Chemical structure of azithromycin.
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Azithromycin is the first macrolide antibiotic belonging to the azalide group. Azithromycin is derived from erythromycin by adding a nitrogen atom into the lactone ring of erythromycin A, thus making the lactone ring 15-membered. Azithromycin is sold under the brand names Zithromax and Sumamed, and is one of the world's best-selling antibiotics. Azithromycin is used for the treatment of respiratory-tract, soft-tissue and genitourinary infections. more...

Zoledronic acid


Azithromycin's name is derived from the azane-substituent and erythromycin. Its accurate chemical name is

(2R,3S,4R,5R,8R,10R,11R,12S,13S,14R)-13- -2-ethyl- 3,4,10-trihydroxy-3,5,6,8,10,12,14-heptamethyl -11--1-oxa- 6-azacyclopentadecan-15-one.


A team of Pliva's researchers, Gabrijela Kobrehel, Gorjana Radobolja-Lazarevski and Zrinka Tamburasev led by Dr Slobodan Dokic, discovered azithromycin in 1980. It was patented in 1981, and was later found by Pfizer's scientists while going through patent documents. In 1986 Pliva and Pfizer signed a licensing agreement which gave Pfizer exclusive rights for the sale of azithromycin in Western Europe and the United States. Pliva brought their azithromycin on the market in Central and Eastern Europe under the brand name of Sumamed in 1988, and Pfizer Zithromax in 1991.

Available forms

Azithromycin is commonly administered in tablet or oral suspension. It is also available for intravenous injection.

Mechanism of action

Azithromycin prevents bacteria from growing by interfering with their protein synthesis. Azithromycin binds to the 50S subunit of the bacterial ribosome, and thus inhibits translation of mRNA. Azithromycin has similar antimicrobial spectrum as erythromycin, but is more effective against certain gram-negative bacteria, particularly Hemophilus influenzae.


Unlike erythromycin, azithromycin is acid-stable and can therefore be taken orally without being protected from gastric acids. It is readily absorbed, and diffused into most tissues and phagocytes. Due to the high concentration in phagocytes, azithromycin is actively transported to the site of infection. During active phagocytosis, large concentrations of azithromycin are released. The concentration of azithromycin in the tissues can be over 50 times higher than in plasma. This is due to ion trapping and the high lipid solubility.


Azithromycin's half-life is approximately 2 days, and it's fairly resistant to metabolic inactivation. Its main elimination route is through excretion in the biliary fluid, and some can also be eliminated through urinary excretion. Azithromycin is excreted through both of these elimination routes mainly in unchanged form.

Side effects

Most common side effects are gastrointestinal; diarrhea, nausea, abdominal pain and vomiting.


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Diary: from a week in practice
From American Family Physician, 8/1/05 by John O'Handley


Estella, a middle-aged Hispanic patient, visited the mobile clinic for exudative tonsillitis four days ago. The result of her rapid strep test was positive, but her type I allergy to penicillin precluded the use of a beta-lactam antimicrobial for treatment. I was left with azithromycin (Zithromax) because our pharmacy on the mobile clinic is limited, but I warned Estella that if she was unable to swallow the pills or if her condition did not improve, she would have to go to the emergency department. Estella took the medication but did not improve, and the swelling in her neck became more pronounced. A friend took her to the emergency department today, and a computed tomography scan confirmed the presence of loculated fluid in the right tonsil. She was given intravenous clindamycin (Cleocin) and underwent local incision and drainage of the tonsillar abscess. Estella was fortunate. We sometimes complain about the disarray of our medical system, but in the mobile clinic, at least, emergency patients are not turned away for lack of resources.


"The thing that hangs down in my throat hurts," Idel, a young Somali woman, said. Idel speaks some English, but we still need an interpreter. Her chief complaint, sore throat, had been bothering her for three years. Her uvula was almost atrophic but was slightly inflamed on its tip--certainly not consistent with the symptoms she described. I was surprised by the duration of symptoms. She had been to the clinic several times in the past year for various complaints, but never seemed to improve. "None of the medicines helped," said Idel. Looking through the chart, I found that antibiotics, antihistamines, analgesics, and decongestants had been no help. Testing for the streptococcal antigen had been a dead end. "I also have a cough," Idel further explained. At this point, the medical student and I looked at each other and realized the diagnosis had been there all along. "Do you have any heartburn?" I asked. "Yes," she affirmed, pointing to her chest. Gastroesophageal reflux disease seemed so obvious now. In this instance, the process of diagnosing took a circuitous route. It was not until I probed a little deeper that everything fell into place.


Success stories happen even on the streets, but it is rare for patients to return to the mobile clinic to give thanks for the care they received. George came to the mobile clinic two weeks ago "ready to die." Weakness and abdominal pain had been increasing for two weeks, and he knew something had to be done. He had curtailed his daily intake of four 40-oz beers, but even abstinence did not improve the symptoms that drove him to seek medical help. By the time he reached the mobile clinic, his pallor, hypotension, and pained expression forced me to opt for immediate transfer to the emergency department. From there, he was admitted after examination and tests revealed he had a hemoglobin of 9.8 g and an ulcer two thirds the circumference of the duodenum. A transfusion and initiation of a proton pump inhibitor did wonders for his condition. George felt like a new man, and today his gratitude for the help he received knew no bounds. The nurses and staff who previously had been so solicitous of his welfare were overjoyed at his new appearance. Whether George would follow through on his abstinence from alcohol was hard to say, but if his resolve was anything like the gratitude he was expressing, he would be successful in his struggle.


Monty is from a good family, but his bipolar disorder severely affected his integration into society. Formerly homeless, he now lives in a small room in a low-income housing project. He came to the mobile clinic today after five days of rib pain on his left side. Monty is normally a quiet, reserved individual, but today the floodgates opened and he talked about everything except his immediate problem. I redirected the conversation to his rib pain. It had begun when he was trying to reach some chocolate pudding in a dumpster behind a grocery store. Monty had successfully procured the chicken wings and spareribs that recently had been disposed of, but dessert was a little deeper inside the dumpster. As he strained against the metal side to reach the pudding, he felt something "pop." The point tenderness and irregularity of his left sixth rib indicated a fracture. I reassured him it would heal in four to six weeks and gave him something for the pain. I didn't need to warn him about the dangers of his hunting and gathering methods: Monty had learned his lesson.


Michael, a tall, strapping, middle-aged man, had lost his construction job and had been living in a shelter for two days. He came to the mobile clinic because of pain and swelling in his right knee. Two weeks earlier, he had been playing basketball when a sudden pivot caused knee pain and a loud "pop." A visit to a local emergency department had followed, and Michael told us that yellow fluid was drained from his knee after a radiograph showed no bony injury. I was somewhat skeptical of the color of the effusion; because it was associated with an acute injury, I would have expected bloody fluid. The effusion had now returned and was causing him a good deal of pain. T.B., the fourth-year medical student with me this month, examined Michael and reported a medial effusion, tenderness over the medial collateral ligament (MCL), and no warmth or redness. Michael wanted the fluid removed, believing it was the main cause of his pain, and T.B. aspirated 18 mL of yellow serous fluid from the medial aspect of the knee. In discussing the case with an orthopedic surgeon later, I was told that a tear of a cruciate ligament or bony injury within the joint would give a bloody effusion, but a tear of the MCL, because it is extra-articular, could result in a sympathetic serous effusion. This information clarified my thinking on knee effusions and also reinforced my confidence in Michael's ability to provide an accurate history. Michael felt much relief with his smaller knee and promised to follow up with the orthopedic clinic to ensure a satisfactory resolution of his problem.


Salme has had seizures since her childhood in Somalia. She was running low on her supply of phenytoin (Dilantin) and had developed a headache over the past two days. "This warns me that I may have a seizure," she said through our interpreter. Neurologically, she was intact. Because she had had no recent medical care, I examined her abdomen and found what felt like a 20-week-sized fetus. "Have you felt this before?" I queried. "I haven't noticed anything different," she replied. "Could you be pregnant?" I asked. Salme attested to the fact that she was not married and had regular periods, the last one 10 days ago. Could it be a fibroid, a solid tumor, or a cyst? I thought, trying to make sense of the opposing information from the history and physical examination. Would a urine pregnancy test be an insult to her veracity? I went ahead and ordered one, and she complied without objection. The test confirmed what I had suspected. Salme seemed nonplussed and did not acknowledge how the conception came about. My thoughts went back to other patients who presented with a headache as the sole symptom of pregnancy. For Salme, it was a harbinger of a seizure. The unexpected outcome of the visit was accepted with a quiet resignation.

After years spent in private family practice and in academia, John O'Handley, M.D., is medical director of the Mount Carmel Outreach Program in Columbus, Ohio. The program provides free medical care to uninsured and homeless patients throughout the city on a mobile coach clinic. Dr. O'Handley continues to see private patients two mornings a week.

Address correspondence to John O 'Handley, M.D., 6150 East Broad Street, Columbus, OH 43213 (e-mail:

To preserve patient confidentiality, the patients' names and identifying characteristics have been changed in each scenario. Any resemblance to actual persons is coincidental.

COPYRIGHT 2005 American Academy of Family Physicians
COPYRIGHT 2005 Gale Group

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