penicillin G antibiotics and beta lactam antibiotic

Beta lactam PenicillinG

1. USES OF PENICILLIN G
Aqueous solution
High doses for – Meningitis, Gas gangren,
Bacterial endocarditis
Meningitis Dose – 20 LQ2H IV
Usual Adult Dose – 10 LQ6H
Moderate dose – Lung abscess,
Streptococcus pyogens
Low doses –
Procaine Penicillin is preferred – Given IM Q12H
Benzathine Penicillin – IM once a week-syphilis
prophylaxis of rheumatic fever – once in 3 weeks.

2. Oral penicillins
Penicillin V – Phenoxymethyl penicillin –
semisynthetic product
Use : Mild Respiratory Tract Infection 125 or 250
mg Q 6H
Broad Spectrum Penicillins
Orally Effective – Amoxycillin, Ampicillin
Spectrum – G+ve, and G-ve,
Salmonella, Hemophilus
These are not  lactamase resistant
Advantages of Amoxycillin – orally effective
Bioavailability is excellent. Given Thrice / day
Use : Respiratory Tract Infection – Sinusitis, Otitis
media, UTI, H.Pylori

4. Ampicillin:
Useful for GI infections - Shigella, Bacillary
dysentry
Limitation – causes diarrhea
Bacmpicillin:
Prodrug - converted to ampicillin in the body
Better absoprtion than ampicillin.
Dose twice a day

5. Beta Lactamase Inhibitors
Clavulanic acid
Sulbactum
Tazolactam
Combination with penicillin
Useful for penicillinase resistant organisms

6. Mode of action:
Clavulanic acid has a structure resembling
penicillanic acid.  lactamase has more
affinity for clavulamic acid which binds the
enzyme leaving amoxycillin molecule to act
on micro-organism. Clavulanic acid has no
antibacterial action.
Preparations: Amoxycillin + Clavulanic acid
Ampicillin + Sulbactam (Given IV because
oral bioavailability is poor)

7. PENICILLINASE RESISTANT PENICILLINS
Resistant to  lactamase
Methicillin, Nafcillin – Parenteral
Cloxacillin, Dicloxacillin – Orally effective
Use: S. Aureus infection (Cephalexin is an
alternative)
Methicillin resistant S.Aureus – MRSA
Some strains of S.aureus are resistant to
methicillin and other antibiotics. Why?

9. Mechanism of Resistance
Penicillin Binding Proteins are not accessible
to penicillin OR
PBP is altered chemically, so that penicillin
fails to bind to them.
Drugs useful to treat MRSA
VANCOMYCIN + RIFAMPICIN

10. BROAD SPECTRUM PENICILLINS
Carboxy penicillins
Carbenicillin
Ticarcillin
Use: Pseudomonas and protieus
Can be combined with gentamicin
Ticarcillin + tobramycin
ADR – Allergic reactions, bleeding due to malfunctioning
of platelets.
Ureidopenicillins
Piperacillins – Effective against pseudomonas, Klebsiella