Commercial Quinolone Ear Drops Cause Perforations in Intact Rat Tympanic Membranes.

HYPOTHESIS: Commercial quinolone ear drops may promote the development of perforations (TMPs) in intact tympanic membrane (TMs). BACKGROUND: Quinolone ear drops have been associated with TMPs after myringotomy +/- tube placement in a drug-specific manner and potentiation by steroids. METHODS: Rats were randomized to six groups (10/group), with one ear receiving otic instillation of dexamethasone, ofloxacin, ciprofloxacin, ofloxacin + dexamethasone, ciprofloxacin + dexamethasone, or neomycin + polymyxin + hydrocortisone-all commercial formulations and at standard clinical concentrations-and the contralateral ear receiving saline, twice daily for 10 days. TMs were assessed over 42 days. RESULTS: No TMPs were seen in ears treated with saline, dexamethasone, or neomycin. At day 10, TMPs were seen in one of 10 ofloxacin- and three of 10 ciprofloxacin + dexamethasone-treated ears (p = 0.038). At day 14, the ofloxacin TMP healed. In contrast, the three ciprofloxacin + dexamethasone TMPs remained and one new TMP developed in this group. A ciprofloxacin and an ofloxacin + dexamethasone-treated ears also had TMPs (p = 0.023). By day 21, the ofloxacin + dexamethasone TMP and two of four of the ciprofloxacin + dexamethasone TMPs healed but two new TMPs were seen in ciprofloxacin + dexamethasone ears (p = 0.0006). At day 28, 1 of 10 ciprofloxacin and 4 of 10 ciprofloxacin + dexamethasone-treated ears had TMPs (p = 0.0006). By day 35, only one ciprofloxacin + dexamethasone had TMP (p = 0.42). All TMPS were healed at day 42. CONCLUSIONS: Application of commercial quinolone ear drops can cause TMPs in intact TMs. This effect appears to be drug-specific and potentiated by steroids.

Synthesis and in vitro characterization of novel dextran-methylprednisolone conjugates with peptide linkers: effects of linker length on hydrolytic and enzymatic release of methylprednisolone and its peptidyl intermediates.

To control the rate of release of methylprednisolone (MP) in lysosomes, new dextran-MP conjugates with peptide linkers were synthesized and characterized. Methylprednisolone succinate (MPS) was attached to dextran 25 kDa using linkers with 1-5 Gly residues. The release characteristics of the conjugates in pH 4.0 and 7.4 buffers, blood, liver lysosomes, and various lysosomal proteinases were determined using a size-exclusion and/or a newly developed reversed-phase HPLC method capable of simultaneous quantitation of MP, MPS, and all five possible MPS-peptidyl intermediates. We synthesized conjugates with >or=90% purity and 6.9-9.5% (w/w) degree of MP substitution. The conjugates were stable at pH 4.0, but released MP and intact MPS-peptidyl intermediates in the pH 7.4 buffer and rat blood, with faster degradation rates for longer linkers. Rat lysosomal fractions degraded the conjugates to MP and all the possible intermediates also at a rate directly proportional to the length of the peptide. Whereas the degradation of the conjugates by cysteine peptidases (papain or cathepsin B) was relatively substantial, no degradation was observed in the presence of aspartic (cathepsin D) or serine (trypsin) proteinases, which do not cleave peptide bonds with Gly. These newly developed dextran conjugates of MP show promise for controlled delivery of MP in lysosomes.

Dextran-methylprednisolone succinate as a prodrug of methylprednisolone: immunosuppressive effects after in vivo administration to rats.

PURPOSE: To study the immunosuppressive activities of a macromolecular prodrug of methylprednisolone (MP), dextran-methylprednisolone succinate (DEX-MPS), in rats. METHODS: Single 5 mg/kg (MP equivalent) doses of MP or DEX-MPS were administered intravenously to rats, and blood and spleen samples were collected over 96 h. The immunosuppressive activity was determined by the effects of the free or dextran-conjugated drug on the mitogen-stimulated spleen lymphocyte proliferation. Additionally, the number of lymphocytes in the spleen cell suspensions was estimated. Further, the plasma and spleen concentrations of the conjugated and free MP were determined using size-exclusion and reversed-phase chromatographic methods, respectively. RESULTS: Both MP and DEX-MPS injections resulted in the inhibition of the spleen lymphocyte proliferation. However, the maximal effect of DEX-MPS was significantly (P < 0.003) more intense (approximately 100% inhibition) and delayed (24 h) relative to that of MP (approximately 50% inhibition at 2 h). The DEX-MPS injection also resulted in a significantly (P < 0.0001) higher decline in the estimated number of spleen lymphocytes (approximately 80% at 24 h), compared with the MP injection (approximately 30% at 2 hr). Whereas the plasma and spleen concentrations of MP could not be measured at > or = 2 h after the drug injection, relatively high concentrations of DEX-MPS persisted in plasma and spleen for 24 h and 96 h, respectively. CONCLUSION: Dextran-methylprednisolone conjugate can effectively deliver the corticosteroid to its site of action for immunosuppression, resulting in more intense and sustained effects when compared with the free drug administration.

High-performance liquid chromatographic assay for methylprednisolone and its soluble prodrug esters in dog plasma.

A high-performance liquid chromatographic method with ultraviolet detection (lambda max = 243 nm) has been developed for the simultaneous determination of methylprednisolone (MP) and its water-soluble prodrug esters methylprednisolone hemisuccinate (MPS) and N,N,N'-triethylethylenediamine amide of 6 alpha-methylprednisolone-21-hemisuberate hydrochloride (TMPS) in dog plasma. A reversed-phase liquid chromatographic separation was performed on a Microsorb C8 (3 microns) column equipped with a C8 5-microns guard column. The mobile phase composition was water--acetonitrile--methanol--dimethyloctylamine--acetic acid (65.5:34:0.4:0.04:0.04). The methyl ester of phenethylcarbamate was employed as an internal standard. The chromatographic responses were linear up to 25 micrograms/ml for MP, 70 micrograms/ml for MPS, and 95 micrograms/ml for TMPS. The sensitivity of the assay by ultraviolet detection is approximately 4, 8, and 12 ng/ml of plasma for MP, MPS and TMPS, respectively. The assay variability in terms of 95% confidence limit for each steroid is less than 4.5%. Plasma concentration--time curves are reported for MP, MPS, and TMPS after intravenous administration of MPS and TMPS equivalent to 3, 10 and 30 mg MP per kg body weight of dog. The assay methodology is simple, selective and reproducible for the quantitative determination of MP, MPS and TMPS in dog plasma.