Molecular structure of amoxicillin
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Amoxicillin (INN) or amoxycillin (former BAN) is a moderate-spectrum β-lactam antibiotic used to treat bacterial infections caused by susceptible microorganisms. It is usually the drug of choice within the class because it is better absorbed, following oral administration, than other beta-lactam antibiotics. Amoxicillin is susceptible to degradation by β-lactamase-producing bacteria, and so may be given with clavulanic acid to increase its susceptability (see below). It is currently marketed by GlaxoSmithKline under the trade name Amoxil®. more...

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Mode of action

Amoxicillin acts by inhibiting the synthesis of bacterial cell walls. It inhibits cross-linkage between the linear peptidoglycan polymer chains that make up a major component of the cell wall of Gram-positive bacteria.

Microbiology

Amoxicillin is a moderate-spectrum antibiotic active against a wide range of Gram-positive, and a limited range of Gram-negative organisms. Some examples of susceptible and resistant organisms, from the Amoxil® Approved Product Information (GSK, 2003), are listed below.

Susceptible Gram-positive organisms

Streptococcus spp., Diplococcus pneumoniae, non β-lactamase-producing Staphylococcus spp., and Streptococcus faecalis.

Susceptible Gram-negative organisms

Haemophilus influenzae, Neisseria gonorrhoeae, Neisseria meningitidis, Escherichia coli, Proteus mirabilis and Salmonella spp.

Resistant organisms

Penicillinase producing organisms, particularly penicillinase producing Staphylococcus spp. Penicillinase-producing N. gonorrhoeae and H. influenzae are also resistant

All strains of Pseudomonas spp., Klebsiella spp., Enterobacter spp., indole-positive Proteus spp., Serratia marcescens, and Citrobacter spp. are resistant.

The incidence of β-lactamase-producing resistant organisms, including E. coli, appears to be increasing.

Doubling the routinely given concentration (in pediatrics) of amoxicillin has been shown to eradicate intermediately resistant organisms (Red Book, 2003 Report of the Committee on Infectious Diseases, American Academy of Pediatrics).

Amoxicillin and Clavulanic acid

Amoxicillin is sometimes combined with clavulanic acid, a β-lactamase inhibitor, to increase the spectrum of action against Gram-negative organisms, and to overcome bacterial antibiotic resistance mediated through β-lactamase production. This formulation is referred to as co-amoxiclav (British Approved Name), but more commonly by proprietary names such as Augmentin® and Clamoxyl®.

Proprietary Preparations

The patent for amoxicillin has expired. Thus amoxicillin is marketed under many trade names including: Actimoxi®, Amoxibiotic®, Amoxicilina®, Pamoxicillin®, Lamoxy®, Ospamox®, Polymox®, Trimox®, Tolodina®, Wymox® and Zimox®.

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New Help for Urinary Tract Infections
From FDA Consumer, 6/1/95 by Evelyn Zamula

Though men don't escape urinary tract infections - especially as they age and their prostates cause problems - women get the lion's share of UTIs, about 25 times more often than men. Most of these infections are uncomplicated: They occur in otherwise healthy women and girls who have normal urinary tracts and normal urinary functioning and no underlying physical problems.

The National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health estimates that by age 30, half of all women experience at least one UTI, and about 20 percent of these women will have recurrent UTIs. Each year, UTIs are responsible for more than 6 million doctor visits and about $4.5 billion in health-care costs. Only upper respiratory tract infections account for more absenteeism in working women.

The urinary tract consists of the kidneys, ureters, bladder, and urethra. The kidneys - bean-shaped organs weighing about 4 to 6 ounces in the adult and located below the ribs toward the middle of the back - filter liquid waste from the blood that passes through them to produce urine. Urine passes from the kidneys down through two narrow tubes called ureters to the bladder, a triangular-shaped organ in the lower abdomen. The bladder acts as a reservoir for urine until it is emptied out through the urethra, a tube leading from the bladder to outside the body.

When limited to the urethra, an infection of the urinary tract is called urethritis. More often than not, however, bacteria travel up a woman's one-and-a-half-inch-long urethra to the bladder, where they may cause cystitis, the most common urinary tract infection. A more serious condition called pyelonephritis results when bacteria from the bladder ascend to the kidneys via the ureters.

Before the modern drug era, doctors prescribed the urinary antiseptic Mandelamine (methenamine mandelate), cranberry juice, and diets that acidified the urine to prevent and treat recurrent UTIs. In many cases, this treatment was ineffective, and women who had recurrent UTIs ultimately suffered kidney failure. By the 1940s, the antimicrobial sulfa drugs had been introduced and proved very effective in treating UTIs. The explosive development of broad-spectrum antibiotics that began about the same time with the discovery of penicillin - and continued with the development of tetracyclines, erythromycin and cephalosporins - provided more options in treating UTIs.

New Drugs

In the last few years, FDA has approved a group of drugs called quinolones (including ciprofloxacin [Cipro], enoxacin [Penetrex], norfloxacin [Noroxin], ofloxacin [Floxin], cinoxacin [Cinobac], and lomefloxacin [Maxaquin]) for treating both uncomplicated UTIs and more serious urinary tract disorders. Philip Hanno, M.D., chairman of the urology department and professor of urology at Temple University, Philadelphia, Pa., says that with quinolones, "... you don't have to bring people into the hospital to get good levels of antibiotics that can treat pseudomonas and other gram-negative organisms. Previously, we had to use parenteral antibiotics [intravenous medications]. I do think they're overused, though, and resistance to them is developing."

Each group of drugs affects bacteria in the urine differently, either by interfering with reproduction, or depriving them of certain enzymes necessary for their growth. Successful treatment depends on the concentration of the bacteria-fighting drug in the urine.

Normal urine is sterile. An average adult passes about 3 pints of urine each day, but the amount varies, depending on how much food and drink are consumed.

The urinary system is constructed to repel infection. Valve-like structures at the lower ends of the ureters prevent urine from backing up (called vesicoureteral reflux) into the kidneys, where it could cause damage. When infection occurs, urination helps wash bacteria out of the bladder.

Symptoms of Infection

Sometimes a person can have a UTI without having symptoms. But usually UTIs are accompanied by such discomforts as pain and a burning sensation during urination, frequent urination - often passing no more than a few drops at a time-and a feeling that the bladder doesn't feel empty even after urinating. The urine may look cloudy, or may have a bloody tinge. A person with a UTI may feel tired and shaky, sick all over. Often, women feel pressure above the pubic bone and men feel fullness in the rectum. Chills and fever, flank pain, nausea, and vomiting suggest kidney involvement.

Common Culprits

Many bacteria can cause UTIs in women, but the most common are Escherichia coli (E. coli), responsible for over 80 percent of infections. Normally, these bacteria reside in the gastrointestinal tract, but they may also be present in the vaginal and rectal areas, and on the skin of the perineum, the band of flesh between the anus and the vagina. Sexually transmitted microorganisms Chlamydia trachomatis and T-mycoplasma (Ureaplasma) can cause UTIs in both men and women. These infections are usually confined to the urethra and reproductive organs.

Women can acquire UTIs after sexual intercourse. Many women have their first bout of cystitis after they become sexually active; in fact, "honeymoon cystitis" was once a common name for this affliction. Data from a variety of studies suggest that during sexual intercourse, bacteria in the vaginal area can be pushed into the urethral opening and move up into the bladder, making it one of the most important risk factors for developing uncomplicated UTIs.

Using a diaphragm for contraception can be an additional risk factor for UTIs. The diaphragm may press on the neck of the bladder, preventing it from emptying completely and leaving a pool of stagnant urine for bacteria to grow in. Bacteria may also enter the urinary tract when the diaphragm is inserted and removed and when it is left in place longer than recommended by the labeling or the doctor. Recently, researchers found an association between UTIs and sexual intercourse when women use a spermicide or a diaphragm/spermicide or when their partners use a condom with spermicidal foam. Thomas Hooton, M.D., and Walter Stamm, M.D., in the March 1991 issue of Medical Clinics of North America report that spermicides increase colonization of the vagina with bacteria, thus increasing risk of bladder infection.

Pregnant women get about the same number of UTIs as nonpregnant, sexually active women of childbearing age. However, when a pregnant woman gets a UTI, it is more likely to travel upwards to the kidneys. Since a woman can have bacteria in her urine, but no symptoms, it's important that urine cultures be-performed on the first prenatal visit and at intervals thereafter. Studies have shown an association between bacteria in the urine in the first trimester and the subsequent development of acute pyelonephritis. Pregnant women with UTIs can be treated with antibiotics, but, as always, the drug's effectiveness, the stage of pregnancy, the mother's health, and the potential effects on the fetus have to be carefully considered.

Not all UTIs are a result of sexual activity. Another common source of infection is the catheter, a tube that is placed in the bladder to drain off urine when a patient is unconscious, very ill, recovering from surgery, or incontinent. About 900,000 UTIs are contracted in hospitals each year, and up to 90 percent of these infections are associated with indwelling catheters. Avoiding unnecessary catheterization is the best way to prevent such UTIs. When a catheter is necessary, strict antiseptic techniques must be used by medical personnel when inserting and maintaining this device to prevent the introduction of bacteria into the bladder.

Diabetics run a higher risk of UTIs because their immune systems are suppressed. Additionally, their urine is rich in glucose, which is a good growing medium for any bacteria that enter the bladder.

Diagnosis

Though a urinalysis can tell the doctor bacteria are present in the urine, only a urine culture can identify the particular organism. Which drug will be effective and the length of time it is used depend both on the patient's history and what the culture reveals. Since a UTI can cause excruciating discomfort-and since many medications are effective against a UTI-most doctors prefer to treat patients with symptoms without waiting the 48 hours or so for culture results. The medication can be changed at that time, if necessary.

Doctors may treat routine, uncomplicated UTIs with trimethoprim (Trimpex), trimethoprim/ sulfamethoxazole (Bactrim, Septra, Cotrim), amoxicillin (Amoxil, Trimox, Wymox), nitrofurantoin (Macrodantin, Furadantin), ampicillin, and other drugs. Many of these drugs cause side effects, such as rash, itching, nausea, diarrhea, abdominal cramping, difficulty in breathing, and sensitivity to sunlight. Tetracyclines, cotrimoxazole, nitrofurantoin, and quinolones are not recommended for pregnant women. Patients should report all known allergies, such as an allergy to penicillin or sulfa drugs, to the doctor before treatment begins.

Types of Therapy

Doctors can use single-dose therapy, a three-day course of drugs, or a longer regimen. Studies have shown that a single dose of trimethoprim or cotrimoxazole, for instance, is effective in treating uncomplicated bacterial cystitis and asymptomatic bacterial infections in sexually active women and in girls with normal urinary tracts. Not only do single-dose therapies save money, but they are simple to take-thus promoting compliance-well-tolerated, and preferred by patients. In addition, they produce fewer side effects and less risk of developing resistant organisms. And, for pregnant women, a single dose of some drugs also poses less danger to the fetus.

Not all urologists like single-dose therapy. "I rarely use it," says Hanno, unless it's someone who's very responsible and has not had symptoms for a long time-generally people who are on self-treatment programs-and won't panic if symptoms don't go away after one dose. Then they can take one dose of medicine and that's it. But since it usually takes two or three days for the symptoms to go away even if you sterilize their urine with one dose, you know that they're going to call you back after taking one pill. I find it makes more sense to put people on the three-day therapy."

Urologists deal with recurrent UTIs in several ways. When women have three or more symptomatic UTIs a year, some urologists may prescribe low doses of an antimicrobial drug, such as trimethoprim/sulfamethoxazole or nitrofurantoin, to be taken daily for six months or longer as a preventative. Taken at bedtime, the drug remains in the bladder the whole night and is thus more effective. Other urologists prefer to give their patients medications to be taken on alternate nights or even three nights a week. When sexual intercourse is the culprit, one dose of an antibiotic after sex has proved a safe, effective and inexpensive treatment for preventing recurrent urinary tract infections.

Since illness is apt to strike at inconvenient times, women subject to recurrent UTIs often panic when they feel symptoms coming on and don't have immediate access to a doctor. "What most urologists do, once we have established that it's a recurrent urinary infection from reinfection-which makes up about 99 percent of UTIs in women-is give them a prescription to keep with them," says Hanno. "At the first sign of infection they take antibiotics for three days. If symptoms don't get better in three days, then it's worthwhile to do a urine culture, to see if something unusual is going on."

UTIs in Men

Men have lower rates of uncomplicated UTIs than women for various reasons. The longer male urethra, the greater distance between the urethral opening and the anus (the usual source of bacteria), and the drier environment surrounding the urethra present less opportunity for bacteria to enter the urinary tract. Another plus is that the prostate secretes fluid with antibacterial properties.

"UTIs are uncommon in men," says Hanno. "They usually reflect some anatomic abnormality or bladder dysfunction, and they're usually related to a deep-seated problem."

The male prostate is often involved in UTIs. An enlarged prostate can slow urine flow by squeezing the urethra, which it surrounds, thus setting the stage for a UTI. It works the other way, too. When the prostate is infected (prostatitis), the infection soon spreads to the bladder. UTIs in males are usually treated by long-course therapy of 14 to 21 days, especially when the prostate is involved.

When infections in either men or women persist despite treatment and are caused by the same strain of bacteria, the doctor checks for problems in the urinary system. The intravenous urogram (often incorrectly called the intravenous pyelogram) is an important diagnostic tool: The radiologist injects an iodine-containing liquid dye into the veins. As the dye concentrates in the kidneys and urine and flows through the ureters and bladder, x-ray pictures are taken that outline the urinary tract and reveal any abnormalities.

Another valuable test-especially for babies and people who cannot tolerate the dye used in the intravenous urogram-is done by ultrasound, which gives pictures from the echo patterns of sound waves bounced back from the urinary organs. Doctors may also perform a cystoscopy, where they look into the bladder with a cystoscope, an instrument made of a hollow tube with several lenses and a light source. The doctor can see tumors or other lesions in the bladder, or sediment from urinary stones.

Fortunately, most UTIs don't require such measures. Most healthy adults with normally functioning urinary tracts who have UTIs can be safely and effectively treated with a variety of medications. And, with prompt treatment, they will experience no long-term damage to the urinary system.

How Women Can Prevent UTIs

Here are some suggestions to help prevent UTIs:

* Drink at least eight glasses of water a day, in addition to the coffee, tea, cola drinks, and other beverages you normally drink. Frequent urination flushes bacteria out of the bladder and makes urinary symptoms, if you get a UTI, more bearable. Some doctors advise drinking large amounts of cranberry juice, which acidifies the urine and makes it less hospitable to bacteria.

* Wipe from front to back to prevent bacteria in the anal area from entering the vagina and urethra.

* Empty the bladder shortly before and after sex.

* Wash the genital area before sex with plenty of warm water. Bacteria from the vaginal, anal and perineal areas can be introduced into the urethra during sex.

* Check with your gynecologist if you suspect a diaphragm is contributing to your problems. You may need another size, or perhaps another method of birth control.

* Use some sort of water-soluble lubricant, such as a vaginal jelly (not petroleum jelly), if your vagina feels dry and uncomfortable during sex, especially if you're past menopause. Bruised tissues may become irritated, even infected.

* Avoid using feminine hygiene products, such as sprays, deodorants or douches, which may irritate the urethra.

* Change sanitary pads and tampons frequently during menstruation.

* Avoid using hot tubs-because the water is not hot enough to kill bacteria-and highly chlorinated pools, because too much chlorine may irritate the genital area.

* Don't use perfumed toilet paper, heavily scented soaps and powders in the vaginal area, or bubble baths. (Some bubble bath products warn that they can cause urinary tract irritation.) Some laundry detergents, bleaches, and fabric softeners leave residues that can be irritating or cause allergic reactions. Try unscented laundry detergents or soaps if you are sensitive.

* Take showers instead of baths, because showers wash bacteria away.

* Avoid wearing tight jeans, bodysuits and pantyhose. The heat generated by tight clothing makes it easier for bacteria in your genital area to grow. Replace nylon underclothing with cotton underwear.

Evelyn Zamula is a freelance writer in Potomac, Md.

COPYRIGHT 1995 U.S. Government Printing Office
COPYRIGHT 2004 Gale Group

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