Tonsillar tissue penetration of dirithromycin after multiple doses.

Dirithromycin is a new macrolide antibiotic that is effective against group A beta-hemolytic streptococcal pharyngotonsillitis. This prospective, multicenter, randomized study compared the serum and tonsil tissue concentrations of erythromycylamine (to which dirithromycin is rapidly converted by nonenzymatic hydrolysis during absorption) and erythromycin after 5- and 10-day regimens of dirithromycin and erythromycin, respectively. Thirty-nine patients undergoing elective tonsillectomy but without active tonsillitis were assigned in randomized fashion to receive dirithromycin 500 mg orally once daily (n = 22) or erythromycin base 250 mg orally four times daily (n = 17). Data from 12 patients receiving dirithromycin and 10 receiving erythromycin were eligible for analysis. Mean serum concentrations (+/-standard deviation) of erythromycylamine and erythromycin were 0.20 +/- 0.07 microgram/mL and 0.12 +/- 0.25 microgram/mL, respectively, after the 5-day regimen and 0.17 +/- 0.10 microgram/mL and 1.57 +/- 3.16 micrograms/mL, respectively, after the 10-day regimen. The mean serum concentration of erythromycin after 10 days was skewed by the data for one of the six patients in the group (concentration of > 8 micrograms/mL). Mean concentrations of erythromycylamine in tonsil tissue were 4.62 +/- 0.97 micrograms/ g after 5 days and 3.47 +/- 2.84 micrograms/g after 10 days. Concentrations in tonsillar tissue were undetectable in all patients given erythromycin for 5 days and in 4 of the 6 patients given erythromycin for 10 days. The high concentrations of erythromycylamine in tonsillar tissue agree with the clinical efficacy seen in the treatment of group A beta-hemolytic streptococcal tonsillopharyngitis with dirithromycin.

Drug interactions of macrolides: emphasis on dirithromycin.

OBJECTIVE: To describe the drug interactions of dirithromycin, a new macrolide, and to compare them with those of other macrolides. DATA SOURCES: A literature search was performed using MEDLINE to identify articles published between January 1980 and July 1995 concerning the drug interactions of macrolides. Published abstracts were also examined. All studies using dirithromycin were performed under the sponsorship of Eli Lilly and Company. DATA SYNTHESIS: Erythromycin, the first macrolide discovered, is metabolized by the cytochrome P450 enzyme system. By decreasing their metabolism, erythromycin can interact with other drugs metabolized by the cytochrome P450 enzymes. The lack of such interactions would be a desirable feature in a newer macrolide. We describe studies performed to detect any interactions of dirithromycin with cyclosporine, theophylline, terfenadine, warfarin, and ethinyl estradiol. The studies showed that dirithromycin, like azithromycin, is much less likely to cause the interactions detected with clarithromycin and erythromycin. A review of the literature showed differences among macrolides in their abilities to inhibit cytochrome P450 enzymes and, thus, to cause drug-drug interactions. Erythromycin and clarithromycin inhibit cytochrome P450 enzymes, and have been implicated in clinically significant interactions. Azithromycin and dirithromycin neither inhibit cytochrome P450 enzymes nor are implicated in clinically significant drug-drug interactions. CONCLUSIONS: Dirithromycin, a new macrolide, does not inhibit the cytochrome P450 enzyme system. The concomitant use of dirithromycin with cyclosporine, theophylline, terfenadine, warfarin, or ethinyl estradiol was studied in pharmacokinetic and pharmacodynamic studies. In vitro, dirithromycin did not bind cytochrome P450. In healthy subjects, erythromycin increases the clearance of cyclosporine by 51%, whereas dirithromycin causes no significant changes in the pharmacokinetics of cyclosporine. In kidney transplant recipients, administration of dirithromycin was associated with a significant (p < 0.003) decrease of 17.4% in the clearance of cyclosporine. In patients taking low-dose estradiol, the administration of dirithromycin caused a significant (p < 0.03) increase of 9.9% in the clearance of ethinyl estradiol; escape ovulation did not occur. Unlike erythromycin and clarithromycin, dirithromycin had no significant effects on the pharmacokinetics of theophylline, terfenadine, or warfarin. The alterations typical of drug interactions that are based on inhibition of the cytochrome P450 system occurring with erythromycin and clarithromycin were not observed with dirithromycin.

Comparison of dirithromycin and penicillin for treatment of streptococcal pharyngitis.

In the treatment of group A beta-hemolytic streptococcal pharyngitis, penicillin is the drug of choice and erythromycin is the alternative. In a double-blind, randomized study, dirithromycin, a new macrolide, was compared with penicillin for the treatment of streptococcal pharyngitis. Of 121 patients who were treated with dirithromycin, 96.7% manifested a favorable clinical response, and of 136 patients treated with penicillin, 94.2% manifested a favorable clinical response. Streptococci were eradicated from the pharynges of 85.3% of 116 dirithromycin-treated patients and 82.5% of 126 penicillin-treated patients who returned for follow-up. There were no statistically significant differences in efficacy between the two groups. The incidence of abdominal symptoms was higher in dirithromycin-treated patients. Being as efficacious as penicillin and having the advantages over erythromycin of once-daily dosing and the lack of drug interactions, dirithromycin is an alternative to penicillin in the treatment of streptococcal pharyngitis for patients 12 years of age and older.

Long-term safety and tolerability of tadalafil in the treatment of erectile dysfunction.

OBJECTIVE: To assess the long-term safety and tolerability of tadalafil for patients with erectile dysfunction (ED). PATIENTS AND METHODS: This was a multicentre, open-label, 24-month extension trial involving 1173 men with ED. The mean age was 57 (range 23-83) years and 74.8% of patients were taking concomitant medications for comorbid conditions, including diabetes mellitus in 30.5% of men and hypertension in 29.5%. These patients had participated in 1 of 5 previous 8-week or 12-week randomised, double-blind, placebo-controlled tadalafil studies. In the present trial, the starting 10mg dose of tadalafil could be increased to 20mg if the patient could not achieve satisfactory intercourse or reduced to 5mg for an adverse event that was persistent, intolerable and judged by the investigator to be related to tadalafil. RESULTS: Four hundred ninety-three (42.0%) men completed 24 months of treatment. In addition, a further 234 (19.9%) completed 18 months of treatment due to a sponsor decision to reduce the study duration. The total tadalafil exposure was 1676.0 patient-years. Tadalafil was safe and well tolerated. Headache (15.8%), dyspepsia (11.8%), nasopharyngitis (11.4%), and back pain (8.2%) were the most common treatment-emergent adverse events. The rate of discontinuations due to adverse events for this 18-24-month study was 6.3% and the rate for any individual event was <1%. Serious adverse events occurred in 8.6% of patients. No consistent pattern of serious adverse events assessed as causally associated with tadalafil administration was observed. None of the four deaths that occurred during the study was assessed as tadalafil related. There were no clinically significant laboratory or electrocardiographic findings or changes in vital signs in mean baseline-to-endpoint analysis attributable to tadalafil. Tadalafil administration was not causally associated with drug-induced hepatotoxicity, neutropenia, thrombocytopenia, or renal dysfunction. CONCLUSION: Tadalafil at doses of 5, 10, or 20mg taken as needed up to once daily for 18 to 24 months was safe and well tolerated. These findings support the long-term use of tadalafil in the clinical management of erectile dysfunction.