High TFV concentrations were achieved rapidly in the GT of all subjects after single and multiple doses and potently reduced BP and GT HIV-1 RNA levels.

The objective of the study was to measure antiretroviral exposures in four physiological compartments during pregnancy, delivery, and postpartum. This prospective, open-label, longitudinal study collected paired blood plasma (BP) and genital tract (GT) aspirates antepartum, at delivery, and up to 12 weeks postpartum. Antiretroviral cord BP and amniotic fluid concentrations were also measured. Drug concentrations were analyzed by validated high-performance liquid chromatography/UV and liquid chromatography/tandem mass spectrometry methods, with secondary compartment concentrations presented as the percentage of BP. Fourteen women taking lamivudine plus zidovudine and either lopinavir-ritonavir (n ‫؍‬ 7), nelfinavir (n ‫؍‬ 6), or nevirapine (n ‫؍‬ 1) were enrolled; four also received tenofovir. GT penetration relative to BP was highest for the nucleoside reverse transcriptase inhibitors compared to the protease inhibitors and nevirapine. Only antepartum nelfinavir GT penetration was significantly higher than in the second trimester (geometric mean ratio [GMR], 179.3) or third trimester (GMR, 41.9). Compared to nonpregnant historical controls, antepartum GT penetration was significantly lower (P < 0.05) for zidovudine (GMR, 0.25) and lopinavir (GMR, 0.03); postpartum lopinavir GT penetration continued to be significantly lower (GMR, 0.27). Cord BP exposures were highest for lamivudine and tenofovir (>100%), with cord BP levels of the remaining drugs ranging from 49 to 86% of that of the respective BP level. Amniotic exposures for lamivudine, zidovudine, tenofovir, and nelfinavir were >100%, nevirapine exposure was 53%, and lopinavir and ritonavir exposures were <6% that of BP. We conclude that GT, cord BP, and amniotic fluid exposures vary within and between antiretroviral drug classes and biologic sites. Measurement of antiretroviral exposure in maternal genital secretions, cord BP, and amniotic fluid may be needed to identify signals of subtherapeutic or supratherapeutic drug exposure.

AimsA non-invasive proposed method for measuring CYP3A activity is the urinary 6 β -hydroxycortisol:cortisol ratio. This ratio has been used as an indicator of CYP3A induction and inhibition, with mixed results. This investigation evaluated the relationship between a validated, biomarker, intravenous midazolam clearance and the urinary cortisol ratio under constitutive conditions and with the influence of a moderate CYP3A inhibitor. MethodsThis was a sequential, cross-over study design. Intravenous midazolam 0.025 mg kg − 1 was administered to 10 male and 10 female subjects once every 14 days for 4 months. Fluvoxamine 150 mg day − 1 was given to all subjects during the last two visits. Total body clearance of midazolam and urinary 6 β -hydroxycortisol:cortisol molar ratio were used as biomarkers of hepatic CYP3A activity. ResultsNo significant correlations were found between these two markers ( r 2 < 0.5, P > 0.05). Larger interindividual and intra-individual variability in CYP3A activity was observed in 6 β -hydroxycortisol:cortisol ratios compared with midazolam clearances. With fluvoxamine therapy, midazolam clearance values decreased approximately 1.5-fold and cortisol ratios decreased approximately 1.9-fold. ConclusionsThe high intra-individual variability of the urinary cortisol ratio, compared with midazolam, makes this a suboptimal CYP3A phenotyping tool.

We appreciate the comments of Dr Fenske [1] in the above letter. However, we disagree with his conclusions regarding the utility of the cortisol ratio once time of day and fluid intake are controlled.First, it is incorrect to assume that a population has similar corticosteroid production patterns. To this end, morning spot urine collections have been utilized for the cortisol ratio with little success. For example, Tran et al.[2] demonstrated a high intra-individual variability (>50%) in the cortisol ratio obtained from a morning spot urine. Sleep-wake cycles affect the timing of peak cortisol concentrations [3] and episodic cortisol secretion occurs from adrenal glands in response to such varied factors as stress, nutrition and environment [4,5]. Therefore, we disagree with Dr Fenske and believe that our collection of a 24-h urine sample for the cortisol ratio in fact assisted in normalizing for variable peak cortisol concentration times.Although Dr Fenske is correct in stating that the variability of urinary 6b-hydroxycortisol:cortisol ratios can be influenced by fluid intake [6], urine production and elimation can also be influenced by such factors as insensible losses and fluid shifts from positioning [7]. To this end, it would be unlikely that a group of individuals given the same amount of fluid over 24 h would have the same urine flow and volume. Although Furuta et al. [8] have stated that the urinary ratio of 6b-hydroxycortisol:cortisol was valid when the renal clearance of cortisol was constant, even within the same subject there were 2.1-4.6-fold variations in the renal clearance of cortisol. It has also been demonstrated that higher fluid intake (5 l) increases the secretion of free cortisol disproportional to metabolites (17-hydroxycorticosteroids), whereas normal fluid intake does not [6]. In our study, the average urine volume was 530 ml and ranged from 375 ml to 915 ml. This is within the range of normal fluid intake and urine production. Median (range) intra-individual variability (as measured by the coefficient of variation) in urine volume was 25.5% (12.2-26.3%). Therefore, the high interor intra-individual variability of the urinary 6b-hydroxycortisol:cortisol ratio found in our study was probably a result of other factors than just fluid intake.In summary, Dr Fenske has highlighted the impracticality of controlling all factors that can possibly contribute to high inter-or intra-individual variability of the urinary 6b-hydroxycortisol:cortisol ratio. Therefore, we believe Dr Fenske's comments further endorse our conclusion that the urinary 6b-hydroxycortisol:cortisol ratio is a suboptimal phenotyping tool.