Stabilizing effect of inorganic phosphate salts on antibiotic-steroid ophthalmic preparations

Utility of nuclear magnetic resonance spectroscopy to characterize the structure of dexamethasone sodium phosphate inclusion complexes with cyclodextrins in solution and to analyze potential competitive effects

The interaction between dexamethasone sodium phosphate (DSP) and four cyclodextrin (CyD) derivatives [2,6-di-O-beta-cyclodextrin (DIMEB), gamma-cyclodextrin (gamma-CyD), and hydroxypropyl-beta-cyclodextrin with either 2.7 or 4.6 degrees of substitution (HPbetaCyD 2.7 and HPbetaCyD 4.6, respectively)] was investigated by proton nuclear magnetic resonance spectroscopy (1H NMR). The data suggested the formation of inclusion complexes in solution in which B and C rings of the molecule are located inside the cavity. Nevertheless, the structure, in terms of depth within CyD, depends on the derivative considered. Molecular mechanics calculations of DSP complexes with DIMEB and gamma-CyD support the NMR results. The potential displacement of DSP from the CyD cavity by usual ophthalmic drugs (e.g., polymyxin B, trimethoprim, and benzalkonium chloride) was determined by NMR. The technique has been found useful to analyze this problem in pharmaceutical preparations.

Ethylenediamine, profile of a sensitizing excipient

Ethylenediamine is an excipient with many industrial and pharmaceutical uses. It is included in creams as a stabilizer and in aminophylline as the counter ion of theophylline. Ethylenediamine is one of the most frequent contact sensitizers, producing local and generalized reactions. Besides, many cases of systemically induced dermatitis have also been described both after oral, rectal and intravenous use. Inhalation of ethylenediamine or aminophylline dust may provoke rhinitis and asthmatic reactions. In contrast to these delayed reactions only one immediate reaction of the urticarial type after intravenous use has been described. Ethylenediamine shows cross-reactions with antihistamines of the ethylenediamine derivative group, with edetate, other amines, piperazine and hydroxyzine. Ethylenediamine shows a short half-life of about 0.55 h and a small volume of distribution of 0.133 l/kg. After oral administration its bioavailability is about 0.34, due to a substantial first-pass effect. Renal excretion of the unchanged substance amounts to only about 18% after intravenous and 3% after oral administration. It behaves independently from theophylline after administration of aminophylline. Good alternatives are now available for the pharmaceutical applications of ethylenediamine. Theophylline itself is well absorbed orally; for the intravenous administration the N-methylglucamine salt is sufficiently soluble. Suppositories containing pure theophylline are commercially available in some countries, but the experience with this product is relatively small.