Methods of Measuring Penicillin Concentrations in Body Fluids

Abstract

Inhibition of bacterial growth is the basis of the three methods commonly used for determining the potency of penicillin solutions. With the Oxford cup method (Abraham et al., 1941; Foster and Woodruff, 1944), penicillin is allowed to diffuse out into agar plates from small glass cups, and the diameters of the zones of inhibition of bacterial growth are measured. In dilution methods (Foster and Woodruff, 1943; Rammelkamp, 1942), the smallest amount of penicillin which will completely inhibit bacterial growth in solid or liquid media is the standard with which unknowns are compared. In turbidimetric methods, a range is selected in which bacterial growth is proportional to penicillin concentration, and a standard curve is constructed from turbidimetric measurements of the bacterial suspensions.

The Relative Activity of Penicillins F, G, K, and X Against Spirochetes and Streptococci in Vitro

“…Streptococcidal assay. The method used for the assay of streptococcidaI activity was a modification of those described by Rammelkamp (1942) and Kirby and Rantz (1944). The stock penicillin solution was diluted in beef infusion broth to a concentration of 1:8,000,000 or 1:16,000,000.…”

Studies on Penicillin in Blood

“…Incubation for 6 hours at 37 C. sensitivity to penicillin. Figure 1 represents a typical standard curve obtained after 7 hours' incubation in proteose peptone medium with added yeast extract and glucose.2 Kirby and Rantz (1944) have reported that the addition of serum to brain heart infusion cultures of a hemolytic streptococcus causes very marked nonspecific growth stimulation. We have investigated the effects of serum and plasma addition upon staphylococcus growth in a series of media.…”