bacteriostatic and bactericidal - penicilins, cephalosporins, degradation, uses, classification with sturctures

1. MEDICINAL CHEMISTRY III
B. Pharmacy III/IV (Second sem.)
Dr. K. Purna Nagasree
M.Pharm. (BITS, Pilani), Ph.D., PDF (DST, WOSA)
Associate Professor
VIGNAN INSTITUTE OF PHARMACEUTICAL
TECHNOLOGY
(Approved by PCI, AICTE New Delhi and affiliated to JNTUK)
ANISO 9001:2015, ISO 14001:2015, OHSAS 18001:2007 Certified institution, beside VSEZ, Duvvada,
Vishakapatnam-530049, Andhra Pradesh, India
2021

2.  Antibiotics: Historical background, Nomenclature,
Stereochemistry, Structure activity relationship, Chemical
degradation classification and important products of the
following classes.
 β-Lactam antibiotics: Penicillin, Cepholosporins, β- Lactamase
inhibitors, Monobactams
 Aminoglycosides: Streptomycin, Neomycin, Kanamycin
 Tetracyclines: Tetracycline, Oxytetracycline, Chlortetracycline,
Minocycline, Doxycycline
Unit I

3.  Sir Alexander Fleming - 1929, accidentally discovered the
antibacterial properties of penicillin
 Chain and Florey -1939
 Penicillin was clinically used - 1941
 In 1942, Waksman proposed the search of actinomycetes and
discovered streptomycin in 1944.
 synthetic and semisynthetic agents.
Introduction

4. Mechanism of action of
β-Lactam antibiotics

5. Penicillins
1. Early penicillins
2. Penicillinase-resistant penicillins
3. Broad-spectrum penicillins Ampicillin, Amoxycillin
Penicillin G, Penicillin V
Methicillin, Oxacillins, cloxacillins etc
4. Anti-pseudomonal penicillins Carbencillin, Ticarcillin

6. Degradation of penicillins

8.  Penicillenic acid Penicillin Penicilloic acid
Penillic acid Penilloic acid
Penamaldic acid
Penicillamin+Penaldic acid Penicilloldehyde
Acid Alkali

9.  The cephalosporins were isolated from the fungus Cephalosporium acremonium
in 1948 by Pro Tzu, Newton, and Abraham (1953)
 Cephalosporins contain dihydrometathiazine ring, while penicillin contains a
tetrahydrothiazole (thiazolidine) ring
 The cephalosporins are much more acid stable than the corresponding
penicillins,.
 Cephalosporins can be divided into three classes:
1. Cephalosporin N: penicillin-like structure - a derivative of 6-aminopenicillanic acid.
2. Cephalosporin P: An acidic antibiotic, which is steroidal in nature
.
3. Cephalosporin-C: It is a true cephalosporin and it is a derivative of 7 amino-
cephalosporanic acid – semi synthetic derivatives
Cephalosporins

10.  Cepham is the name given to the unsubstituted bicyclic
lactam.
Cephalosporins

11. a. Orally administered: cephalexin, cephradine, and cefaclor
b. Parentrally administered: cephalothin, cephapirin, cephacetrile, and
cefazedone. These agents are sensitive to β-lactamase
c. Resistant to β-lactamase and parentrally administered: cefuroxime,
cefamandole, cefoxitin
d. Metabolically unstable: cephalothin and cephapirin
Classification
Cephalosporins
(Route of administration)

12.  First generation cephalosporins - Cephalexin, cephadroxil,
cephradine and cephalothine
 Second-generation cephalosporins - Cefaclor, cefamandole
 Third-generation cephalosporins – Cefotaxime,
ceftizoxime
 Fourth generation – Cefepime, Cefpirome
Classification
Cephalosporins

13. Degradation of
cephalosporins
In prescence of strong acids - inactive lactone

14. SAR of cephalosporins
1. 7-Acylamino substituents:
(i) Acylation of amino group generally increases the potency against gram-
positive bacteria, but decreases gram-negative potency.
(ii) Substituents on the aromatic ring that increases lipophilicity provide
higher gram- positive activity and generally lower gram-negative activity.
(iii) The phenyl ring in the side-chain can be replaced with other heterocycles
with improved spectrum of activity and pharmacokinetic properties, and
these include thiophene, tetrazole, furan, pyridine

15.  2. C-3 substituents:
 influences pharmacokinetic and pharmacological properties as well as
antibacterial activity. Modification at C-3 position has been made to reduce
the degradation of cephalosporins.
(i) The benzoyl ester - improved gram-positive activity but lower gram-negative
activity.
(ii) Pyridine and imidazole- show improved activity against P. aeruginosa.
 azide ion with relatively low gram-negative activity.
(iii) aromatic thiols of 3-acetoxy group results in an enhancement of activity
against gram-negative bacteria with improved pharmacokinetic properties.
(iv) Replacement of acetoxy group at C-3 position with —CH3, Cl has resulted in
orally active compounds.
SAR of cephalosporins

16. 3. Introduction of C-7 α-methoxy group shows higher resistance to hydrolysis
by β-lactamases
4. Oxidation of ring sulphur to sulphoxide or sulphone greatly diminishes or
destroys the antibacterial activity.
5. Replacement of sulphur with oxygen leads to oxacepam with increased
antibacterial activity, with methylene group - greater chemical stability and a
longer half-life.
6. The carboxyl group of position-4 has been converted into ester prodrugs to
increase bioavailability of cephalosporins, and these can be given orally as well.
Examples include cefuroxime axetil and cefodoxime proxetil.
7. Olefinic linkage at C 3-4 is essential for antibacterial activity. Isomerization of
the double bond to 2-3 position leads to great losses in antibacterial activity
SAR of
cephalosporins

17. Classes of antibiotics and their spectrum of activity

20.  It is more resistant to inactivation by gastric juice than
penicillin G and better absorbed from the gastro intestinal (GI)
tract.
 Penicillin V is given to treat ‘trench mouth’.
 It is useful in the treatment of streptococcal pharyngitis,
pneumonia, arthritis, meningitis, and endocarditis caused by S.
pyogenes.
Penicillin
V

21.  It is particularly resistant to inactivation by the penicillinase
found in Staphylococci, Bacillus cereus
 Methicillin sodium has been introduced for use in the
treatment of Staphylococci infections caused by the strains
resistant to other penicillins.
 It is given by IM or by slow IV infusion every 4–6 h.
Methicillin

22.  Use should be restricted to the treatment of infections caused
by Staphylococci that are resistant to penicillin G
Oxacillins (Phenyl methyl Isoxazolyl
penicillins)

23.  It is used to treat urinary tract infections and respiratory tract
infections
 The α-amino group plays an important role in the broader
activity.
 Ampicillin stable to acid hydrolysis and instable to alkaline
hydrolysis. Pivampicillin is a prodrug of ampicillin
Ampicillin

24.  It is effective in the treatment of systemic and urinary tract
infections.
 The carboxyl group is thought to provide improved penetration
of the molecule through the cell wall barriers of gram-negative
bacilli as compared with other penicillins.
 acid labile being a malonic acid derivative, it decarboxylates
readily to penicillin G.
 It has low toxicity, and interferes with platelet function resulting
in bleeding
Carbenicillin

25.  It is particularly recommended for urinary tract infection
 The α-amino group of cephalexin renders it acid stable.
 The 3-methyl group is responsible for the metabolic stability.
Cephalexin (phenyl acetamido 7ACA)

26.  a second-generation cephalosporin antibiotic with bactericidal
activity.
 Cefamandole is active against Haemophilus and gram-negative
bacilli susceptible to other cephalosporins.
 solutions are stored for 24 h at room temperature or up to 96 h
by refrigeration
Cefamandole

27.  It is a beta lactamase resistant cephalosporin, used in lower
respiratory infection and meningitis
 Cefpirome (4th generation) is used to treat susceptible infections,
including urinary and respiratory tract infections, skin infections,
septicaemia, and infections in immuno-compromised patients.
Ceftizoxime sodium
2-(2-amino-1,3-thiazol-4-yl)-2-(methoxyimino)acetyl] 7 ACA

28.  cephalosporins
Allergic manifestation: The cephalosporins should be avoided or
used with caution in individuals allergic to penicillins.
When cefamandole or cefoperazone is ingested with alcohol, a
disulphiram like effect is seen
ii. Bleeding: Bleeding can occur with cefemandole or
ceforperazone because of antivitamin K effects. But the
administration of the vitamin overcomes this problem.
Adverse reactions

29.  Penicillins- Anaphylactic shock
 Common allergic reactions to penicillin include rashes etc itchy
eyes, and swollen lips, tongue, or face.
 In rare cases, an allergy to penicillin can cause an anaphylactic
reaction (in an hour) which can be deadly
 Epinephrine
Adverse reactions

30.  Unlike other beta-lactams, the monobactam contains a nucleus
with no fused ring attached. Thus, there is less probability of
cross-sensitivity reactions.
 Example:
 Aztreonam
Monobactams

31.  Although they exhibit negligible antimicrobial activity, they contain the
β-lactam ring.
 prevent the inactivation of β-lactam antibiotics by binding the β-
lactamases

 they are co-administered with β-lactam antibiotics. These drugs are
irreversible inhibitors of β-lactamase
 these bind the enzyme and do not allow it to interact with the
antibiotic
Beta lactamase inhibitors