1 Penicillins: Benzylpenicillin, phenoxymethylpenicillin Flashcards

1
Q

what are the indications for benzylpenicillin and phenozymethylpenicillin? (beta-lactamase sensitive)

A

1) Streptococcal infection, including tonsillitis, pneumonia
2) Endocarditis (usually with gentamicin) and skin and soft tissue infections (with flucloxacillin).
3) Meningococcal infection e.g. meningitis, septicaemia.
Clostridial infection, for

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2
Q

what is the spectrum of activity for Benzylpenicillin and phenoxymethylpenicillin?

A

1) Relatively narrow antimicrobial spectrum, with activity against some Gram-positive organisms and Gram-negative cocci
2) Not active against Gram-negative bacilli (rods)
3) Antimicrobial spectrum is relatively narrow, they are often combined with other antibiotics

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3
Q

outline the MoA of Benzylpenicillin and phenoxymethylpenicillin?

A

1) bactericidal

2) Prevent peptidoglycan cross-linking → Inhibit bacterial cell wall synthesis

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4
Q

list some of the adverse effects caused by Benzylpenicillin and phenoxymethylpenicillin?

A

1) Penicillin allergy affects 1–10%. Usually presents as a skin rash 7–10 days after first exposure or 1–2 days after repeat exposure (subacute IgG-mediated)
2) Less commonly an immediate life-threatening IgE-mediated anaphylactic reaction occurs: hypotension, bronchospasm, and pharyngeal and laryngeal oedema.
3) Neurological toxicity (convulsions and coma) can with very high-doses or accumulation due to severe renal impairment.

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5
Q

who should Benzylpenicillin and phenoxymethylpenicillin be used in caution with?

A

1) dose reduction in renal impairment.

2) penicillin allergy- Allergy to all penicillins , also may react to cephalosporins and other β-lactam antibiotics

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6
Q

Outline some of the interactions with regards to penicillins?

A

All penicillins reduce renal excretion of methotrexate, increasing the risk of toxicity.

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7
Q

how are benzylpenicillin and phenoxymethylpenicillin administered

A

1) Benzylpenicillin- (IV or IM) only, as hydrolysis by gastric acid prevents GI absorption. used for serious infections
2) Phenoxymethylpenicillin- stable in the presence of gastric acid and so can be taken orally as tablets or in solution. Not for serious infections because absorption can be unpredictable

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8
Q

Where antibiotics are required to treat a young person with a sore throat caused by an unknown organism, which penicillin would be selected?

A

phenoxymethylpenicillin, not amoxicillin- If the sore throat is due to Epstein–Barr virus (glandular fever), amoxicillin treatment commonly causes a rash.

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9
Q

what is Benzathine benzylpenicillin indicated for?

A

treatment of early syphilis and late latent syphilis; it is given by intramuscular injection

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10
Q

what is Phenoxymethylpenicillin commonly used in the treatment and prevention of?

A

1) respiratory-tract infections in children, for streptococcal tonsillitis
2) prophylaxis against streptococcal infections following rheumatic fever and against pneumococcal infections following splenectomy or in sickle-cell disease

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