Ganesh Cherala

Impact of obesity on oral contraceptive pharmacokinetics and hypothalamic-pituitary-ovarian activity

BACKGROUND This study was conducted to determine whether increased body mass index (BMI) affects oral contraceptive (OC) pharmacokinetics and suppression of hypothalamic-pituitary-ovarian (HPO) axis activity. STUDY DESIGN Ovulatory reproductive-age women with normal weight (BMI <25 kg/m(2); n=10) and with obesity (BMI >30 kg/m(2); n=10) received OCs for two cycles (prospective cohort). Subjects were admitted for two 48-h inpatient stays at the beginning and end of the hormone-free interval. Ethinyl estradiol and levonorgestrel (LNG) levels were evaluated during both inpatient stays. Gonadotropin pulsatility (follicle-stimulating hormone and luteinizing hormone) was measured during the second inpatient stay. Estradiol (E(2)) and progesterone (P) were measured daily during inpatient stays and twice per week in Cycle 2. RESULTS BMI was greater in the obese compared to the normal-BMI group [37.3 kg/m(2) (SD, 6.0) vs. 21.9 kg/m(2) (SD, 1.6); p<.05]. The LNG half-life was significantly longer in the obese group (52.1+/-29.4 vs. 25.6+/-9.3 h, p<.05), which correlated with a lower maximum LNG concentration on Cycle 2, Day 1 [1.9 ng/mL (SD, 0.5) vs. 2.5 ng/mL (SD, 0.7)] and a longer time to reach steady state (10 vs. 5 days) in obese women. There were no significant differences in volume of distribution between groups. LH pulse parameters did not differ statistically between groups but trended toward greater HPO activity in the obese group. Additionally, more obese (6/10 vs. 3/10 normal BMI, p>.05) women exhibited E(2) levels consistent with development of a dominant follicle and P levels consistent with ovulation (2/10 vs. 1/10) during Cycle 2. CONCLUSIONS Compared to women with normal BMI, obese women exhibit differences in OC pharmacokinetics that are associated with greater HPO activity.

Metabolism and pharmacokinetics of contraceptive steroids in obese women: a review.

The effect of obesity on drug metabolism and pharmacokinetics is poorly understood, and this is particularly true in regard to contraceptive steroids. This article will review the known and theoretical physiologic and pharmacologic interactions between obesity and contraceptive steroids.

Daptomycin Pharmacokinetics in Adult Oncology Patients with Neutropenic Fever

ABSTRACT Daptomycin is the first antibacterial agent of the cyclic lipopeptides with in vitro bactericidal activity against gram-positive organisms, including vancomycin-resistant enterococci, methicillin-resistant staphylococci, and glycopeptide-resistant Staphylococcus aureus. The pharmacokinetics of daptomycin were determined in 29 adult oncology patients with neutropenic fever. Serial blood samples were drawn at 0, 0.5, 1, 2, 4, 8, 12, and 24 h after the initial intravenous infusion of 6 mg/kg of body weight daptomycin. Daptomycin total and free plasma concentrations were determined by high-pressure liquid chromatography. Concentration-time data were analyzed by noncompartmental methods. The results (presented as means ± standard deviations and ranges, unless indicated otherwise) were as follows: the maximum concentration of drug in plasma (Cmax) was 49.04 ± 12.42 μg/ml (range, 21.54 to 75.20 μg/ml), the 24-h plasma concentration was 6.48 ± 5.31 μg/ml (range, 1.48 to 29.26 μg/ml), the area under the concentration-time curve (AUC) from time zero to infinity was 521.37 ± 523.53 μg·h/ml (range, 164.64 to 3155.11 μg·h/ml), the volume of distribution at steady state was 0.18 ± 0.05 liters/kg (range, 0.13 to 0.36 liters/kg), the clearance was 15.04 ± 6.09 ml/h/kg (range, 1.90 to 34.76 ml/h/kg), the half-life was 11.34 ± 14.15 h (range, 5.17 to 83.92 h), the mean residence time was 15.67 ± 20.66 h (range, 7.00 to 121.73 h), and the median time to Cmax was 0.6 h (range, 0.5 to 2.5 h). The fraction unbound in the plasma was 0.06 ± 0.02. All patients achieved Cmax/MIC and AUC from time zero to 24 h (AUC0-24)/MIC ratios for a bacteriostatic effect against Streptococcus pneumoniae. Twenty-seven patients (93%) achieved a Cmax/MIC ratio for a bacteriostatic effect against S. aureus, and 28 patients (97%) achieved an AUC0-24/MIC ratio for a bacteriostatic effect against S. aureus. Free plasma daptomycin concentrations were above the MIC for 50 to 100% of the dosing interval in 100% of patients for S. pneumoniae and 90% of patients for S. aureus. The median time to defervescence was 3 days from the start of daptomycin therapy. In summary, a 6-mg/kg intravenous infusion of daptomycin every 24 h was effective and well tolerated in neutropenic cancer patients.

Analysis of tacrolimus and creatinine from a single dried blood spot using liquid chromatography tandem mass spectrometry.

Long term therapeutic drug monitoring and assessment of renal function are required in renal transplant recipients on immunosuppressant therapy such as tacrolimus. Dry blood spots (DBS) have been used successfully in the clinic for many years and offers a convenient, simple and non-invasive method for repeated blood tests. We developed and performed a preliminary validation of a method for the analysis of tacrolimus and creatinine from a single DBS using liquid chromatography-tandem mass spectrometric (LC-MS/MS). Tacrolimus and creatinine were extracted from a 6mm punch with a mixture of methanol/acetonitrile containing ascomycin and deuterated creatinine as internal standards. A 10 μl aliquot of the extract was analyzed directly after dilution for creatinine with normal phase high performance liquid chromatography and multiple reaction monitoring. The remainder of the extract was processed and analyzed for tacrolimus. The lower limit of quantification for tacrolimus was 1 ng/ml with accuracy of 0.34% bias and precision (CV) of 11.1%. The precision ranged from 1.33% to 7.68% and accuracy from -4.44% to 11.6% bias for the intra- and inter-day analysis. The lower limit of quantification of creatinine was 0.01 mg/dL with precision of 7.94%. Accuracy was based on recovery of additional creatinine spiked into whole blood samples and ranged from -2.45% bias at 5 mg/dL to 3.75% bias at 0.5 mg/dL. Intra- and inter-day precision was from 3.48 to 4.11%. The assay was further validated with DBS prepared from pediatric renal transplant recipients. There was excellent correlation between the levels of tacrolimus and creatinine obtained from the clinical laboratory and the DBS method developed. After additional validation, this assay may have a significant impact on compliance with medication intake as well as potentially lowering the cost associated with intravenous blood draws in clinical laboratories.

Aprepitant Pharmacokinetics and Assessing the Impact of Aprepitant on Cyclophosphamide Metabolism in Cancer Patients Undergoing Hematopoietic Stem Cell Transplantation

Aprepitant, a neurokinin antagonist, is an effective antiemetic agent in chemotherapy for delayed nausea and vomiting. The study objective was to evaluate the pharmacokinetics of aprepitant and concurrent cyclophosphamide (CY), often a component of hematopoietic stem cell transplant (HSCT) conditioning regimen, in cancer patients undergoing HSCT. Forty subjects were randomized to either aprepitant or placebo in addition to standard antiemetics. Aprepitant or placebo was started 1 hour before the first chemotherapy or radiation dose for HSCT conditioning and administered daily until 4 days after infusion of the hematopoietic cell graft (for a total of 10–12 days). Serial blood samples were collected for aprepitant and CY plus 2 important CY metabolites. The results indicate that aprepitant is well absorbed and does not auto‐induce its metabolism. No significant drug interaction was observed with CY or its metabolites. A significant portion of the patients had subtherapeutic aprepitant concentrations; however, chemotherapy‐induced nausea and vomiting were effectively managed. No dosage adjustment was necessary, and administration of aprepitant in HSCT at the prescribed dosage of 125 mg orally on day 1 and 80 mg orally on each consecutive day through day +4 after HSCT was well tolerated with no significant changes in CY pharmacokinetic parameters.

Pharmacokinetic study of lipoic acid in multiple sclerosis: Comparing mice and human pharmacokinetic parameters

Lipoic acid is a natural anti-oxidant available as an oral supplement from a number of different manufacturers. Lipoic acid administered subcutaneously is an effective therapy for murine experimental autoimmune encephalomyelitis, a model of multiple sclerosis. The aim of this study was to compare serum lipoic acid levels with oral dosing in patients with multiple sclerosis with serum levels in mice receiving subcutaneous doses of lipoic acid. We performed serum pharmacokinetic studies in patients with multiple sclerosis after a single oral dose of 1200 mg lipoic acid. Patients received one of the three different racemic formulations randomly: tablet (Formulation A) and capsules (Formulations B and C). Mice pharmacokinetic studies were performed with three different subcutaneous doses (20, 50 and 100 mg/kg racemic lipoic acid). The pharmacokinetic parameters included Maximum Serum Concentrations (Cmax in μg/ml) and area under the curve 0—infinity (AUC 0—infinity in μg*min/ml). We found mean Cmax and AUC 0—infinity in patients with multiple sclerosis as follows: group A (N = 7) 3.8 ± 2.6 and 443.1 ± 283.9; group B (N = 8) 9.9 ± 4.5 and 745.2 ± 308.7 and group C (N = 8) 10.3 ± 3.8 and 848.8 ± 360.5, respectively. Mean Cmax and AUC 0—infinity in the mice were: 100 mg/kg lipoic acid: 30.9 ± 2.9 and 998 ± 245; 50 mg/kg lipoic acid: 7.6 ± 1.4 and 223 ± 20; 20 mg/kg lipoic acid: 2.7 ± 0.7 and 119 ± 33. We conclude that patients taking 1200 mg of lipoic acid from two of the three oral formulations achieved serum Cmax and AUC levels comparable to that observed in mice receiving 50 mg/kg subcutaneous dose of lipoic acid, which is a highly therapeutic dose in experimental autoimmune encephalomyelitis. A dose of 1200 mg oral lipoic acid can achieve therapeutic serum levels in patients with multiple sclerosis.

Impact of obesity on the pharmacokinetics of levonorgestrel-based emergency contraception: single and double dosing

OBJECTIVE To determine if differences exist in the pharmacokinetics (PK) of levonorgestrel-based emergency contraception (LNG-EC) in obese and normal body mass index (BMI) users and test whether doubling the dose of LNG-EC in obese women increases total and free (active) LNG serum concentrations. STUDY DESIGN Healthy, reproductive-age women with obese and normal BMIs received 1.5mg LNG orally (ECx1) and then in a subsequent menstrual cycle, the obese group also received 3mg LNG (ECx2). Dosing occurred during the follicular phase. Total and free LNG PK parameters were obtained via serum samples through an indwelling catheter at 0, 0.5, 1, 1.5, 2, and 2.5h. The primary outcome was the difference in total and free LNG concentration maximum (Cmax) between ECx1 and ECx2 in the obese group. RESULTS A total of 10 women enrolled and completed the study (normal BMI=5, median 22.8kg/m(2), range 20.8-23.7; obese BMI=5, 39.5kg/m(2), range 35.9-46.7). The total LNG Cmax for obese subjects following ECx1 (5.57±2.48ng/mL) was significantly lower than the level observed in normal BMI women (10.30±2.47, p=.027). Notably, ECx2 increased the Cmax significantly (10.52±2.76, p=.002); approximating the level in normal BMI subjects receiving ECx1. Free LNG Cmax followed a similar pattern. CONCLUSION Obesity adversely impacts both the total and free Cmax levels of LNG EC and this likely explains its lack of efficacy in obese women. Doubling the dose appears to correct the obesity-related PK changes but additional research is needed to determine if this also improves EC effectiveness in obese women. IMPLICATIONS This study demonstrates that obesity interferes with the pharmacokinetics of LNG EC, and that doubling the dose may be an effective strategy to improve its efficacy in obese women.

Maternal protein restriction during pregnancy and lactation in rats imprints long-term reduction in hepatic lipid content selectively in the male offspring

Maternal protein restriction during pregnancy and lactation reduces whole body lipid stores and alters lipid homeostasis in the adult offspring. Lipid homeostasis in the body is regulated, in part, by the liver via the metabolic processes of synthesis and utilization of lipids. The present study tested the hypothesis that maternal protein restriction will imprint changes in hepatic lipid metabolism and thereby alter the hepatic lipid content of the adult offspring. Pregnant rats were fed purified diets containing 19% protein (control group) or 8% protein (low-protein group) throughout pregnancy and lactation. On day 28, pups from both groups were weaned onto regular laboratory chow. On days 65 and 150, male and female pups from each litter in both groups were killed and blood and liver collected. Maternal protein restriction was found to reduce birth weight and produce long-term reduction in the body weight of the offspring. On day 65, liver triglyceride content was decreased by 40% in the male offspring that were fed a low-protein diet. The reduction in liver triglyceride content persisted until day 150, at which time it was accompanied by decreases in hepatic cholesterol content. No such changes were observed in the female offspring. To determine if the alterations in liver lipid content resulted in compensatory changes in liver carbohydrate stores, hepatic glycogen content was measured in male offspring. Hepatic glycogen content was similar between the 2 groups on days 65 and 150. In conclusion, the present study in rats showed that maternal protein restriction during pregnancy and lactation imprints long-term changes in hepatic lipid content selectively in the male offspring.

Correcting oral contraceptive pharmacokinetic alterations due to obesity: a randomized controlled trial.

OBJECTIVE To determine if increasing the hormone dose or eliminating the hormone-free interval improves key pharmacokinetic (PK) alterations caused by obesity during oral contraceptive (OC) use. STUDY DESIGN Obese [body mass index (BMI)≥30 kg/m(2)], ovulatory, otherwise healthy, women received an OC containing 20 mcg ethinyl estradiol (EE)/100 mcg levonorgestrel (LNG) dosed cyclically (21 days active pills with 7-day placebo week) for two cycles and then were randomized for two additional cycles to the following: continuous cycling (CC, a dose neutral arm using the same OC with no hormone-free interval) or increased dose (ID, a dose escalation arm using an OC containing 30 mcg EE/150 mcg LNG cyclically). During Cycles 2, 3 and 4, outpatient visits were performed to assess maximum serum concentration (Cmax), area under the curve (AUC0-∞) and time to steady state as well as pharmacodynamics. These key PK parameters were calculated and compared within groups between baseline and treatment cycles. RESULTS A total of 31 women enrolled and completed the study (CC group, n=16; ID group, n=15). Demographics were similar between groups [mean BMI: CC, 38 kg/m(2) (S.D. 5.1); ID, 41 kg/m(2) (S.D. 7.6)]. At baseline, the key LNG PK parameters were no different between groups; average time to reach steady state was 12 days in both groups; Cmax were CC: 3.82±1.28 ng/mL and ID: 3.13±0.87 ng/mL; and AUC0-∞ were CC: 267±115 h ng/mL and ID: 199±75 h ng/mL. Following randomization, the CC group maintained steady-state serum levels whereas the ID group had a significantly higher Cmax (p<.001) but again required 12 days to achieve steady state. However, AUC was not significantly different between CC (412±255 h ng/mL) and ID (283±130 h ng/mL). Forty-five percent (14/31) of the study population had evidence of an active follicle-like structure prior to randomization and afterwards this decreased to 9% (3/31). CONCLUSION Both increasing the OC dose and continuous dosing appear to counteract the impact of obesity on key OC PK parameters. IMPLICATIONS Obesity adversely affects the pharmacokinetics of very low dose OC pills. Although the impact of these changes on OC efficacy is still under debate, PK parameters can be normalized in obese users by continuous dosing or increasing to a low-dose pill.

Application of platelet function testing to the bedside

The ability to test platelet reactivity in clinical practice could help in making informed decisions on both initiation and titration of anti-platelet drug therapies. However, many barriers still remain to the effective implementation of such techniques. Many tests used in the research literature are not yet available for practical, clinical use. Platelet aggregometry, while informative and currently available for bedside use, needs additional research before routine clinical use can be recommended. This review will highlight and update contemporary issues of bedside platelet testing for the clinician and comment on future areas of clinical research.