TABLE 1.

Quantification of efavirenz in PBMCs isolated by the present method and a previously reported method^a

Source	Intracellular efavirenz concnb (μM)
	Previous method with one tubec	Previous method with new tubesd	Present methode
Spiked donor bloodf	110 ± 19	4.6 ± 1.7	97 ± 17
Patient 1	Not assayed	3.8 ± 1.3	63 ± 24
Patient 2	Not assayed	1.1 ± 0.3	71 ± 11

^aThe method reported by Almond et al. (1) was used for isolation of PBMCs for comparison with the present method.

^bEfavirenz was quantified by LC-MS/MS. Intracellular concentrations were calculated, taking 0.25 pl as the volume of a single cell (5). Data are expressed as means ± standard deviations (n = 3).

^cWashing of PBMCs in ice-cold PBS was carried out three times in the same microcentrifuge tube.

^dSuspension of PBMCs in ice-cold PBS was transferred into a new microcentrifuge tube for centrifugation before each of three washings.

^eIntracellular efavirenz concentrations were determined as described in the legend to Fig. 2.

^fHIV-uninfected donor blood was spiked with efavirenz at 10 μM.