Table 2.

A comparison of the geometric mean levonorgestrel serum concentrations by time since levonorgestrel implant initiation between efavirenz users and efavirenz nonusers

	Efavirenz nonusers		Efavirenz users		Efavirenz users/efavirenz nonusers
Months from contraceptive initiation	n	Geometric mean levonorgestrela (90% CI)	n	Geometric mean levonorgestrela (90% CI)	Geometric mean ratio (90% CI)	p valueb
Day 3	12	950 (810–1110)	29	440 (370–520)	0.47 (0.35–0.61)	< .0001
1	12	610 (530–700)	30	370 (310–430)	0.60 (0.46–0.79)	.002
3	12	590 (510–680)	27	290 (220–390)	0.50 (0.33–0.76)	.001
6	12	530 (450–620)	26	280 (210–370)	0.53 (0.34–0.82)	.004
12	5	650 (560–760)	11	340 (260–440)	0.52 (0.34–0.78)	.008
18	10	550 (490–620)	22	220 (130–360)	0.40 (0.19–0.84)	.01
24	8	530 (440–640)	18	200 (120–330)	0.39 (0.18–0.81)	.007
27	7	600 (490–740)	12	170 (100–290)	0.28 (0.14–0.58)	.0004
30	5	580 (430–780)	7	150 (80–310)	0.27 (0.12–0.61)	.01

^aIn pg/mL.

^bBased on Wilcoxon Mann–Whitney exact test due to small number of efavirenz nonusers.