Penicillin is capable of forming many types of esters and salts which alter the extent 
and rate of absorption. Penicillin V (phenoxymethylpenicillin) has given higher blood and 
tissue levels than potassium G (5). 
Accumulation in Tissues 
Before discussing distribution and accumulation in body fluids and tissues, a general 
statement on excretion appears desirable. After oral administration, by far the most 
extensive pathway of excretion is in the feces. After intravenous or intramuscular injec- 
tion the largest amount is excreted inthe urine with usually only small amounts appearing 
in the feces. In both methods of administration the bile contains the antibiotic and resorp- 
tion from the gastrointestinal tract occurs. The concentration in urine and bile is usually 
10 to 100 times higher than the concentration in blood serum. 
Practically all data obtained to date onthe distribution and accumulation of antibiotics 
have been determined by microbiological techniques wherein the material under assay 
must be active against the test organism employed. One must keep in mind that this may 
or may not give a complete picture of the fate of the antibiotic. 
When given in adequate dosage levels, the antibiotic can be found in most of the body 
fluids and tissues suchas peritoneal, pericardial, pleural, and ascitic fluids, kidney, liver, 
spleen, intestine, muscle, brain, cerebrospinal fluid (C.S.F.), all parts of the eye, bile, 
urine, milk, saliva, and in the fetus and its circulation. 
Once absorbed most antibiotics appear to followa diffusion gradient and appear in all 
the tissues. However, there are some exceptions to this generalization--neomycin is 
apparently not found in C.S.F.; bacitracin inC.S.F.is not found in man but found in dogs nor 
is it found in the anterior part of the eye; erythromycin is not found in the brain and only 
in traces in C.S.F. (2,5,7). 
Most studies on the concentration of the antibiotic in blood serum have been obtained 
on humans. The results for any one species cannot be applied to another specie without 
serious reservations. The administration of aconstantoral dosage produces serum levels 
in swine that are double those found in poultry (7). Similarly, with various cycline anti- 
biotics the blood level in rats was found to be 10 times higher than those in rabbits (11). 
An intramuscular dose of 15mg./kg. produced serum levels in dogs that were 2 to 5 times 
higher than in rabbits. 
There was a large difference among individuals receiving the same dosage and it was 
not influenced by exercise (2,5,7). Inflammation will permit the antibiotic to diffuse into 
organs where it otherwise is not usually found (5). 
On a constant dosage the serum concentration may be different with animals of dif- 
ferent ages. In chickens when given the antibiotic as a constant percent of the diet the 
difference in blood levels at different ages werecorrelated with the feed intake per pound 
of body weight (6,7). In humans the renal clearance of bicillin ( a penicillin ester) was 
found to decrease as age increased. 
Blood levels of chlortetracycline were not affected by the presence of milk products 
in the diet except as they altered calcium content, nor by the addition of 2 to 8 percent 
fat, but the presence of vitamin D in the diet increased the blood levels of this antibiotic 
(7). 
The amount of antibiotic in the tissues is a function of amount and length of adminis- 
tration as well as a function of route of administration as mentioned previously. 
When chlortetracycline was given to calves for 3 months at the approximate rate of 
50 mg./day it was found in the bile, feces, urine, liver, kidney, and blood. None was found 
in other tissues such as muscle, thymus,and similar glands. Oral administration resulted 
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