19 Jan

Test and treat strategies for Helicobacter: PATIENTS AND METHODS part 2

Test and treat strategies for Helicobacter: PATIENTS AND METHODS part 2

In each arm, the first-line regimen for H pylori eradication was omeprazole 20 mg, clarithromycin 500 mg and metroni­dazole 500 mg bid for seven days (OCM). The second-line regimen, used for OCM failures, was omeprazole 20 mg bid, clarithromycin 500 mg bid and amoxicillin 1000 mg bid for seven days. When a third attempt at H pylori eradication was necessary, ranitidine 150 mg bid, bismuth subsalicylate 524 mg qid, metronidazole 250 mg qid and tetracycline 500 mg qid were prescribed for two weeks. Probability inputs: Point estimates of path probabilities for the decision tree were extracted from a review of the pub­lished literature (Table 1). Articles were identified from computerized searches of the MEDLINE database (1966 to 1998) and from hand searches of recent review article bibli­ographies. For each probability, a plausible range of values for sensitivity analysis was chosen to reflect uncertainty in the literature. Where a necessary probability could not be found in the literature, a reasonable point estimate was cho­sen empirically and a wide range of plausible values was used for the sensitivity analysis.

The prevalence of H pylori infection among dyspeptic pa­tients was assumed to be 30% (range 10% to 50%). Among H pylori-positive patients, the prevalence of PUD was assumed to be 35% (20% to 50%) versus 3% among those without Hpylori. The sensitivity and specificity of the C-UBT for detection of H pylori were estimated at 96% and 98%, respectively (70% to 100%). The Hpy- lori serology assay was assigned a sensitivity of 85% and a specificity of 79% (70% to 95%) based on a published meta- analysis and a third-party technical review.

The effectiveness of H pylori eradication therapy was as­sumed to be 90% (range 60% to 100%). With suc­cessful eradication, 95% of ulcers were assumed to heal versus 76% if eradication failed. A four-week course of rani- tidine was considered to heal 70% of ulcers, while a six-week course of omeprazole monotherapy healed 90%. H pylori-negative patients who were given eradication ther­apy in error because of a false-positive noninvasive test were assigned an ulcer healing rate of 85% because they had re­ceived a seven-day course of omeprazole.

The one-year recurrence rate of H pylori-positive PUD without maintenance therapy was assumed to be 70% (50% to 100%), while that following successful eradication of the organism was assumed to be 4% (0% to 20%). Throughout the model, it was assumed that 75% of ulcers were symptomatic and 1% of new ulcers presented with com­plications such as bleeding or perforation.

TABLE 1 Probabilities applied in the decision analysis model

Variable

Base case probabilities

Probability ranges for sensitivity analysis

Reference(s)

Prevalence of
Helicobacter pylori

0.30

0.10-0.50

17-21

Prevalence of PUD if H pylori-positive

0.35

0.20-0.50

22

Prevalence of PUD if H pylori-negative

0.03

N/A

22

Sensitivity of 13C-UBT

0.96

0.70-1.00

23-25

Specificity of 13C-UBT

0.98

0.70-1.00

23-25

Sensitivity of serology

0.85

0.70-0.95

26,27

Specificity of serology

0.79

0.70-0.95

26,27

Effectiveness of H pylori eradication

0.90

0.60-1.00

28,29

PUD healing after four weeks of ranitidine

0.70

N/A

30,31

PUD healing after six weeks of omeprazole

0.90

N/A

30,31

PUD healing after one week of omeprazole

0.85

N/A

30,31

Recurrence rate of PUD over one year if H
pylori-positive

0.75

0.05-1.00

32,33

Recurrence rate of PUD over one year if H
pylori-negative

0.04

0-0.20

32,33

Proportion of ulcers with associated symptoms

0.75

N/A

32

Relapse rate of NUD

0.65

0.00-1.00

37

Because no therapy has demonstrated conclusive efficacy in NUD, the symptomatic response rate of NUD to any ther­apy was considered equivalent to the placebo response rate reported in clinical trials. In particular, despite recent con­troversy, no benefit was assumed from H pylori eradication in H pylori-positive NUD (34-36). Hence, the one-year symp­tomatic relapse rate regardless of therapy was estimated to be 65% (0% to 100%).
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