Comprehensive Antibiotics and Resistance Mechanisms: Key Concepts for Medical Students

Multidrug resistance

Organisms that are resistant to one or more classes of antimicrobial drugs.

Therapeutic drug monitoring

The process of measuring drug levels to ensure efficacy and prevent toxicity.

Minimum inhibitory concentration (MIC)

The lowest concentration of an antibiotic that inhibits the growth of a microorganism.

Time-dependent killing

Antibiotic efficacy that depends on the duration of time the drug concentration is above the MIC.

Concentration-dependent killing

Antibiotic efficacy that depends on the peak concentration of the drug relative to the MIC.

Once-daily dosing vs. multidaily dosing

Comparison of antibiotic administration frequency, where once-daily dosing may improve adherence and reduce toxicity.

Peak and trough blood levels

The highest and lowest concentrations of a drug in the bloodstream, respectively.

Synergistic effects

Enhanced effect of two or more antibiotics used together compared to their individual effects.

Postantibiotic effect (PAE)

The continued suppression of bacterial growth after a short exposure to an antibiotic.

Methicillin-resistant Staphylococcus aureus (MRSA)

A type of bacteria that is resistant to many antibiotics, including methicillin.

Vancomycin-resistant Enterococcus (VRE)

Enterococcus bacteria that have developed resistance to vancomycin.

Extended-spectrum beta-lactamases (ESBLs)

Enzymes produced by some bacteria that confer resistance to a wide range of beta-lactam antibiotics.

Klebsiella pneumoniae carbapenemase (KPC)

An enzyme that makes bacteria resistant to carbapenem antibiotics.

Aminoglycosides

A class of antibiotics that are bactericidal and prevent protein synthesis, primarily effective against gram-negative bacteria.

Gentamicin

An aminoglycoside antibiotic used to treat serious infections caused by gram-negative bacteria.

Neomycin

An aminoglycoside antibiotic used topically and orally to decontaminate the GI tract.

Tobramycin

An aminoglycoside antibiotic used to treat infections caused by certain gram-negative bacteria.

Amikacin

An aminoglycoside antibiotic used to treat infections caused by multidrug-resistant bacteria.

Aminoglycosides: Indications

Used to kill gram-negative bacteria and for certain resistant gram-positive infections.

Aminoglycosides: Adverse Effects

Serious toxicities including nephrotoxicity and ototoxicity, requiring monitoring of drug levels.

Quinolones

A class of antibiotics also known as fluoroquinolones, effective against gram-negative and some gram-positive organisms.

Ciprofloxacin

A fluoroquinolone antibiotic used to treat various infections, including anthrax.

Levofloxacin

A fluoroquinolone antibiotic used for respiratory and urinary tract infections.

Moxifloxacin

A fluoroquinolone antibiotic effective against a range of infections, including respiratory infections.

CNS Adverse Effects

Includes headache, dizziness, insomnia, depression, restlessness, and convulsions.

GI Adverse Effects

Includes nausea, vomiting, diarrhea, constipation, thrush, and increased liver function studies.

Cardiac Adverse Effects

Includes prolonged QT interval.

Integumentary Adverse Effects

Includes rash, pruritus, urticaria, and flushing.

Other Adverse Effects

Includes ruptured tendons, tendonitis, fever, chills, blurred vision, and tinnitus.

Black box warning

Indicates an increased risk of tendonitis and tendon rupture associated with quinolones.

Clindamycin (Cleocin)

Used for chronic bone infections, GU infections, intraabdominal infections, and other serious infections; may cause pseudomembranous colitis.

Linezolid (Zyvox)

A new class of antibiotics (oxazolidinones) used to treat vancomycin-resistant Enterococcus faecium, hospital-acquired, and skin structure infections; may cause hypotension and serotonin syndrome.

Metronidazole (Flagyl)

Used for anaerobic organisms, intraabdominal and gynecologic infections, and protozoal infections; has several drug interactions.

Nitrofurantoin (Macrodantin)

Primarily used for urinary tract infections; use carefully if renal function is impaired; may cause fatal hepatotoxicity.

Quinupristin/Dalfopristin (Synercid)

A 30:70 combination antibiotic used for bacteremia and infections caused by vancomycin-resistant Enterococcus; may cause arthralgias and myalgias.

Vancomycin (Vancocin)

Treatment of choice for MRSA and other gram-positive infections; must monitor blood levels to prevent toxicity; may cause ototoxicity and nephrotoxicity.

Pseudomembranous colitis

Also known as antibiotic-associated colitis, Clostridium difficile diarrhea, or C. difficile infection, it can be caused by clindamycin.

Hypotension

A potential adverse effect of linezolid, especially if taken with selective serotonin reuptake inhibitors (SSRIs).

Serotonin syndrome

A condition that may occur if linezolid is taken with SSRIs.

Tyramine-containing foods

Consumption of these foods can cause reactions when taken with linezolid.

Renal function impairment

Nitrofurantoin should be used carefully in patients with this condition.

Bacteremia

A condition that quinupristin/dalfopristin (Synercid) is used to treat.

MRSA

Methicillin-resistant Staphylococcus aureus, a type of bacteria that vancomycin is effective against.

Red man syndrome

A reaction that may occur with vancomycin, leading to flushing and itching.

Antihistamine

A medication that may be ordered to reduce the effects of Red man syndrome.

neuromuscular blocking effects

Additive effects that may occur in patients receiving neuromuscular blockers while on vancomycin.

Infusion time for vancomycin

Should be infused over 60 minutes to prevent rapid infusion effects.

daptomycin (Cubicin)

The only drug of the new class known as lipopeptides, used to treat complicated skin and soft-tissue infections caused by susceptible gram-positive bacteria.

Mechanism of action of daptomycin

Not completely known, but it binds to gram-positive cells in a calcium-dependent process and disrupts the cell membrane potential.

colistimethate (Coly-Mycin)

A polypeptide antibiotic that disrupts the bacterial membrane of susceptible strains of gram-negative bacteria, commonly referred to as colistin.

Acute respiratory failure

A serious adverse effect that can occur when colistimethate is administered by inhalation.

telavancin (Vibativ)

A lipoglycopeptide indicated for the treatment of skin and skin structure infections caused by susceptible gram-positive organisms.

Adverse effects of telavancin

Include renal toxicity, infusion-related reactions, and QT prolongation.

Nursing implications before therapy

Include assessing drug allergies, hepatic, renal, and cardiac function, and obtaining thorough patient health history.

Cultures before antibiotic therapy

It is essential to obtain cultures from appropriate sites before beginning antibiotic therapy.

Patient instructions for antibiotics

Patients should take antibiotics exactly as prescribed and for the length of time prescribed, without stopping early.

Signs of superinfection

Include fever, perineal itching, cough, lethargy, or any unusual discharge.

Medication safety

Check the name of the medication carefully due to many drugs that sound alike or have similar spellings.

Monitoring therapeutic effects

Includes improvement of signs and symptoms of infection, return to normal vital signs, negative culture and sensitivity tests, and disappearance of fever, lethargy, drainage, and redness.

Monitoring adverse reactions

Essential for ensuring patient safety during antibiotic therapy.

Ciprofloxacin (Cipro)

An antibiotic anticipated to be prescribed for office workers exposed to a potential anthrax threat.

Drug interactions

Each class of antibiotics has specific adverse effects and drug interactions that must be carefully assessed and monitored.

Antibiotics

Medications used to treat bacterial infections.

Empiric Therapy

Treatment of an infection before specific culture information has been reported or obtained.

Definitive Therapy

Antibiotic therapy tailored to treat organism identified with cultures.

Prophylactic Therapy

Treatment with antibiotics to prevent an infection, as in intraabdominal surgery or after trauma.

Therapeutic Response

Decrease in specific signs and symptoms of infection are noted (fever, elevated WBC, redness, inflammation, drainage, pain).

Subtherapeutic Response

Signs and symptoms of infection do not improve.

Superinfection

A secondary infection that occurs during the treatment of a primary infection.

Pseudomembranous Colitis

An inflammation of the colon caused by the bacterium Clostridium difficile.

Resistance

The ability of bacteria to withstand the effects of an antibiotic.

Food-Drug Interactions

Interactions between food and medications that can affect the efficacy of the drug.

Host Factors

Patient-specific factors that can influence the effectiveness of antibiotic therapy.

Allergic Reactions

Adverse immune responses to medications, including antibiotics.

Classes of Antibiotics

Includes sulfonamides, penicillins, cephalosporins, macrolides, quinolones, aminoglycosides, and tetracyclines.

Mechanism of Action

Interference with cell wall synthesis, protein synthesis, DNA replication, or acting as a metabolite to disrupt critical metabolic reactions inside the bacterial cell.

Bactericidal

Antibiotics that kill bacteria.

Bacteriostatic

Antibiotics that inhibit growth of susceptible bacteria, rather than killing them immediately; will eventually lead to bacterial death.

Sulfonamides

One of the first groups of antibiotics, often combined with another antibiotic.

Sulfamethoxazole/Trimethoprim

A combination antibiotic known as Bactrim, Septra, or Co-trimoxazole, commonly used in clinical practice.

Sulfamethoxazole Mechanism of Action

Bacteriostatic action that prevents synthesis of folic acid required for synthesis of purines and nucleic acid.

Sulfamethoxazole Indications

Effective against both gram-positive and gram-negative bacteria, including treatment of UTIs caused by susceptible strains.

Sulfamethoxazole Adverse Effects

Can cause hemolytic and aplastic anemia, agranulocytosis, thrombocytopenia, photosensitivity, and other side effects.

Beta-Lactam Antibiotics

Includes penicillins, cephalosporins, carbapenems, and monobactams.

Penicillins

A class of antibiotics that includes natural penicillins, penicillinase-resistant penicillins, aminopenicillins, and extended-spectrum penicillins.

Penicillins Mechanism of Action

Penicillins enter the bacteria via the cell wall and bind to penicillin-binding protein, disrupting normal cell wall synthesis, leading to cell lysis.

Penicillins Indications

Prevention and treatment of infections caused by susceptible bacteria, including gram-positive bacteria.

Allergic reactions to penicillins

Occur in 0.7% to 4% of treatment courses.

Common allergic reactions to penicillins

Urticaria, pruritus, angioedema.

Increased allergy risk

Those allergic to penicillins have an increased risk of allergy to other beta-lactam antibiotics.

Cephalosporins contraindication

Only those patients with a history of throat swelling or hives from penicillin should not receive cephalosporins.

Common adverse effects of penicillins

Nausea, vomiting, diarrhea, abdominal pain.

Penicillins interactions

Many interactions including NSAIDs, oral contraceptives, warfarin, and others.

Clavulanic acid purpose in Augmentin

B. It inhibits the action of the enzymes produced by beta-lactamase-producing bacteria.

First generation cephalosporins

Good gram-positive coverage and poor gram-negative coverage.

Examples of first generation cephalosporins

Cefadroxil (Duricef, Ultracef), Cephradine (Velosef), Cefazolin (Ancef), Cephalexin (Keflex).

First generation cephalosporins usage

Used for surgical prophylaxis and for susceptible staphylococcal infections.

Second generation cephalosporins

Good gram-positive coverage and better gram-negative coverage than first generation.

Examples of second generation cephalosporins

Cefaclor (Ceclor), Cefprozil (Cefzil), Cefoxitin (Mefoxin), Cefuroxime (Zinacef).

Second generation cephalosporins usage

Used prophylactically for abdominal or colorectal surgeries and also kills anaerobes.