Related Articles

The positively charged polysaccharide chitosan is able to increase precorneal residence time of ophthalmic formulations containing active compounds when compared with simple aqueous solutions. The purpose of the study was to evaluate tear concentration of tobramycin and ofloxacin after topical application of chitosan-based formulations containing 0.3% wt/vol of antibiotic and to compare them with 2 commercial solutions: Tobrex® and Floxal®, respectively. The influence of the molecular weight, deacetylation degree, and concentration of 4 different samples of chitosan on pharmacokinetic parameters (area under the curve values [AUCeff] and time of efficacy [teff]) of tobramycin and ofloxacin in tears was investigated over time. It was demonstrated that the 2 chitosan products of high molecular weight (1350 and 1930 kd) and low deacetylation degree (50%) significantly increased antibiotic availability when compared to the controls, with AUCeff showing a 2-to 3-fold improvement. The time of efficacy of ofloxacin was significantly increased from about 25 minutes to 46 minutes by the chitosan of higher Mw (1930 kd) at a concentration of 0.5% wt/vol, whereas a similar performance was achieved by a chitosan of low Mw (580 kd) at a concentration of 1.5% wt/vol in the case of tobramycin.

Introduction

The standard postsurgical treatment of wounds after dermatologic procedures is currently limited. Topical corticosteroids have been used successfully in postoperative management of ophthalmologic surgeries that involve the skin of the eyelid. In particular, tobramycin 0.3%/dexamethasone 0.1% ophthalmic ointment is considered the “gold standard” of steroid-antibiotic fixed combinations and is marketed worldwide as an agent used to control postsurgical inflammation and prevent postsurgical infection. The purpose of this study is to evaluate both the efficacy and safety of tobramycin–dexamethasone ointment for the postsurgical management of Mohs or dermatologic surgery in comparison to white petrolatum.

Methods

The authors employed a half-scar study in which patients who underwent skin cancer removal surgery were given tobramycin–dexamethasone ointment and white petrolatum to apply to each half of their wound for 2 weeks. The study was double blinded, and physicians and the patients independently evaluated the scars for cosmetic appearance at 2 and 6 weeks postoperatively. The evaluation criteria included judging which side of the wound looked better based on color, thickness, and discomfort.

Results

Eighteen patients were enrolled, of which 13 patients completed the three phases of the study. After 6 weeks the wounds did not show a statistically significant difference in color, thickness, or discomfort on either side.

Conclusion

Results obtained to date suggest that the application of tobramycin–dexamethasone ointment to wounds after dermatologic surgery does not promote better wound healing than white petrolatum. These findings indicate that a topical steroid and antibiotic ointment may not be an effective intervention in improving postoperative outcomes in dermatologic surgeries.

Hydroxylamine was evaluated and found to be a highly effective agent for the in vitro prevention of penicillin inactivation of tobramycin. This inactivation reaction resulted in an underestimation of tobramycin concentrations and was dependent on time, temperature, amount and type of penicillin, and amount of tobramycin. Plasma samples containing tobramycin and three clinically relevant concentrations of ticarcillin, carbenicillin, azlocillin, or piperacillin were incubated with and without hydroxylamine, and tobramycin concentrations were monitored at 0, 12, 24, 48, and 72 h. The inactivation reaction was found to be completely inhibited by hydroxylamine (1 mg/ml) compared with a 27 to 50% loss of measured tobramycin concentration in the unprotected tobramycin-penicillin samples. Hydroxylamine did not interfere with the Emit enzyme immunoassay (Syva Co.) at either high or low tobramycin concentrations. Hydroxylamine was effective in inhibiting the tobramycin inactivation at both room and refrigerator temperatures and was 100% effective in protecting tobramycin on a 1:1 molar basis.

The in vitro and in vivo inactivation of tobramycin by carbenicillin, ticarcillin, or piperacillin was investigated by the enzyme immunoassay method in clinically employed dosages. After the addition of an 80-mg dose of tobramycin to 4- to 5-g doses of a penicillin in 100 ml of 0.9% saline or distilled water, the degradation profile of tobramycin appeared to follow a biexponential pattern of decay. Remarkable losses (30 to 40%) of tobramycin combined with carbenicillin or ticarcillin were observed within 1 h, as compared with the later decline. The combination of tobramycin with piperacillin was least inactivating. When the admixture of tobramycin with carbenicillin or piperacillin used in the in vitro study was infused to six volunteers over 1 h, the observed maximum concentrations of tobramycin were on the average 66 and 74% for carbenicillin and piperacillin, respectively, of that observed after tobramycin alone was given. In contrast, the value obtained for tobramycin in combination with piperacillin was close to 90% of the control value. The elimination half-lives of tobramycin combined with the penicillins were slightly shorter than those of tobramycin alone, indicating that the interaction occurs even in patients with normal renal function.

To provide insight into polyaspartic acid nephroprotection and differences in aminoglycoside renal toxicity between two rat strains, the single-dose pharmacokinetics of tobramycin was examined in the presence and absence of polyaspartic acid. Following a single subcutaneous 6.5-mg/kg dose of tobramycin alone, higher aminoglycoside concentrations were measured in Sprague-Dawley rats than in Fischer rats (P < 0.05). Simultaneous administration of polyaspartic acid (50 mg/kg) and tobramycin did not alter the concentrations of tobramycin in serum. The amount of tobramycin in renal tissue and the amount recovered in urine over a 24-h period were greater in both rat strains when tobramycin and polyaspartic acid were given concomitantly. In summary, polyaspartic acid did not alter the concentrations in serum achieved after a single dose of tobramycin in two different rat strains but did result in higher renal concentrations and greater urinary excretion of tobramycin.

Purpose:

To compare the kinetics and speed of kill of Streptococcus pneumoniae and Haemophilus influenzae on exposure to three topical ophthalmic antibiotic solutions.

Materials and methods:

Bacterial conjunctivitis isolates of S. pneumoniae and H. influenzae were exposed to 1:1000 dilutions of moxifloxacin 0.5%, tobramycin 0.3%, gentamicin 0.3%, and water (control). At 15, 30, 60, 120, and 180 minutes after exposure, aliquots were collected, cells were cultured, and viable cell counts were determined using standard microbiological methods.

Results:

Moxifloxacin achieved 99.9% kill (3-log reduction) at approximately 2 hours for S. pneumoniae and at 15 minutes for H. influenzae. Tobramycin and gentamicin did not achieve 3-log reduction of S. pneumoniae during the 180-minute study period. An increase in bacterial growth was noted for these isolates. Gentamicin took more than 120 minutes to achieve the 3-log reduction of H. influenzae and tobramycin did not reach the 3-log reduction of this pathogen during the 180-minute study period.

Conclusion:

Moxifloxacin killed S. pneumoniae and H. influenzae in vitro faster than tobramycin and gentamicin, suggesting its potential clinical benefit as a first-line treatment for bacterial conjunctivitis to minimize patient symptoms and to limit the contagiousness of the disease.

Purpose.

Lacritin is a human tear glycoprotein that promotes basal tear protein secretion in cultured rat lacrimal acinar cells and proliferation of subconfluent human corneal epithelial cells. When topically added to rabbit eyes, lacritin promotes basal tearing. Despite these activities on several species, lacritin's presence in nonprimate tears or other tissues has not been explored. Here we probed for lacritin in normal horse tears.

Methods.

Sequences were collected from the Ensembl genomic alignment of human LACRT gene with high-quality draft horse genome (EquCab2.0) and analyzed. Normal horse tears were collected and assayed by Western blotting, ELISA, and mass spectrometry. Newly generated rabbit antibodies, respectively, against N- and C-terminal regions of human lacritin were employed.

Results.

Identity was 75% and 45%, respectively, at nucleotide and protein levels. Structural features were conserved, including a C-terminal amphipathic α-helix. Anti-C-terminal antibodies strongly detected a ∼13 kDa band in horse tears that was validated by mass spectrometry. In human tears, the same antibody detected uncleaved lacritin (∼24 kDa) strongly and C-terminal fragments of ∼13 and ∼11 kDa weakly. Anti-N-terminal antibodies were slightly reactive with a ∼24 kDa horse antigen and showed no reaction with the anti-C-terminal–reactive ∼13 kDa species. Similar respective levels of horse C-terminal versus N-terminal immunoreactivity were apparent by ELISA.

Conclusions.

Lacritin is present in horse tears, largely as a C-terminal fragment homologous to the mitogenic and bactericidal region in human lacritin, suggesting potential benefit in corneal wound repair.

Protein evidence for the first nonprimate lacritin is described.

The kinetics of the postantibiotic effect (PAE) during one dosing interval of tobramycin against Staphylococcus aureus and Pseudomonas aeruginosa was investigated. We determined the PAE at different time points during this dosing interval of 12 h in an in vitro pharmacokinetic model simulating human pharmacokinetics in which the half-life of tobramycin was adjusted to 2.4 +/- 0.2 h. Using an enzymatic method to inactivate tobramycin, we determined PAEs in samples extracted from the model at 1, 5, 8, and 12 h, corresponding with tobramycin concentrations of 20, 5, 2, and 1 times the MIC for the test organism. The PAE decreased significantly from 2.5 h at 1 h to 0 h at 12 h. No change in MIC was observed for the strains during the experiments. We conclude that the PAE decreases with decreasing tobramycin concentrations during a 12-h dosing interval and completely disappears after the concentration has reached the MIC for the test organism. On the basis of these observations, the emphasis that is placed on the PAE in discussions about the optimal dosing interval in aminoglycoside therapy is questionable.

Background

Chronic dry eye disease often requires long-term therapy. Tear film alterations in the setting of dry eye may include reduced tear volume as well as an increase in inflammatory cytokines and osmolarity. Topical cyclosporine ophthalmic emulsion 0.05% (Restasis®; Allergan Inc, Irvine, CA) is indicated to increase tear production in patients with dry eye and reduced tear production presumed to be due to ocular inflammation. This study was designed to evaluate the efficacy of a second trial of topical cyclosporine in patients with dry eye who were previously considered treatment failures.

Materials and methods

This multicenter (three cornea practices) retrospective chart review evaluated clinical outcomes in patients with dry eye who received a second trial of cyclosporine after a prior treatment failure, defined as prior discontinuation of topical cyclosporine after less than 12 weeks.

Results

Thirty-five patients, most of whom were female (71.4%) and Caucasian (62.9%), were identified. Prior discontinuation was most commonly due to burning/stinging (60%). The median duration of second treatment was 10 months (range 1 week to 45 months). Physician education was provided in the second trial in 97.1% of cases. At initiation of the second trial of cyclosporine, 10 (28.6%) patients received courses of topical corticosteroids. Physicians reported on a questionnaire that 80% of patients achieved clinical benefit with a second trial of cyclosporine.

Conclusion

A repeat trial with topical cyclosporine can achieve clinical success. Direct patient education via the physician and staff may be key to success. Proper patient education may overcome adherence issues, particularly with respect to the need for long-term treatment of chronic dry eye. This study has the usual limitations associated with a retrospective chart review, and future prospective studies are warranted.

To explore more effective therapy for Pseudomonas aeruginosa, 264 recent clinical isolates were tested by agar dilution using gentamicin and tobramycin alone and combined with carbenicillin to seek synergistic effects. Synergism was defined as a fourfold or greater decrease in the minimal inhibitory concentration of each drug in a pair. At a concentration of 3.12 μg/ml, gentamicin inhibited 73% of the strains and tobramycin inhibited 98%. The gentamicin-carbenicillin combination was synergistically active against 57% of the strains, and tobramycin-carbenicillin was active against 46%. The effect did not correlate with either susceptibility or resistance to gentamicin or tobramycin alone. The data suggest that tobramycin or tobramycin plus carbenicillin may provide alternate therapy where susceptibility to gentamicin or synergism between gentamicin and carbenicillin cannot be demonstrated; however, the degree of susceptibility to either aminoglycoside antibiotic alone cannot be used to predict a synergistic effect.

Concentrations of three anti-infective agents in tear film were monitored after one topical application in rabbits. Ofloxacin concentrations exceeded the MIC for 90% of the organisms tested (MIC90) (gram-negative and gram-positive organisms) for 240 min. Tobramycin concentrations exceeded the MIC90 for 10 min. Gentamicin concentrations exceeded the MIC90 for 20 min for gram-positive organisms and 120 min for gram-negative organisms.

Images

The pharmacokinetics, distribution, and plasma and renal clearance of a new aminoglycoside antibiotic, tobramycin, was studied in the treatment of 18 elderly male patients (average age, 69 years) with urinary tract infections. Ten of these patients had normal renal function and eight had impaired renal function of various degrees. After administration of 1 mg of tobramycin/kg of body weight every 6 to 8 h (two to three times the half-life), urine concentrations were found to be sufficient in the treatment of urinary tract infections caused by susceptible organisms. The renal clearance of tobramycin during constant intravenous infusion was also studied in eight patients. Good correlation was found between the patients serum creatinine and the half-life of tobramycin. The half-life of tobramycin in patients with normal renal function (serum creatine [Formula: see text] to 1.5 mg/100) was on the average 3 h. For practical purposes, therefore, the dosage of tobramycin in the treatment of urinary tract infections should be 1 mg/kg of body weight every 6 to 8 h in patients with normal renal function. For patients with impaired renal function, the dosage interval is calculated by multiplying the patients' serum creatinine by six. If the dosage intervals are kept unchanged, the dosage must be divided by the patients' serum creatinine. The initial loading dose should always be 1 mg/kg. The total renal clearance of tobramycin (92% of the glomerular filtration rate) was not influenced by the administration of probenecid, which indicates that tobramycin is excreted only by glomerular filtration.

The effect of bladder surgery on the pharmacokinetics of tobramycin in hospitalized patients was studied. Fourteen patients with vesical neoplasia undergoing urinary tract surgery were given tobramycin in a dose of 2 mg/kg of body weight. Each patient received the dose at the induction of anesthesia, about 1 h before surgical incision. For seven patients, the drug was also administered 3 weeks later when nutritional conditions were normal. The pharmacokinetic parameters were determined by a two-compartment open model. Except for renal clearance, no significant difference appeared between pharmacokinetic parameters determined from serum data during peri- and postoperative periods. During this work, tobramycin excretion in urine was studied. Twenty-four hours after drug administration, the mean urine tobramycin levels were 25.5 +/- 9.06 and 41.6 +/- 21.5 micrograms/ml after peri- and postoperative administration, respectively; these values were higher than the MICs for most urinary tract pathogens. Seventy-two hours after perioperative administration, the mean value was still elevated (3.54 micrograms/ml), but 72 h after postoperative administration, the urinary tobramycin concentration was not detectable. The percentages of tobramycin recovered unchanged in urine were 54 and 79% after peri- and postoperative administration, respectively. When tobramycin was administered during surgery, a long terminal log-linear phase, with a mean half-life of 25.6 h, was detected. The ratio of renal clearance to total body clearance was 0.52 and 0.79 after peri- and postoperative administration, respectively.

Bacterial conjunctivitis appears to resolve more rapidly when treated with appropriate topical antimicrobial agents. In this multicenter, randomized, double-blind study of efficacy and safety, patients with presumed bacterial external eye infections were assigned to topical therapy with 0.3% norfloxacin or 0.3% tobramycin. A total of 120 patients were enrolled. Of the total, 65 had documented bacterial infections and were evaluable; 59 of these patients had bacterial conjunctivitis. All of the patients with documented infections were cured or improved regardless of the drug treatment regimen or in vitro susceptibility testing results. The most common bacteria isolated were Haemophilus influenzae, Streptococcus pneumoniae, alpha-hemolytic streptococci, Staphylococcus aureus, and Staphylococcus sp. No patients had serious adverse reactions attributed to their therapy. Norfloxacin ophthalmic solution seems to be a safe, effective, and appropriate agent for the treatment of bacterial external eye infections.

In a rabbit model of adenoviral keratoconjunctivitis, the combination of topical dexamethasone 0.1%/povidone-iodine 0.4% (FST-100) had clinical and antiviral efficacy. FST-100 had no ocular toxicity.

Purpose.

To determine the efficacy of a new formulation of topical dexamethasone 0.1%/povidone-iodine 0.4% (FST-100) in reducing clinical symptoms and infectious viral titers in a rabbit model of adenoviral keratoconjunctivitis.

Methods.

Rabbit corneas were inoculated bilaterally with 2 × 106 plaque-forming-units (PFU) of adenovirus type 5 (Ad5) after corneal scarification. Animals were randomized 1:1:1:1 (five rabbits per group) to FST-100, 0.5% cidofovir, tobramycin/dexamethasone (Tobradex; Alcon Laboratories, Fort Worth, TX) ophthalmic suspension, and balanced salt solution (BSS; Alcon Laboratories). Treatment began 12 hours after viral inoculation and continued for 7 consecutive days. The eyes were clinically scored daily for scleral inflammation (injection), ocular neovascularization, eyelid inflammation (redness), friability of vasculature, inflammatory discharge (pus), and epiphora (excessive tearing). Eye swabs were collected daily before treatment for the duration of the study. Virus was eluted from the swabs and PFU determined by titration on human A549 cells, according to standard procedures.

Results.

The FST-100 treatment resulted in significantly lower clinical scores (P < 0.05) than did the other treatments. The 0.5% cidofovir exhibited the most ocular toxicity compared with FST-100, tobramycin/dexamethasone, and balanced salt solution treatments. FST-100 and 0.5% cidofovir significantly (P < 0.05) reduced viral titers compared with tobramycin/dexamethasone or balanced salt solution.

Conclusions.

FST-100 was the most efficacious in minimizing the clinical symptoms of adenovirus infection in rabbit eyes. FST-100 and 0.5% cidofovir were both equally effective in reducing viral titers and decreasing the duration of viral shedding. By providing symptomatic relief in addition to reducing infectious virus titers, FST-100 should be a valuable addition to treatment of epidemic adenoviral keratoconjunctivitis.

The objective of the present study was to determine the pharmacokinetics and efficacies of liposomal and conventional formulations of tobramycin against Burkholderia cepacia in a model of chronic lung infection. Male Sprague-Dawley rats were inoculated intratracheally with 106 CFU of a very resistant strain of B. cepacia (strain BC 1368; MIC, 128 μg/ml) to establish lung infection. A 1,200-μg dose of tobramycin was administered intratracheally as a liposomal formulation and as a conventional formulation. Rats were anesthetized and exsanguinated by cardiac puncture at different times over 24 h to assess pulmonary tobramycin concentrations and the number of residual CFU. Pharmacokinetic parameters were calculated by using a two-compartment model with NONMEM. The mean half-life at the β phase (t1/2β) and the pulmonary exposure (the area under the concentration-time curve [AUC]) of liposomal tobramycin were 19.7 h (coefficient of variation [CV], 24.2%) and 6,811 μg · h/lungs (CV, 19.7%), respectively. The pharmacokinetics of conventional tobramycin were statistically different, with a t1/2β and AUC of 12.9 h (CV, 31.4%) and 821 μg · h/lungs (CV, 15.0%), respectively. Pearson chi-square analyses were performed on residual CFU data distributed in the following categories: <103, 103 to 105, and >105. Differences in CFU data between formulations showed a statistical trend (P < 0.10) when data from all time points were used, and statistically significant differences were found after 12 h (P < 0.05), with greater eradication achieved with the liposomal formulation. In conclusion, intratracheal administration of tobramycin in liposomes was associated with marked changes in the pharmacokinetics of the drug in the lung and an apparent trend for a prolonged efficacy against B. cepacia. These results support the hypothesis that inhalation of liposomal tobramycin may improve the management of chronic pulmonary infections caused by resistant bacteria in patients with cystic fibrosis.

A total of 201 critically ill patients were studied during 267 courses of gentamicin or tobramycin treatment (139 gentamicin courses and 128 tobramycin courses). Of these 267 courses, pharmacokinetic and clinical data were obtained for 240 (120 gentamicin and 120 tobramycin). The data collected for pharmacokinetic analysis included measurements of serial blood and urine levels, urinary excretion of beta 2-microglobulin, protein levels, and granular casts. A two-compartment model was used to assess tissue accumulation, and in 89 courses the predicted accumulation was confirmed by cumulative urine collection or postmortem tissue analysis. As groups, the patients given gentamicin and tobramycin did not differ in age, weight, creatine clearance, total dose given, duration of treatment, initial aminoglycoside through serum levels, number of dosage adjustments, concurrent use of furosemide, or concurrent cephalosporins. Previous aminoglycoside treatment (usually gentamicin) had occurred more frequently in the tobramycin treated patients (P less than 0.01), and more males than females received tobramycin (P less than 0.05). Pharmacokinetic assessments of renal damage were based on both changes in glomerular filtration rate (serum creatinine levels, creatinine clearance) and renal tubular damage (beta 2-microglobin, casts), but only patients with elevated aminoglycoside tissue levels leading to renal tubular damage and subsequent creatinine clearance decreases were considered to have experienced aminoglycoside nephrotoxicity. In the pharmacokinetic analysis of nephrotoxicity, 29 gentamicin courses (24%) and 12 tobramycin courses (10%) were complicated by nephrotoxicity (P less than 0.01). The 201 study patients were also evaluated independently for clinical nephrotoxicity (defined as a serum creatinine level increase of 0.5 mg/dl or more). Clinical nephrotoxicity occurred at rates of 37% in the gentamicin-treated group and 22% in the tobramycin-treated group (P less than 0.02). In these similar groups of critically ill patients, tobramycin was less nephrotic than gentamicin.

Previous studies have demonstrated synergy between an aminoglycoside and a beta-lactam for treating Pseudomonas aeruginosa infections. Cystic fibrosis patients are prone to infection by this bacterium, which becomes very resistant with recurrent antibiotic treatments. The purpose of this study was to evaluate the susceptibility patterns of 122 isolates of P. aeruginosa isolated from cystic fibrosis patients to five individual antibiotics (tobramycin, ceftazidime, piperacillin, ticarcillin, and imipenem) and to four antibiotic combinations (tobramycin associated with one of the other antibiotics). Strains were selected because of their resistance to individual antimicrobial agents, which ranged from 21.3% for imipenem to 56.5% for tobramycin. By using an automated broth microdilution method, we were able to demonstrate synergy against 39 strains (32%) with tobramycin-ticarcillin, against 38 strains (31%) with tobramycin-piperacillin, against 47 strains (39%) with tobramycin-ceftazidime, and against 23 strains (19%) with tobramycin-imipenem. Of the 122 isolates, 77 (63%) were rendered significantly susceptible to at least one of the four antibiotic combinations by synergy. These results suggest that when appropriate technology is available, susceptibility to antibiotic combinations greatly improves the guide to antibiotic therapy for infections due to P. aeruginosa in cystic fibrosis patients.

The lipopeptidic antibiotic daptomycin is reported to reduce experimental tobramycin nephrotoxicity (D. Beauchamp, M. Pellerin, P. Gourde, M. Pettigrew and M. G. Bergeron, Antimicrob. Agents Chemother. 34:139-147, 1990; C. A. Wood, H. C. Finkbeiner, S. J. Kohlhepp, P. W. Kohnen, and D. C. Gilbert, Antimicrob. Agents Chemother. 33:1280-1285, 1989). In an attempt to explain these results, the in vivo and in vitro interactions between daptomycin and tobramycin were studied. Tobramycin alone and preincubated with negatively charged phospholipid bilayers (liposomes) was dialyzed against increasing concentrations of daptomycin in buffer at pH 5.4. A significant drop in the concentration of tobramycin was observed when daptomycin was added to the opposite half cells. Furthermore, daptomycin induced a concentration-dependent release of lipid-bound tobramycin. Gold labeling experiments showed that daptomycin could be incorporated into phospholipid layers. Female Sprague-Dawley rats were treated with daptomycin alone, with tobramycin alone, or with the combination over 2 to 10 days. Levels of daptomycin and tobramycin in serum were similar in all groups. The levels of tobramycin in the renal cortex increased significantly with time and, on day 10, reached values of 654 +/- 122 and 844 +/- 298 micrograms/g of tissue (mean +/- standard deviation; not significant) in animals treated with tobramycin and the combination of daptomycin-tobramycin, respectively. No significant difference was observed in the levels of tobramycin in the kidneys between animals treated with tobramycin or the daptomycin-tobramycin combination at any time. By contrast, daptomycin levels were significantly higher in the renal cortexes of animals treated with daptomycin-tobramycin in comparison with those in the renal cortexes of animals treated with daptomycin alone on days 6,8, and 10 (P < 0.01). For immunogold labeling studies, animals were killed 4 h after a single injection of daptomycin alone or daptomycin in combination with tobramycin. Daptomycin was found throughout the matrixes of the lysosomes of proximal tubular cells of animals treated with daptomycin alone. In animals treated with the combination of daptomycin and tobramycin, daptomycin was associated with intralysosomal myeloid bodies. Our results suggest that daptomycin might attenuate experimental aminoglycoside nephrotoxicity by interacting with the aminoglycoside, perhaps electrostatically, and thereby protecting intracellular targets of toxicity.

Images

Three procedures (radioimmunoassay, fluorescence immunoassay, and enzyme immunoassay) for the determination of gentamicin and tobramycin levels were compared. These systems were evaluated on the basis of accuracy, reproducibility, specificity, and cost. All three systems showed a high degree of accuracy and precision. The fluorescence immunoassay gave significantly lower values for gentamicin and tobramycin at levels below 5 microgram/ml. Of the three systems, the radioimmunoassay was the least expensive, provided that a minimum of 10 analyses were performed daily; single tests required more technical time and were more costly. Costs of single tests by fluorescence immunoassay and enzyme immunoassay systems were similar. The enzyme immunoassay system performed equally well for both gentamicin and tobramycin in giving rapid and accurate results.

Purpose

To use a rabbit model of induced autoimmune dacryoadenitis to evaluate the efficacy of topical ophthalmic cyclosporine A (CsA).

Methods

Autoimmune dacryoadenitis was induced by injecting autologous peripheral blood lymphocytes, which had been activated in a mixed cell reaction with acinar cells isolated from one inferior lacrimal gland (LG), back into the donor animal’s remaining inferior LG. Schirmer’s test, tear breakup time, and rose Bengal staining were assessed. Animals with established disease were treated topically with either CsA or Endura twice daily for 5 months.

Results

Without treatment tear production and tear stability were abnormal for 6 months, and clear signs of ocular surface defects were evident. Severe immune cell infiltration was observed in the LG. Long-term CsA treatment increased tear production only slightly, but the severity of LG histopathology decreased noticeably. CD4+ T-cell infiltration of the LG was decreased and infiltration by MHC class II-expressing cells was also decreased. For the Endura-treated group tear production did not improve, rose Bengal scores remained high, and histopathology showed infiltration comparable to the untreated group, but by the end of the study the tear breakup time did improve.

Conclusions

The rabbit model of autoimmune dacryoadenitis had signs of chronic dry eye disease 6 months after induction of disease. Tear production improved slightly with CsA treatment and CD4+ T-cell infiltration decreased significantly in the LG. This suggests that some Sjögren’s patients may benefit from long-term CsA treatment.

Abstract

Purpose

To use a rabbit model of induced autoimmune dacryoadenitis to evaluate the efficacy of topical ophthalmic cyclosporine A (CsA).

Methods

Autoimmune dacryoadenitis was induced by injecting autologous peripheral blood lymphocytes, which had been activated in a mixed cell reaction with acinar cells isolated from one inferior lacrimal gland (LG), back into the donor animal's remaining inferior LG. Schirmer's test, tear breakup time, and rose Bengal staining were assessed. Animals with established disease were treated topically with either CsA or Endura twice daily for 5 months.

Results

Without treatment tear production and tear stability were abnormal for 6 months, and clear signs of ocular surface defects were evident. Severe immune cell infiltration was observed in the LG. Long-term CsA treatment increased tear production only slightly, but the severity of LG histopathology decreased noticeably. CD4+ T-cell infiltration of the LG was decreased and infiltration by MHC class II-expressing cells was also decreased. For the Endura-treated group tear production did not improve, rose Bengal scores remained high, and histopathology showed infiltration comparable to the untreated group, but by the end of the study the tear breakup time did improve.

Conclusions

The rabbit model of autoimmune dacryoadenitis had signs of chronic dry eye disease 6 months after induction of disease. Tear production improved slightly with CsA treatment and CD4+ T-cell infiltration decreased significantly in the LG. This suggests that some Sjögren's patients may benefit from long-term CsA treatment.

The objectives of this study were to investigate the bactericidal activity in serum of cefotaxime alone or in combination with tobramycin against clinical strains and to determine the influence of tobramycin on the pharmacokinetics of cefotaxime. The peak bactericidal activity in serum of cefotaxime alone against Klebsiella oxytoca, Enterobacter aerogenes, Serratia marcescens, Pseudomonas cepacia, and Listeria monocytogenes varied between 1:4 and 1:256. Bactericidal activity could still be detected at 6 h against K. oxytoca and L. monocytogenes. The addition of tobramycin increased the bactericidal activity of cefotaxime against E. aerogenes from 1:16 to 1:128 (P less than 0.01). Cefotaxime recovery from urine was significantly decreased when tobramycin was added. Our data are comparable with those of other investigators who have shown a limited increase in the bactericidal activity of cefotaxime when aminoglycosides are added.

This study was performed to determine the clinical pharmacokinetics of tobramycin in six patients with cystic fibrosis (CF) after inhalation of 600 mg. Tobramycin was administered with an ultrasonic nebulizer (WISTO SENIOR). Blood and urine were sampled until 24 h after inhalation. Maximum tobramycin levels in serum varied from 0.19 to 2.57 mg/liter (mean 1.27 mg/liter; standard deviation, 1.07 mg/liter). Systemic availability (calculated from urinary output) ranged from 6.0 to 27.4% (mean, 17.5%; standard deviation, 8.8%). The results illustrate that, provided that the systemic availability of tobramycin is a reflection of pulmonary deposition, inhalation studies with CF patients should have a concentration-controlled design. Furthermore, reliance on dose recommendations from the literature for a new patient starting on this treatment is not justified, but it is mandatory that deposition kinetics be studied for each patient and for each nebulizer. It may well be that, with higher levels of deposition, dosages lower than those recommended in the literature will suffice to obtain the desired clinical effect. In addition, the reverse may also be the case.

The pharmacokinetics of tobramycin and clindamycin were examined in patients undergoing peritoneal dialysis for chronic renal failure. Peak serum levels of tobramycin in functionally anephric patients were less than expected, probably secondary to a larger volume of distribution. Peritoneal dialysis resulted in a significant clearance of tobramycin, with a resultant reduction in serum half-life. The present data suggest that, if bactericidal serum levels of tobramycin are to be maintained in patients undergoing peritoneal dialysis, a parenteral loading dose be administered, followed by either (i) an identical dose every third half-life or (ii) one-half the loading dose every half-life. However, optimal therapy is best achieved by monitoring serum levels to insure appropriate drug dosage. Peak serum levels of clindamycin in functionally anephric patients were approximately twofold greater than those expected in normals after an identical parenteral dose. It is, therefore, recommended that the administered dose of this agent in functionally anephric patients be one-half of that required to produce desired peak serum levels in patients without renal impairment. Peritoneal clearance of clindamycin during dialysis was shown to be essentially zero, indicating that dialysis does not affect clindamycin disposition.