A novel method for collecting and detecting amoxycillin in urine: a tool for testing antibiotic compliance in the community

Wei Shen Lima, Sarah Ganderb, Roger G. Finchb and John T. Macfarlanea,*

a Respiratory Medicine and b Department of Infectious Diseases, Nottingham City Hospital, Hucknall Road, Nottingham NG5 1PB, UK


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Assessing compliance to prescribed antibiotics in community studies of respiratory tract infections is difficult. We describe a simple method for collecting and detecting amoxycillin in urine using urine dip-sticks in conjunction with a bioassay. Urine was collected at timed intervals from eight healthy volunteers following oral amoxycillin administration. Dip-sticks inoculated with urine collected 1 and 8 h after antibiotic resulted in mean zones of inhibition of 1.75 and 1.37 cm, respectively. Amoxycillin activity remained demonstrable 14 days after inoculation of dip-sticks with urine. Dip-sticks inoculated with urine from control subjects who had not taken amoxycillin did not cause inhibition.


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Lower respiratory tract infections (LRTI) result in an estimated 21.9 million general practice (GP) consultations per year in the UK and cost £62.5 million at 1992/1993 prices.1 The role of antibiotics in the management of LRTI is debated. Meanwhile, the inappropriate use of antibiotics for LRTI in the community is felt to be important in the development of antimicrobial resistance. Consequently, the UK government has highlighted this area as meriting further research.2

Currently, assessing compliance to prescribed antibiotics for LRTI in the community depends on either patient history, ‘pill counting’ or the collection and measurement of antibiotic levels in blood, urine or other tissue samples. The first two methods are unreliable while the last is complicated and impractical, requiring special arrangements for the collection and delivery of biological samples.

We describe a pilot study of a novel method for the collection of urine and the detection of amoxycillin activity therein that is simple and can be readily applied to community studies.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Eight healthy volunteers (four male) without any active comorbid conditions and who were not on any other antibiotic were each prescribed four doses of amoxycillin 500 mg every 8 h. Compliance was checked by history and pill count.

(i) Samples of urine from two volunteers were collected at approximately 2 h intervals for 14 h after the final dose of amoxycillin. Urine dip-sticks (Diabur-Test 5000, Boehringer Mannheim, East Sussex, UK) were dipped into the urine for c. 20 s, removed and air-dried according to the manufacturers' instructions for the testing of glucose in urine. The ends of the dip-sticks containing the 25 mm filter squares were then snipped off and placed on to 4 mm (± 0.5 mm) deep agar plates (Blood Agar Base No. 2 with 7% defibrinated horse blood, Oxoid Ltd, Basingstoke, UK) seeded with Staphylococcus aureus (NCTC 6571) as indicator organism (105 cfu/mL). Following overnight incubation at 37°C, plates were examined for zones of inhibition. The presence of a zone of inhibition of any size was taken to indicate the presence of antibiotic. Urine from two healthy control subjects was tested in the same manner.

(ii) The remaining six volunteers each submitted five dip-sticks wetted with urine collected just after the final evening amoxycillin dose and another five dip-sticks wetted with urine collected first thing the following morning (c. 8–10 h later). Each set of five dip-sticks was air-dried and placed in a plain paper envelope which was kept on a bench top at room temperature until ready for testing 1, 2, 5, 7 and 14 days later.

One investigator (S.G.) performed the microbiological tests for the detection of amoxycillin activity blind to the study subjects and controls. The study was approved by the Nottingham City Hospital Ethics Committee and written informed consent was obtained from all study participants.


    Results
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
(i) Urine dip-sticks inoculated with urine collected 1 h after the last dose of amoxycillin (1 h) resulted in a mean ± s.d. inhibition zone diameter around the dried dip-stick filter squares of 1.75 ± 0.4 cm. Inhibition of growth was demonstrable in urine collected up to 8 h in both cases (zone diameters 1.0 and 1.75 cm) and up to 13 h for one subject (zone diameter 1.0 cm). No inhibition was detected from urine obtained from the controls.

(ii) Urine dip-sticks inoculated with urine collected at 0 and 8–10 h, air-dried, kept at room temperature and tested up to 2 weeks later continued to cause inhibition of growth (TableGo). For urine collected at 0 h, a small decrease in the mean ± s.d. zone diameter was noted when testing was performed 14 days after urine collection (day 14) compared with testing performed on the day of urine collection (day 0) (1.2 ± 0.3 cm versus 1.4 ± 0.3 cm, respectively). The corresponding figures for urine collected at 8–10 h were 1.4 ± 0.1 cm and 1.6 ± 0.2 cm. In all instances, the decrease in zone diameter was evident by day 5 with no further decrease noted thereafter.


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Table. Persistence of amoxycillin activity in urine collected on urine dip-sticks
 

    Discussion
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
We have shown that urine dip-sticks (Diabur-5000), in conjunction with a standard bioassay, can be used as a simple and convenient tool for the collection of urine samples for the detection of amoxycillin in urine. Our findings are consistent with the known pharmacokinetics of amoxycillin. The half-life of amoxycillin in adults is 0.7–1.4 h, being slightly longer in the elderly.3 About 45–80% of an oral dose of amoxycillin is excreted unchanged in the urine in the first 6 h via glomerular filtration and tubular secretion with lesser amounts excreted thereafter. A urinary concentration of 300 mg/L has been reported after a 250 mg dose. Metabolism to penicilloic acid occurs only to a limited extent (10–20%).4,5 The sensitivity of the bioassay described for the detection of amoxycillin is demonstrated by our ability to consistently detect inhibition of growth in urine collected 8 h after oral dosing in all subjects tested.

In addition, we found that the ‘active’ dip-sticks could still inhibit growth even after being kept for 2 weeks at room temperature. The urine dip-sticks themselves did not contribute to bactericidal activity as evidenced by the absence of any activity seen with dip-sticks inoculated with urine from control subjects who were not on antibiotics.

The choice of urine dip-stick was guided by our intention to use a simple instrument widely available to doctors. Other urine dip-sticks are available for the detection of protein, blood, pH and ketones in urine. These dip-sticks were not tested and therefore it is not known if the reagents found on these dip-sticks would result in detectable inhibition of growth measured by the bioassay described. It is likely that ‘blank’ urine dip-sticks without any active reagents would be equally effective at capturing excreted amoxycillin from urine. However, such dip-sticks are not readily available commercially.

Community studies of the role of antibiotics in the management of upper and lower respiratory tract infections are important if we are to reduce the use of antibiotics.2 Patient groups involved comprise mainly children and young adults. Collecting blood or urine samples from these patients to test for antibiotic compliance is timeconsuming, inconvenient, uncomfortable and expensive. It is also complicated by the need for special transport arrangements for the delivery of samples to the relevant test centre including the strict regulations for the posting of biological samples. We advocate the use of urine dip-sticks as an innovative means of collecting urine which can later be subject to simple yet sensitive testing for amoxycillin activity. Using this system, patients will be able to sample their urine before going to bed, air-dry the dip-stick overnight and post the dried dip-stick to the study centre for testing the following morning. A clinical trial is planned to evaluate the acceptability of this approach in assessing patient compliance to antibiotics.

Conclusion

We describe an innovative method using urine dip-sticks in conjunction with a biological qualitative assay for the capture and detection of amoxycillin excreted in urine. Once validated, this method may be applied in community studies of the management of respiratory tract infections for the testing of patient compliance to antibiotics.


    Acknowledgments
 
We would like to thank all the healthy volunteers who took part, and the British Lung Foundation for supporting this study through a research grant.


    Notes
 
* Corresponding author. Tel: + 44-115-9691169, ext. 46723; Fax: + 44-115-9627723. Back


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
1 . Guest, J. F. & Morris, A. (1997). Community acquired pneumonia: the annual cost to the National Health Service in the UK. European Respiratory Journal 10, 1530–4.[Abstract/Free Full Text]

2 . Standing Medical Advisory Committee. (1998). The Path of Least Resistance. Department of Health, London, UK.

3 . Brogden, R. N., Heel, R. C., Speight, T. M. & Avery, G. S. (1979). Amoxycillin injectable: a review of its antibacterial spectrum, pharmacokinetics and therapeutic use. Drugs 18, 169–84.[ISI][Medline]

4 . Gordon, R. C., Regamey, C. & Kirby, W. M. M. (1972). Comparative clinical pharmacology of amoxicillin and ampicillin administered orally. Antimicrobial Agents and Chemotherapy 1, 504–7.[ISI][Medline]

5 . Cole, M. & Ridley, B. (1978). Absence of bioactive metabolites of ampicillin and amoxycillin in man. Journal of Antimicrobial Chemotherapy 4, 580–2.[ISI][Medline]

Received 10 March 2000; returned 5 June 2000; revised 5 July 2000; accepted 2 August 2000