Penicillins Flashcards
What is the other name for Benzylpenicillin sodium?
Penicillin G
What is the other name for phenoxymethylpenicillin?
Penicillin V
The letter “V” looks like a phoenix! :)
What is the route of administration of benzylpenicillin sodium (Penicillin G)?
slow IV injection, IV infusion, or IM
What is the route of administration for Phenoxymethylpenicillin (Penicillin V)?
Oral
Is benzylpenicillin sodium (Penicillin G) inactivated by beta-lactamases?
Yes
What organisms does benzylpenicillin sodium (Penicillin G) have activity against? (9)
Effective against the following infections:
- Many streptococcal (including pneumococcal)
- Gonococcal
- Meningococcal
- Anthrax
- Diptheria
- Tetanus
- Gas-gangrene
- Leptospirosis
- Syphilis
Is benzylpenicillin sodium (Penicillin G) well-absorbed by the GIT?
No, inactivated by gastric acid and poorly absorbed; therefore must be given by injection
What organisms does phenoxymethylpenicillin (Penicillin V) have activity against?
Similar spectrum of activity to Penicillin G but less active; gastric acid-stable so it is suitable or oral administration
*should not be used for serious infections because absorption can be unpredictable and plasma concentrations are variable
What are the primary indications for phenoxymethylpenicillin (Penicillin V)? (5)
- RTIs in children
- Streptococcal tonsillitis
- Continuing treatment after one or more injections of benzylpenicillin sodium (Penicillin G) when clinical response has begun
- Prophylaxis against streptococcal infections following rheumatic fever
- Prophylaxis against pneumococcal infections following splenectomy or in SCA
**not suitable for serious infections due to unpredictable absorption and plasma concentration eg meningococcal or gonococcal infections
What is the route of administration of phenoxymethylpenicillin (Penicillin V)?
Oral; gastric acid-stable but unpredictable absorption and plasma concentration
Which penicillins are penicillinase-resistant?
Penicillinase-resistant penicillins (AKA “second generation penicillins”) resist hydrolysis of the beta-lactam ring by bacterial enzymes, particularly STAPH
- Flucloxacillin
- Temocillin
- Neticillin
- Naficillin
- Oxacillin
“Naf for staph”
Is benzylpenicillin active against staph?
No, most staphylococci are now resistant to benzylpenicillin because they produce penicillinases (beta-lactamases)
How is flucloxacillin administered?
Oral (acid-stable, well-absorbed by the gut) or injection
What are the indications for temocillin?
Temocillin is a beta-lactamase-resistant penicillin (second gen) with activity against gram-negatives
Should be reserved for treatment of infections caused by beta-lactamase-producing strains of gram-NEGATIVE bacteria, including those resistant to third-generation cephalosporins
**NOT active against pseudomonas or acinetobacter
Which penicillins are considered broad-spectrum?
Ampicillin and amoxicillin
(Activity against certain gram (+) and gram (-) organisms BUT is inactivated by penicillinases including those produced by staph aureus and common gram (-) bacilli eg E.coli, H.influenza)
Can ampicillin be used as empirical therapy in hospitalized patients?
NOOO; because many common organisms have developed resistance (almost all staph, 60% e.coli, 20% Hib) sensitivity should be checked before prescribing ampicillin, especially in hospitalized patients
What are the main indications of ampicillin?
- Exacerbations of chronic bronchitis (strep pneumo, Hib)
- Middle ear infections (strep pneumo, non-resistant strains of Hib)
- UTIs (well-excreted in the bile and urine)
What is the oral bioavailability of ampicillin?
When given by mouth, less than half the dose is absorbed by the gut, with absorption further decreased by the presence of food in the gut
Are maculopapular rashes associated with ampicillin and amoxicillin caused by penicillin allergy?
No; this is not a true allergy, and almost always occurs in patients with glandular fever —> therefore broad spectrum penicillins should NOT be used in empirical treatment of sore throat (phenoxymethylpenicillin is first line)
*risk of rash is also increased in patients with acute or chronic lymphocytic leukemia or in CMV infection
What is the spectrum of activity of amoxicillin?
Amoxicillin is a derivative of ampicillin and has similar antibacterial properties (activity against gram (+) and gram (-) bugs)
Although it is considered a broad-spectrum penicillin, it is inactivated by penicillinases produced by almost all staph, 60% of e.coli, 20% of Hib, and should therefore not be used as “blind” treatment of infections, especially in hospitalized patients who are more likely to be infected by penicillinase-producing bugs; sensitivity should be checked first
How does amoxicillin compare to ampicillin? (3)
- Better absorption when given by mouth, producing higher plasma and tissue concentrations
- Absorption not affected by presence of food in the stomach
- Amoxicillin is used to treat Lyme disease, while ampicillin is not
What is co-amoxiclav?
Amoxicillin + clavulanic acid (a betalactamase-inhibitor)
Like broad spectrum penicillins ampicillin and amoxicillin PLUS activity against beta-lactamase-producing bacteria resistant to amoxicillin ie resistant strains of staph, E.coli, and Hib, AS WELL AS bacteroides and klebsiella
What is the spectrum of activity of co-amoxiclav?
Like amoxicillin PLUS activity against beta-lactamase resistant strains of staph aureus, E.coli, and H.influenza PLUS gram negatives Bacteroides and Klebsiella
When is co-amoxiclav indicated?
Should be reserved for infections likely, or known, to be caused by amoxicillin-resistant beta-lactamase-producing strains
