TABLE 3.

30-day Risk Difference Estimates of Pyelonephritis versus Nitrofurantoin Initiators by Index Antibiotic Agent, Overall and by Subgroup (Intention-to-treat Analyses)

	Risk Difference, % (95% CI) versus Nitrofurantoina
	First-line agents	Non-first-line Agents			Non-recommended agents
	TMP/SMX	Fluoroquinolone	Broad-spectrum β-lactam	Narrow-spectrum β-lactam	AMX/AMP
Overall analyses
Crude	0.2 (0.2–0.2)	0.1 (0.0–0.1)	0.3 (0.2–0.4)	0.2 (0.1–0.3)	0.1 (0.0–0.3)
Weighted	0.2 (0.2–0.2)	0.1 (0.0–0.1)	0.2 (0.1–0.4)	0.1 (0.0–0.2)	0.1 (0.0–0.3)
Subgroup analyses (weighted)
Age group, y
18–24	0.2 (0.1–0.2)	0.0 (−0.1–0.0)	0.3 (0.0–0.6)	0.0 (−0.1–0.2)	0.2 (−0.2–0.6)
25–29	0.3 (0.2–0.4)	0.1 (0.1–0.2)	0.5 (0.1–0.9)	0.1 (−0.1–0.3)	0.3 (−0.1–0.9)
30–34	0.3 (0.2–0.4)	0.1 (0.1–0.2)	0.5 (0.0–1.0)	0.0 (−0.1–0.2)	−0.2 (−0.3−−0.1)
35–39	0.1 (0.1–0.2)	0.1 (0.0–0.1)	0.0 (−0.2–0.1)	0.1 (−0.1–0.3)	0.1 (−0.2–0.5)
40–44	0.1 (0.0–0.2)	0.0 (0.0–0.1)	0.1 (−0.2–0.3)	0.1 (−0.1–0.4)	0.1 (−0.2–0.6)
Year
2006–2008	0.2 (0.1–0.2)	0.1 (0.0–0.2)	0.3 (0.0–0.7)	0.1 (−0.1–0.3)	0.2 (−0.1–0.6)
2009–2011	0.2 (0.1–0.2)	0.0 (0.0–0.1)	0.2 (0.0–0.5)	0.0 (−0.1–0.1)	0.2 (−0.1–0.6)
2012–2015	0.2 (0.2–0.3)	0.0 (0.0–0.1)	0.2 (0.0–0.4)	0.1 (0.0–0.2)	0.1 (−0.1–0.3)
Region of residence
Northeast	0.1 (0.0–0.2)	0.0 (0.0–0.1)	0.0 (−0.2–0.4)	0.2 (−0.1–0.5)	0.1 (−0.2–0.5)
Midwest	0.2 (0.1–0.3)	0.1 (0.0–0.1)	0.3 (0.0–0.6)	0.1 (0.0–0.3)	0.4 (0.0–0.8)
South	0.2 (0.1–0.2)	0.0 (0.0–0.1)	0.2 (0.0–0.4)	0.0 (−0.1–0.1)	0.0 (−0.2–0.3)
West	0.3 (0.2–0.3)	0.1 (0.0–0.2)	0.4 (0.1–0.8)	0.1 (0.0–0.2)	0.2 (−0.2–0.7)
Initial laboratory testingb
None	0.2 (0.1–0.3)	0.1 (0.0–0.1)	0.2 (−0.2–0.5)	−0.1 (−0.2–0.0)	−0.1 (−0.4–0.2)
Urinalysis only	0.2 (0.2–0.3)	0.0 (0.0–0.1)	0.3 (0.0–0.6)	0.0 (−0.1–0.1)	0.3 (0.0–0.7)
Culture ± urinalysis	0.1 (0.1–0.2)	0.1 (0.0–0.1)	0.2 (0.0–0.5)	0.2 (0.0–0.3)	0.1 (−0.1–0.4)
No culture	0.2 (0.2–0.3)	0.0 (0.0–0.1)	0.3 (0.1–0.5)	0.0 (−0.1–0.1)	0.2 (0.0–0.5)

Abbreviations: AMX/AMP indicates amoxicillin or ampicillin; CI, confidence interval; PS, propensity score, TMP/SMX, trimethoprim-sulfamethoxazole.

^aPropensity score (PS) weighting was implemented by standardized mortality ratio weighting where patients were weighted to reflect the covariate distributions in the nitrofurantoin treatment group. The nitrofurantoin cohort was given a weight of 1 and each comparator PS/(1 – PS), in which PS is the propensity score of nitrofurantoin initiators in the study population. The PS models were estimated using the following covariates: age, month, year, geographic region, provider type, drug or alcohol abuse, deficiency anemias, chronic pulmonary disease, depression, psychoses, hypertension, obesity, initial receipt of urinalysis, and initial receipt of urine culture.

^bSample size of the subgroups for the pyelonephritis analysis: none (n=163,184), urinalysis only (n=425,718), culture ± urinalysis (n=545,772), and no culture (n=588,902).

^cSample size of the subgroups for the prescription switch analysis: none (n=164,088), urinalysis only (n=427,793), culture ± urinalysis (n=548,830), and no culture (n=591,881).