An open, randomized, multicentre study compared the efficacy and safety of the prototype, azalide, azithromycin, and erythromycin in the treatment of atypical pneumonias. Azithromycin was administered for five days at a dosage of 250 mg bd on day 1 and 250 mg once daily on days 2 to 5. Erythromycin was given for ten days at 500 mg qid. Causative pathogens were identified by serological methods. Of 57 patients treated with azithromycin, Mycoplasma pneumoniae and Chlamydia psittaci were identified in 31 and eight patients, respectively. Of 44 patients treated with erythromycin, M. pneumoniae and C. psittaci were identified in 24 and eight patients, respectively. There were no therapeutic failures in either treatment group. Side effects were observed in one of 57 patients on azithromycin and in six of 44 patients on erythromycin. Azithromycin appears to be as effective as erythromycin in the treatment of atypical pneumonias and better tolerated.

Azithromycin, a macrolide antibiotic with an enhanced antimicrobial spectrum, was found to have a longer half-life than erythromycin, with marked tissue penetration. The pharmacokinetics of azithromycin after oral administration were compared with those of erythromycin in rats (200 mg kg-1) and rabbits (80 mg kg-1). Concentrations of azithromycin in liver, lung, kidney, ileum, and brain were higher than serum concentrations. The slow decline in tissue concentrations was evident from the biphasic elimination profile. Thus, advantageous pharmacokinetic properties and the broader antimicrobial spectrum of azithromycin relative to erythromycin appear to further support its therapeutic potential.

4'-Deoxy-10,l l ,12,1 3-tetrahydrodesmycosin was prepared in six-step reactions. Antibacterial screening shows retained antibacterial spectrum of tylosin with some improvementagainst tylosin-sensitive Staphylococci and Haemophilus influenze. However,pharmacokinetic data demonstrated rapid distribution from blood in tissues and prolonged maintenance in all tissues, especially in the lungs, in comparison with tylosin. 10,1 1,12,13-Tetrahydrodesmycosin, a 16-membered macrolide antibiotic is obtained by selective catalytic hydrogenation of desmycosin in the C-10, C-ll, C-12, C-13 position, or by mild acid hydrolysis of previously prepared 10, 1 l^n-tetrahydrotylosm1). 1 6-Membered macrolides: rosamycin2) and mycinami-cins3) with desosamine (4/-deoxy-mycaminose) in the C-5 position instead of mycaminose,were found to be active against some strains of Gram-negative and macrolide resistent Gram-positive bacteria. Deoxygenation of C-4' hydroxyl group of desmyco-sin40, 1 9-deformyl-desmycosin5) or related 1 6-membered macrolide, neospiramycin6), has already been accomplished. In preceding papers4'5) it was shown that the 4'-deoxy derivatives of desmycosin exhibit enhanced activity in comparison to those of corresponding 4'hydroxy compounds. Contrary to expectation C-4'

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