Drug therapy of urinary tract infections

CHAPTER 89


Drug therapy of urinary tract infections


Urinary tract infections (UTIs) are the most common infections encountered today. In the United States, UTIs account for over 7 million visits to healthcare providers each year. Among sexually active young women, 25% to 35% develop at least one UTI a year. Among elderly women in nursing homes, between 30% and 50% have bacteriuria at any given time. UTIs occur much less frequently in males, but are more likely to be associated with complications (eg, septicemia, pyelonephritis).


Infections may be limited to bacterial colonization of the urine, or bacteria may invade tissues of the urinary tract. When bacteria invade tissues, characteristic inflammatory syndromes result: urethritis (inflammation of the urethra), cystitis (inflammation of the urinary bladder), pyelonephritis (inflammation of the kidney and its pelvis), and prostatitis (inflammation of the prostate).


UTIs may be classified according to their location, in either the lower urinary tract (bladder and urethra) or upper urinary tract (kidney). Within this classification scheme, cystitis and urethritis are considered lower tract infections, whereas pyelonephritis is considered an upper tract infection.


UTIs are referred to as being complicated or uncomplicated. Complicated UTIs occur in both males and females and, by definition, are associated with some predisposing factor, such as calculi (stones), prostatic hypertrophy, an indwelling catheter, or an impediment to the flow of urine (eg, physical obstruction). Uncomplicated UTIs occur primarily in women of child-bearing age and are not associated with any particular predisposing factor.


Several classes of antibiotics are used to treat UTIs. Among these are sulfonamides, trimethoprim, penicillins, aminoglycosides, cephalosporins, fluoroquinolones, and two urinary tract antiseptics: nitrofurantoin and methenamine. With the exception of the urinary tract antiseptics, all of these drugs are discussed at length in other chapters. The basic pharmacology of the urinary tract antiseptics is introduced here.




Organisms that cause urinary tract infections


The bacteria that cause UTIs differ between community-acquired infections and hospital-acquired (nosocomial) infections. The majority (more than 80%) of uncomplicated, community-acquired UTIs are caused by Escherichia coli. Rarely, other gram-negative bacilli—Klebsiella pneumoniae, Enterobacter, Proteus, Providencia, and Pseudomonas—are the cause. Gram-positive cocci, especially Staphylococcus saprophyticus, account for 10% to 15% of community-acquired infections. Hospital-acquired UTIs are frequently caused by Klebsiella, Proteus, Enterobacter, Pseudomonas, staphylococci, and enterococci; E. coli is responsible for less than 50% of these infections. Although most UTIs involve only one organism, infection with multiple organisms may occur, especially in patients with an indwelling catheter, renal stones, or chronic renal abscesses.



Specific urinary tract infections and their treatment


In this section, we consider the characteristics and treatment of the major UTIs: acute cystitis, acute urethral syndrome, acute pyelonephritis, acute bacterial prostatitis, and recurrent UTIs. Most of these can be treated with oral therapy at home. The principal exception is severe pyelonephritis, which requires IV therapy in a hospital. Drugs and dosages for outpatient therapy in nonpregnant women are summarized in Table 89–1.



TABLE 89–1 


Regimens for Oral Therapy of Urinary Tract Infections in Nonpregnant Women





































































































































Drug Dose Duration
ACUTE CYSTITIS
First-Line Drugs
Trimethoprim/sulfamethoxazole 160/800 mg 2 times/day 3 days
Trimethoprim 100 mg 2 times/day 3 days
Nitrofurantoin 100 mg 2 times/day 7 days
Ciprofloxacin 250 mg 2 times/day 3 days
Norfloxacin 400 mg 2 times/day 3 days
Levofloxacin 250 mg once daily 3 days
Second-Line Drugs
Nitrofurantoin (macrocrystals) 50–100 mg 4 times/day 7 days
Nitrofurantoin (monohydrate/ macrocrystals) 100 mg 2 times/day 7 days
Fosfomycin 3 gm once 1 day
ACUTE UNCOMPLICATED PYELONEPHRITIS
First-Line Drugs
Trimethoprim/sulfamethoxazole 160/800 mg 2 times/day 14 days
Trimethoprim 100 mg 2 times/day 14 days
Ciprofloxacin 250–500 mg 2 times/day 14 days
Levofloxacin 250 mg once daily* 10 days
Second-Line Drugs
Amoxicillin (with clavulanic acid) 500 mg 3 times/day 14 days
Cephalexin 500 mg 4 times/day 14 days
Cefotaxime 1 gm 3 times/day 14 days
Ceftriaxone 1–2 gm once daily 14 days
COMPLICATED URINARY TRACT INFECTIONS
Trimethoprim/sulfamethoxazole 160/800 mg 2 times/day 7–14 days
Norfloxacin 400 mg 2 times/day 7–14 days
Ciprofloxacin 250–500 mg 2 times/day 7–14 days
Levofloxacin 500 mg once daily 7–14 days
Amoxicillin (with clavulanic acid) 500 mg 3 times/day 7–14 days
Cephalexin 500 mg 3 times/day 7–14 days
PROPHYLAXIS OF RECURRENT INFECTIONS
Trimethoprim/sulfamethoxazole 40/200 mg† at bedtime 3 times/wk 6 months
Trimethoprim 100 mg at bedtime 6 months
Nitrofurantoin 50–100 mg at bedtime 6 months
Norfloxacin 200 mg at bedtime 6 months


image


*For infection due to E. coli without concurrent bacteremia.


†One-half of a single-strength tablet.



Acute cystitis


Acute cystitis is a lower urinary tract infection that occurs most often in women of child-bearing age. Clinical manifestations are dysuria, urinary urgency, urinary frequency, suprapubic discomfort, pyuria, and bacteriuria (more than 100,000 bacteria per milliliter of urine). It is important to note that many women (30% or more) with symptoms of acute cystitis also have asymptomatic upper urinary tract infection (subclinical pyelonephritis). In uncomplicated, community-acquired cystitis, the principal causative organisms are E. coli (80%), Staph. saprophyticus (11%), and Enterococcus faecalis.


For community-acquired infections, three types of oral therapy can be employed: (1) single-dose therapy, (2) short-course therapy (3 days), and (3) conventional therapy (7 days). Single-dose therapy and short-course therapy are recommended only for uncomplicated, community-acquired infections in women who are not pregnant and whose symptoms began less than 7 days before starting treatment. As a rule, short-course therapy is more effective than single-dose therapy and hence is generally preferred. Advantages of short-course therapy over conventional therapy are lower cost, greater adherence, fewer side effects, and less potential for promoting emergence of bacterial resistance. Conventional therapy is indicated for all patients who do not meet the criteria for short-course therapy. Among these are males, children, pregnant women, and women with suspected upper tract involvement.


As indicated in Table 89–1, several drugs can be used for treatment. For uncomplicated cystitis, trimethoprim/sulfamethoxazole and nitrofurantoin are drugs of first choice. In communities where resistance to these drugs exceeds 20%, the fluoroquinolones (eg, ciprofloxacin, norfloxacin) are good alternatives. When adherence is a concern, fosfomycin, which requires just one dose, is an attractive choice. As a rule, beta-lactam antibiotics (eg, amoxicillin; cephalexin and other cephalosporins) should be avoided. Why? Because they are less effective than the alternatives, and less well tolerated.

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Jul 24, 2016 | Posted by in NURSING | Comments Off on Drug therapy of urinary tract infections

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