Effect of obesity on the pharmacokinetics of drugs in humans

Impact of hospital guideline for weight-based antimicrobial dosing in morbidly obese adults and comprehensive literature review

WHAT IS KNOWN AND OBJECTIVE

Obesity is a significant burden on the healthcare system in the United States, and determining the appropriate antimicrobial dosing regimen in morbidly obese patients is challenging. Morbidly obese patients have documented differences in pharmacokinetic and pharmacodynamic properties compared to normal-weight patients, which impact antibiotic efficacy and toxicity. The Food and Drug Administration does not recognize obesity as a special population and does not require pharmaceutical companies to perform studies specific to obese patients. However, there are an increasing number of post-approval studies in obese patients, and this manuscript reviews available clinical and pharmacokinetic literature regarding weight-based antimicrobial agents. Additionally, we describe a single-centre approach to optimize dosing in morbidly obese patients.

METHODS

A comprehensive literature search was performed on 15 weight-based antimicrobials in the setting of obesity: acyclovir, aminoglycosides, amphotericin B, cidofovir, colistimethate, daptomycin, flucytosine, foscarnet, ganciclovir, quinupristin/dalfopristin, trimethoprim/sulfamethoxazole, vancomycin and voriconazole. A weight-based antimicrobial dosing guideline for morbidly obese patients was developed. An analysis of guideline compliance and cost analysis were performed following guideline implementation.

RESULTS AND DISCUSSION

This review describes the pharmacokinetic changes that occur in obese patients, including increased volume of distribution, altered hepatic metabolism, renal excretion and changes in protein binding. The majority of weight-based antimicrobials result in increased serum concentrations in morbidly obese patients compared to normal-weight patients when the calculated dose is based on actual body weight.

WHAT IS NEW AND CONCLUSION

This review demonstrates different antibiotic pharmacokinetic properties are altered in obese patients that could impact efficacy and toxicity. A single-centre guideline for weight-based antimicrobial dosing in obesity was developed and provides recommendations for using ideal body weight, adjusted body weight or actual body weight when calculating antimicrobial doses. However, more research is needed to better elucidate optimal dosing of weight-based antimicrobials in obesity, with particular focus on efficacy and toxicity.

Fluconazole pharmacokinetics in a morbidly obese, critically ill patient receiving continuous venovenous hemofiltration

Current fluconazole dosing strategies can be described using either standardized doses (800 or 400 mg) or as weight-based dosing recommendations (12 mg/kg loading dose followed by 6 mg/kg maintenance dose). The ideal method of fluconazole dosing is still unclear for certain patient populations, such as those receiving renal replacement therapy or the morbidly obese. We describe a 48-year-old man with a body mass index of 84 kg/m(2) who was receiving continuous venovenous hemofiltration (CVVH) and was treated with fluconazole by using a weight-based dose determined by lean body weight, infused at a rate of 200 mg/hour. Blood samples were collected at hour 0 (i.e., ~24 hrs after the loading dose was administered) and at 3.5, 6.8, and 11.3 hours after the start of the 600-mg maintenance dose, infused over 3 hours. Pharmacokinetic parameters calculated were maximum serum concentration 9.64 mg/L, minimum serum concentration 5.98 mg/L, area under the serum concentration-time curve from 0-24 hours (AUC0-24 ) 184.75 mg/L•hour, elimination rate constant 0.0199 hour(-1) , elimination half-life 34.8 hours, and total body clearance 3.25 L/hour. Our data, when combined with previously published literature, do not support using a linear dose-to-AUC approximation to estimate drug dosing needs in the critically ill patient population receiving CVVH. In addition, our results suggest that morbidly obese patients are able to achieve pharmacodynamic goals defined as an AUC:MIC ratio higher than 25 by using a lean body weight for fluconazole dosing calculations.

H1-antihistamines exacerbate high-fat diet-induced hepatic steatosis in wild-type but not in apolipoprotein E knockout mice

We examined the effects of two over-the-counter H1-antihistamines on the progression of fatty liver disease in male C57Bl/6 wild-type and apolipoprotein E (ApoE)-/- mice. Mice were fed a high-fat diet (HFD) for 3 mo, together with administration of either cetirizine (4 mg/kg body wt) or fexofenadine (40 mg/kg body wt) in drinking water. Antihistamine treatments increased body weight gain, gonadal fat deposition, liver weight, and hepatic steatosis in wild-type mice but not in ApoE-/- mice. Lobular inflammation, acute inflammation, and necrosis were not affected by H1-antihistamines in either genotype. Serum biomarkers of liver injury tended to increase in antihistamine-treated wild-type mice. Serum level of glucose was increased by fexofenadine, whereas lipase was increased by cetirizine. H1-antihistamines reduced the mRNA expression of ApoE and carbohydrate response element-binding protein in wild-type mice, without altering the mRNA expression of sterol regulatory element-binding protein 1c, fatty acid synthase, or ApoB100, in either genotype. Fexofenadine increased both triglycerides and cholesterol ester, whereas cetirizine increased only cholesterol ester in liver, with a concomitant decrease in serum triglycerides by both antihistamines in wild-type mice. Antihistamines increased hepatic levels of conjugated bile acids in wild-type mice, with the effect being significant in fexofenadine-treated animals. The increase was associated with changes in the expression of organic anion transport polypeptide 1b2 and bile salt export pump. These results suggest that H1-antihistamines increase the progression of fatty liver disease in wild-type mice, and there seems to be an association between the severity of disease, presence of ApoE, and increase in hepatic bile acid levels.

Controlling on-demand gastric acidity in obese subjects: a randomized, controlled trial comparing a single dose of 20 mg rabeprazole and 20 mg omeprazole

Background

Obesity is associated with a risk of gastroesophageal reflux disease. The pharmacodynamic efficacy of proton pump inhibitors has not been specifically evaluated in obese subjects. The aim of this study was to compare the antisecretory response to a single oral dose of 20 mg rabeprazole, 20 mg omeprazole and placebo in obese subjects.

Methods

Gastric pH was monitored for 24 hours on three separate occasions in eighteen H. pylori-negative, asymptomatic obese subjects. Subjects were given omeprazole, rabeprazole or placebo in a randomized order and in a double-blind fashion. The main analysis criterion was 24-h percent of time post dose with intragastric pH above 3; secondary criteria were percentage of time above pH 4, median pH, [H+] concentrations and nocturnal acid breakthrough (NAB). Results were analyzed using linear mixed models and Wilks test comparing variances.

Results

24-h median [IQ] percentages of time with gastric pH above 3 and 4 were higher with rabeprazole than omeprazole (46 [37–55] vs. 30 [15–55] %, 9 [5-11] % for placebo) but the differences did not reach statistical significance (p = 0.11 and 0.24, respectively). Median acid concentrations were significantly lower with rabeprazole than with omeprazole and placebo (22 [14–53] vs. 54 [19–130] and 95 [73–170] mmoles/l, p < 0.01) for all periods. The number of NAB was significantly lower with rabeprazole than with omeprazole (median 1 [1,2] vs. 2 [1-3], p = 0.04). Variances of 24-h data (pH above 3 and 4, median pH, [H+] concentrations) were significantly lower with rabeprazole than with omeprazole (p < 0.0001).

Conclusions

In asymptomatic obese subjects the gastric antisecretory response to a single dose of rabeprazole and omeprazole was strong and not significantly different between drugs despite a significantly more homogeneous response with rabeprazole.

Trial registration

ClinicalTrial.gov: NCT01136317

Joint feedback analysis modeling of nonesterified fatty acids in obese Zucker rats and normal Sprague-Dawley rats after different routes of administration of nicotinic acid

Data were pooled from several studies on nicotinic acid (NiAc) intervention of fatty acid turnover in normal Sprague-Dawley and obese Zucker rats in order to perform a joint PKPD of data from more than 100 normal Sprague-Dawley and obese Zucker rats, exposed to several administration routes and rates. To describe the difference in pharmacodynamic parameters between obese and normal rats, we modified a previously published nonlinear mixed effects model describing tolerance and oscillatory rebound effects of NiAc on nonesterified fatty acids plasma concentrations. An important conclusion is that planning of experiments and dose scheduling cannot rely on pilot studies on normal animals alone. The obese rats have a less-pronounced concentration-response relationship and need higher doses to exhibit desired response. The relative level of fatty acid rebound after cessation of NiAc administration was also quantified in the two rat populations. Building joint normal-disease models with scaling parameter(s) to characterize the "degree of disease" can be a useful tool when designing informative experiments on diseased animals, particularly in the preclinical screen. Data were analyzed using nonlinear mixed effects modeling, for the optimization, we used an improved method for calculating the gradient than the usually adopted finite difference approximation.

Pharmacokinetic changes and dosing modification of aminoglycosides in critically ill obese patients: a literature review

The objective of the paper is to review the literature and provide recommendations for use of aminoglycoside antibiotics in critically ill obese patients. Literature search in PubMed for all articles on the use of aminoglycosides in critically ill obese patients was conducted, and all articles related to pharmacokinetics in obesity were reviewed. Bibliographies of all searched manuscripts were also reviewed in an attempt to find additional references. Although aminoglycoside pharmacokinetics have been described in detail, data on aminoglycoside use and appropriate dose modification in critically ill obese patients are very limited. Knowledge on aminoglycoside pharmacokinetics and use in critically ill obese patients is incomplete. Pathophysiologic changes in obesity can result in sub- or supra-therapeutic aminoglycoside plasma concentrations, especially in the presence of sepsis. Rigorous clinical studies are needed to establish aminoglycoside dosing guidelines in critically ill obese patients with sepsis.

Body mass index as a prognostic factor in organophosphate-poisoned patients

Organophosphate poisoning is a serious clinical entity and considerable morbidity and mortality. Several factors have been identified to predict outcomes of organophosphate poisoning. Organophosphates are lipophilic and therefore predicted to have a large volume of distribution and to rapidly distribute into tissue and fat. Thus, toxic effects of organophosphate would be expected to last longer in obese patients. We investigated the relationship between obesity and clinical course in 112 acute organophosphate-poisoned patients from an initial medical record review of 234 patients. One hundred twenty-two patients were excluded: 6 were children, 14 had an uncertain history of exposure and of uncertain agent, 10 were transferred to another hospital, 67 were discharged from the emergency department because their toxicity was mild, 21 had carbamate poisoning, and 4 did not have height or weight checked. Clinical features, body mass index, Glasgow Coma Scale, laboratory findings, serum cholinesterase activity, electrocardiogram finding, management, and outcomes were examined. The lipid solubility of the implicated organophosphate was characterized by its octanol/water coefficient. Forty of 112 patients were obese. Obese patients who were poisoned by high lipophilicity organophosphate compounds had a need for longer use of mechanical ventilation, intensive care unit care, and total length of admission. Body mass index can provide a guide to physicians in predicting clinical course and management in organophosphate-poisoned patients.

Pharmacologic prevention of venous thromboembolism in obese patients

Venous thromboembolism, a collective term for pulmonary embolism and deep venous thrombosis accounts for a large amount of mortality and morbidity in hospitalized patients. Obesity has been considered as an important risk factor for the development of venous thromboembolism. Anticoagulation with fixed doses of low molecular weight heparin, anti-factor Xa inhibitors and unfractionated heparin is widely used in hospitals and has shown to be an effective measure in prevention of venous thromboembolism in multiple major randomized, double-blind controlled trials. Appropriate dosing of anticoagulation in obese patients is still controversial, since obese and morbidly obese population of patients is consistently underrepresented or often excluded from most clinical trials, raising a concern for adequacy of standard dosing in this high risk population.

Pharmacokinetics of human chorionic gonadotropin injection in obese and normal-weight women

CONTEXT

Obese women have poorer in vitro fertilization outcomes, but underlying mechanisms remain unclear.

OBJECTIVE

The objectives of the study were to compare the pharmacokinetics of human chorionic gonadotropin (hCG) and ovarian steroid hormone production, after subcutaneous (s.c.) and intramuscular (i.m.) injection of hCG in obese and normal-weight women.

DESIGN AND SETTING

This was a randomized, experimental study.

PATIENTS OR OTHER PARTICIPANTS

Twenty-two women aged 18-42 years with body mass index of 18.5-24.9 (normal) or 30-40 kg/m(2) (obese).

INTERVENTIONS

Participants received im urinary hCG or s.c. recombinant hCG and returned for a second injection type after a 4-week washout. Intramuscular injections were performed under ultrasound guidance. Blood was taken 0, 0.5, 1, 2, 4, 6, 8, 12, 24, and 36 hours after injection.

MAIN OUTCOME MEASURES

hCG was measured at each time point; estradiol, progesterone, 17-hydroxyprogesterone (17-OHP), testosterone (T), dehydroepiandrosterone, and SHBG were measured at 0 and 36 hours.

RESULTS

Twenty-two women completed the study. In both normal-weight and obese women, peak serum concentration (Cmax), area under the curve (AUC), and average hCG concentration were higher after i.m. injection as compared with s.c. injection (all P < .003). Obese women had markedly lower Cmax, AUC, and average hCG concentration after s.c. injection as compared with normal-weight women (P = .02, P = .009, and P = .008, respectively). After i.m. injection, Cmax, AUC, and average concentration were similar for normal-weight and obese women (P = .31, P = .25, and P = .18, respectively). Thirty-six percent of obese women had muscular layers beyond the reach of a standard 1.5 inch needle. hCG caused a significant rise in 17-OHP in both obese and normal-weight women and an increase in T in obese but not normal-weight women (all P < .04).

CONCLUSIONS

Subcutaneous injection yields lower hCG levels in obese women. Standard-length needles are insufficient to administer i.m. injections in many obese women.

Challenges in the optimisation of post-operative pain management with opioids in obese patients: a literature review

An increasing number of obese patients are undergoing surgery, particularly bariatric and orthopaedic surgery. The physiological differences between obese and normal-weight subjects may modify not only anaesthetic requirements during surgery but also post-operative analgesic management, raising a number of challenges in a critical period. In this review, we analyse studies of post-operative pain management with opioids in obese subjects. We discuss the genetic factors common to pain and obesity and the factors potentially modifying opioid pharmacokinetics and pharmacodynamics in obese patients, and we analyse the overall efficacy and safety of opioids for pain management during the post-operative period in obese patients. Both modifications to surgical methods and additional analgesic treatments to decrease the requirement for opioids may improve early rehabilitation and quality of care and reduce adverse effects in obese patients.

Obesity and low back pain: relationships and treatment

SUMMARY Low back pain (LBP) and obesity (defined as BMI ≥30 kg/m(2)) are common problems in the general population. The treatment of LBP is not clearly defined and has variable success in different populations and time-frames. When a person presents with LBP who also meets the criteria for obesity, many questions are raised as to the value of weight-loss treatments and the success and/or safety of usual treatments of LBP, especially exercise. Based on the current medical literature for the treatment of LBP in patients who are obese: there should be attempts at weight loss (nonsurgical or surgical), especially if the person is in the morbidly obese (BMI >40 kg/m(2)) range; all usual forms of exercise and physical therapy treatments are possible and can be beneficial without increased concerns for injury; and, if necessary, invasive treatments such as spinal injections or surgery are potentially beneficial and have similar complication rates to the nonobese population. These options should be offered when medically necessary and appropriate.

On-demand proton pump inhibitory treatment in overweight/obese patients with gastroesophageal reflux disease: are there pharmacodynamic arguments for using higher doses?

BACKGROUND

Increased body mass index (BMI) is associated with a higher risk of gastroesophageal reflux disease (GORD).

AIM

To investigate whether overweight/obesity affects proton pump inhibitor pharmacodynamics when used in a single dose in patients with GORD.

METHODS

Post hoc analyses by patient BMI were performed on data from two single-center, double-blind, single-dose, crossover studies comparing the pharmacodynamics of rabeprazole 20 mg and pantoprazole 40 mg in GORD patients with a history of nocturnal heartburn. The primary endpoint was the mean percentage of time with intragastric pH >4 between lean and overweight/obese patients (BMI <25 and ≥25).

RESULTS

24 h baseline intragastric pH values were not different between BMI groups. The pharmacodynamic effects of both proton pump inhibitors were not significantly different between BMI groups, and no evidence was found for an interaction between BMI and treatment. As compared with pantoprazole, rabeprazole showed a significantly greater effect on the antisecretory response for both BMI groups.

CONCLUSIONS

Overweight/obesity in GORD patients does not appear to affect the antisecretory efficacy of a single dose of rabeprazole and pantoprazole. These data do not support adapting the dosage of rabeprazole and pantoprazole according to BMI in GORD patients when administered as an on-demand therapy schedule.

Pharmacogenomics of episodic migraine: time has come for a step forward

Migraine is characterized by heterogeneous behavior in response to drugs. Many resources have been invested in attempting to unravel the genetic basis of migraine, while the role of genetics in responses to currently available drugs has received less attention. We performed a systematic literature search identifying original articles pertaining to pharmacogenomics of episodic migraine. Few primary studies on the pharmacogenomics of symptomatic and preventive medication in episodic migraine were found. The number of patients studied in the individual articles ranged from 40 up to 130. There was a strong heterogeneity among these studies. We believe that pharmacogenomics studies, if properly designed, could contribute towards optimizing the treatment and reducing the burden of migraine, in turn helping patients and optimizing resources. Our knowledge on the pharmacogenomics of migraine is growing too slowly, and concerted measures should be undertaken to speed up the process.

The effect of molecular subtype and body mass index on neo-adjuvant chemotherapy in breast cancer patients

The aim of the present study was to analyze the effect of subtype and body mass index (BMI) on neo-adjuvant chemotherapy (NAC) and postoperative prognosis. Two-hundred and forty nine patients who underwent surgery after NAC were included. A multivariate analysis and survival analysis were used to clarify the relationship between BMI, subtype, and NAC. In the logistic regression model, the pCR rate had a significant relationship with the subtype and tumor stage. In the non-pCR group, more overweight patients had significantly a worse disease-free survival (DFS) compared to normal range patients (Log lank test, p < 0.05). In the Cox proportional hazards model, subtype and tumor stage were significantly associated with decreased DFS. In conclusion, patients with the ER (+), HER (-) type and a high BMI had a high risk for recurrence when they achieved non-pCR after NAC.

Pharmacogenomics, pharmacokinetics and pharmacodynamics: interaction with biological differences between men and women

Pharmacological response depends on multiple factors and one of them is sex-gender. Data on the specific effects of sex-gender on pharmacokinetics, as well as the safety and efficacy of numerous medications, are beginning to emerge. Nevertheless, the recruitment of women for clinical research is inadequate, especially during the first phases. In general, pharmacokinetic differences between males and females are more numerous and consistent than disparities in pharmacodynamics. However, sex-gender pharmacodynamic differences are now increasingly being identified at the molecular level. It is now even becoming apparent that sex-gender influences pharmacogenomics and pharmacogenetics. Sex-related differences have been reported for several parameters, and it is consistently shown that women have a worse safety profile, with drug adverse reactions being more frequent and severe in women than in men. Overall, the pharmacological status of women is less well studied than that of men and deserves much more attention. The design of clinical and preclinical studies should have a sex-gender-based approach with the aim of tailoring therapies to an individual's needs and concerns.

Obesity during pregnancy alters maternal oxidant balance and micronutrient status

OBJECTIVE

Little is known about the effect of obesity on inflammatory status in pregnant women. The objective of this study was to determine the effect of obesity on markers of inflammation, oxidative stress and micronutrient status in obese pregnant women and their infants compared with lean controls (Lc).

STUDY DESIGN

This was a prospective case-control study. A total of 15 obese (Ob; body mass index (BMI) >30 kg m(-2)) and 15 lean (BMI 18-25 kg m(-2)) women were recruited based on prepregnancy BMI. Vitamins A, B6, C, E and 25-hydroxyvitamin D (25(OH)D), zinc, red blood cell (RBC) folate, C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor-α and oxidized and reduced glutathione were measured from maternal blood between 24 and 28 weeks of gestation. Vitamins A, B6, C and E, 25(OH)D, zinc, red blood cell folate, CRP and IL-6 were measured from cord blood at delivery.

RESULT

Ob pregnant women have statistically significantly lower levels of vitamin B6, vitamin C, vitamin E, RBC folate, higher CRP and IL-6 levels and higher ratio of oxidized to reduced glutathione compared with Lc pregnant women. Infants born to Ob mothers did not have statistically significantly higher measures of inflammation or oxidative stress. There were no differences in micronutrient concentrations between Lc and Ob infants, but folate, vitamin B6 and zinc levels correlated strongly between mother and infant. There was no statistically significant difference in any parameter between Ob and Lc cord blood.

CONCLUSION

Ob pregnant women have increased inflammation and oxidative stress, and lower levels of nutritional antioxidant defenses compared with Lc pregnant women. We speculate that lower antioxidant defenses combined with increased oxidative stress and inflammation may contribute to the adverse outcomes associated with pregnancy in Ob women.

Endotherapy for and tailored approaches to treating GERD, and refractory GERD

This paper presents commentaries on how endoluminal antireflux procedures compare to laparoscopic fundoplication; new endoscopic procedures being studied to treat refractory gastroesophageal reflux disease (GERD); the new Stretta; the relationship between obesity and proton pump inhibitor (PPI) resistance; data concerning acid hypersensitivity and sensory receptors (vallinoid, TRPV1) causing refractory GERD; whether microscopic esophagitis is relevant in determining symptoms of non-erosive reflux disease (NERD); how concomitant functional gastrointestinal disorders affect the PPI response in NERD; the evidence that a functional esophagus is associated with inflammatory bowel syndrome (IBS); the role of GABA agonists in the treatment of refractory GERD; the role of biofeedback and antidepressants in refractory GERD; and endoluminal fundoplication using the EsophyX device.

[Antiplatelet therapy: resistance to traditional antiaggregation drugs and role of new antiplatelet agents]

Platelet aggregation plays a key role in the development of major cardiovascular events (MACE) related to atherothrombosis. Since the appearance of coronary stenting, the importance of measuring and modulating platelet activity has considerably increased in the scientific literature during the last decade. Double antiplatelet therapy with aspirin and clopidogrel administrated to stent carriers has widely demonstrated its efficacy in the prevention of MACE compared with aspirin alone. These benefits are also present when a conservatory approach is chosen for acute coronary syndrome management. However, there are an important number of patients who develop MACE despite optimal dual antiplatelet therapy, most likely related to an incomplete platelet activity inhibition. Many studies suggest an important inter-individual variability in the response to the drugs, maybe related, at least in part, to the use of different assessment techniques of platelet aggregation. Other authors suggest an incomplete platelet inhibition as a possible explanation for the presence of MACE in patients under optimal antiplatelet therapy. Resistance to usual drugs has become a clinically relevant issue that requires an individual approach where new antiplatelet agents, such as prasugrel or ticagrelor, could play an important role as stated in current consensus documents.

Refractory GERD: increased body mass index is associated with persisting acid exposure but not hypersensitive esophagus or functional heartburn

OBJECTIVE

To compare the incidence of persistent abnormal acid exposure, hypersensitive esophagus (HE), and functional heartburn (FH) in obese/overweight and normal-weight patients referred for impedance-pH monitoring, because of persisting gastroesophageal reflux disease (GERD) symptoms despite therapy with proton pump inhibitors (PPIs). ΜETHODS: Patients with normal endoscopy and typical GERD symptoms, despite PPI therapy twice daily, underwent 24-h impedance-pH monitoring while on therapy. Distal esophageal acid exposure (% time pH<4) was measured and reflux episodes were classified into acid or nonacid. A positive symptom index was defined when at least 50% of symptom events were preceded by reflux episodes. Patients were categorized as those with persistent abnormal acid exposure, those with HE, and those with FH. The incidence of persistent abnormal acid exposure, HE, and FH between overweight/obese patients (BMI≥25 kg/m) and normal-weight patients (BMI<25 kg/m) was subsequently evaluated.

RESULTS

A total of 246 patients (women: 158, men: 88, increased BMI: 151, normal BMI: 95, mean age 55, range 18-75 years) were included. Persistent abnormal acid exposure was found in 39 patients (increased BMI: 31, normal BMI: 8), HE in 77 patients (increased BMI: 43, normal BMI: 34), and FH in 118 patients (increased BMI: 69, normal BMI: 49). When comparing BMI among all three groups, patients with increased BMI were more likely to have acid reflux than HE or FH (P=0.03).

CONCLUSION

In patients with GERD symptoms refractory to double-dose PPI therapy, those with increased BMI are more likely to have persistent abnormal acid exposure than HE or FH.

Physiologically based pharmacokinetic models for the optimization of antiretroviral therapy: recent progress and future perspective

Anti-HIV therapy is characterized by the chronic administration of antiretrovirals (ARVs), and consequently, several problems can arise during the management of HIV-positive patients. ARV disposition can be simulated by combining system data describing a population of patients and in vitro drug data through physiologically based pharmacokinetic (PBPK) models, which mathematically describe absorption, distribution, metabolism and elimination. PBPK modeling can find application in the investigation of clinically relevant scenarios, while providing the opportunity for a better understanding of the mechanisms regulating drug distribution. In this review, we have analyzed the most recent applications of PBPK models for ARVs and highlighted some of the most interesting areas of use, such as drug–drug interaction, pharmacogenetics, factors regulating absorption and tissue penetration, as well as therapy optimization in special populations. The application of the PBPK modeling approach might not be limited to the investigation of hypothetical clinical issues, but could be used to inform future prospective clinical trials.

Obesity and the response to intensified diuretic treatment in decompensated heart failure: a DOSE trial substudy

BACKGROUND

Obesity could attenuate diuretic effectiveness in treatment of acute decompensated heart failure (HF).

METHODS AND RESULTS

The DOSE trial randomized 308 subjects with acute HF to low- versus high-intensification intravenous diuretic therapy. We tested for statistical interactions between obesity and dosing strategy across clinical end points. After 72 hours of treatment, obese subjects (body mass index >30 kg/m(2); n = 173) had greater volume loss than nonobese subjects (n = 119) but similar improvements in dyspnea and freedom from congestion. Both groups had greater fluid loss with high-intensification treatment. Obese subjects had a higher incidence of worsening renal function (WRF) at 72 hours with low-intensification treatment, compared with nonobese subjects. In contrast, nonobese and obese subjects had similar incidence of WRF with high-intensification treatment. There were no differences between obese and nonobese subjects in time to discharge and 60-day freedom from death, emergency department visit, or rehospitalization.

CONCLUSIONS

The incidence of WRF was greater in obese than in nonobese subjects with low-intensification treatment. However, the frequency of WRF was equivalent in obese and nonobese subjects with high-intensification treatment. Additional studies are needed to assess whether obese patients with acute HF benefit from an initial high-intensification treatment strategy.

Preoperative risk reduction: strategies to optimize outcomes

The success of hernia repair is measured by absence of recurrence, appearance of the surgical scar, and perioperative morbidity. Perioperative surgical site occurrence (SSO), defined as infection, seroma, wound ischemia, and dehiscence, increases the risk of recurrent hernia by at least 3-fold. The surgeon should optimize all measures that promote healing, reduce infection, and enhance early postoperative recovery. In the population with ventral hernia, the most common complication in the immediate perioperative period is surgical site infection. This article reviews several preoperative measures that have been reported to decrease SSOs and shorten length of hospital stay.

A comparison of duloxetine plasma levels in postbariatric surgery patients versus matched nonsurgical control subjects

BACKGROUND

Bariatric surgery such as the Roux-en-Y gastric bypass (RYGB) is currently used as a treatment for severe obesity. Alteration of the gastrointestinal tract by this procedure suggests a potential for clinically significant alterations in the bioavailability of ingested medications including antidepressants.

OBJECTIVES

The purpose of this trial was to determine to what extent the RYGB procedure alters the area under the plasma concentration/time curve (AUC(0-infinity)) of the antidepressant, duloxetine.

METHODS

Ten subjects who were 1 year post-RYGB where compared with healthy control subjects matched for body mass index, age, and sex. Ultrarapid or poor metabolizers for cytochrome P450 2D6 were excluded from the study. Subjects received a single dose of 60 mg of duloxetine. Nineteen plasma samples were obtained during 72 hours to characterize the plasma level profile.

RESULTS

The mean AUC(0-infinity) was significantly smaller for the postbariatric surgery (PBS) group (646.74 ng × h/mL [SD, 79.70; range, 539.57-791.62], P = 0.017) compared to the nonsurgical control group (1119.91 ng × h/mL [SD, 593.40; range, 415.5-2426.56]). The Tmax was also significantly shorter for the PBS group (2.2 hours) compared to the nonsurgical control group (6 hours; P = 0.005). No significant difference in Cmax or half-life was identified.

CONCLUSIONS

To our knowledge, this is the first reported study exploring duloxetine pharmacokinetics PBS. This trial found that the bariatric surgery group was exposed to only 57.7% of duloxetine as compared to the nonsurgery group. This finding suggests that clinicians need to monitor patients closely after bariatric surgery and that further exploration of the effects of bariatric surgery on antidepressant pharmacokinetic parameters is warranted.

Pharmacokinetic analysis of piperacillin administered with tazobactam in critically ill, morbidly obese surgical patients

STUDY OBJECTIVE

To evaluate the steady-state pharmacokinetic and pharmacodynamic parameters of piperacillin in morbidly obese, surgical intensive care patients.

DESIGN

Open-label single-center prospective study.

SETTING

Level I trauma center and university-affiliated teaching institution.

PATIENTS

Nine morbidly obese (body mass index [BMI] 40.0 kg/m² or higher) hospitalized patients admitted to the trauma and surgical intensive care service who were treated with piperacillin-tazobactam between December 15, 2010, and April 18, 2012.

INTERVENTION

Patients received intravenous piperacillin-tazobactam 4.5 g every 6 hours, administered as a 30-minute infusion.

MEASUREMENTS AND MAIN RESULTS

Patients' blood samples were collected after the administration of the fourth, fifth, or sixth dose (i.e., at steady state). Serum piperacillin concentrations were determined by using a validated high-performance liquid chromatography assay; these concentrations were used to estimate pharmacokinetic parameters, and 5000-patient Monte Carlo simulations were performed. The probability of target attainment for 50% or higher of the dosing interval during which free (unbound) drug concentrations exceeded the minimum inhibitory concentration (%fT > MIC) of likely pathogens was calculated for piperacillin at various MICs. Patient demographic and clinical characteristics included a mean ± SD total body weight of 164 ± 50 kg, BMI of 57 ± 15.3 kg/m², and age 57 ± 11 years, and a median Acute Physiology and Chronic Health Evaluation II score of 22 (interquartile range 21-26). Compared with values previously reported in other populations, the volume of distribution was increased in the study patients, and total system clearance was decreased. The net result was a mean ± SD half-life of 3.7 ± 1.2 hours compared with ~1 hour reported in other populations. This contributed to an extended %fT > MIC for likely pathogens. Results from all nine patients showed %fT > MIC of 100% at the susceptibility breakpoint MIC of 16 mg/L and 85% or higher at an MIC of 32 mg/L.

CONCLUSION

The pharmacokinetics of piperacillin is altered in morbidly obese, surgical intensive care patients. The use of standard-dosage piperacillin-tazobactam 4.5 g intravenously every 6 hours was shown to be an appropriate dosage for this study population.

Chemotherapy dosing in overweight and obese patients with cancer

Retrospective and prospective preclinical and clinical data have demonstrated an association between chemotherapy dose intensity and both clinical efficacy and toxicity. The optimum tolerable and effective dose and schedule of chemotherapeutic agents is based on data from dose-finding studies and early clinical trials. There is considerable evidence that reductions in the recommended dose intensity often occurs in actual clinical practice, particularly among overweight and obese patients with cancer. With increasing rates of obesity, and variation and uncertainty about appropriate dosing of chemotherapy in obese patients, ASCO has generated clinical practice guidelines for appropriate chemotherapy dosing for obese adult patients with cancer. Without evidence of any increase in treatment-related toxicity among obese patients receiving chemotherapy, the guidelines recommend that, after considering any accompanying comorbidities, chemotherapy dosing should be calculated based on body surface area using actual weight, rather than an estimate or idealization of weight. While further research is needed, pharmacokinetic studies support the use of actual body weight to calculate chemotherapy doses for most chemotherapy drugs in obese patients. We highlight the issue of chemotherapy dosing in this population, how a more personalized approach can be achieved, as well as discussing areas for further research.

Subtherapeutic linezolid concentrations in a patient with morbid obesity and methicillin-resistant Staphylococcus aureus pneumonia: case report and review of the literature

OBJECTIVE

To report a case of subtherapeutic linezolid concentrations in a patient with morbid obesity.

CASE SUMMARY

A 34-year-old male with morbid obesity (265 kg, body mass index 82 kg/m(2)) was admitted for severe sepsis due to respiratory failure requiring emergent intubation and treatment of community-acquired pneumonia. Admission tracheal aspirate culture revealed methicillin-resistant Staphylococcus aureus (MRSA) for which vancomycin was prescribed. Therapy subsequently was changed to linezolid, because the patient's clinical status worsened, with significant hypoxia (partial pressure of arterial oxygen/fraction of inspired oxygen [PaO2/FiO2] ratio 145), increasing leukocytosis (white blood cell count from 10,800/μL on admission to 15,400/μL on hospital day 6), and persistent fever (38.3 °C). After 48 hours of linezolid monotherapy, the patient remained febrile with continued leukocytosis, worsening hypoxemia, and a persistently positive MRSA culture from a repeat endotracheal aspirate. Linezolid serum concentrations were obtained and vancomycin was reinstituted, after which the patient began to improve (afebrile, improving PaO2/FiO2 ratio, decreasing leukocytosis). On hospital day 12, the patient removed his endotracheal tube, and a sputum sample was obtained for culture. The patient's clinical status subsequently declined, prompting addition of cefepime to his antibiotic regimen. This sputum culture revealed not only MRSA, but also quinolone-resistant Escherichia coli. After completing treatment for both organisms the patient was discharged home.

DISCUSSION

Limited data on linezolid dosing in the morbidly obese population show lower serum drug concentrations than those in nonobese patients, but no clinical failure has been reported when treating MRSA skin and soft tissue infections or MRSA tracheitis. In our patient, low steady-state linezolid serum concentrations (peak 4.13 μg/mL [reference 15-27] and trough 1.27 μg/mL [reference 2-9]) were thought to contribute to his poor clinical response.

CONCLUSIONS

To our knowledge, this is the first report of subtherapeutic linezolid concentrations correlated with decreased clinical effectiveness when during treatment of MRSA pneumonia in a patient with morbid obesity.

Does weight-adjusted anti-tumour necrosis factor treatment favour obese patients with Crohn's disease?

BACKGROUND

Adalimumab (ADA) is a subcutaneous anti-tumour necrosis factor (anti-TNF) agent, effective in inducing and maintaining remission in Crohn's disease (CD). Unlike Infliximab (IFX), ADA dosing is not weight adjusted and dose frequency is based on clinical response.

AIM

To determine whether obesity is a risk factor for early loss of response (LOR) to anti-TNF treatment and whether weight-adjusted anti-TNF treatment is favourable.

MATERIALS AND METHODS

A hospital database of CD patients receiving anti-TNF treatment was analyzed retrospectively. The relationship between time to LOR and BMI was examined by Kaplan-Meier (KM) survival curves and a Cox proportional hazards model.

RESULTS

ADA patients: Of the 54 patients (46 BMI<30 and 8 BMI≥30), KM estimation indicated a significantly shorter time to dose escalation in the BMI of at least 30 (χ=6.117, P=0.01). The Cox proportional hazards model showed that an increased hazard of LOR to ADA is related to increases in BMI (P=0.04). IFX patients: Of the 76 patients (62 BMI<30 and 14 BMI≥30), KM estimation showed that the differences in survival curves were not significant (χ=1.933, P=0.16) for the BMI groups. This was supported by the Cox proportional hazard model (P=0.36).

CONCLUSION

BMI appears to be important in predicting ADA efficacy (LOR) in CD. IFX appears to overcome this reduction of efficacy in obese patients. A prospective study evaluating the effect of weight on anti-TNF drug response and serum drug levels is warranted.

Effect of blood protein concentrations on drug-dosing regimes: practical guidance

In this article the importance of blood proteins for drug dosing regimes is discussed. A simple mathematical model is presented for estimating recommended drug doses when the concentration of blood proteins is decreased. Practical guidance for drug dosing regimes is discussed and given in the form of a figure. It is demonstrated that correction of drug dosing regimes is needed only for when there is a high level of drug conjugation with blood proteins and a high degree of hypoalbuminaemia. An example of the use of this model is given.

Attitudes and opinion about adverse drug events of women living in a city of south Italy

BACKGROUND/AIM

Perception of risk of adverse drug events (ADEs) is different between health and nonhealth professionals, but these differences have not been investigated sufficiently in the general population. Women are more affected by ADEs. With the aim to investigate ADE risk perception in a sample of nonhealth professional women of South Italy, we carried out a phone survey.

METHODS

Phone survey based on a structured questionnaire on educational level, type of work, lifestyle, comorbidity, and medication used of 1,050 inhabitants of the city of Messina (Italy).

RESULTS

744 responders, divided into an ADE group (n = 162) and a non-ADE group, were analyzed. Most used drugs were nonsteroidal anti-inflammatory drugs (37.0%) and antibiotics (29.6%). Reported disorders related to drug intake were general malaise (25.9%), gastrointestinal complaints (24.1%), and skin reactions (20.4%). Younger age and higher educational level, along with allergic diseases and food intolerances were more frequently reported in the ADE group. Women from the ADE group were better informed about drug risks (p < 0.001).

CONCLUSIONS

Higher risk perception for ADEs in women is associated with higher educational level, food intolerance/allergic diseases, and choice of alternative or complementary medicines. Difference in perception of risk exists within the female population, which can cause overreporting or underreporting of ADEs.

Pharmacokinetic properties of anti-influenza neuraminidase inhibitors

Neuraminidase inhibitors are the mainstay of anti-influenza treatment. Oseltamivir is the most widely used drug but is currently available only as an oral formulation. Resistance spreads rapidly in seasonal H1N1 influenza A viruses, which were universally resistant in 2008, because of the H275Y mutation in the neuraminidase (NA) gene. Oseltamivir is a prodrug for the active carboxylate metabolite. Ex vivo conversion in blood samples may have confounded early pharmacokinetic studies. Oseltamivir shows dose linear kinetics, and oseltamivir carboxylate has an elimination half-life (t(1/2) β) after oral administration in healthy individuals of approximately 7.7 hours. Oseltamivir carboxylate is eliminated primarily by tubular secretion, and both clearance and tissue distribution are reduced by probenecid. The H275Y mutation in NA confers high-level oseltamivir resistance and intermediate peramivir resistance but does not alter zanamivir susceptibility. Zanamivir is available as a powder for inhalation, and a parenteral form is under development. Zanamivir distributes in an apparent volume of distribution approximating that of extracellular water and is rapidly eliminated (t(1/2) β of approximately 3.0 hours). Peramivir is slowly eliminated (t(1/2) β of 7.7-20.8 hours) and is prescribed as either a once-daily injection or as a single infusion. Laninamivir is a recently developed slowly eliminated compound for administration by inhalation.

Pharmacokinetics of anidulafungin in critically ill patients with candidemia/invasive candidiasis

The pharmacokinetics of intravenous anidulafungin in adult intensive care unit (ICU) patients were assessed in this study and compared with historical data from a general patient population and healthy subjects. Intensive plasma sampling was performed over a dosing interval at steady state from 21 ICU patients with candidemia/invasive candidiasis. All patients received the recommended dosing regimen (a 200-mg loading dose on day 1, followed by a daily 100-mg maintenance dose), except for a 54-year-old 240-kg female patient (who received a daily 150-mg maintenance dose instead). Plasma samples were assayed for anidulafungin using a validated liquid chromatography-tandem mass spectrometry method. Pharmacokinetic parameters in ICU patients were calculated by a noncompartmental method. With the exclusion of the 240-kg patient, the median (minimum, maximum) age, weight, and body mass index (BMI) of 20 ICU patients were 57 (39, 78) years, 65 (48, 106) kg, and 23.3 (16.2, 33.8) kg/m(2), respectively. The average anidulafungin area under the curve over the 24-hour dosing interval (AUC(0-24)), maximum concentration (C(max)), and clearance (CL) in 20 ICU patients were 92.7 mg · h/liter, 7.7 mg/liter, and 1.3 liters/h, respectively. The exposure in the 240-kg patient at a daily 150-mg dose was within the range observed in ICU patients overall. The average AUC(0-24) and Cmax in the general patient population and healthy subjects were 110.3 and 105.9 mg · h/liter and 7.2 and 7.0 mg/liter, respectively. The pharmacokinetics of anidulafungin in ICU patients appeared to be comparable to those in the general patient population and healthy subjects at the same dosing regimen.

Inadequate therapeutic response to a recommended antituberculosis fixed-dose combination regimen in an overweight patient with Mycobacterium bovis infection

OBJECTIVE

To report a case of an overweight man with lymph node tuberculosis due to Mycobacterium bovis, a part of the Mycobacterium tuberculosis complex, treated with fixed-dose combination (FDC) chemotherapy.

CASE REPORT

Following guidelines, according to the patient's weight (92 kg), we prescribed the maximum recommended doses of isoniazid-rifampin-pyrazinamide FDC. It led initially to underdosing, with a poor clinical outcome, justifying increased doses and a complex regimen using separate drugs (isoniazid 600 mg, rifampin 1200 mg, and levofloxacin 1000 mg) to achieve therapeutic drug concentrations and clinical response.

DISCUSSION

Usually recommended doses of FDC chemotherapies may be inappropriate in overweight patients. We discuss here the different factors that may be involved in poor clinical outcomes, particularly the consequences of excess weight on drug metabolism: drug-drug interaction, FDC use, generic formulation use, intestinal malabsorption, and acetylation profile.

CONCLUSIONS

Therapeutic drug monitoring in overweight patients may be useful in the clinical setting to help clinicians individualize drug therapeutic regimens and optimize drug response, adherence, and safety.

Pharmacokinetic study of major bioactive components in rats after oral administration of extract of Ilex hainanensis by high-performance liquid chromatography/electrospray ionization mass spectrometry

Ilex hainanensis Merr. is commonly used as a folk remedy for treating hypertension, dyslipidemia and inflammation in Traditional Chinese Medicine (TCMs) and it also has great potential to treat non-alcoholic fatty liver disease (NAFLD). Chlorogenic acid, kaempferol-7-O-β-d-glucoside, and ilexgenin A are three major bioactive components in I. hainanensis extract. In this study, a rapid, sensitive and convenient LC-MS method was developed for their simultaneous determination in the plasma of normal and NAFLD rats. The method was validated in terms of selectivity, linearity and sensitivity, and shows advantages in monitoring the pharmacokinetic behaviors of these three compounds. Results revealed the pharmacokinetic behaviors of chlorogenic acid, kaempferol-7-O-β-d-glucoside, and ilexgenin A could be significantly changed in NAFLD rats after oral administration of I. hainanensis extract compared with normal rats. The areas under the plasma concentration-time curve (AUC) and maximum plasma concentration (Cmax) of the three analytes were greatly decreased and the plasma clearance (CL) for kaempferol-7-O-β-d-glucoside, Ilexgenin A were greatly increased in NAFLD rats. Meanwhile, the mean residence time (MRT) of kaempferol-7-O-β-d-glucoside and Ilexgenin A were increased in the NAFLD rats. This is the first report on the determination of the major bioactive components in rat plasma after oral administration of I. hainanensis extract. These results provided a meaningful basis for evaluating the clinical application of this medicine.

Dose adjustment strategy of cyclosporine A in renal transplant patients: evaluation of anthropometric parameters for dose adjustment and C0 vs. C2 monitoring in Japan, 2001-2010

The optimal use and monitoring of cyclosporine A (CyA) have remained unclear and the current strategy of CyA treatment requires frequent dose adjustment following an empirical initial dosage adjusted for total body weight (TBW). The primary aim of this study was to evaluate age and anthropometric parameters as predictors for dose adjustment of CyA; and the secondary aim was to compare the usefulness of the concentration at predose (C0) and 2-hour postdose (C2) monitoring. An open-label, non-randomized, retrospective study was performed in 81 renal transplant patients in Japan during 2001-2010. The relationships between the area under the blood concentration-time curve (AUC0-9) of CyA and its C0 or C2 level were assessed with a linear regression analysis model. In addition to age, 7 anthropometric parameters were tested as predictors for AUC0-9 of CyA: TBW, height (HT), body mass index (BMI), body surface area (BSA), ideal body weight (IBW), lean body weight (LBW), and fat free mass (FFM). Correlations between AUC0-9 of CyA and these parameters were also analyzed with a linear regression model. The rank order of the correlation coefficient was C0 > C2 (C0; r=0.6273, C2; r=0.5562). The linear regression analyses between AUC0-9 of CyA and candidate parameters indicated their potential usefulness from the following rank order: IBW > FFM > HT > BSA > LBW > TBW > BMI > Age. In conclusion, after oral administration, C2 monitoring has a large variation and could be at high risk for overdosing. Therefore, after oral dosing of CyA, it was not considered to be a useful approach for single monitoring, but should rather be used with C0 monitoring. The regression analyses between AUC0-9 of CyA and anthropometric parameters indicated that IBW was potentially the superior predictor for dose adjustment of CyA in an empiric strategy using TBW (IBW; r=0.5181, TBW; r=0.3192); however, this finding seems to lack the pharmacokinetic rationale and thus warrants further basic and clinical investigations.

New challenges in hemophilia: long-term outcomes and complications

For the past 5 decades, the care for hemophilia patients has improved significantly to the point that a newborn with hemophilia living in a developed nation can expect to have a normal lifespan and a high quality of life. Despite this, there are several new challenges that the hemophilia community will face in the coming years. First, the hemophilia community will soon be challenged with adopting a variety of new agents into clinical practice. Second, the normalization of patients' lives as a result of improved treatment has led to new problem areas, including obese/overweight hemophiliacs and osteoporosis. In addition, although mortality rates are similar to those of the healthy population, morbidities such as hemophilic arthropathy still occur. Third, the cost of care continues to rise, both due to the development of expensive new therapies and to the costs of managing problems such as obesity and osteoporosis. Finally, most patients in the world with hemophilia receive little to no care and although this is an enormous challenge, it must be confronted. This review discusses some new challenges facing developing nations and their care for hemophilia patients. In summary, in hemophilia in the coming few years, several new challenges will need to be confronted.

Effect of diabetes mellitus on pharmacokinetic and pharmacodynamic properties of drugs

The effects of diabetes mellitus on the pharmacokinetics and pharmacodynamics of drugs have been well described in experimental animal models; however, only minimal data exist for humans and the current knowledge regarding the effects of diabetes on these properties remains unclear. Nevertheless, it has been observed that the pharmacokinetics and pharmacodynamics of drugs are changed in subjects with diabetes. It has been reported that diabetes may affect the pharmacokinetics of various drugs by affecting (i) absorption, due to changes in subcutaneous adipose blood flow, muscle blood flow and gastric emptying; (ii) distribution, due to non-enzymatic glycation of albumin; (iii) biotransformation, due to regulation of enzymes/transporters involved in drug biotransformation; and (iv) excretion, due to nephropathy. Previously published data also suggest that diabetes-mediated changes in the pharmacokinetics of a particular drug cannot be translated to others. Although clinical studies exploring the effect of diabetes on pharmacodynamics are still very limited, there is evidence that disease-mediated effects are not limited only to pharmacokinetics but also alter pharmacodynamics. However, for many drugs it remains unclear whether these influences reflect diabetes-mediated changes in pharmacokinetics rather than pharmacodynamics. In addition, even though diabetes-mediated pharmacokinetics and pharmacodynamics might be anticipated, it is important to study the effect on each drug and not generalize from observed data. The available data indicate that there is a significant variability in drug response in diabetic subjects. The discrepancies between individual clinical studies as well as between ex vivo and clinical studies are probably due to (i) the restricted and focused population of subjects in clinical studies; (ii) failure to consider type, severity and duration of the disease; (iii) histopathological characteristics generally being missing; and (iv) other factors such as varying medication use, dietary protein intake, age, sex and obesity. The obesity epidemic in the developed world has also inadvertently influenced the directions of pharmacological research. This review attempts to map new information gained since Gwilt published his paper in Clinical Pharmacokinetics in 1991. Although a large body of research has been conducted and significant progress has been made, we still have to conclude that the available information regarding the effect of diabetes on pharmacokinetics and pharmacodynamics remains unclear and further clinical studies are required before we can understand the clinical significance of the effect. An understanding of diabetes-mediated changes as well as of the source of the variability should lead to the improvement of the medical management and clinical outcomes in patients with this widespread disease.