antibiotic lecture 5 meds

8/4/2019 Antibiotic Lecture 5 Meds

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Introduction to Antibiotic Therapy

Catherine Fleming, M.D.


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Reasons to initiate antibiotics

Definite infection

Probable diagnosis of infection

Clinically ill patient (sepsis)

fever, hypotension, tachycardia

neutropenia


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Empiric vs definitive therapy

Empiric treatment:

antibiotics directed against an unknown pathogen

and/or suspected infection

Definitive treatment:

antibiotics directed against a known pathogen


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Principals of antibiotic Rx

Step 1What is the infection?

Establish:

1. Infection vs non infectious illness

2. Suspected site

Use history/physical exam and investig


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Principals of antibiotic Rx

Step 2What are the most likely microorganisms?

- Probable bacterial pathogens for thisinfection

- Likelihood of resistant bacteria:

Community vs Hospital acquired(nosocomial)

Host factors


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Host Factors that Affect Treatment

- Risk for resistant or unusual floraImmunosuppression

Nosocomial infection

Travel

-Are any antibiotics contraindicated or require doadjustment

Allergies, Age, Renal function

Liver disease, Pregnancy, lactationDrug interactions


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Antibiotic Properties

Spectrum of activity

Bactericidal or bacteriostatic

Tissue PenetrationSide effects

Interactions

Dosing regimen


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Host factors: age

Neonate: decreased renal function

Children: avoid drugs that affect

bone/cartilage formation (tetracycline,quinolones)

Elderly: decreased renal function, hearing

impairment, poor absorption, increased AE


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Host factors: renal function

Antibiotics may cause renal failure

tubular dysfunction-aminoglycosides

acute interstitial nephritis- beta lactams

Dose adjustments may be required

Suspect decreased creatinine clearance

in diabetes, elderly


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Allergies

10% population have Penicillin allergy

rash can get cephalosporinsAnaphylaxis/hives no cephalosporins


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Host factors: liver disease

Hepatotoxicity: TB meds (INH),

sulfa drugs (bactrim), tetracyclines

Altered dosing for hepatically excreted drugs

Suspect inapparent disease amongalcoholics, hepatitis B & C infection


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Drug Interactions

Coumadin erythromycin, quinolone Theophylline macrolides, ciprofloxacin Phenytoin fluconazole rifampin OCP Ampicillin, rifampin Alcohol disulfiram-like metronidazole

Seldane macrolides, ketoconazole


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Drug factors:

Spectrum of activity

Gram-positive versus Gram-negative

Aerobic vs anaerobic

Narrow spectrum versus extended spectrum

Resistant to bacterial modifying enzymes:

- beta lactamase

- aminoglycoside phosphotransferase (aph)


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Penetration to site of infection

Bone: quinolones, clindamycin

CNS: 3rd generation cephalosporins, newermacrolides, metronidazole, sulfa

Kidney: all renally excreted drugs

concentrate in the kidney


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Additional antibiotic factors

influencing choice Side effect profile;

Imipenim-seizures

Septrin-bone marrow suppression

Formulation; Erythromycin IV-CHF

Septrin

Dosing Schedule;

Erythromycin qid vs Azithromycin qdNafcillan Q4 hours vs Vancomycin bid

Interactions


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Choosing the correct antibiotic

Site of infection

Likely pathogens

Host factors

Antibiotic properties

Hospital Formulary

Cost


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Case 1A

A 24 year old woman presents with pain and

burning with urination, urinary hesitancy,

urgency and frequency. She is febrile to

102F, nauseated, vomiting, and dehydrated.

On examination there is right costovertebral

angle (CVA) tenderness.


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Case 1A

She has a history of a urinary tract infection 3

years prior.

There is no history of recent antibiotic use.

She sexually active, not using birth control.

She is allergic to penicillin


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Case 1A

What is the infection: pyelonephritis

What are the probable organisms:

Gram (-): E coli, Klebsiella Gram (+):Enterococci, Staph sapprophyticus

Anaerobes:

antibiotic resistance unlikely


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Case 1A

What host factors affect treatment ?

cannot take PO, and needs IV Rx

sexually active ?? pregnant

penicillin allergic, although need to determine

what the allergy is


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Case 1A

What drug factors affect treatment ?

Appropriate spectrum activity:

Appropriate renal penetration:

hospital has 3 antibiotics against E.coli: gentamicin: anaminoglycoside

ampicillin: a penicillin

ciprofloxacin: a quinolone


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Aminoglycosides

(gentamicin)

Mode of action: bind to 30 S ribosome, bacteriocidal

Spectrum of activity: aerobic Gram (-), synergy for

Gram (+), no anaerobes

Metabolism: excreted unchanged via kidney

Distribution: poor tissue penetration

Side effects: renal and ototoxic

neuromuscular paralysis with succinylcholine Interactions:other nephro toxic drugs (furosemide)


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Quinolones

(ciprofloxacin)

Mode of action: DNA gyrase inhibition, bacteriocidal

Spectrum of activity: Gram (-), moderate Gram (+).

No anaerobes Distribution: good penetration eg bone, prostate

Side effects: GI upset, photosensitivity, ? cartilage

erosion in young

Interactions: Coumadin, theophylline

Restricted - resistance


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Penicillins (ampicillin)

Mode of action: blocks cell wall synthesis

Spectrum: streptococci, E coli, Enterococcus, oral

anaerobes

Distribution: extracellular, CNS

Side effects:

Allergic: rash, anaphylaxis, interstitial nephritis

CNS: seizures

GI: diarrhea


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Case 1A

Antibiotic choice

Penicillin allergy: Nausea ampicillin

Pregnancy test: (-) quinolone

No renal failure gentamicin

Vomiting IV

Of these: gent and amp preferable

Quinolones restricted due to resistance


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Case 1B

Your next patient is a 25 year old woman with a

similar history except that she is currently

taking amoxicillin for an ear infection(interchangeable with ampicillin)

The hospital has >25% of E coli resistant toampicillin


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Case 1B

Choose either gentamicin or ciprofloxacin IV

If she is discharged on oral ciprofloxacin,

counsel her against suntanning (or chooseanother antibiotic)


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Case 1A

The first woman was treated with ampicillin

Two days into treatment urine cultures yield Ecoli resistant to ampicillin, but sensitive to

gentamicin and ciprofloxacin

What do you do ?


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Case 2

An 85 year old man admitted 3 days ago after

a fall is transferred to the medical service with

fever and confusion. He is ill appearing with a

fever of 103.6F and BP 120/80.

Exam: enlarged prostate, indwelling foley

Investigations: WBC 25k CXR clear.


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Case 2

Likely infection: Pyelonephritis

Likely pathogens:

E coli, Klebsiella, enterococci, hospital gram

negatives

Nosocomial infection increased chance of

resistant organisms


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Case 2

What host factors affect treatment?

Advanced age chance of baseline renal

dysfunction (need to calculate Creatinineclearance)

Medication interactions


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Case 2

Choice of antibiotic:

Gentamicin relatively contraindicated

because of potential for renal dysfunctionAmpicillin poor choice (for E coli or

Klebsiella) because of risk of resistance

ciprofloxacin

Case 3


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Case 3

56 year old alcoholic

Admitted with fevers, cough and mental status changes24 hours

Smoker, no IDU

Examination: unkempt, thin

Creps rt lung, bronchial breathing through out

WCC 25k, cr 90, alt 40 ast 90, bili 25, alb 40, INR 1.0

HIV ()


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Community acquired pneumonia


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Likely organisms



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Likely organisms

Pneumococcus

H influenza

Legionella

Gram negatives

Klebsiella

E coli

Staph aureus

Anaerobes TB

Antibiotic choice


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Antibiotic choice

Normal renal function

No allergies

Liver function?

No other meds

Choice?

Augmentin + klacid

Cefotaxime + Klacid

Cefotaxime + Moxifloxacin


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antibiotic lecture 5 meds

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