Potency and stability of extemporaneous nitroglycerin infusions

The potency and stability of extemporaneous intravenous nitroglycerin (NTG) solutions prepared according to methods currently used in three hospitals were studied. Intravenous NTG solutions were prepared and packaged according to three hospitals' protocols. The NTG solutions varied in concentration (32 microgram/ml); source (one of two manufacturers' sublingual NTG tablets or 10% NTG adsorbate in lactose); and storage (ambient room temperature or refrigerated). The concentration of NTG in the i.v. solutions was determined spectrophotometrically. Nitroglycerin was found to be stable for at least 70 days when stored in glass containers, regardless of source, diluent (5% dextrose in water or normal saline) and storage temperature. The loss of NTG from solution, after storage for seven days in plastic i.v. bags, was greater when stored at room temperature (55%) than when refrigerated (30%). Adsorption was shown to be responsible for this phenomenon because intact drug was completely recovered from the plastic i.v. bags after methanol elution. The results of this study allow formulation of recommendations regarding the extemporaneous preparation of i.v. NTG solutions.