Penicillin

Penicillin (PCN) is derived from molds that you sometimes see on bread and fruit. It was discovered in 1940 and remains the most effective—and least toxic—antimicrobial drug. Penicillin weakens the cell wall of a bacteria resulting in the rupture and destruction of a cell, which is called lysis.

Penicillin is most active against gram-positive bacteria and some gramnegative bacteria. However, it isn't active against bacteria that contain enzymes that destroy penicillin.

There are four types of penicillin:

1. Basic (natural)

2. Penicillinase-resistant (resistant to beta-lactamase inactivation)

3. Aminopenicillins (broad spectrum)

4. Extended-spectrum

Besides route, dose, and time, drugs are also characterized by pregnancy category, protein-binding, and half-life. Pregnancy category indicates if the drug has been tested using pregnant women and how safe the drug might be if used during pregnancy. Penicillin is categorized by its usefulness against bacterial enzymes capable of destroying the drug. Four different classifications of antibiotics exist that contain the beta-lactam ring and are more active against gram-negative cell wall organisms and decrease its susceptibility to enzymes that inactivate the antibiotic. Protein-binding is when a drug binds to plasma proteins. When a drug is bound to a protein it is not available for therapeutic use. The percent of protein binding is the amount of drug that can't be used until it is released when the free drug or the amount not bound to protein is excreted from the body. Half-life is the amount of time for half the drug to be eliminated from the body.

The category appears at the top of the table if the value of the category applies to all the drugs in a table, otherwise the category appears beneath the name of the drug in the table.

There are several precautions that must be taken when administering penicillin. If penicillin is given PO, avoid giving this medication an hour before and an hour after the patient has eaten. However, food doesn't have any effect on amoxicillin, amoxicillin and clavulanate, and bacampicillin. Give penicillin with a full glass of water and not with acidic fruit juices.

If penicillin is administered IV, give it slowly because penicillin contains a large amount of potassium that can cause heart failure in patients with renal insufficiency.

Before penicillin is administered, the patient must be assessed for a number of conditions. One of the most important is allergies. An allergic reaction to penicillin can be anywhere from a mild rash to anaphylactic shock and death.

Furthermore, don't administer penicillin to patients who have:

• Ulcerative colitis and other GI diseases.

• Mononucleosis (a skin rash may develop with use of ampicillin or bacampicillin).

• A low-salt diet (parenteral carbenicillin and ticarcillin have high sodium content

• Impaired renal function (a lower dose may be given in such cases).

After penicillin is administered, monitor the patient for:

• Serum electrolytes for hyperkalemia (elevated potassium) and/or hyperna-turemia (elevated sodium)

• Unusual weight loss (especially in the elderly)

• Prothrombin Time (PT) (bleeding times)

Descriptions of medication throughout this chapter use the following abbreviations:

PB

protein-binding

IV

intravenous

tM

half-life

IM

intramuscular

UK

unknown

A

adult

PO

by mouth

C

child

Basic (Natural) Penicillin

Pregnancy Category: B

Protein-Binding

: 65%

Half-Life: '/2 hour

Route

Dose

Time

Penicillin G

PO

200,000-500,000

Every 4 to 6 hours

IV

1-5 mu

Every 4 to 6 hours

IM

1.2-2.4 micro units

Single dose

Penicillin V (take on empty stomach)

PO

125-500 mg

Every 8 hours

Penicillinase-Resistant Penicillin

Pregnancy Category: B

Half-Life: V2-I hour

Route

Dose

Time

cloxacillin (Tegopen)

Protein-Binding: 90%

PO

Every 6 hours

IV

250-500 mg

Every 4 to 6 hours

dicloxacillin (Dynapen)

Protein-Binding: 90%

PO

125-250 mg

Every 6 hours

methicillin (Staphcillin)

Protein-Binding

: 25%-40%

IV

1 g

Every 6 hours

IM

1 g

Every 4 to 6 hours

nafcillin (Unipen)

Protein-Binding: 90%

PO

250 mg-1 g

Every 4 to 6 hours

IV

0.5-1.5 g

Every 4 hours

IM

500 mg

Every 4 to 6 hours

Penicillinase-Resistant Penicillin (continued)

oxacillin (Prostaphlin)

Protein-Binding: 95%

PO

0.5-1 g

Every 4 to 6 hours

IV

250-1 g

Every 6 hours

IM

250-1 g

Every 4 to 6 hours

Aminopenicillins (Broad Spectrum) Penicillin

Pregnancy Category: B

Route

Dose

Time

amoxicillin (Amoxil)

Protein-Binding: 20%

Half-Life: 1-1.3 hours

PO

250-500 mg

Every 8 hours

amoxicillin + potassium clavulanate (Augmentin, Clavulin)

Protein-Binding: 25%

Half-Life: 1-172 hours

PO

5000 mg

Every 8 hours

ampicillin (Polycillin, Omnipen)

Protein-Binding: 15%-28%

Half-Life: 1-2 hours

PO

250-500 mg

Every 6 hours

IV

250-500 mg

Every 8 hours

IM

250-500 mg

Every 8 hours

ampicillin and sulbactam (Unasyn)

Protein-Binding: 28%-38%

Half-Life: 1-2 hours

IV

1.5-3 g

Every 6 hours

IM

1.5-3 g

Every 6 hours

bacampicillin (Spectrobid)

Protein-Binding: 17%-20%

Half-Life: 1 hour

PO

499-800 mg

Every 12 hours

Extended-spectrum Penicillin

Pregnancy Category: B

Route

Dose

Time

carbenicillin (Geocillin)

Protein-Binding: 50%

Half-Life: 1-172 hours

PO

0.5-1 g

Every 6 hours

IV

50-83.3 mg/kg

Every 4 hours

IM

50-83.3 mg/kg

Every 4 hours

mezlocillin (Mezlin)

Protein-Binding: 30%-40%

Half-Life: 72-1 hour

IV

33.3-58.3 mg/kg

Every 4 hours

IM

33.3-58.3 mg/kg

Every 4 hours

piperacillin (Pipracil)

Protein-Binding

: 16%-22%

Half-Life: 0.6-1.5 hours

IV

3-4 g

Every 4 to 6 hours

IM

3-4 g

Every 4 to 6 hours

piperacillin + tazobactam (Zosyn, Tazocin)

Protein-Binding: Unknown

Half-Life: 0.7-1.2 hours

IV

3.375-4 .5 g

Every 6 to 8 hours

ticarcillin (Ticar)

Pregnancy Category: C

Protein-Binding: 45%-65%

Half-Life: 72-172 hours

IV

1-4 g

Every 6 hours

IM

1 g

Every 6 hours

ticarcillin + clavulanate (timentin)

Protein-Binding: 45%-65%

Half-Life: 1-172 hours

IV

33.3-50 mg

Every 4 hours

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