Pharmacology

1. Kenya Medical Training College
Department of Orthopaedic and
Trauma Medicine
PHARMACOLOGY II
Year: 2022 Semester: 2
Session 2
Topic: Classification of Antibiotics
Date: 5th
April 2022
By: Carol Babu

2. Learning Objectives
By the end of this unit you should be able to:
▪ Classify penicillins
▪ Discuss mode of action of penicillins
▪ Describe Pharmacokinetics of penicillins
▪ Discuss the adverse reactions of penicillins

3. Classification of antibiotics
1. Beta lactams
• Have a beta lactam ring
• Examples – Penicillins, Cephalosporins,
Monobactam

4. Cont…
2. Aminoglycosides
• Have an amino acid and a glycoside in their
structures
• Examples – Gentamycin, Kanamycin, Streptomycin,
Amikacin, Tobramycin, vancomycin
3. Sulphonamides
• Are derivatives of sulphanolamide
• Includes sulphamethoxazole and
sulphadimidine

5. 4. Tetracyclines
• Have a 4 ring structure in there make up
• Includes tetracycline, doxycycline,
minocycline, oxytetracycline

6. 5. Macrolides
• Contain a macrocyclic lactone ring in their
structure
• Includes erythromycin, azithromycin,
clarithromycin
6.Polypeptides
• Includes bacitracin, colistin, polymixin B

7. 7. Quinolones
• Includes nalidixic acid, norfloxacin,
ofloxacin,ciprofloxacin, perfloxacin
8. Nitrofurans
• Nitrofurantoin
• Nitrofurazone
• Furazolidine

8. 9. Lincosamides
Lincomycin, clindamycin
10. Others
• Chloramphenicol

9. Penicillins
Sources
1. Natural penicillins – from a mould called
penicillium
2. Synthetic penicillins – Basic penicillin ring is
created through a fermentation process
• Penicillins produced thru a fermentation
process are called semi-synthetic

10. Classification of penicillins
A. Synthetic penicillins
1. Beta lactamase resistant penicillins
• Cloxacillin
• Oxaciliin
• Methicillin
• Flucloxacillin

11. 2. Extended (wide) spectrum penicillins
• Amino penicillins such as
✔ Ampicillin
✔ Prodrugs e.g Pivampicillin
✔ Ampicillin analogues e.g Amoxicillin, Amoxicillin/
Clavulinic acid

12. • Amidino penicillins e.g Pivmecillin, Mecillinan
• Carboxy penicillins e.g Carbenicillin.
• Ureido penicillins e.g Mezlocillin, Azlocillin

13. B. Natural penicillins
• Benzyl penicillins – Pen G or Crystalline
penicillin
• Phenoxymethyl penicillin – Pen V

14. Mode of action of penicillins
• Penicillins interfere with cell wall synthesis
• They form cross linkages with the Beta
lactam bonds and cell wall
• Penicillins are bactericidal
• Resistance develops when the bacteria
produce beta lactamase enzyme that
destroys the drug.

15. Pharmacokinetics
Absorption – variable
• Some penicillins are denatured by acids in the
stomach and can therefore not be given orally e.
g benzyl penicillin
• Pen V is absorbed in the ilium but has a very
short half life
Distribution – Extracellular fluid
Metabolism -Liver

16. Excretion . Mainly via renals through
active tubular secretion and filtration
• Excretion can be delayed by drugs that
compete for anion transport
mechanisms e.g Probenizid

17. Adverse reactions of penicillins
• These are the drug unintended effects and
includes:
✔ Allergic reactions- skin rash, urticaria,
angioneurotic edema, anaphylactic shock. Cross
allergies occur with cephalosporins and
monobactams
✔ Diarrhea
✔ Neutropenia
✔ Convulsions and electrolyte imbalance

18. A). Natural penicillins
Benzyl penicillin
• Usually used when high doses of plasma
concentration of penicillin is needed.
• It is administered parenterally. Half life 30min
• It is highly protein bound and 80 % is excreted
via the kidneys
• Administration – IM with peak plasma conc.
30-60min, IV with peak conc. almost
immediately

19. Clinical uses
• Gram positive organisms- streptococcus
pneumonia, beta haemolytic streptococcus,
clostridia species, bacillus anthracis,
actinomyces israeli, leptospira

20. Benzanthine penicillin
• A sustained release preparation
• Gives low plasma concentration that lasts 3-4wks
• Not used for acute infections
• Mainly used for chemoprophylaxis for strep pyogenes
to prevent rheumatic fever
• Dose – 900mg or 1.2mu IM in children
- Adults 2.4mu monthly.
Adverse reaction- Extremely painful, anaphylactic shock

21. B). Synthetic penicillins
a). Beta lactamase resistant penicillins
• Prevents the beta lactamase from getting to the
beta lactam bond
• Used to treat infections such as Staphylococcus
spp especially the beta lactamase group
• Examples – cloxacillin, flucloxacillin, methicillin,
nafcillin, oxacillin

22. Cloxacillin
• Half life 30min
• Resist acid degradation
• Food interferes with absorption
• Formulations oral and parenteral
• Dose 500mg 6hrly

23. Flucloxacillin
• A pro drug of cloxacillin
• Half life 50min
• More fully absorbed than cloxacillin
• Available for oral and parenteral use

24. b). Extended spectrum penicillins
• Covers both Gram neg as well as Gram positive
organisms
Ampicillin
• Acid stable
• Well absorbed orally
• Can be given orally, IM or IV
• Dose 500mg -2g 6hrly
• Highly concentrated in bile and excreted
unchanged in urine

25. Amoxicillin/clavulinic acid
• Clavulinic acid is a beta lactam compound
produced from a fungus streptomyces
clavuliginus.

26. • Clavulinic acid has no antibacterial properties
but protects the penicillin from bacteria that
produces beta lactamase
• Administered orally or IV
• Common side effects include diarrhea and skin
rash resembling measles
NB: Other inhibitors of bacteria enzyme
penicilinase are sulbactam, tazobactum-
piperacillin