Recovery

When the fermenters contain maximum titres of penicillin, the mold mycelium is removed by filtration or centrifugation. In current practice the mycelium as well as the exhausted liquid residues are usually discarded. Feeding trials by the Bureau of Animal Industry, however, indicate that the dried mycelium and the culture-liquor residues may be successfully used in poultry feeds. The remaining clear broth is immediately chilled to prevent the development of bacterial contaminants which would otherwise quickly destroy the penicillin. Recovery practices differ, but a common procedure is to set the pH of the broth at pH 2.0 to 3.0 and then extract all of the free penicillin into a solvent such as amyl acetate, butyl alcohol, or chloroform. Penicillin is also subject to rapid decomposition in the presence of strong acids or alkali, and this destruction is tremendously accelerated at elevated temperatures. The extraction step, therefore, should be carried out as rapidly as possible and at a low temperature. The solvent containing the penicillin is then extracted with aqueous sodium bicarbonate to yield a solution of the sodium salt. To concentrate the penicillin further, it can be transferred back and forth between various solvents and buffer solutions of appropriate PH. An alternative procedure lure is to adsorb the penicillin from the filtered broth on charcoal, then remove it with a solvent, and purify it.

The final concentrated solution of sodium penicillin is then vacuum dried. This may be done in the same containers in which it is subsequently marketed, or the penicillin may be dried in bulk and added to vials in weighed amounts. Generally these are small rubber-stoppered vials of 20 milliliter capacity. To use the penicillin it is only necessary to pierce the stopper with a sterile hypodermic needle and redissolve the penicillin salt in sterile saline or water. As marketed, penicillin is a white to pale yellow powder generally containing about 60 to 90 percent of sodium penicillin and assaying from 1,000 to 1,500 units per milligram. The remaining portion represents salts of organic acids contained in the broth and other nontoxic impurities carried over in the recovery operations. While penicillin is usually recovered and marketed as the sodium salt, other salts such as potassium, calcium, or barium penicillin have been prepared to meet special needs. In recent months a few manufacturers have come out with crystalline products containing essentially pure penicillin. It seems probable that in the near future penicillin will be generally marketed in this form.

Before they are sold, samples of all commercial lots of penicillin are carefully tested by the Food and Drug Administration for toxicity and for the presence of pyrogens, or fever-producing substances.

Chemistry and Production

The chemistry of penicillin has been thoroughly investigated by many workers in university, Government, and industrial laboratories collaborating under the joint supervision of the Committee on Medical Research, Washington, D. C., and the Medical Research Council, London. The intense interest in this chemistry was due in great part to the belief held during the early days of commercial production that the enormous military needs could be met only if chemical synthesis were accomplished. A practical synthesis of penicillin, however, was not realized during the war; fortunately, the production by fermentation proved adequate.

So far, six naturally occurring penicillins have been isolated in the pure state and all have the same empirical chemical formula, C9H1104SN2 R. All of the penicillins show the same qualitative action against micro organisms. The quantitative differences in potency (from 900 to 2,300 units per mg.) between the penicillins depend on the nature of the R-group. Of the different penicillins, penicillin X, first isolated by Stodola, Wachtel, and Coghill of this laboratory, is of unusual interest in that new, highly active penicillins can be produced from it by substitution reactions.

Before January 1943, the commercial production of penicillin was negligible, although much valuable clinical information had been obtained. In the 5-month period ending May 1943, 400 million units were produced, or roughly enough penicillin to treat 400 hospitalized cases. In the following month, 425 million units were produced and since June 1943 production has climbed steadily and rapidly. In the latter part of 1945, monthly production reached a level of approximately 800 billion units; during the 30 months after July 1943 it increased more than a thousandfold. In May 1946 approximately 2,700 billion units were produced, with an estimated value of approximately $15,000,000. There is every reason to anticipate still greater production. During the period from June 1943 to July 1946, the price of penicillin dropped from $20 per 100,000 units (acknowledged to be less than cost) to about 55 cents per 100,000 units. Parallel with the increase in production and the decrease in price there has been a steady improvement in the quality of the drug manufactured. Penicillin, as marketed in 1943, commonly contained about 100 u/per mg. of pure sodium penicillin; now the average is very much higher, with 1,500 u/per mg. of material not uncommon.