Stability of Antibiotics and Amino Acids in Two Synthetic l -Amino Acid Solutions Commonly Used for Total Parenteral Nutrition in Children

Abstract

The stability and interaction at 290C of ampicillin, carbenicillin, gentamicin, and polymyxin B were examined in a common electrolyte solution, invertose darrow, and in two synthetic L-anmno acid solutions, one commercial (vamin with fructose; Vitrum) and the other a neonatal preparation modified for use in newborn infants. The concentration of amino acids was measured before and after the addition of these antibiotics. The concentration of antibiotics was measured over a 24-h period with a microbiological method. The concentration of ampicillin in invertose darrow fell 52%, and in vamin with fructose it fell 69%, whereas in the neonatal preparation the fail was only 22%. The concentration of carbenicillin in vamin with fructose fell 37%, and in the neonatal preparation it fell 31%. The combination of ampicillin or carbenicillin with gentamicin or polymyxin B did not influence the activity of the penicillins. The concentration of gentamicin and polymyxin B was unchanged in all solutions over a 24-h period. With the exception of cystine, the concentration of all amino acids remained constant after 24 h in the neonatal preparation with and without the different combinations of antibiotics. For cystine there was a fall of 20 to 30%.Since the appearance of intravenous solutions containing synthetic amino acids and lipid, it has become possible to cover patients' needs for protein, energy, electrolytes, vitamins, and essential fatty acids by so-called total parenteral nutrition (TPN). Within the last few years, this treatment has been used successfully even in small newborn infants. To avoid contamination of the solutions during infusion, it is necessary to use a closed infusion system. Addition of antibiotics to the solutions before the start of the infusion would therefore be preferable to intravenous injection via the system or intramuscular injections, which may often cause problems, particularly in very small newborns with reduced muscle mass. Furthermore, by adding antibiotics to the fluids, which are infused via a pump, it is possible to maintain a steady-state concentration higher than the minimal inhibitory concentration for most bacterial strains. Aminoglycosides administered in such a way have been shown to result in a high cure rate in adults (1).