Antibiotics other than penicillin--Figure 6 shows a comparison of some of the other 
antibiotics most commonly used to treat dairy cattle diseases. Aureomycin persisted the 
longest in milk (2 days) after one parenteral injection, although none of the antibiotics 
showed any tendency to persist much longer thanthe shortest persisting penicillin product. 
Terramycin was not found in the milk of some cows given an intravenous injection of 1 gm. 
or intramuscular injections of 1 to 3 gm. (3,58). Tetracycline may persist longer with 
larger doses than the 2 mg./1b. of body weight; however, in the case of dihydrostreptomycin 
increasing the dose from 6.25 mg.to12.5mg./lb. of body weight did not increase the time 
of persistence (82). Three daily intramuscular injections of 6.25 mg./lb. of body weight of 
dihydrostreptomycin did increase the maximal time this antibiotic was found in the milk 
to 2-1/4 days (54 hours) (82). On the other hand, the intravenous injection of 10 gm. of 
Aureomycin daily for 6 days did not appear to cause any increase in the persistence of 
this antibiotic in milk (43). 
Sulfonamides--Figure 7 shows a comparison of various sulfonamides given paren- 
terally at different dose levels. The persistence of the sulfonamides in milk after one 
injection depends upon the dose and the type of sulfonamide. The two sulfonamides not 
commonly used, sulfabromomethazine and sulfamethoxypyradazine, lasted the longest. 
Therefore, we might conclude that the more commonly used sulfonamides do not persist 
in the milk any longer than 48 hours after a single injection. The only exception is sul- 
famethazine which lasted 48 hours but was not tested at the dose of 1.5 gr./lb. of body 
weight. The maximal concentrations of the sulfonamides when last detected in the milk 
ranged from 0.1 to 1.2 mg./100 ml. of milk (59,69,70,71). 
THE ORAL ADMINISTRATION OF ANTIBIOTICS AND SULFONAMIDES 
Antibiotics--Mastitis is not treated by the oraladministrationof antibiotics, although 
some of the antibiotics are fed at low levels to control bloat and prevent infections (ac- 
cording to some advertisements) and could appear in the milk. Skaggs and Miller (65) 
reported a level of 0.05 u./ml. of milk when two cows were fed daily as little as 177.8 mg. 
(173,400 units) of procaine penicillin in the concentrate feed. These levels increased to 
0.10 and 0.15 unit when the daily dose was 277.8 mg. (270,500 units). This work has not 
been confirmed in recent experiments since twocows were fed one daily dose of 1 million 
units of potassium penicillin for 10 days without any penicillin being detected in the milk 
(82). Negative results were also obtained whentwo cows were fed 5 million units daily for 
5 days with each of two daily feedings containing half the dose (82). Further work is 
needed to clarify these discrepancies. In addition, bacitracin did not appear in the milk 
when 0.5 gm. was fed once a day in the grain for 10 days, nor did streptomycin when 0.5 
gm. was fed twice a day for 5 days (82). 
Loosli and Warner (44) first reported that no Aureomycin was found in the milk of 
cows that had received 700 mg. per day for 10 days. Martin, et al. (46) also had negative 
results when they fed Aureomycin daily atthe rate of 32 mg./100 lbs. of body weight or an 
average of 390 mg. per cow. Since then Henderson, et al. (25) and Shor, et al. (62) have 
found Aureomycin in the milk when cows were fed at levels of 0.5 mg./lb. of body weight 
per day and higher. No Aureomycin was found when a dose of 0.1 mg./lb. of body weight 
was fed daily. Using the data of Shor et. al. (62), it was calculated that during the feeding 
of Aureomycin at the level of 0.5 mg./lb., the average concentration was 0.045, ug./ml. 
of milk, which increased to 0.083, wg./ml. when 1.0 mg./lb. was fed. 
Sulfonamides--Figure 8 shows the persistence of sulfonamides in the milk after oral 
administration. Sulfabromomethazine persisted for 3 days in the milk after a single dose; 
however, 2 days was the longest time any of the more commonly used sulfonamides lasted. 
The size of the dose does not seem to have any marked effect on their persistence. 
Although data are only presented for sulfanilamide, it would appear that dosing for several 
days may cause these drugs to persist longer after the last dose is given. The maximal 
time that sulfanilamide persisted after one dose was 48 hours, whereas when cows were 
given the drug for 6 consecutive days it persisted in the milk for 90 hours after the last 
dose (48,49). On the other hand, Gildow, et al. (19) fed cows sulfanilamide at the rate of 
10 to 15 gm./100 1b. of body weight daily for 9 days and found that the drug disappeared 
from the blood and milk within 48 hours after feeding was stopped. 
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