Beta-lactems (Penicillins and Cephalsporins)

Question 1

4 Classes of Beta-lactam antibiotics

Answer 1

Penicillins

Cephalosporins

Monobactams
(Monobactams work only against aerobic gram-negative bacteria, Neisseria, Pseudomonas)

Carbapenems

Question 2

Penicillin

Answer 2

MOA: Inhibits the synthesis of baterial cell wall

Naturally occurring penicillin: Benzyl penicillin (Penicillin
G) and phenoxypenicillins (Penicillin V)

Semisynthetic: Penicillins Resistant to Staphylococcal β-
lactamase (Methicillin, Nafcillin, Oxacillin, Cloxacillin,
Dicloxacillin)
:Extended-Spectrum Penicillins (Aminopenicillins i.e ampicillin,
amoxicillin)
:Beta lactamase inhibitors (Clavulanic acid, Sulbactum)

Question 3

Common examples of Penicillins

Answer 3

penicillin V.
penicillin G (Pfizerpen, Permapen)
amoxicillin (Amoxil)
ampicillin (Unasyn)
methicillin
nafcillin (Nallpen)
oxacillin (Bactocill)
dicloxacillin

Question 4

Adverse effects of Penicillin

Answer 4

Common: Haematologic, G.I, Metabolic, Others

Hypersentivity reactions:
A. Immediate hypersensitivity(20 minutes): Pruritis, anaphylactic shock.
B. Intermediate reactions (48 hours): Cutaneous lesions, urticarial.
C. Delayed hypersensitivity (1 week or more): Hemolytic anemia, leukopenia.

Toxicity : Rare and reversible: Convulsions, agitation

Question 5

Drug interactions of Penicillin with other drugs

Answer 5

1. Ampicillin: Oral contraceptive failure
2. Warfarin: Decreased effect due to increased metabolism
3. Rifampicin (enzyme inducer): Inhibits penicillins effects
4. Antacids: Increased penicillin absorption
5. Probenecid: Decreased penicillin excretion by competing for elimination sites in the kidney.
6. Metoclopramide: Decreased penicillin absorption
7. NSAIDs: Displaces protein bound penicillin, therefore more free and active penicillin.

Question 6

Cephalosporins

MOA: Cell wall synthesis inhibitor (Bactericidal)

Answer 6

1st generation: Cephalexin
2nd generation: Cefuroxime
3rd generation: Ceftriaxone
4th generation: Cefepime
5th generation: Ceftaroline

Adverse reactions: allergic reactions, nephrotoxicity

Question 7

Drug interactions: Cephalosporins

Answer 7

1. Alcohol: Disulfiram-like reaction
2. Warfarin: Interferes with Vit. K metabolism, potentiates effect
3. NSAIDs and antiplatelets: increased risk of bleeding
4. Oral contraceptives: Decreased efficacy
5. Probenecid: inhibits tubular secretion of cephalosporin
6. Geriatrics: Renal impairment may require dose reduction