antibiotics - a rational approach

Dr. Soulat Hafeez

House Officer

Medical Unit 4

Definition Of Antibiotic

A chemical substance produced by micro organisms, which has the capacity to inhibit the growth of or to kill other micro organisms

Antibiotic TherapyIdeally is determined by isolation and antibiotic susceptibility

of the offending.Usually not available in ER.Abx treatment initiated on clinical diagnosis and likely

organism involved.Early empirical treatment may be lifesaving.

THERAPY BASED ON

1. Site of infection

2. Safety of the agent

3. State of the patient (age, renal, hepatic funtions etc)

4. Cost of the therapy

Appropriate Use of AbxEmploy empirically when there is a

reasonable clinical suspicion of infectionChoose antibiotics active against the most

likely organism(s)Choose antibiotics known to penetrate

involved tissueUse correct doses of antibiotics – don’t

underdose

Appropriate Use of Abx…cont’d

Know when bacterostatic antibiotics are adequate or bacterocidal drugs are required

In serious, potentially life-threatening infections, start broad, then de-escalate after cultures back

Stop antibiotics when infection resolved or when evidence accumulates against existence of infection

Inappropriate Use of AbxWong antibioticWrong dose of right drugUsing a 2nd or 3rd line drug when a first line drug

could still be usedUsing antibiotics in situations when antibiotics are not

indicatedContinuing antibiotics when infection is resolved or

not likelyKeeping coverage broad when cultures reveal a single

organismReacting to culture results by starting antibiotics

without considering the significance of the culture

Common Mistakes in Diagnosing InfectionBase diagnosis on a single positive data point

when other data points are negative React to a positive culture when there is no

clinical evidence of infectionUse serial cultures to determine when

infection has resolved Obtain cultures randomly when clinical

suspicion of infection is low

First Step: Determine WhetherCulture Represents Real PathogenColonizer: Any organism actually present in

or on patient, but does not invade tissue or cause clinical disease

Contaminant: Any organism growing in culture that is not actually present in or on the patient, but came from the environment into the culture medium

Three Examples1. A +ve sputum culture taken from a patient without

fever, leukocytosis, new infiltrate or pulmonary symptoms should be taken as a colonizer

2. A +ve urine culture taken from a patient without dysuria, frequency, and with a small to moderate amount of WBC in the U/A has asymptomatic bacteriuria

3. A +ve wound culture taken from a clean appearing, granulating wound that is not painful, has no purulence in a patient with no fever and a normal WBC, represents a colonizer (rather than a true pathogen) and should not be treated

Sputum CulturePathogen if:Sputum is grossly

purulentPatient is febrileInfiltrates on CXR> 5-10 WBC per hpf< 5-10 epithelial

cells per hpf

Colonizer if:Sputum is scant,

clear or whitePatient is afebrileNo infiltrates on

CXR< 5-10 WBC per hpf> 5-10 epithelial

cells per hpf

Urine CulturePathogen if:> 100,000 cfuIf urinalysis reveals:

> 10 WBCPos. Leuk. EsterasePos. nitriteFew or no epi’s

If patient symptomatic

Contaminant if:10,000 cfu or lessIf urinalysis reveals:

< 10 WBCNeg. Leuk. EsteraseNeg. nitriteMany epi’s

If patient asymptomatic

Drugs Absolutely C/I in Pregnancy ----- “Category X Drugs”Mnemonic “SAFE Mom Takes Really Good

Care”

SULFONAMYIDES, AMINOGLYCOSIDES, FLUOROQUINOLONES, ERYTHROMYCIN.

METRONIDAZOLETETRACYCLINERIBAVIRINGRISEOFULVINCHLORAMPHENICOL

ABX TO AVOID IN CHILDREN UNDER 18

Abx TO AVOID IN LACTATING MOTHERS

ABX TO AVOID IN RENAL FAILURENote, here add drugs that are

contraindicated and drugs that can be administered but with reduced dose.

ABX TO AVOID IN HEPATIC FAILURE.SAME AS FOR RENAL FAILURE.

Meningitis

1. Initiate Empirical Antibiotic Therapy2. All patients with head trauma,

immunocmpromised states, known malignancies, or focal nerological findings (including stupor/coma) should undergo neuroimaging study prior to Lumbar Puncture

3. Obtain CSF D/R sample, if not C/I4. If Bacterial Meningitis is suspected, initiate

empirical antibiotic therapy even prior to Imaging and LP

Principles of Management

Clinical FeaturesFever, Headache, Neck stiffness, and Change

in Mental Status75% of patients have atleast 2 out of these 4

features

Antibiotics for Empirical Treatment of Bacterial Meningitis

Infants < 3 months Ampicillin + Cefotaxime

Adults < 55 years Ceftriaxone + Vancomycin

Adults with Alcoholism or debilitating illness

Ceftriaxone + Vancomycin+ Ampicillin

Hospital acquired, post neuro- surgery, neutropenic patients

Ceftazidime + Vancomycin+ Ampicillin

Pneumonia

Principles of ManagementClassify the pneumonia :

1. Community Acquired, or2. Health-Care Associated

Hospital Acquired Ventilator Associated

Determine severity: CURB 65 Pneumonia Severity Index

Definition of Health-Care Associated Pneumonia Health-Care Associated Pneumonia has any

one of the following features:Hospitalization for > 48 hoursHospitalization for > 2 days in prior 3 monthsAntibiotic therapy in prior 3 monthsChronic dialysisHome wound careContact with a family member who has MDR

infection

Severity of PneumoniaCURB 65

ConfusionUrea > 7 mmolR/R > 30BP : Systolic < 90 ; Diastolic < 60 mmHgAge > 65 years

Score: 0 - 1 --------- Out- patient treatment

2 --------- In patient: Non ICU >2 --------- ICU care

Empirical Antibiotic Treatment of Community Acquired Pneumonia

Outpatients 1. Macrolide ( Clarithro or Azithro)2. Doxycycline3. Respiratory FQ ( Moxi or Gemi or Levo)4. B-Lactam plus Macrolide

In Patients: Non ICU 1. Respiratory FQ ( Moxi or Gemi or Levo)2. B-Lactam plus Macrolide

In Patients : ICU 1. B-Lactam plus Macrolide2. B-Lactam plus FQ

If Pseudomonas is suspected

1. B-Lactam plus FQ2. B-Lactam plus Aminoglycoside3. B-Lactam plus FQ plus Aminoglycoside

If MRSA is suspected Add Linezolid or Vancomycin

Empirical Antibiotic Treatment of Health Care Associated Pneumonia

No risk for MDR Pathogens

1. B – Lactam ( Ceftriaxone 2 gm IV OD) alone

2. FQ alone3. Ertapenem alone

Risk Factors for MDR pathogens

1. B – Lactam ( 3rd / 4th Gen Cephalosporin or Tazocin) plus FQ / Aminoglycoside plus Linezolid/ Vancomycin

Urinary Tract Infections

Principles of ManagementAlways obtain Urine C/S ( except in

uncomplicated cystitis in women)Identify and Correct (if possible)

predisposing factorsRelief of symptoms does not indicate

bacteriologic cureEach course of treatment should be classified

as a Cure or Failure

Treatment Regimens for Bacterial UTI