Antibiotic Stability
ABSTRACT & COMMENTARY
Synopsis: Knowledge of the duration of the stability of antimicrobial preparations assists in the optimization of outpatient intravenous antibiotic therapy.
Source: Stiles ML, Allen LV. Stability of nafcillin sodium, oxacillin sodium, penicillin G potassium, penicillin G sodium and tobramycin sulfate in polyvinyl chloride drug reservoirs. Am J Health-Syst Pharm 1997;54:1068-1070.
This article looks at the stability of four penicillin preparations and of tobramycin in polyvinyl chloride reservoirs. The particular reservoirs used in this study are 100 mL containers that attach to the CADD series ambulatory infusion pumps manufactured by Sims-Deltec, Inc. Table 1 summarizes the results of their stability study.
TABLE
Stability Stability at 25ºC at 5°C (Room Antibiotic Concentration Diluenta (Refrigeration) Temperature)
Nafcilli20 mg/mL SW 14 days 3 days
Nafcilli120 mg/mL SW 14 days 3 days
Oxacilli 120 mg/mL SW 14 days 3 days
Penicillin G
Potassium 100,000 U/mL SW 3 days
Penicillin G
Potassium 200,000 U/mL SW 14 days 3 days
Penicillin G
Sodium 100,000 U/mL SW 3 days
Penicillin G
Sodium 200,000 U/mL SW 3 days
Tobramyci1 mg/mL NS 14 days 3 days
Tobramyci10 mg/mL NS 14 days 3 days
a SW = Sterile Water for Injection NS = 0.9% Sodium Chloride Injection
n COMMENT BY THOMAS SCHLEIS, MS, RPH
In the hospital setting, the stability of medications is generally not of major concern because most medications are stable for 24 hours at room temperature or under refrigeration, and in most hospitals medications are prepared every 24 hours. In the outpatient setting, however, the stability of medications becomes of great importance. If a medication reservoir can be replaced every three days instead of daily, patient convenience and compliance is enhanced, and the cost of supplies and preparation time are reduced.
There are a number of cautions to consider when reviewing stability studies. Stability of one manufacturer’s preparation may not be applicable to another’s. Also, one needs to consider the stability differences that may occur between different infusion devices, such as syringes vs. minibags vs. glass bottles. In most cases, drug stability is consistent among different infusion systems, but some authors believe that stability data are only applicable if it is performed in the specific infusion device it will be administered with.1
One drawback of this particular study is that they did not look at the maximum stability range for the medications studied. The authors also did not perform frozen stability studies. Oxacillin, for example, has been previously shown to be stable for up to seven days at room temperature, and we routinely administer a week’s worth of therapy in a single infusion container to our home care patients. When an ambulatory infusion pump is used, the drug can be conveniently and accurately administered. New data presented in this study include stability of tobramycin at a concentration of 10 mg/mL. Although this work had been previously performed by others, it was not reported in the literature. The concentration of 10 mg/mL allows for convenient administration of once-daily doses of tobramycin in a syringe pump, such as 300 mg in 30 mL of normal saline.
Reference
1. Lima, HA. Drug stability and compatibility: Special considerations for home care. Infusion 1996;2:10-16.
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