease metabolism Signup and view all the answers

Which of the following is a consequence of the interaction between sulfamethoxazole/trimethoprim and warfarin?

Increased bleeding risk Signup and view all the answers

Study Notes

### Introduction

Clinically significant drug-drug interactions may occur between antibiotics and medications with narrow therapeutic windows.
This includes medications like warfarin, phenytoin, theophylline, calcineurin inhibitors, and carbamazepine.

Warfarin

Several antibiotics interfere with warfarin metabolism through the cytochrome P450 system.
Warfarin is metabolized by CYP 1A2, 2C9, and 3A4.
Warfarin potentiation can also occur due to the inhibition of vitamin K epoxide reductase by certain cephalosporins containing the N-methylthiotetrazole side chain.
Cefotetan is the only remaining cephalosporin with this side chain in general use.
Infections themselves can potentiate warfarin by inhibiting CYP P450 systems through interferon release.

Phenytoin

Phenytoin metabolism can be inhibited by metronidazole and sulfamethoxazole/trimethoprim through their effects on CYP 2C8/9.
Azole antifungals can also inhibit phenytoin metabolism through their interaction with CYP 2C8/9 and 2C19.

Theophylline

Erythromycin and clarithromycin decrease theophylline clearance by inhibiting CYP 1A2 leading to theophylline toxicity.
Ciprofloxacin can also interact with theophylline but the mechanism is unclear.

Calcineurin Inhibitors

Azole antifungals inhibit cyclosporine and tacrolimus metabolism through their interaction with CYP 3A4.
Clarithromycin and erythromycin can also inhibit cyclosporine and tacrolimus metabolism through their effect on CYP 3A4.
Quinupristin/dalfopristin can also inhibit cyclosporine and tacrolimus metabolism.

Important Considerations

Drug interaction onset with warfarin may require several days to weeks.
Phenytoin interactions may be delayed by 10 to 14 days or longer.
Effects of azoles on calcineurin inhibitors may take 5-7 days to plateau.
Careful monitoring of therapeutic drug levels and dosage adjustments are crucial for all interactions.

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Description

Test your knowledge about clinically significant drug-drug interactions involving antibiotics and medications with narrow therapeutic windows. This quiz covers key points about how certain antibiotics affect the metabolism of warfarin and phenytoin, along with implications for patient care.