the cell wall of the bacteria concerned. Briefly, this inhibition prevents conversion of
muramic acid in the cell wall to new cell wall material. The organism thus cannot survive
or grow.
d. Solubility and Stability. Penicillin is a high-molecular- weight organic acid,
and as such is not soluble in water. Its salts, however, are soluble. The potassium salt
is most frequently used. These solutions are stable at a pH of 5 through 8 for about 2
weeks. They must be buffered to maintain their pH. Potassium penicillin G is stable at
room temperature, but its solution should be kept refrigerated.
e. Adverse Reactions. Possible reactions include urticarial reactions, serum
sickness, dermatitis, and anaphylactic shock. Topical applications may produce
sensitivity; therefore, it should not be used indiscriminately. The few cases of
anaphylactic shock that occur are so severe that sensitivity tests should be performed
before administering this agent. Other than allergic reactions, penicillin produces few
adverse effects.
f. Standardization. The potency of penicillin is expressed in terms of
international units. One unit is equivalent to 0.6 mcg of crystalline sodium penicillin G.
There are 1,667 units in 1 mg.
g. Acquired Resistance to Penicillin. The massive use of penicillin in the past
has promoted the development of strains resistant to penicillin. One of the chief
bacterial means of resisting penicillin is to produce an enzyme called penicillinase,
which destroys penicillin. As a consequence, semisynthetic penicillins not so
susceptible to penicillinase have been developed. These should be used only when the
other penicillins--penicillin G, penicillin V, and ampicillin--are not effective in treating a
particular malady.
5-14. POTASSIUM PENICILLIN G FOR INJECTION
Potassium penicillin G is also known as aqueous penicillin G or crystalline
penicillin G.
a. Indications. This is the penicillin of choice for intravenous administration. It
is effective against most gram-positive cocci and bacilli, some gram-negative cocci, and
some spirochetes. (In addition, some species of gram-negative bacilli are sensitive to
high concentrations of the drug obtained with intravenous therapy. These include most
strains of E. coli, all strains of Proteus mirabilis, Salmonella and Shigella, and some
strains of Aerobacter aerogenes and Alcaligenes faecalis.) Potassium penicillin G for
injection is indicated in the therapy of severe infections caused by penicillin G-sensitive
microorganisms when rapid and high penicillin blood levels are required. Therapy
should be guided by culture and sensitivity studies and by clinical response. The
following infections will usually respond to adequate doses of potassium penicillin G for
injection.
MD0913
5-12