Here are the key steps I would follow in selecting an appropriate antibiotic for a patient: 1. Determine if antibiotic treatment is truly necessary based on diagnosis, severity of symptoms, risk factors for complications, etc. Not all infections require antibiotics. 2. Consider the most likely causative organism(s) based on infection type, patient factors, local resistance patterns. Select an antibiotic with appropriate spectrum of activity. 3. Check for any antibiotic allergies and select an agent from a different class if needed. 4. Adjust for special populations like pregnancy, renal dysfunction, liver disease - may need to avoid certain drugs, lower doses, or extend intervals. 5. Determine dosage, administration route, frequency and treatment

1. Dr. Lokesh
Garg
M.B.B.S. M.D.

2.  One of the most commonly used group of drugs.
 A medical doctor has to know the definite clinical pharmacology
of antibiotics, how to select & use them rationally.
- Avoid adverse effects on the patient
- Avoid emergence of antibiotic resistance
- Avoid unnecessary increases in the cost of health care

3.  Definition
Antibiotics are substances that kill or inhibit the growth
of micro-organisms.
 Bacteriostatic
Bactericidal

4. Based on their mechanism of
action, antibiotics can be divided
into the following classes:
 Inhibitors of Cell Wall synthesis
 Inhibitors of Protein synthesis
 Inhibitors of Nucleic Acid synthesis

5. This class includes:
 Penicillin
 Cephalosporin
 Carbapenems
 Monobactams
 Vancomycin
 Beta lactamase inhibitors
B – lactam
antibiotics

6. Category Parenteral Agents Oral Agents
Natural Penicillins Penicillin G Penicillin V
Antistaphylococcal
penicillins
Nafcillin, oxacillin Dicloxacillin
Aminopenicillins Ampicillin Amoxicillin and
Ampicillin
Aminopenicillin + β-
lactamase inhibitor
Ampicillin-sulbactam Amoxicillin-
clavulanate
Extended-spectrum
penicillin
Piperacillin, ticaricillin Carbenicillin
Extended-spectrum
penicillin + β-lactamase
inhibitor
Piperacillin-tazobactam,
ticaricillin-clavulanate
THE PENICILLINS

7. Class Examples Routes of
administration
First generation Cephalexin/cefadroxil
Cefazolin
Oral
i.v.
Second
generation
Cefuroxime
Cefoxitin
Oral/ i.v.
Third generation Cefixime
Ceftriaxone/cefotaxim
Ceftazidime
Oral
i.v.
i.v.
Fourth
generation
Cefipime i.v.

8.  Adverse Effects
 Allergic reactions: itch, rash,
fever, angioedema, rarely
anaphylactic reaction
 GI upset and diarrhoea
 Interstitial nephritis and
increased renal damage in
combination with
aminoglycosides
Pharmacokinetics
 Bactericidal
 Safe in pregnancy
 Dosage needs to be
reduced in cases of
impaired renal function.

9. This class includes:-
 Macrolides- erythromycin, clarithromycin, azithromycin
 Lincosamides- clindamycin
 Aminoglycosides- gentamicin, tobramycin, amikacin,
netilmicin,neomycin, streptomycin.
 Tetracyclines- tetracycline, doxycycline,minocycline
 Chloramphenicol

10. Pharmacokinetics:
 Bacteriostatic
 Dose adjustment in renal
failure is not necessary
Adverse Effects :
 GI upset
 Cholestatic jaundice
 Prolongation of QT interval
(erythromycin)
 Theophylline, oral anticoagulants
cannot be administered
simultaneously

11. PharmacokineticsPharmacokinetics
 Bectericidal
 Negligible oral absorption
 Dose adjustment is
critical in renal
impairment
Adverse Effects
 Ototoxic (permanent)
Avoid concurrent use of
other ototoxics drugs for eg.
Lasix , minocycline
 Nephrotoxic ( reversible):
use cautiously with other
nephrotoxic drugs

12. Pharmacokinetics
Bacteriostatic
Best oral absorption in fasting
state
 Adverse Effects
 Contraindicated in renal failure
(except doxycycline and minocycline)
 Nausea, diarrhoea
 Binds to metallic ions in bones and teeth (to
be avoided in children and
in pregnancy)
 Phototoxic skin reactions

13. This group includesThis group includes ::
 Sulphonamides: Sulfamethoxazole, sulfadoxine
 Trimethoprim
 Quinolones: Ciprofloxacin, levofloxacin, pefloxacin, ofloxacin, norfloxacin,
gatifloxacin, moxifloxacin, sparfloxacin
 Rifampicin
Azoles: This group includes-
 Antibacterial- Metronidazole, secnidazole, tinidazole,
 Antihelminth- Albendazole, Mebendazole, thiabendazole

14. Pharmacokinetics
 Bactericidal
 Well absorbed orally with
good bioavailability
 Dose reduction necessary in
renal failure
Adverse Effects
 Fatal marrow dysplasia and
haemolysis in G6PD
deficiency
 Skin and mucocutaneous
reactions: Stevens- Johnson
syndrome
 Contraindicated in
pregnancy

15. Pharmacokinetics
 Bectericidal
 Well absorbed after oral
administration
 Dose adjustment required
in renal impairment
(except moxifloxacin and trovafloxacin)
 These two drugs are
contraindicated in hepatic
Adverse Effects
 GI side effects
 CNS effects such as restlessness,
headache, insomnia, confusion and
seizures in the elderly
 Rare skin reactions
 Should be avoided in pregnancy
 Not routinely recommended for use in
patients under 18 years
of age

16. Pharmacokinetics
 Almost completely
absorbed after oral
administration (60% after
rectal administration).
Adverse Effects
 Metallic taste
 Severe vomiting if taken with
alcohol (disulfiram like
syndrome )

19.  CNS: Meningitis, brain abscess etc
 Respiratory: URTI, Pneumonia, Lung abscess, Bronchiectasis
 CVS: Acute rheumatic fever, Infective endocarditis
 GIT and HBS: Cholera, Bacillary dysentery, Enteric fever,
gastroenteritis, peritonitis,liver abscess
 Genitourinary: UTI, pyelonephritis, STDs
 Skin : Cellulitis necrotizing fascitis
 Musculoskeletal: Osteomyelitis, Septic arthritis
 Mycobacterial Infections: Tuberculosis, Leprosy
 Chlamydial Infections
 Systemic Infections: Sepsis syndrome

21.  62 year old male presents to your clinic with c/o: Cough with
expectoration x 4days
◦ Intermittent fever, measured to 100.8
◦ Chest pain – Rt side
 PMHx
◦ Healthy
o No H/O hospitalization in recent past
o not on any medication
 Drink socially , non smoker

22.  Exam
VS – temp 100.3, P 92, RR 18, Spo2 - 96% on room air, BP
123/75
HEENT – normal
Neck – normal w/o palpable LN or TMG
Lungs – Bronchial breath sound in I/S , I/A on Rt side, clear at
bases,
CV – normal
Legs – no edema

25. Case 1

26.  Community –acquired Pneumonia (CAP)
 Recent onset of
- Fever
- Productive cough
- TLC
- CXR
 Why CAP
- Healthy adult with no H/O hospitalization in recent past
& was not taking any antibiotics

28. Common Outpatient Bacterial Etiologies

30. AntibioticsAntibiotics
 Oral macrolide
 Erythromycin
 Azithromycin
 Clarithromycin
This patient’s pneumonia is mild
Previously healthy
No antibiotics in past 3 months

31.  In patients who are older, have comorbid illnesses
Levofloxacin Moxifloxacin
 In patients treated with antibiotics within the last 90 days.
 Respiratory quinolones
Moxifloxacin
Levofloxacin
Gemifloxacin
or
 B- lactam
Amoxicillin + Clavunate
Cefuroxime

33.  Beta-lactam + macrolide
Ceftriaxone or cefotaxime
Erythromycin, azithromycin, or clarithromycin
OR
 Fluoroquinolone with antistreptococcal activity
Levofloxacin or moxifloxacin

40. Trimethoprim/sulfamethoxizole x 3 days
women with risk factors, complicated UTI
Fluoroquinolone x 3 days:
 Ciprofloxacin
 Norfloxacin
 Ofloxacin
Nitrofurantoin x 7 days

41.  Initial drug selections:
Fluoroquinolones
Ciprofloxacin
Levofloxacin
Cephalosorin

Ceftriaxone

Cefotaxime
+ Amikacin

42.  57 years male painful rash on his right leg. 5 days
ago he developed a blister on his foot after wearing a
new pair of shoes.
c/o fever with chills
 PMHx – COPD, high cholesterol
Social – stopped tobacco two years ago.

43.  Exam
 Temp 101.2 otherwise stable , APPP
 Exam unremarkable except for
 Lungs – few inspiratory rales
 Right leg …

47.  Outpatient Treatment: non-MRSA
Antistaphylococcal penicillin
Dicloxacillin
First-generation cephalosporin

Cephalexin
 Inpatient Treatment: non-MRSA
 Amoxicillin + Clavunate
 Clindamycin is a good alternate with penicillin allergy
 Surgical opinion

48.  A 43 year old male presents with 10 days of purulent
rhinorrhea, subjective fevers, and facial headaches.
 PMHx – HTN, high cholesterol
 Meds – lisinopril/HCTZ
 FamHx – noncontributory

49. Exam
 HEENT – VS normal tenderness over right maxillary sinus
 Exam otherwise unremarkable
 Diagnosis?
 Sinusitis

51. Mild Acute Bacterial Sinusitis (ABS)
Amoxicillin
Amoxicillin/clavulanate
Cefuroxime axetil
Cefpodoxime
Or
antistrep. fluoroquinolones:
Levofloxacin
Moxifloxacin

52.  Drug option in the case of allergies to penicillin
and cephalosporin with Mild ABS:
◦ Doxycycline
◦ Trimethoprim/sulfamethoxizole
◦ Azithromycin
◦ Clarithromycin

53.  Drug option in the case of allergies to penicillin and
cephalosporin with Moderate to Severe ABS:
◦ Antipneumococcal fluoroquinolone:
 Levofloxacin
 Moxifloxacin

55. 42 years male with 5 days of progressive diffuse
headache, mildly stiff neck,fever vomiting, confusion.
PMHx – none known
PSHx - none

56. Exam
 VS: T 100.9, Pulse 96, RR 16, BP 138/82
 Gen: mildly ill appearing
 Mental status: orientation to place & person not time
 HEENT: mild photophobia
 Neck: mild pain with flexion (kernig sign +ve )
 Skin: no rash


57.  Lab.-
 TLC - 16000
 DLC - N80 L18
 CECT Head - normal study
 CSF - TLC – 412
DLC – N 96 L4
protein – 110mg/dl
suger - 23 mg/dl

60.  Adults(<55years) and children>3 months old:
 High dose ceftriaxone or cefotaxime
+
 Vancomycin 1gm IV BD
 Adults > 55years of age , patient with alcoholism
or other debilitating illness
 High dose ceftriaxone /cefotaxime
+ Vancomycin 1gm IV BD
+ Ampicillin 2gm/ 4horly
2gm IV BD

61. Cholera:
Tetracycline 250 mg 6-hourly for 3 days,
Doxycycline 300 mg single dose or Ciprofloxacin 1
g in adults
Bacillary Dysentery:
Ciprofloxacin 500 mg 12-hourly for 3 days
Helicobacter pylori Infection:
Two antibiotics (from amoxicillin, clarithromycin
and metronidazole) for 7 days

62. Aetiology: Salmonella typhi and Salmonella paratyphi A and B
Ciprofloxacin 500 mg 12-hourly
Ofloxacin 400 mg every 12 hourly
Ceftriaxone 2gm IV BD
Azithromycin 1gm once daily x 5 days
Treatment should be continued for minimum 10 days.
Or
5 days after resolution of fever

63.  Aetiology (pyogenic): E.coli, various streptococci
(amoebic): Entamoeba histolytica
 Management:
o Pyogenic: Combination of antibiotics e.g3rd gen
cephalosporin, gentamicin and metronidazole
o Amoebic: Metronidazole (800 mg 8-hourly for 10 days)
or tinidazole (2 g daily for 3 days)
Luminal amoebicide-diloxanide furoate (500 mg 8-
hourly for 10 days)

64. Gastro-Intestinal:

Ancylostoma, Ascaris:
Albendazole 400 mg single dose or Mebendazole 100
mg 12 hourly for 3 days
Tissue parasite:

Filariasis: Caused by Wuchereria bancrofti
 Treatment: Diethylcarbamazine 6 mg/kg body wt.
orally in 3 divided doses for 12 days.

65.  Avoid tetracycline
 Staining of teeth and bones in babies
 Acute yellow atrophy of lever , pancreatitis in mother
 Avoid sulfa drugs in the third trimester
 May be associated with kernicterus
 Avoid aminoglycosides
 Kidney toxicities
 Can cause foetal ear damage
 Fluoroquinolones
Concerns about cartilage development

66.  Treat the Mother first and the baby will appreciate it 
 Penicillins and cephalosporins are generally safe in
pregnancy.
 Macrolides are generally safe
- They may increase nausea early on

67. Is antibiotic necessary
What is the most
appropriate antibiotic
H/O
Allergy
Pregnancy
Renal dysfunction
Liver Disease
Dose/Frequency/Route/Duration
Monitor side effects