Long-term Prophylactic Therapy in Recurrent UTI

Recurrent urinary tract infections (UTIs): Definition and epidemiology

Recurrent UTIs are symptomatic UTIs that are common among otherwise healthy women with anatomically and physiologically normal urinary tracts.¹Kodner CM, Thomas Gupton EK. Recurrent urinary tract infections in women: diagnosis and management. Am Fam Physician. 2010 Sep 15;82(6):638-43.   Recurrent UTIs are defined as ≥ 2 infections in six months or ≥3 infections in one year and are thought to represent re-infection than relapse.²Hooton TM, Gupta K. Recurrent urinary tract infection in women. Uptodate. Available from: https://www.uptodate.com/ stc ontents/recurrent-urinary-tract-infection-in-women [Accessed on 31 May 2017].

UTIs are clinically divided into complicated and uncomplicated. Uncomplicated UTIs affect healthy individuals with no structural or neurological urinary tract abnormalities. These infections are differentiated into lower UTIs (cystitis) and upper UTIs (pyelonephritis). Complicated UTIs are associated with patients having predisposing medical conditions like immunosuppression, renal failure, renal transplantation, pregnancy and the presence of foreign bodies such as calculi, indwelling catheters or other drainage devices.¹Kodner CM, Thomas Gupton EK. Recurrent urinary tract infections in women: diagnosis and management. Am Fam Physician. 2010 Sep 15;82(6):638-43.  ³Flores-Mireles AL, Walker JN, Caparon M, Hultgren SJ. Urinary tract infections: epidemiology, mechanisms of infection and treatment options. Nat Rev Microbiol. 2015 May;13(5):269-84.

UTIs account for nearly 25% of all infections in women and about 50-60% of women will experience a UTI in their lifetime. Normally, recurrences occur within three months of the original in fection, and 80% of recurrent UTIs are re-infections.⁴Al-Badr A and Al-Shaikh G. Recurrent Urinary Tract Infections Management in Women: A Review. Sultan Qaboos Univ Med J. 2013 Aug; 13(3):359-367.

A study by Foxman B reported that of college women with a first UTI, 27% had at least one culture confirmed recurrence within the following six months, and 2.7% experienced a second recurrence over the same period. Another study reported that 53% of women older than 55 years and 36% of younger women had a recurrence within one year.¹Kodner CM, Thomas Gupton EK. Recurrent urinary tract infections in women: diagnosis and management. Am Fam Physician. 2010 Sep 15;82(6):638-43.

In the United States, 70-80% of complicated UTIs are attributable 3t o indwelling catheters, accounting for 1 million cases per year. Predictors of UTIs include symptoms following intercourse, signs or symptoms of pyelonephritis, and prompt resolution of symptoms with antibiotics.¹Kodner CM, Thomas Gupton EK. Recurrent urinary tract infections in women: diagnosis and management. Am Fam Physician. 2010 Sep 15;82(6):638-43.

Pathophysiology

Although UTI is caused by both Gram-positive and Gram-negative organisms, the most common causative agent is uropathogenic Escherichia coli (UPEC).³Flores-Mireles AL, Walker JN, Caparon M, Hultgren SJ. Urinary tract infections: epidemiology, mechanisms of infection and treatment options. Nat Rev Microbiol. 2015 May;13(5):269-84.   UPEC binds to the epithelium of the vagina and urethra with the help of virulence factors like fimbrae and enhance their ability to cause cystitis. According to studies on animal models, Escherichia coli can remain latent in large bacterial reservoirs within the host and be reactivated to cause infection in the future.

A 2007 study reported the presence of intracellular bacterial communities of UPEC in the urine samples of women with acute uncomplicated cystitis.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.   Most Escherichia coli are destroyed by the host defence mechanisms within days, but in antibiotic resistant state small clusters of intracellular Escherichia coli per sist for some months.⁴Al-Badr A and Al-Shaikh G. Recurrent Urinary Tract Infections Management in Women: A Review. Sultan Qaboos Univ Med J. 2013 Aug; 13(3):359-367.

Apart from Escherichia coli, pathogens that can cause UTI include Staphylococcus epidermidis, Staphylococcus saprophyticus, Proteus mirabilis, Klebsiella pneumoniae. Klebsiella and group B streptococcus infections are common in diabetic patients while Pseudomonas infections are more common in chronically catheterised patients.⁴Al-Badr A and Al-Shaikh G. Recurrent Urinary Tract Infections Management in Women: A Review. Sultan Qaboos Univ Med J. 2013 Aug; 13(3):359-367.   In patients with indwelling catheters, spinal cord injuries, or structural abnormalities of the urinary tract, Proteus mirabilis infection is common.¹Kodner CM, Thomas Gupton EK. Recurrent urinary tract infections in women: diagnosis and management. Am Fam Physician. 2010 Sep 15;82(6):638-43.

Presentation

Symptoms of acute lower UTI include:⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

• Dysuria
• Urinary frequency
• Suprapubic pain plus or minus haematuria

Differential diagnoses include vaginitis, acute urethritis, interstitial cystitis, and pelvic inflammatory disease. The above symptoms appear to be highly predictive of true disease. Probability of a positive culture is 81% if dysuria, urinary frequency, and haematuria are present in the absence of vaginal discharge.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Symptoms after intercourse, a prior history of pyelonephritis, absence of nocturia, and quick resolution of symptoms (48 hours) after initiation of treatment are the positive predictive factors for recurrent UTIs, while presence of nocturia and persistence of symptoms between episodes of treated infection are the negative predictors.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Risk factors

In young women frequency of sexual intercourse is the main risk factor leading to recurrent UTIs. This and other risk factors are listed in Table 1.¹Kodner CM, Thomas Gupton EK. Recurrent urinary tract infections in women: diagnosis and management. Am Fam Physician. 2010 Sep 15;82(6):638-43.

Risk factors in premenopausal and postmenopausal women are described under the following headers.

Premenopausal women

In young women, suffering from recurrent UTIs, behavioural risk factors like frequency of intercourse, use of a spermicide, and new sexual partners play an important role. Rate of vaginal and periurethral colonisation with Escherichia coli is increased due to intercourse and spermicide exposure. Non-behavioural risk factors like history of UTI before age 15 and a maternal history of UTI are also responsible for recurrent UTI in young women. This suggests that there are also anatomic and genetic factors involved. Most women with recurrent UTI do not have any functional or anatomic abnormalities of the urinary tract, and extensive radiologic and cystoscopic examination is not indicated.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

In urologically normal women, dysfunctional voiding patterns with increased tone of the external sphincter during micturition can also be associated with recurrent UTI.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Postmenopausal women

The vaginal flora in premenopausal women comprises of 90% lactobacilli. Lactobacilli protects against colonisation with uropathogens such as Escherichia coli Loss of oestrogen at menopause results in vaginal epithelium thinning and reduced amounts of glycogen and as a consequence the environment turns hostile to lactobacilli, decreasing its numbers. The resulting increase in vaginal pH leads to an increased propensity for colonisation with uropathogens.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Postmenopausal women who suffer from incontinence, have significant pelvic floor prolapse and elevated post-void residual volumes are at increased risk for recurrent UTI. Also, women with non-secretor status for histocompatibility blood-group antigens are at increased risk of recurrent UTI.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Non-secretor status is a more significant risk factor in postmenopausal than in premenopausal women. Other important factors for recurrent UTI in postmenopausal woman are a previous history of UTI and diabetes mellitus.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Investigation

All the women with recurrent UTI should :⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

• Evaluate urogenital anatomy and oestrogenisation of vaginal tissues and to detect prolapse.
• Measure post-void residual urine volume.
• Perform screening for diabetes in patients with risk factors like family history and obesity.
• Perform imaging of the upper urinary tract and cystoscopy in case the infection is due to Proteus, Pseudomonas, Enterobacter and Klebsiella, as it indicates structural abnormalities and renal calculi.
• Perform complete urologic workup in women who have persistent haematuria after resolution of infection.

Algorithm for the assessment of women presenting with one or more UTI symptoms is shown in Figure 1¹Kodner CM, Thomas Gupton EK. Recurrent urinary tract infections in women: diagnosis and management. Am Fam Physician. 2010 Sep 15;82(6):638-43.  .Urine cultures serve as gold standard for diagnostic exactness and provide specific information about the uropathogen and its antibiotic susceptibilities. In symptomatic women concentration of >10²Hooton TM, Gupta K. Recurrent urinary tract infection in women. Uptodate. Available from: https://www.uptodate.com/ stc ontents/recurrent-urinary-tract-infection-in-women [Accessed on 31 May 2017].   CFU/mL is sufficient to document infection without compromising specificity.¹Kodner CM, Thomas Gupton EK. Recurrent urinary tract infections in women: diagnosis and management. Am Fam Physician. 2010 Sep 15;82(6):638-43.  ⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Treatment

Antimicrobial therapy is the main treatment for UTIs. The main objective of antimicrobial therapy is to eradicate the growth of bacteria in the urinary tract. Antibiotics administration should be for a limited period of time to prevent bacterial resistance, to ensure patient compliance and to be patient-friendly. Before prescribing antimicrobials, it is important to consider the susceptibility of the infecting bacteria, the concentrations of uropathogens in the urine and the urinary complaint, especially in case of septicaemia or parenchymal infection, as antimicrobials levels are higher in the urine than in serum.⁴Al-Badr A and Al-Shaikh G. Recurrent Urinary Tract Infections Management in Women: A Review. Sultan Qaboos Univ Med J. 2013 Aug; 13(3):359-367.

The current standard therapy for the treatment of recurrent UTI is a 3-day course of trimethoprim/sulfamethoxazole (TMP/SMX).⁴Al-Badr A and Al-Shaikh G. Recurrent Urinary Tract Infections Management in Women: A Review. Sultan Qaboos Univ Med J. 2013 Aug; 13(3):359-367.   The Infectious Disease Society of America (IDSA) in 1999 suggested TMP/SMX as the first-line treatment for recurrent UTI. These agents are generally recommended for empiric therapy. A 3-day course is recommended as it is associated with lower cost, better compliance and lower frequency of adverse reactions than a 7- to 10-day regimen. Considering the increasing prevalence of TMP/SMX resistance among uropathogen, it is important to examine the risk factors like diabetes, recent hospitalisation and antibiotic use in the last 3 to 6 months and recent TMP/SMX use.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Fluoroquinolones are not recommended as first-line treatment because of their greater expense and concerns regarding the promotion of quinolone resistance. But it can be used as first-line treatment in women suspecting antimicrobial resistance or being allergic or intolerant to more conventional therapy and for women in areas where resistance to TMP/SMX is >15% to 20%⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Nitrofurantoin

Increasing rate of multidrug resistance is a major obstacle in the medical management of UTIs. Trimethoprim, broad-spectrum antibiotic, in vitro is prone to resistance. Another important drawback to the use of TMP/SMX is that it is vulnerable to cross6r esistance from other antibiotics.⁶Agarwal M, Rattan A. Nitrofurantoin sensitivity pattern pan India. WJPR. 2017;6(2):464-494.

In case of fluoroquinolones, there is growing resistance among pathogens and other microorganisms and hence these drugs should be kept as optional therapies for acute cystitis.⁶Agarwal M, Rattan A. Nitrofurantoin sensitivity pattern pan India. WJPR. 2017;6(2):464-494.   Recently, The US Food and Drug Administration (USFDA) have warned that the risk of fluoroquinolones outweighs their benefits for patients with sinusitis, bronchitis, and uncomplicated UTIs who have other treatment options.⁷FDA advises restricting fluoroquinolone antibiotic use for certain uncomplicated infections; warns about disabling side effects that can occur together. US Food and Drug Administration. Available from: https://www.fda.gov/Drugs/DrugSafety/ucm500143.htm [Accessed on th16 Jun 2017].

Unlike many other antimicrobials, nitrofurantoin has the advantage of withstanding the growing antimicrobial resistance and has started becoming the empirical treatment of choice. A study by Olson et al., in 2009 found no Escherichia coli resistant to nitrofurantoin compared to TMP/SMX.⁶Agarwal M, Rattan A. Nitrofurantoin sensitivity pattern pan India. WJPR. 2017;6(2):464-494.

Nitrofurantoin is a safe and effective agent and is administered for a minimum of 7 days, as single dose regimens are less effective than 3- to 7-day regimens. As suspicion for TMP/SMX resistance increases nitrofurantoin and fluoroquinolones become better options.¹Kodner CM, Thomas Gupton EK. Recurrent urinary tract infections in women: diagnosis and management. Am Fam Physician. 2010 Sep 15;82(6):638-43.  ⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Nitrofurantoin treats recurrent UTI by sterilising the urine and inhibiting bacterial attachment, while fluoroquinolones and TMP/SMX act by inhibiting the recovery rate of uropathogens(mainly Escherichia coli ) from the faecal reservoir.⁴Al-Badr A and Al-Shaikh G. Recurrent Urinary Tract Infections Management in Women: A Review. Sultan Qaboos Univ Med J. 2013 Aug; 13(3):359-367.

Prevention of recurrent UTI

Lifestyle modification

An alternative form of contraception should be offered to women using spermicide containing contraception. Though numerous studies report no association between recurrent UTI and pre- and post-coital patterns, frequency of urination, delayed voiding habits, use of hot tubs, bubble baths, tight clothing, bicycle riding and the volume of fluid consumed, behavioural approaches are not harmful.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Antimicrobial prophylaxis

Numerous options are available for the prevention and management of recurrent UTI. Antibiotic choice should depend on community patterns of resistance, adverse effects and local costs. The three management strategies considered for recurrent UTI are described below.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Continuous prophylaxis

Continuous prophylaxis can be given daily at bedtime. One study recommend prophylaxis on alternate nights or 3 nights per week, while according to other study weekly prophylaxis was better than monthly prophylaxis.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Post-coital prophylaxis

A study conducted by Melekos MD et al., reported similar outcomes between sexually active women taking post-coital ciprofloxacin and women taking ciprofloxacin daily. Other study suggested that post-coital approach might be a better option for sexually active women with UTI. Post-intercourse prophylaxis is advantageous because it produces fewer side effects, as women take only one-third of antibiotic used in daily prophylaxis.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Acute self-treatment

Self-treatment is best for women who are not suitable for longterm prophylaxis or who are not willing to take it. These women should be reminded to call their healthcare provider if the symptoms are not resolved completely within 48 hours. The patient identifies episodes of infection on the basis of symptoms, performs her own culture, and initiates a standard 3-day course of empiric treatment. Antimicrobial agents with minimal side effects are recommended, because this approach could lead to some degree of overtreatment.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

The effectiveness of antimicrobial agents to prevent recurrent UTIs seems to arise through 2 mechanisms. First, agents like TMP/SMX and norfloxacin decrease the rate of recovery of aerobic Gram-negative uropathogens such as Escherichia coli from the faecal reservoir. Nitrofurantoin in contrast, decreases the recurrence rate by intermittently sterilising the urine and possibly by inhibiting bacterial attachment.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Other preventive modalities

Antibiotics are usually effective in treating acute infections, but emergence of drug-resistant bacteria has reduced their efficacy. Therefore, it is important that alternative prevention strategies be developed. Other potential strategies for the treatment of recurrent UTI are described below.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Acupuncture

Various studies demonstrate the role of acupuncture in preventing recurrent UTIs and conclude acupuncture to be a valuable alternative to antibiotic therapy.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Probiotics

The presence of Lactobacillus into the vagina is believed to stop the ascension of uropathogens into the bladder. Current studies suggest the beneficial effect of probiotics, and most authors consider this approach promising, but further research is needed be fore probiotics can be recommended for prevention of UTI.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Cranberry juice and tablets

Cranberry juice and tablets contain compound called tannin, or proanthocyanidin, which reduces Escherichia coli vaginal colonisation. Although studies have reported the efficacy of consuming cranberry juice or tablets in preventing recurrent UTIs, an updated Cochrane review showed that the evidence for its benefit in preventing UTIs is little and hence cranberry juice cannot be recommended any longer for UTI prevention.⁴Al-Badr A and Al-Shaikh G. Recurrent Urinary Tract Infections Management in Women: A Review. Sultan Qaboos Univ Med J. 2013 Aug; 13(3):359-367.

Potassium citrate

Alkalisation of urine by alkaliser potassium citrate can be used to alle viate symptoms of dysuria.⁹Bonnici JJ, Lentini F. Urinary tract infections in the community. JMCFD. 2014;3(2);10-17.   Symptomatic relief by potassium citrate is experienced by female patients with cystitis.¹⁰Balakrishnan I. Dealing with urinary tract infections. The pharmaceutical Journal. 2011;287:687-690.

Flavoxate

Nine clinical trials have shown effectiveness of flavoxate in urinary tract disorders.¹¹Gould S. Urinary tract disorders. Clinical comparison of flavoxate and phenazopyridine. Urology. 1975 May;5(5):612-5.   Flavoxate increases bladder capacity and reduces pressure in patients with cystitis with no side effects.¹²Servedio C. The use of flavoxate in cystitis and renal colic. Curr Med Res Opin. 1974;2(8):449-54.

Oestrogen

Lactobacillus proliferation in the vaginal epithelium is mediated by oestrogen. It reduces pH and avoids vaginal colonisation by uropathogens. Oestrogen levels and lactobacilli numbers drop after the menopause which makes postmenopausal women susceptible to UTIs.⁴Al-Badr A and Al-Shaikh G. Recurrent Urinary Tract Infections Management in Women: A Review. Sultan Qaboos Univ Med J. 2013 Aug; 13(3):359-367.

Vaginal oestrogen use reduces recurrent UTIs by 36-75% and has minimal systemic absorption. A Cochrane review in post-menopausal women with recurrent UTIs reported that, vaginal oestrogens prevented recurrent UTIs, but oral oestrogen did not, when compared to a placebo. Local oestrogen cream twice a week and an oestradiol releasing vaginal ring are both effective in reducing recurrent UTI attacks.

Although both reduce UTIs by restoring vaginal flora and reducing pH, there is reappearance of vaginal lactobacilli at least after 12 weeks when using an oestrogen vaginal ring. Vaginal oestrogen topical creams are cheaper than an oestradiol-releasing vaginal ring but have more side effects.⁴Al-Badr A and Al-Shaikh G. Recurrent Urinary Tract Infections Management in Women: A Review. Sultan Qaboos Univ Med J. 2013 Aug; 13(3):359-367.

Vaccines

An injectable vaccine that was developed in Switzerland was found to be effective and reported no adverse events in pregnant woman or offspring. To avoid the adverse reactions of the parenteral vaccine, four mucosal vaccines were developed as a vaginal suppository or an oral tablet, but the vaccine’s benefit seemed to decline after the last dose. FimCH is the only parenteral vaccine that is under development and has been proved to be safe in phase I clinical trial. No data of phase II clinical trial is available.⁵Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.

Conclusion

UTIs are some of the most common clinical bacterial infections in women. Recurrent UTIs, mainly caused due to re-infection by the same pathogen, are less common. One in four healthy women with UTI will suffer from recurrences. The most common risk factor in young and pre-menopausal women is sexual intercourse and Escherichia coli is the most commonly isolated uropathogen. Women with recurrent UTIs need to be properly investigated by urinalysis, urine cultures and other radiological techniques in order to rule out causes of recurrence, as well as to assess possible anatomical or functional urinary tract abnormalities. Although standard UTI therapy starts with antimicrobial therapy, alternative strategies are available to reduce exposure to antibiotics, such as the use of methenamine salts, probiotics, cranberry juice, immuno-prophylaxis and vaginal oestrogens in postmenopausal women. Continuous antibiotic prophylaxis, post-coital prophylaxis, and acute self-treatment are costeffective treatment strategies for reducing the number of recurrent UTIs in some patients.

References

1. Kodner CM, Thomas Gupton EK. Recurrent urinary tract infections in women: diagnosis and management. Am Fam Physician. 2010 Sep 15;82(6):638-43.
2. Hooton TM, Gupta K. Recurrent urinary tract infection in women. Uptodate. Available from: https://www.uptodate.com/ stc ontents/recurrent-urinary-tract-infection-in-women [Accessed on 31 May 2017].
3. Flores-Mireles AL, Walker JN, Caparon M, Hultgren SJ. Urinary tract infections: epidemiology, mechanisms of infection and treatment options. Nat Rev Microbiol. 2015 May;13(5):269-84.
4. Al-Badr A and Al-Shaikh G. Recurrent Urinary Tract Infections Management in Women: A Review. Sultan Qaboos Univ Med J. 2013 Aug; 13(3):359-367.
5. Epp A, Larochelle A. Recurrent Urinary Tract infection. SOGC Clinical Practice Guideline. 2010;32(11):1082-1090.
6. Agarwal M, Rattan A. Nitrofurantoin sensitivity pattern pan India. WJPR. 2017;6(2):464-494.
7. FDA advises restricting fluoroquinolone antibiotic use for certain uncomplicated infections; warns about disabling side effects that can occur together. US Food and Drug Administration. Available from: https://www.fda.gov/Drugs/DrugSafety/ucm500143.htm [Accessed on th16 Jun 2017].
8. Data on file.
9. Bonnici JJ, Lentini F. Urinary tract infections in the community. JMCFD. 2014;3(2);10-17.
10. Balakrishnan I. Dealing with urinary tract infections. The pharmaceutical Journal. 2011;287:687-690.
11. Gould S. Urinary tract disorders. Clinical comparison of flavoxate and phenazopyridine. Urology. 1975 May;5(5):612-5.
12. Servedio C. The use of flavoxate in cystitis and renal colic. Curr Med Res Opin. 1974;2(8):449-54.