Sunday, June 3, 2018

Facebook: Penicillin

This is answer to one of the questions on chemotherapy posted on medicowesome facebook.
Question is as follow.

Which of the following statement about penicillin G is true

1) It is commonly administered orally.
2) It has a broad spectrum of antibacterial activity.
3) It can be used for the treatment of rate bite fever.
4) Concomitant probenecid decreases it's duration of action.

Answer is 3- It can be used for the treatment of rate bite fever.

Explanation:

Penicillins belongs to the group of Beta-Lactam antibiotics.
These group includes compounds having Beta-Lactam ring in their structure. Apart from penicillin beta-lactam antibiotic group includes following classes:-

Cephalosporins
Monobactams
Carbapenems

You can remember them as
"See PCM"

C(See)-Cephalosporins
P-Penicillin
C-Carbapenems
M-Monobactams

Now, coming to Penicillin G

1) It is not effective orally because of breakdown by acid in the stomach.
Hence, a seprate class of penicillins are introduced which are acid resistant.

A very famous mnemonic is: VODKA
V= Penicillin V
O= Oxacillin
D= Dicloxacillin
K= Cloxacillin
A= Ampicillin and Amoxycillin

2) It has short duration of action due to rapid excretion from kidney. To overcome this we do one of the two things
a) Benzathine and procaine groups are added to penicillin G
Benzathine is longest acting penicillin G
b) Probenecid can be administered with penicillins. It inhibits the tubular secretions.

3) Penicillin G has narrow spectrum of antibacterial activity. Several new penicillins with extended spectrum are added. They are as follow.

CAT Action MAP.
C= Carbenicillin
A= Ampicillin
T= Ticarcillin
A= Amoxicillin
M= Mezlocillin
A= Azlocillin
P= Piperacillin

4) It is first choice of drug for:-

Mnemonic: SMARt GV loves yogurt.
S=Syphilis
M=Meningococcal meningitis
A=Actinomycosis
R=Rat bite fever
t
G=Group A and B streptococcal infections
V=Viridian streptococcal endocarditis
L=Leptospirosis
Y=Yaws

Some important points to remember:

1) All drugs having beta lactamse ring are bacteriocidal.
2) They act on PBP(Penicillin binding proteins) present on cell membrane.
3) MRSA occur due to alterations in PBPs, hence no beta lactams are useful against it.

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