Erythromycin and Friends
========================

þ Comparison:
 - azithromycin (e.g., Zithromax): QDx5d, better H. Flu than Biaxin
 - clairithromycin (e.g., Biaxin): BIDx10D, better staph/strep than Zithromax
 - dirythromycin (e.g., Dynabac): quite poor staph/strep coverage

þ Azithromycin (e.g., Zithromax):
 - liquid comes as 15cc bottle of 100mg/5cc.
 - can use as single dose oral treatment for Chlamydia (1g PO Stat)
   Cost to pharmacy is $19.32 for 1g; cost to patient about $50
   (vs. about $10 to patient for generic doxycycline 100 BID for 10 days)
 - Now available as 1 gram packet, can be taken with food, and costs Mercy's
   pharmacy $15 vs. $19.32 for four 250 mg capsules.  Patient cost at Mercy:
   $61.32 for the four capsules, $32 for the one-gram packet.
 - Cost of Z-pack quoted in Med Ltr 1/30/98: $37.31
   As opposed to $65.20 for 250 BID x 10 D of Biaxin, or
   about $10 for a course of erythro.
 - Per Hank Freedy, Mercy Pharmacist, 1/2/95, azithromycin is better than
   clarithromycin for covering H. Flu.  He also thinks that even though it's
   not approved for sinusitis, a 5-day course is probably adequate and cheaper
   to the patient.
 - IV azithromycin
  + for community-acquired pneumonia instead of cefuroxime + erythro
  + covers
   - pneumococcus
   - H flu
   - atypicals (Legionella, mycoplasma, chlamydia)
   - staph aureus
   - M. catarrhalis
  + IV dose: 500 mg IV daily

þ Why many like Zithromax better than Biaxin:
  1) It can be given to pregnant patients.
  2) It apparently does not interact with certain drugs such as terfenadine
     and cause torsade des pointes.
  3) Price (azithromycin is cheaper)
  4) Ease of use (azithromycin is once a day, for just 5 days)
  5) Side effect profile (clarithromycin can cause an irritating metallic
     taste which does not occur with azithromycin)
  6) Route of administration (Azithromycin is now also available in an IV
     formulation.)
  7) Ergotism (Erythromycin and Clarithromycin can cause ergotism in
     patients taking ergotamines, while it is not clear that azithromycin
     will do this.)
  8) Safety profile (In addition to terfenadine, clarithromycin causes
     problems with theophylline, carbamazepine, cyclosporin, the
     antiepileptics, carbamazepine and phenytoin, terfenadine, warfarin, oral
     contraceptives, agents used in the management of gastritis and peptic
     ulcer and zidovudine that do not seem to be found with azithromycin [with
     the exception of antacids].)
   - One significant problem with azithromycin at our institution is that
     there is significant strep resistance.  For community-acquired pneumonia,
     we now use a penicillin + azithromycin cocktail.
     --Jon Handler, M.D.

þ Comparitive MICs for macrolides
                Staph and Strep         Chlamydia       H. Flu/Paraflu
Erythro         1                       1               1
Azithro         0.25                    0.5             2-8
Clairithro      2                       16              0.5
[Zuckerman JM, Kaye KM: The Newer Macrolides Azythromycin and Clarithromycin,
Infect Dis Clin North Am 1995; 9:731.]
Some will try to overcome this by using a combination of PCN + azithromycin.

þ Why Tina likes Biaxin better than Zithromax for pneumonia
 - The easiest question for me to answer is the last one-- azithromycin should
   not be used in cases of suspected bacteremia due to low serum
   concentrations. (Azithromycin has a 2-4 fold higher MIC than ery for staph
   and strep.)  Tissue concentrations for azith range from 10- to 150-fold
   higher than serum concentrations, so MIC data based on serum concentration
   may not be relavent for tissue-directed therapy.
       I prefer to see clarithromycin (rather than azith) used for
   uncomplicated community acquired pneumonia. Clarith and its 14-OH
   metabolite have synergistic activity against H. flu.; and it has better
   activity than ery against strep and other common culprits for pneumonia.
   Plus, the lung is so highly "vascularized" that I'd rather see effective
   concentrations in the blood as well.
       Here's a couple references:
   Clin Pharm 1992;11:137-52
   Ann Pharmacother 1992;26:46-55
   Regards,
   --Tina Denetclaw, Pharm.D. BCPS