Penicillin Pharmacology: Introduction | Types | Classification of penicillin | PDF, PPT Download

Introduction:

Penicillin is a a group of variable spectrum antibiotics possessing bactericidal action via the mechanism of cell wall synthesis inhibition. Penicillin is obtained either from natural and semisynthetic source.

It has high therapeutic index i.e a broader margin of safety.

Naturally penicillin is obtained from filamentous fungi pencillium crysogenum/notatum.

In 1928 penicillin was discovered accidently by Alexander fleming when he was working on growth of staphylococci. He named it penicillin but he did not isolated it.

Later on chain & flory supplied penicillin in bulk for the first time. Both of them were awarded nobel prize.
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Chemistry of penicillin:

The basic nucleus of penicillin is 6-amino-penicillinic acid .

The penicillin’s dual ringed structure consists of thazolidine ring and beta lactam ring . On this basis penicillin is classified under beta lactam antibiotic. The R group attached to beta lactam ring is of crucial importance.

The alkyl group is responsible for various prominent feature of beta lactam antibiotics some of which.

· Spectrum of antibiotics

· Penicillinase sensitivity

· Pharmacokinetic activity

if R is hydrophilic in nature the antibiotic will be considered broad spectrum antibiotic. The R group also determines the activity of penicillinase. For instance when alkyl group is a small group the antibiotic will be penicillinase sensitive i.e will respond to penicillinase enzyme. On the other hand if R (alkyl group) is a bulky group then the antibiotic will be penicillinase non sensitive.

In penicillin-G the R group is a benzyl group (small group) so penicillin-G is penicillinase non-resistant.

Another example is that of Ampicillin in which R is alpha amino benzyl group , And in amoxicillin R group is alpha amino phenol . In oxacillin the R group is 5-methyl-3-phenyl 4-isoxazolyl.

Classification of penicillin:

The classification of penicillin is done on the basis of their senitivity toward penicillinase. This way penicillin may be classified into;

· Penicillinase sensitive penicillins

· Penicillinase resistant penicillins

Penicillinase sensitive penicillins:

Penicillinase sensitive penicillins may further be subdivided into;

1. Short acting penicillins

2. Long acting penicillins

3. Acid resistant penicillins

4. Amino penicillins

5. Carboxy penicillins

This classification is a blend nature based and action based classification

Short acting penicillins:

Short acting penicillins includes Penicillin-G (benzyl penicillin).

Penicillin-G is administered both as IV or IM injectables. It has an action time of 4-6 hours and reach the maximum plasma concentration in this time.

Long acting penicillins:

Long acting penicillins include procaine penicillin and benzathine penicilline.for procain penicilline the duration of action is 12-24 hours & for benzathine penicilline it is from 3 to 4 weeks.

Due to a very large duration of action benzathine penicillin is also known as depot penicillin or repository penicillin. Long acting penicillin is only administered as intramuscular injections.

Acid resistant penicillin:

Acid resistant penicilline include penicillin-V, phenobencillin and propicillin.

Amino penicillins:

Amino penicillins is a clinically important class of penicillins. It include majority of the commonly used antibiotics. Following are examples of amino penicillins.

Ampicilline (penbritin ^R ) , amoxicillin (amoxil ^R ) and ampicillin pro-drugs are included in amino penicillins.

Ampicillin pro-drugs include becampicillin, pivampicilline and telampicillin. This means that these drugs when administered will convert into their active form i.e ampicillin .

Amino penicillins are generally administered in combination therapy generally with Beta lactamase inhibitors . 3 beta lactamase inhibitors are in practice for combination with amino penicillins. They are;

Salbactam, tazobactam and clavulonic acid, Remember them with the Mnemonic “ STC ”. Co-amoxiclave (augmentin ^R ) is a combination therapy including amoxicillin as the antibiotic and clavulonic acid as the beta-lactamase inhibitor.

Another example is that of ampiclox which is a Combination of ampicilline and cloxacillin.

Carboxy penicillin:

Carboxy penicillins include;

· Ticarcillin

· Ticarcilline+clavulonic acid (ticar ^R )

· Carbencillin

· Carbencillin indanyl

· Carfecillin

Penicillinase resistant penicillins:

Penicillinase resistant penicillins are not effected by penicillinase. This class include;

• methicillin.
• nafcelline.
• oxacilline.
• cloxacilline.
• dicloxacilline.

Remember them with the mnemonic MNOCDF .