The conductance of solutions of sodium benzylpenicillinate.

The conductance of solutions of penicillin salts is a governing factor in iontophoretic treatment of infections with this antibiotic. In contrast to the experiments of von Sallmann and Meyer (1) showing an increased transport of penicillin to the aqueous humor of rabbit eyes under a D.C. potential of 45 volts, Hamilton-Paterson (2) states that “penicillin appears to be either a very poor conductor or a non-conductor.” This conclusion Teas based on current measurements in extremely dilute (-25 to 50 units per ml.) sodium penicillin solutions with equipment not designed to investigate ion mobilities. A high D.C. voltage (240 volts) maintained over a period of 1 to 2 hours undoubtedly produced electrolysis of water with attendant pH changes at the electrodes, which in turn were responsible for the observed indicator color changes and for the reported destruction of penicillin, a substance known to be very unstable (3) above pH 10 and below pH 4. Furthermore, the increase in current to be expected from addition of s-10” to 10m4 R;I sodium penicillin was too small (though significant in Hamilton-Paterson’s Experiment 1) to be measured with any certainty in the cell employed, which doubtless had a very high cell constant. It seems inadmissible, despite the experiments cited, that a sodium salt of penicillin should have a negligible conductance, although it is altogether reasonable to expect the penicillin anion to have a lower mobility than most inorganic or small organic anions. This expectation was confirmed by the conductance measurements of aqueous solutions of crystalline sodium benzylpenicillinate (penicillin G) described in this paper.