Effect of posture and sleep on pharmacokinetics. I. Amoxycillin

SWOT and Root Cause Analyses of Antimicrobial Resistance to Oral Antimicrobial Treatment of Cystitis

Nearly 150 million cases of urinary tract infections (UTIs) are reported each year, of which uncomplicated cystitis triggers > 25% of outpatient prescriptions of oral antimicrobial treatment (OAT). OAT aids immune cells infiltrating the urothelium in eliminating uropathogens capable of invading the urothelium and surviving hyperosmotic urine. This self-evident adaptability of uropathogens and the short interval between the introduction of Penicillin and the first report of antimicrobial resistance (AMR) implicate AMR as an evolutionary conserved heritable trait of mutant strains selected by the Darwinian principle to survive environmental threats through exponential proliferation. Therefore, AMR can only be countered by antimicrobial stewardship (AMS) following the principle of the five Ds-drug, dose, duration, drug route, and de-escalation. While convenient to administer, the onset of the minimum inhibitory concentration (MIC) for OAT in urine leaves a window of opportunity for uropathogens to survive the first contact with an antimicrobial and arm their descendant colonies with AMR for surviving subsequent higher urine antimicrobial levels. Meanwhile, the initial dose of intravesical antimicrobial treatment (IAT) may be well above the MIC. Therefore, the widespread clinical use of OAT for cystitis warrants an analysis of the strengths, weaknesses, opportunity, and threats (SWOTs) and a root cause analysis of the AMR associated with OAT and IAT.

PharmoCo: a graph-based visualization of pharmacogenomic plausibility check reports for clinical decision support systems

The first approaches in recent years for the integration of pharmacogenomic plausibility checks into clinical practice show both a promising improvement in the drug therapy safety, but also difficulties in application. One of the difficulties is the meaningful interpretation of the text-based results by the medical practitioner. We propose here as an appropriate and sensible solution to avoid misunderstandings and to include evidence-based, pharmacogenomic recommendations in prescriptions, which should be the graph-based visualization of the reports. This allows for a plausible interpretation and relate complex, even contradictory guidelines. The improved overview over the pharmacogenomics (PGx) guidelines using the graphical visualization makes the medical practitioner's choice of dose and medication more patient-specific, improves the treatment outcome and thus, increases the drug therapy safety.

Computational modeling of drug dissolution in the human stomach: Effects of posture and gastroparesis on drug bioavailability

The oral route is the most common choice for drug administration because of several advantages, such as convenience, low cost, and high patient compliance, and the demand and investment in research and development for oral drugs continue to grow. The rate of dissolution and gastric emptying of the dissolved active pharmaceutical ingredient (API) into the duodenum is modulated by gastric motility, physical properties of the pill, and the contents of the stomach, but current in vitro procedures for assessing dissolution of oral drugs are limited in their ability to recapitulate this process. This is particularly relevant for disease conditions, such as gastroparesis, that alter the anatomy and/or physiology of the stomach. In silico models of gastric biomechanics offer the potential for overcoming these limitations of existing methods. In the current study, we employ a biomimetic in silico simulator based on the realistic anatomy and morphology of the stomach (referred to as "StomachSim") to investigate and quantify the effect of body posture and stomach motility on drug bioavailability. The simulations show that changes in posture can potentially have a significant (up to 83%) effect on the emptying rate of the API into the duodenum. Similarly, a reduction in antral contractility associated with gastroparesis can also be found to significantly reduce the dissolution of the pill as well as emptying of the API into the duodenum. The simulations show that for an equivalent motility index, the reduction in gastric emptying due to neuropathic gastroparesis is larger by a factor of about five compared to myopathic gastroparesis.

Understanding the Complexities and Changes of the Astronaut Microbiome for Successful Long-Duration Space Missions

During space missions, astronauts are faced with a variety of challenges that are unique to spaceflight and that have been known to cause physiological changes in humans over a period of time. Several of these changes occur at the microbiome level, a complex ensemble of microbial communities residing in various anatomic sites of the human body, with a pivotal role in regulating the health and behavior of the host. The microbiome is essential for day-to-day physiological activities, and alterations in microbiome composition and function have been linked to various human diseases. For these reasons, understanding the impact of spaceflight and space conditions on the microbiome of astronauts is important to assess significant health risks that can emerge during long-term missions and to develop countermeasures. Here, we review various conditions that are caused by long-term space exploration and discuss the role of the microbiome in promoting or ameliorating these conditions, as well as space-related factors that impact microbiome composition. The topics explored pertain to microgravity, radiation, immunity, bone health, cognitive function, gender differences and pharmacomicrobiomics. Connections are made between the trifecta of spaceflight, the host and the microbiome, and the significance of these interactions for successful long-term space missions.

Supplying a pharmacy for NASA exploration spaceflight: challenges and current understanding

In order to maintain crew health and performance during long-duration spaceflight outside of low-Earth orbit, NASA and its international partners must be capable of providing a safe and effective pharmacy. Given few directed studies of pharmaceuticals in the space environment, it is difficult to characterize pharmaceutical effectiveness or stability during spaceflight; this in turn makes it challenging to select an appropriate formulary for exploration. Here, we present the current state of literature regarding pharmaceutical stability, metabolism, and effectiveness during spaceflight. In particular, we have attempted to highlight the gaps in current knowledge and the difficulties in translating terrestrial-based drug studies to a meaningful interpretation of drug stability, safety, and effectiveness in space. We hope to identify high-yield opportunities for future research that might better define and mitigate pharmaceutical risk for exploration missions.

Circadian variation in the pharmacokinetics of steady state continuous subcutaneous infusion of growth hormone in adult growth hormone deficient patients

BACKGROUND

Previous studies in growth hormone (GH)-deficient (GHD) patients have indicated a possible diurnal variation in the pharmacokinetics (PK) of GH after subcutaneous (sc) GH administration. Thus, higher GH levels were observed during the night with continuous sc infusion, and increased GH bioavailability was reported following daily sc injections in the evening compared to morning.

OBJECTIVE

The aim was to study whether diurnal variability in the PK of sc administered exogenous GH can be reproduced under standard conditions for all study participants, e.g. supine rest.

DESIGN AND METHODS

Eight male GHD patients (59.8 ± 8 years, body mass index 29.7 ± 4.9 kg/m(2)) received a continuous sc infusion of GH (3mg/24h) for 60 h on two different occasions. Diurnal variation in PK of GH was studied during steady state in the last 24h of the infusion period.

RESULTS

Median GH levels were higher at night time (23:00 h-07:00 h) than during the day (10:00 h-18:00 h) for visit 1 [5.1 (4.5-7.2 ng/ml/0.5h) vs. 4.6 (3.7-5.7 ng/ml/0.5h); p<0.05], and reproducible results of diurnal GH variation were obtained during visit 2 [5.7 (4.6-7.4) ng/ml/0.5h vs. 4.6 (3.8-6.0) ng/ml/0.5h, p<0.05]. Reproducible results between days 1 and 2 were also obtained during 08:30 h-20:30 h and 20:30 h-08:30 h, respectively.

CONCLUSIONS

Previous findings of higher nocturnal GH levels were confirmed during steady state continuous sc GH infusion under standard conditions. The underlying mechanisms, e.g. whether GH absorption, distribution or elimination is primarily affected need to be further elucidated.

Drug structure-transport relationships

Malcolm Rowland has greatly facilitated an understanding of drug structure–pharmacokinetic relationships using a physiological perspective. His view points, covering a wide range of activities, have impacted on my own work and on my appreciation and understanding of our science. This overview summarises some of our parallel activities, beginning with Malcolm’s work on the pH control of amphetamine excretion, his work on the disposition of aspirin and on the application of clearance concepts in describing the disposition of lidocaine. Malcolm also spent a considerable amount of time developing principles that define solute structure and transport/pharmacokinetic relationships using in situ organ studies, which he then extended to involve the whole body. Together, we developed a physiological approach to studying hepatic clearance, introducing the convection–dispersion model in which there was a spread in blood transit times through the liver accompanied by permeation into hepatocytes and removal by metabolism or excretion into the bile. With a range of colleagues, we then further developed the model and applied it to various organs in the body. One of Malcolm’s special interests was in being able to apply this knowledge, together with an understanding of physiological differences in scaling up pharmacokinetics from animals to man. The description of his many other activities, such as the development of clearance concepts, application of pharmacokinetics to the clinical situation and using pharmacokinetics to develop new compounds and delivery systems, has been left to others.

Influence of posture on pharmacokinetics

INTRODUCTION

Body position may influence physiological characteristics, such as perfusion, gastrointestinal function and plasma volume. These characteristics may interact with key factors determining the pharmacokinetics of drugs (dissolution, absorption, distribution, metabolism, excretion).

OBJECTIVES

Based on a systematic literature search, current data on the effect of posture on physiological characteristics and/or pharmacokinetics are summarized, and the relevance of possible effects, such as those presenting in clinical practice and clinical pharmacokinetic studies, is assessed.

RESULTS

Postures which favour rapid gastric emptying (sitting, standing, recumbent right) accelerate the absorption of orally administered drugs. Consequently, these postures favour a shorter time to reach peak plasma drug concentration (t(max)) and a higher maximum plasma drug concentration (C(max)) and--in the case of transient saturation of first-pass metabolism--total exposure (area under the concentration-time curve, AUC) in comparison to recumbent left and supine positions (e.g. nifedipine: AUC 30 and 38% higher in standing and right lateral position vs. left lateral position; C(max) 149 and 80% higher, respectively). The magnitude of these postural effects depends strongly on the nature and amount of liquids and food ingested before drug administration and is most pronounced in the fasting state and after administration with a nonnutrient liquid. Changes in splanchnic-hepatic blood flow (e.g. reduction of estimated hepatic perfusion by 37% in standing vs. supine position) may substantially affect the metabolism of orally administered drugs, especially of those with a high/saturable first-pass metabolism. For highly protein-bound drugs (e.g. phenytoin, imipramine), the total plasma concentration has been found to be approximately 10% higher in standing than lying subjects due to changes in plasma volume.

CONCLUSIONS

Positioning of a patient may be an effective method of enhancing or retarding absorption of some drugs in appropriate clinical situations (e.g. toxic ingestions, bedridden patients). In clinical pharmacokinetic trials, such as bioequivalence studies, defining and maintaining posture precisely is a useful approach for reducing within- and between-subject variability.

Effect of time of administration on the pharmacokinetics and tolerance of doxazosin in healthy male volunteers

A randomized, open-label, two-way crossover study of 24 normotensive, healthy male volunteers with nocturia was conducted to compare morning and evening administration of doxazosin in terms of pharmacokinetics and tolerance. In both the morning and evening phases, participants received doxazosin 1 mg once daily for 10 days, followed by 2 mg once daily for 5 days. Pharmacokinetic data were evaluated from blood samples serially collected for 72 hours after drug administration on the last day of each phase. Vital signs and adverse events were recorded throughout the study. Mean peak plasma concentrations (C(max)) were 16.98 and 15.76 ng/mL after morning and evening administration, respectively. Corresponding mean values of area under the plasma concentration-time curve (AUC0-24) were 227.90 and 253.66 ng.hr/mL, respectively. Statistical analysis of the log-transformed values for C(max) and AUC0-24 indicated that morning and evening administration of doxazosin were bioequivalent. There were no statistically or clinically significant differences between phases for mean apparent half-life (t1/2) or total body clearance. There were no clinically relevant differences in blood pressure or in pulse rate between phases, and no occurrences of orthostatic hypotension. The incidence of adverse experiences during morning and evening administration was similar. Morning and evening administration of doxazosin are equivalent and have similar tolerance profiles.

Factors affecting drug bioavailability in space

Microgravity-induced changes in the bioavailability of drugs may influence the efficacy or toxicity of drugs. The bioavailability of orally administered drugs may be altered by changes in dissolution rate, intestinal microflora, intraluminal enzymes, epithelial enzymes, rate of passage across the gastrointestinal epithelium, gastric emptying rate, intestinal transit time, hepatic first pass metabolism, and gastrointestinal and hepatic blood flow. Limited data from antiorthostatic bed rest and inflight studies provide preliminary evidence that the bioavailability of orally administered drugs in space may be decreased or subject to more interindividual variation than expected from ground-based studies.

The effects of posture on the pharmacokinetics of intramuscular benzylpenicillin

Previous reports have produced conflicting results as to whether changes in posture affected the pharmacokinetics of the penicillins. We have studied the pharmacokinetics of intramuscularly administered benzylpenicillin in normal subjects during bedrest and ambulation and compared it with data obtained following intravenous administration of the same dose to the same subjects under the same conditions. The values of area under the curve, total clearance, mean residence time and renal clearance found during ambulation were 1175 (min.min.l-1), 488 (ml.min-1), 101 (min), and 264 (ml.min-1) (means). The corresponding values for bedrest were 1032 (min.mg.l-1), 544 (ml.min-1), 96.7 (min), and 315 (ml.min-1). There was a significant difference between the areas under the curve with change of posture but not between any of the other pharmacokinetic variables. The differences observed in this study are unlikely to be of clinical relevance. We suggest that the differences between the results of this study and those of previous studies may be related to the level of exercise undertaken by the subjects in the various studies.

The effect of posture on the pharmacokinetics of intravenous benzylpenicillin

We have studied the pharmacokinetics of intravenously administered benzylpenicillin in normal subjects during bedrest and during ambulation. The values of total body clearance, mean residence time, and renal clearance found during ambulation were 487.4 +/- 100.5 ml/min, 36.23 +/- 13.45 min, and 309.4 +/- 93.4 ml/min (means +/- SD). The corresponding values for bedrest were 543.6 +/- 122.6 ml/min, 35.27 +/- 10.21 min, and 324.1 +/- 145.3 ml/min. There were no significant differences between any of these pharmacokinetic variables with the change in posture. These results differ from previously reported results for the effects of posture on the pharmacokinetics of penicillins administered by extravascular routes, and suggest that the absorption of benzylpenicillin may be dependent on posture.

Comparison of the effects of prizidilol and propranolol on renal haemodynamics at rest and during exercise

Effective renal plasma flow and glomerular filtration rate were measured in 22 mild-to-moderate, uncomplicated, essential hypertensive patients during placebo and after 3 months of randomly assigned treatment either with prizidilol (n = 10) or propranolol (n = 12). Measurements were performed at rest and during cycloergometer exercise. For a comparable effect on blood pressure effective renal plasma flow was significantly increased at rest by prizidilol (+9%) and decreased by propranolol (-13.6%); these patterns were maintained during exercise. Glomerular filtration rate was immodified after the treatment with both drugs. It is concluded that prizidilol is an effective hypotensive agent with no deleterious effects on renal haemodynamics.

Effect of posture on ampicillin pharmacokinetics, glomerular filtration rate and renal plasma flow in resting subjects

Differences in drug kinetics between supine rest and ambulation have been reported, but the relative contribution of postural changes and changes in the level of physical activity has not been evaluated. Ampicillin pharmacokinetics, glomerular filtration rate (GFR) and renal plasma flow (RPF) were studied in six male volunteers at rest in the sitting and lying position with an interval of 1 week. After intravenous administration ampicillin kinetics, analyzed according to a two-compartment open model, demonstrated significant changes in drug distribution when the position was changed from lying to sitting: alpha-increased by 50%, V1 and V beta increased by 19% and 22% respectively. Ampicillin clearance, the fraction of dose recovered from urine, GFR and RPF were, however, not influenced by the change in posture. Our data on effects of posture in resting subjects suggest that previously reported differences in drug elimination and RPF between lying and ambulatory subjects are largely due to differences in the level of physical activity.

The pharmacokinetics of furazlocillin in healthy humans

The pharmacokinetics of the novel acylureidopenicillin furazlocillin, 6-[D-2-(3-furfurylidenamino-2-oxo-imidazolidine-1-carboxamido)-2 -(4-hydroxyphenyl)-acetamido]-penicillanic acid and of its penicilloic acid derivative were investigated in five healthy male volunteers after intravenous administration of 2 and 4 g dosages. The volunteers were either in a lying or sitting position throughout the duration of the studies. The concentrations of the drug in plasma and urine were measured by two different methods in parallel: a microbiological assay and a newly developed high pressure liquid chromatography method. The latter method was also applicable for quantitation of the penicilloic acid derivative in these biological fluids. The drug's plasma protein binding (66%) and apparent red cell-plasma partition coefficient (0.055) were concentration independent. The pharmacokinetics of the drug were first order only at the lower dose level. The apparent half lives of three distinguishable phases were, respectively, 4(t1/21), 18 (t1/22), and 64 (t1/2z) min. The total and renal clearances of the drug were, respectively, 303 and 79 ml/min. The latter value implied tubular secretion of the drug. Graphical and digital computer analyses of the data were performed with a linear three compartment body model. Small but consistent deviations from linear kinetics caused by the nonrenal elimination route were observed after administration of the higher dose (4 g). In contrast, renal elimination showed no such dose dependency and was first order. The disposition kinetics of furazlocillin were body position independent. The penicilloic acid derivative of furazlocillin was found in plasma and urine in all the five subjects tested. The percentage of the dose excreted renally as the derivative amounted, respectively, to 5.2 and 7.0% after the lower and higher dosage of furazlocillin, with significant inter- and intrasubject variability. The renal clearance of the derivative was 41 ml/min.

Host factors influencing the response to antimicrobial agents

When the desired clinical response to an antibiotic therapeutic regimen is not achieved, despite appropriate antibiotic selection and organism sensitivity, the clinician must be aware that several host factors exist that may influence the outcome. Examples of the influence of host-related factors on drug disposition have been briefly reviewed in this article. It should be noted, however, that further investigation is needed to determine whether these factors truly exert a significant influence on the outcome of antibiotic utilization.

Clinical pharmacokinetics of high dose mebendazole in patients treated for cystic hydatid disease

The plasma concentrations of mebendazole and its metabolites have been monitored in twelve patients after receiving a 10 mg/kg dose for cystic hydatid disease. The mebendazole plasma concentration-time profiles differed considerably between patients; elimination half-lives ranged from 2.8-9.0 h, time to peak plasma concentration after dosing ranged from 1.5-7.25 h and peak plasma concentrations ranged from 17.5 to 500 ng/ml. The mean peak plasma concentration of mebendazole after an initial dose (69.5 ng/ml) was lower than found in patients during chronic therapy (137.4 ng/ml). The plasma AUCTS for the major metabolites of mebendazole (methyl 5-(alpha-hydroxybenzyl)-2-benzimidazole carbamate and 2-amino-5 benzoylbenzimidazole) were about five times the plasma AUCT found for mebendazole in patients on chronic therapy. It is suggested that the slower clearance of these polar metabolites relative to mebendazole results from enterohepatic recycling. Since mebendazole is also highly plasma protein bound, caution should be observed in administering mebendazole to patients with liver disease. Concentrations of mebendazole found in the tissue and cyst material collected from two patients during surgery ranged from 59.5 to 206.6 ng/g wet weight.