Significance of Protein Binding of Penicillins

A large volume of data on variations in serum penicillin levels has been obtained from work carried out with depot preparations of procaine benzyl penicillin in oil (to be published). Figure 1 shows frequency histograms of blood levels obtained in humans 24 hours after a single fixed dose of the same preparation. Large groups of individuals were involved and there was an interesting difference between Clinic C and the other two clinics. With a preparation of this type there is the added variable of the rate of release of penicillin from the oil depot into the blood stream. In choosing the dose of a penicillin for therapy presumably it should be onse which is adequate even for individuals with the lowest serum levels found in this type of distribution. Usually only mean blood levels are quoted and no idea is given of the range found in a normal population, and no comparison appears to have been made of the ranges of the various penicillins. A penicillin producing a small range of blood levels at any given time would be advantageous.