Plasma Dexamethasone Concentrations Research Articles

Comprehensive ocular and systemic pharmacokinetics of dexamethasone after subconjunctival and intravenous injections in rabbits

Even though subconjunctival injections are used in clinics, their quantitative pharmacokinetics has not been studied systematically. For this purpose, we evaluated the ocular and plasma pharmacokinetics of subconjunctival dexamethasone in rabbits. Intravenous injection was also given to enable a better understanding of the systemic pharmacokinetics. Dexamethasone concentrations in plasma (after subconjunctival and intravenous injections) and four ocular tissues (iris-ciliary body, aqueous humour, neural retina and vitreous) were analysed using LC-MS/MS.Population pharmacokinetic modelling for plasma data from both injection routes were used, and for first time the constant rate of absorption of dexamethasone from the subconjunctival space into plasma was estimated (ka,plasma = 0.043 min−1, i.e. absorption half-life of 17.3 min). Non-compartmental analysis was used for the ocular data analysis and resulting in ocular drug exposure of iris-ciliary body (AUC0-∞= 41984 min·ng/g) > neural retina (AUC0-∞= 25511 min·ng/g) > vitreous (AUC0-∞= 7319 min·ng/mL) > aqueous humour (AUC0-∞= 6146 min·ng/mL). The absolute bioavailability values after subconjunctival injection, reported for the first time, were 0.74 % in aqueous humour (comparable to topical dexamethasone suspensions), and 0.30 % in vitreous humour (estimated to be higher than in topical administration).These novel and comprehensive pharmacokinetic data provide valuable information on the potential for exploiting this route in ocular drug development for treating both, anterior and posterior segment ocular diseases. Moreover, the new generated dexamethasone-parameters are a step-forward in building predictive pharmacokinetic models to support the design of new subconjunctival dexamethasone formulations, which may sustain drug effect for longer period of time.

Evaluation of the effect of glucocorticoid treatment on adrenocortical functions by monitoring endogenous hydrocortisone in horses.

Glucocorticoid preparations have anti-inflammatory effects, and are commonly used in the equine clinical setting; however, such treatments can cause a number of side effects. Adrenal insufficiency is an adverse effect induced by the suppression of adrenal function following drug administration. This study aimed to investigate the influence of two glucocorticoid preparations, dexamethasone and hydrocortisone, on adrenocortical function in horses. The usual doses of dexamethasone and hydrocortisone preparations in equine practice were administered intramuscularly to six horses, and peripheral blood was collected at different time points. Concentrations of dexamethasone and hydrocortisone in the plasma, before and after drug administration, were measured using liquid chromatography-tandem mass spectrometry. Considering circadian rhythms in endogenous hydrocortisone levels, hormone concentrations, before and after drug administration, were compared at the same time of the day. Plasma dexamethasone concentrations were below the limit of quantification at 72 hr post-administration. Plasma hydrocortisone concentrations were significantly lower from 1 to 72 hr after administration. After hydrocortisone preparation administration, plasma hydrocortisone levels were significantly higher until 9 hr, and significantly lower at 24 and 48 hr. The suppression rate of endogenous hydrocortisone ranged over 2.2-5.3% with dexamethasone treatment and 17.5-45.7% with hydrocortisone treatment. The study clearly indicated the effects of glucocorticoids on adrenocortical function in horses and provided basic knowledge about the selection and prescription of glucocorticoid preparations and setting the withdrawal times in equine clinical setting.

Assessment of Plasma-Free Cortisol Concentrations by LC-MS/MS in Patients with Autonomous Cortisol Secretion.

Autonomous cortisol secretion (ACS) of an adrenal incidentaloma (AI) is associated with mild cortisol excess that could result in poor metabolic and cardiovascular outcomes. The biological activity of glucocorticoids depends on the unbound, free fraction. We aimed to evaluate plasma free cortisol (FC) concentrations in patients with ACS in this cross-sectional study. One hundred and ten AI patients in 3 groups; non-functioning (NFA, n=33), possible ACS (n=65), ACS (n=12) were enrolled. Following measurements were conducted: Clinical data and total serum cortisol (TC), plasma corticotrophin (ACTH), serum dehydroepiandrosterone sulfate (DHEA-S), cortisol after 1 mg dexamethasone by both immunoassay and LC-MS/MS (DexF), serum corticosteroid binding globulin (CBG), plasma dexamethasone concentration [DEX] and plasma FC by LC-MS/MS. Patients with ACS featured an unfavorable metabolic profile. Plasma [DEX] and serum CBG levels were similar between groups. Plasma FC was significantly higher in ACS when compared to NFA and possible ACS groups p<0.05 and p<0.01, respectively. In multiple regression analysis DexF (beta=0.402, p<0.001) and CBG (beta=-0.257, p=0.03) remained as the independent predictors of plasma FC while age, sex, BMI, smoking habit, and existing cardiovascular disease did not make a significant contribution to the regression model. In conclusion, the magnitude of cortisol excess in ACS could lead to increased plasma FC concentrations. Further studies in AI patients are needed to demonstrate whether any alterations of cortisol affinity for CBG exist and to establish whether plasma FC concentrations predict the unfavorable metabolic profile in ACS.

Dexamethasone serum concentrations after intravenous administration in horses during race training

Dexamethasone (DXM) sodium phosphate is a widely used corticosteroid for inflammatory conditions in horses, regulated in racing jurisdictions in the USA by a 0.005 ng/ml serum/plasma threshold. This study seeks to describe serum concentrations of DXM at 48 and 72 h after intravenous administration of 20 mg DXM sodium phosphate over 1 to 5 days, and to identify a possible source of DXM overages. 74 horses (39 Thoroughbreds, 13 Standardbreds, 22 Quarter Horses) in active race training received 20 mg DXM sodium phosphate. Serum was collected before injection, at 48 and 72 h post last injection, and analysed by LC/MS-MS (limit of quantification (LOQ) = 2.5 pg/ml). No differences were identified by ANOVA (P≤0.05) for racing breeds, age, gender or the number of days of DXM sodium phosphate administration, so data were pooled for each time point. The DXM serum concentration at 48 h (mean ± standard deviation, range) was 2.18±1.56 pg/ml (&lt;2.5 to 40 pg/ml). Summary statistics could not be derived for 72 h DXM serum concentration data owing to censored data, but ranged from &lt;2.5 to 95.8 pg/ml. There was one extreme outlier (Tukey) at 48 h, and two extreme outliers at 72 h. A separate study was conducted using sedentary experimental horses to determine the likelihood that positive DXM samples could result from environmental transfer. Urine was collected from a mare 2 to 3 h post administration of 20 mg DXM. Hay with 100 ml of the DXM (17 ng/ml) containing urine was offered to each of six experimental horses and blood was collected at 0, 4, 8, 12, 16, 20 and 24 h. All six horses had plasma DXM concentration above the limit of detection and five of six had plasma DXM concentrations above the LOQ for at least one sample time.

Disposition and effect of intra-articularly administered dexamethasone on lipopolysaccharide induced equine synovitis

BackgroundDexamethasone is used for the intra-articular route of administration in management of aseptic arthritis in horses. Despite its widespread use there is very little quantitative data of the disposition and response to dexamethasone. The aim of this study was to investigate and describe the synovial fluid and plasma dexamethasone concentration over time and to explore the relation between synovial fluid concentration and response using clinical endpoints as response biomarkers after IA injection of dexamethasone disodium salt solution in an equine model of synovitis.ResultsInflammation was induced in the radiocarpal joint of six horses by injection of 2 ng lipopolysaccharide (LPS). Two hours later either saline or dexamethasone was injected in the same joint in a two treatment cross over design. Each horse was treated once with one of the six doses dexamethasone used (0.01, 0.03, 0.1, 0.3, 1 or 3 mg) and once with saline. Dexamethasone was quantified by means of UHPLC–MS/MS. Dexamethasone disposition was characterised by means of a non-linear mixed effects model. Lameness was evaluated both objectively with an inertial sensor based system and subjectively scored using a numerical scale (0–5). Joint circumference, skin temperature over the joint and rectal temperature were also recorded. The LPS-challenge induced lameness in all horses with high inter-individual variability. Dexamethasone significantly decreased lameness compared with saline. Other variables were not statistically significant different between treatments. Objective lameness scoring was the most sensitive method used in this study to evaluate the lameness response. A pharmacokinetic/pharmacodynamic model was successfully fitted to experimental dexamethasone and lameness data. The model allowed characterization of the dexamethasone synovial fluid concentration–time course, the systemic exposure to dexamethasone after intra-articular administration and the concentration–response relation in an experimental model of synovitis.ConclusionsThe quantitative data improve the understanding of the pharmacology of dexamethasone and might serve as input for future experiments and possibly contribute to maintain integrity of equine sports.

Plasma Dexamethasone Concentration in Relation to Glucose Response in the Horse

Therapeutic agents capable of altering the performance of horses are monitored in racing and equestrian sports to guarantee horse welfare, fair competition, and integrity of the sport. Dexamethasone is a common glucocorticoid drug for treating horses. Among other effects, dexamethasone is gluconeogenic and increases blood glucose. In this study, plasma samples from two dexamethasone exposure studies were analyzed for glucose using an automated clinical chemistry analyzer. In study one, dexamethasone-21-isonicotinate was administered to six horses at the dose 30 μg/kg intramuscularly. In study two, dexamethasone 21-phosphate disodium salt was administered intravenously to six horses as a bolus dose followed by 3 hours of infusion (bolus + infusion) at four different doses (placebo, 0.1 + 0.07 μg/kg, 1 + 0.7 μg/kg, and 10+7 μg/kg). Plasma dexamethasone concentrations were linked to plasma glucose concentrations by means of a turnover model. The median (range) pharmacodynamic parameters for glucose response for the two studies were as follows: the EC50 value was 0.84 μg/L (0.47–1.50) and 0.85 μg/L (0.75–2.45), the fractional turnover rate of response was 0.18 per h (0.07–0.27) and 0.25 per h (0.17.0.48), and the unaffected baseline of response was 4.20 mmol/L (4.10–6.60) and 5.42 mmol/L (5.22–5.96). These results may be used as input to future studies of the anti-inflammatory response of dexamethasone. The results also enable calculations of irrelevant plasma concentrations to determine whether the presence of a drug is a trace from legitimate medication or not. Therefore, this study provides further evidence for dexamethasone screening limits, which protects the integrity of the sport and the welfare of the horse.

A preliminary study on plasma concentration achieved following intrapterygomandibular space injection of dexamethasone as a route of drug delivery with lignocaine inferior alveolar nerve block-correlation of clinical effects.

To determine the quantity of dexamethasone plasma concentration achieved following intrapterygomandibular space injection of dexamethasone when co-administered with inferior alveolar nerve block correlating with the clinical effects in the postoperative phase. A preliminary prospective study to evaluate the dexamethasone plasma concentration achieved following intrapterygomandibular space injection of dexamethasone with 2% lignocaine inferior alveolar nerve block to achieve hemi-mandibular anesthesia for minor oral surgical procedures and derive clinical correlations. Dexamethasone is a glucocorticoid, chiefly used for the management of postsurgical sequelae like trismus and swelling in maxillofacial surgical practice. Conventionally, parenteral dexamethasone is administered via intravenous or intramuscular route. Intrapterygomandibular space injection is a novel route of steroid delivery described in literature. For minor oral surgical procedures in maxillofacial surgical practice requiring inferior alveolar nerve block, dexamethasone can be administered along with local anesthetic through a single injection as a mixture (twin mix). Prospective double-blind randomized clinical trial was designed to evaluative plasma concentration of dexamethasone achieved following injection of a freshly prepared mixture of 1.8ml of 2% lignocaine with adrenaline (1:200000) and 1ml (4mg) dexamethasone [2.8ml solution of twin mix] in the pterygomandibular space. The 30 candidates included for the trial were randomly split into three study groups (ten each)-(1) control group (C); (2) intramuscular group (IM); (3) intraspace group (IS). The mean plasma dexamethasone concentration at 30min postinjection in group IM was 226.41 ± 48.67ng/ml and for IS group it was 209.67 ± 88.13ng/ml. Post hoc (Bonferroni-Holm test) intergroup comparison for plasma dexamethasone concentration (IM and IS) was found statistically insignificant (P = 0.605). Intraspace route of drug administration can be utilized to deliver dexamethasonized local anesthetics safely with predictable clinical effects in the patients requiring mandibular minor oral surgery under local anesthesia.

Bioavailability and tolerability of nebulised dexamethasone sodium phosphate in adult horses.

Nebulisation of the injectable dexamethasone sodium phosphate (DSP) would offer an inexpensive way of delivering a potent corticosteroid directly to the lungs of horses with asthma. However, this approach would be advantageous only if systemic absorption is minimal and if the preservatives present in the formulation do not induce airway inflammation. To investigate the bioavailability of nebulised DSP and determine whether it induces airway inflammation or hypothalamic-pituitary-adrenal (HPA) axis suppression in healthy adult horses. Randomised crossover experiment. Dexamethasone sodium phosphate was administered to six healthy adult horses at a dose of 5 mg q. 24 h for 5 days via nebulised, or intravenous (i.v.) routes. Plasma dexamethasone concentrations were measured by UPLC/MS-MS to calculate bioavailability. Cytological examination of bronchoalveolar fluid was performed at baseline and after the last dose of DSP. A validated chemiluminescent immunoassay was used to measure basal serum cortisol concentrations. After nebulisation to adult horses, dexamethasone had a mean (±s.d.) maximum plasma concentration of 0.774 ± 0.215 ng/mL and systemic bioavailability of 4.3 ± 1.2%. Regardless of route of administration, there was a significant decrease in the percentage of neutrophils in bronchoalveolar lavage fluid over time. During i.v. administration, basal serum cortisol concentration decreased significantly from baseline to Day 3 and remained low on Day 5. In contrast, basal serum cortisol concentration did not change significantly during administration via nebulisation. Small sample size and short period of drug administration. Dexamethasone sodium phosphate administered via nebulisation had minimal systemic bioavailability and did not induce lower airway inflammation or HPA axis suppression in healthy horses.

Dexamethasone Delivery by an Implant-Mediated Drug Delivery System in the Canine Mandible.

A newly introduced implant-mediated drug delivery system (IMDDS) showed promising results in a rabbit tibia model. The aim of the present study is to evaluate whether dexamethasone administered by the IMDDS has sustained effects in the canine mandible - a different anatomic location, in a different species. IMDDS was installed at the mesial root of the second premolar site in the mandibles of six beagle dogs. After complete healing, 10 mg dexamethasone was administered through the IMDDS. The same amount of drug was administered to five control animals by intramuscular injection. The release pattern was monitored for 2 weeks by measuring plasma drug concentrations. A sustained plasma dexamethasone concentration was detected after a peak at 6 hours until the end of the observation period, despite individual variations. The concentration was lower than reported in the rabbit tibia model. In contrast, plasma concentration of the control group showed an early peak at 2 hours and decreased rapidly. Dexamethasone was effectively released from the IMDDS for a prolonged time in the canine mandible model.

Time-dependent effects of dexamethasone plasma concentrations on glucocorticoid receptor challenge tests

Glucocorticoid challenge tests such as the dexamethasone suppression test (DST) and the combined dexamethasone/corticotropin-releasing hormone (dex-CRH) test are considered to be able to sensitively measure hypothalamic-pituitary-adrenal (HPA) axis activity in stress-related psychiatric and endocrine disorders. We used mass-spectrometry to assess the relationship of plasma dexamethasone concentrations and the outcome of these tests in two independent cohorts.Dexamethasone concentrations were measured after oral ingestion of 1.5mg dexamethasone in two cohorts that underwent a standard (dexamethasone at 23:00h) as well as modified (18:00h) DST and dex-CRH test. The first study population was a case/control cohort of 105 depressed patients and 133 controls in which peripheral blood mRNA expression was also measured. The second was a cohort of 261 depressed patients that underwent a standard dex-CRH test at baseline and after 12 weeks’ treatment with cognitive-behavioral therapy or antidepressants.Dexamethasone concentrations explained significant proportions of the variance in the DST in both the first (24.6%) and the second (5.2%) cohort. Dexamethasone concentrations explained a higher proportion of the variance in the dex-CRH test readouts, with 41.9% of the cortisol area under the curve (AUC) in the first sample and 24.7% in the second sample. In contrast to these strong effects at later time points, dexamethasone concentrations did not impact cortisol or ACTH concentrations or mRNA expression 3hours after ingestion. In the second sample, dexamethasone concentrations at baseline and week 12 were highly correlated, independent of treatment type and response status. Importantly, a case/control effect in the Dex-CRH test was only apparent when controlling for dexamethasone concentrations.Our results suggest that the incorporation of plasma dexamethasone concentration or measures of earlier endocrine read-outs may help to improve the assessment of endocrine dysfunction in depression.

Antileukemic Efficacy of Continuous vs Discontinuous Dexamethasone in Murine Models of Acute Lymphoblastic Leukemia.

Osteonecrosis is one of the most common, serious, toxicities resulting from the treatment of acute lymphoblastic leukemia. In recent years, pediatric acute lymphoblastic leukemia clinical trials have used discontinuous rather than continuous dosing of dexamethasone in an effort to reduce the incidence of osteonecrosis. However, it is not known whether discontinuous dosing would compromise antileukemic efficacy of glucocorticoids. Therefore, we tested the efficacy of discontinuous dexamethasone against continuous dexamethasone in murine models bearing human acute lymphoblastic leukemia xenografts (n = 8 patient samples) or murine BCR-ABL+ acute lymphoblastic leukemia. Plasma dexamethasone concentrations (7.9 to 212 nM) were similar to those achieved in children with acute lymphoblastic leukemia using conventional dosages. The median leukemia-free survival ranged from 16 to 59 days; dexamethasone prolonged survival from a median of 4 to 129 days in all seven dexamethasone-sensitive acute lymphoblastic leukemias. In the majority of cases (7 of 8 xenografts and the murine BCR-ABL model) we demonstrated equal efficacy of the two dexamethasone dosing regimens; whereas for one acute lymphoblastic leukemia sample, the discontinuous regimen yielded inferior antileukemic efficacy (log-rank p = 0.002). Our results support the clinical practice of using discontinuous rather than continuous dexamethasone dosing in patients with acute lymphoblastic leukemia.

Intravitreal Administration of Dexamethasone-Loaded PLGA-TPGS Nanoparticles for the Treatment of Posterior Segment Diseases

The purpose of this research was to investigate the possibility of dexamethasone (DEX)-loaded PLGA-TPGS nanoparticles (NPs) in rabbits after intravitreal administration for the treatment of posterior segment diseases. The DEX-loaded PLGA-TPGS NPs were fabricated and characterized in terms of surface morphology, particle size and size distribution, entrapment efficiency, and in vitro drug release. The animals were classified randomly into two groups: experimental group with thirty rabbits, and control group with eighteen rabbits. Rabbits in the experimental group received intravitreal injections of 0.1 mL of DEX-loaded PLGA-TPGS NPs suspension and the control rabbits received intravitreal injection of 0.1 mL DEX (20 g/L in saline). The DEX concentrations in plasma and the ocular tissues such as the cornea, aqueous humor, lens, iris, vitreous humor, and chorioretina were determined by HPLC. The DEX-loaded PLGA-TPGS nanoparticle suspension were transparent and maintained a sustained release of DEX for about 45 days in vitreous and provided relatively constant DEX levels for more than 30 days with a mean concentration of 3.93 mg/L. Based on the area-under-the-curve (AUC), the bioavailability of DEX in the experimental group was significantly higher than that in the control group administrated with regular DEX. These results suggest that intravitreal administration of DEX-loaded PL.3A-TPGS NPs leads to a sustained release of DEX with a high bioavailability, providing a basis for a novel approach to treat posterior segment diseases.

Pharmacokinetics and pharmacodynamics of dexamethasone after oral administration in apparently healthy horses

To assess pharmacokinetic and pharmacodynamic properties of dexamethasone administered PO as a solution or powder, compared with properties of dexamethasone solution administered IV, in apparently healthy horses. 6 adult horses. Serum cortisol concentration for each horse was determined before each treatment (baseline values). Dexamethasone (0.05 mg/kg) was administered PO (in solution or powdered form) or IV (solution) to horses from which feed had or had not been withheld (unfed and fed horses, respectively). Each horse received all 6 treatments in random order at 2-week intervals; PO and IV administrations of dexamethasone were accompanied by IV or PO sham treatments, respectively. Plasma dexamethasone and serum cortisol concentrations were assessed at predetermined intervals. Maximum plasma dexamethasone concentration after PO administration of powdered dexamethasone in unfed horses was significantly higher than the maximum plasma concentration after PO administration of dexamethasone solution in unfed or fed horses. Mean bioavailability of dexamethasone ranged from 28% to 66% but was not significantly different among horses receiving either formulation PO in the unfed or fed state. After dexamethasone treatment PO or IV, serum cortisol concentrations were significantly less than baseline at 1 to 72 hours in unfed horses and at 2 to 48 hours in fed horses. PO or IV administration of dexamethasone resulted in suppression of cortisol secretion in unfed and fed adult horses; the magnitude of suppression did not differ among treatment groups, and serum cortisol concentrations returned to baseline after 48 to 72 hours.

Pharmacokinetics and tolerance study of intravitreal injection of dexamethasone-loaded nanoparticles in rabbits.

The aim of the study was to investigate the tolerance and pharmacokinetics of dexamethasone (DEX)-loaded poly(lactic acid-co-glycolic acid) nanoparticles (DEX-NPs) in rabbits after intravitreal injection. The DEX-NPs were prepared and characterized in terms of morphology, particle size and size distribution, encapsulation efficiency, and in vitro release. Ophthalmic investigations were performed, including fundus observation and photography, intraocular pressure measurement, and B-scan ocular ultrasonography. There were no abnormalities up to 50 days after administration of DEX-NPs in rabbits. The DEX concentrations in plasma and the ocular tissues such as the cornea, aqueous humor, lens, iris, vitreous humor, and chorioretina were determined by high-pressure liquid chromatography. The DEX-NPs maintained a sustained release of DEX for about 50 days in vitreous and provided relatively constant DEX levels for more than 30 days with a mean concentration of 3.85 mg/L(-1). Based on the areas under the curve, the bioavailability of DEX in the experimental group was significantly higher than that in the control group injected with regular DEX. These results suggest that intravitreal injection of DEX-NPs lead to a sustained release of DEX with a high bioavailability, providing a basis for a novel approach to the treatment of posterior segment diseases.

Outbreak of exogenous Cushing's syndrome due to unlicensed medications

Despite the widespread medical use of glucocorticoids, reports of factitious administration of these hormones have been uncommon. We herein report an outbreak of Cushing's syndrome in Tehran among the addicts using Tamgesic (a brand of Buprenorphine) to help them through the narcotic withdrawal stage, without knowledge of the glucocorticoid content of the black-market drug. Case histories of 19 patients with a final diagnosis of iatrogenic Cushing's syndrome were reviewed. Liquid chromatography/mass spectrometry (LC-Mass) method was used to evaluate glucocorticoid existence in the brand. High performance liquid chromatography was used to determine plasma dexamethasone level. No buprenorphine was present in the vials. Each Tamgesic vial contained 0.4 mg of Dexamethasone disodium phosphate; Heroin was also found in them. The duration of injection abuse and the total dexamethasone intake was 4.5 (1-18) months and 2.6 (0.8-8) mg/day, respectively. Median plasma dexamethasone concentration was 5.8 nmol/l, with a range of 5-8.7. Physical findings of the cases were not different from those of the classic endogenous Cushing's syndrome but their serum cortisol and urinary free cortisol were suppressed. Severe life-threatening complications were demonstrated in five cases. Surreptitious use of steroids resulting in Cushing's syndrome may be more common in opium addicts; a high degree of suspicion is needed to uncover this disorder. Whenever facing a cushingoid appearance in addicts, the possibility of using black market drugs with corticosteroid contents should be kept in mind.

The combined low-dose dexamethasone suppression corticotropin-releasing hormone test as a tool to rule out Cushing's syndrome

It remains to be evaluated whether the combined low-dose dexamethasone suppression corticotropin-releasing hormone test (LDDST-CRH test) may add to the diagnostic approach of patients suspected to have Cushing's syndrome (CS). The aim of the present study was to evaluate whether the LDDST-CRH test may have a place in the diagnostic strategy of CS. Prospective evaluation of a consecutive series of patients with suspected CS from 2004 to 2006. All the subjects underwent the same screening protocol including 1 mg dexamethasone suppression test, 24-h urinary free cortisol (UFC), and midnight serum cortisol, followed by the LDDST-CRH test whose results were not used to establish a definitive diagnosis. Plasma dexamethasone concentration was measured 2 h after the last dose of dexamethasone. Patients qualified for CS when at least two screening tests were positive. Sixteen patients had CS while in the remaining 15 subjects CS was excluded. Even if not statistically significant, the sensitivity and the negative predictive value of the cortisol 15 min after CRH were better than the other tests; on the other hand, the test specificity was lower. All of the patients classified as indeterminate were correctly diagnosed by the LDDST-CRH test. Nevertheless, the repeated assessment of the screening tests and the active follow-up gave the same correct results. In all of the patients misclassified by the LDDST-CRH test, the plasma dexamethasone concentrations were in the normal range. Based on our findings, we suggest that the LDDST-CRH test may still find a place as a rule-out procedure in patients who present with indeterminate results after screening and may be unavailable to repeat testing during follow-up.

Pharmacokinetics of dexamethasone in a rat model of rheumatoid arthritis

Dexamethasone (DEX) is often given for the treatment of rheumatoid arthritis and clinical dosing regimens of DEX have often been based empirically. This study tests whether the inflammation processes in a rat model of rheumatoid arthritis alters the clearance and volume of distribution of DEX when compared with healthy controls. Groups of healthy and arthritic male Lewis rats received either a low (0.225 mg/kg) or high (2.25 mg/kg) intramuscular dose of DEX. Arthritis was induced by intradermal injection of type II porcine collagen in incomplete Freund's adjuvant emulsion at the base of the tail. DEX was dosed in the arthritic animals 22 days post arthritis induction. Plasma DEX concentrations were determined by HPLC. Plasma concentration versus time data were analysed by non-compartmental analysis and pharmacokinetic model fitting using the population pharmacokinetic software NONMEM V. A linear bi-exponential pharmacokinetic model with extravascular input described the data for both healthy and arthritic animals. Clearance was the only parameter determined statistically different between both groups (healthy=1.05 l/h/kg, arthritic=1.19 l/h/kg). The steady-state volume of distribution for both groups was 4.85 l/kg. The slight difference in clearance was visibly undetectable and unlikely to produce meaningful changes in DEX disposition in arthritic rats.

Evidence of cortisol suppression in neonates after major cardiac surgery: is supplementation necessary?

Introduction: Infants and children undergoing major cardiac surgery mount a substantial stress response. Data from a previous investigation suggested that after cardiac surgery infants under 90 days had prolonged suppression of cortisol production (1) that might not be explained as simply due to the use of dexamethasone (used routinely for cardiopulmonary bypass). This study was designed to determine the origins of this suppressed cortisol response.Methods: Local ethics committee approval was granted for the study. Ten neonates due to undergo cardiac surgery using cardiopulmonary bypass were recruited after informed parental consent. A standard anaesthetic technique was used. Baseline blood samples were taken following induction of anaesthesia and arterial line insertion: a dose of dexamethasone (0.5 mg·kg‐1) was then administered as per usual protocol. Blood was taken at release of the cross clamp (ROCC) and then 2, 6, 24, 48 and 72 h later. Blood was not taken at 72 h if the patient no longer had invasive monitoring lines in place. At each time point concentrations of cortisol, adrenocorticotrophic hormone (ACTH) and dexamethasone were measured. Results: Time ACTH (ng·l‐1) Cortisol (nmol·l‐1) Dexamethasone (nmol·l‐1) Baseline 68.7 (38.6–123.0) 647.0 (510.0–1038) 0.8 (0.8–1.0) ROCC 18.3 (11.3–28.7) 439.0 (340.0–556.0) 173.5 (153.3–186) ROCC + 2 11.2 (9.0–14.9) 201.0 (134.0–416.0) 147.8 (114.6–176) ROCC + 6 9.0 (9.0–10.4) 87.5 (49.0–94.0) 60.0 (50.6–103.3) ROCC + 24 9.0 (9.0–13.8) 98.0 (29.0–244.0) 5.1 (2.4–12.6) ROCC + 48 12.6 (9.0–16.4) 302.0 (173.0–451.0) 1.3 (1–3.9) ROCC + 72 12.4 (9.0–26.3) 494.0 (176.0–686.0) 1.7 (1–2.3) Note: Figures above are given as median (interquartile range) for the 10 patients in the study. Statistical analysis was performed after the data had been natural‐log transformed.Plasma cortisol concentrations reached a nadir 6 h post‐ROCC. At 24 h post‐ROCC cortisol was significantly below baseline (P &lt; 0.05), and was undetectable in four patients (&lt;30 nmol·l‐1). 48 h post‐ROCC; eight out of 10 patients still had a cortisol level below baseline. Plasma ACTH concentrations were also suppressed up to 48 h post‐ROCC (P &lt; 0.05). However, plasma dexamethasone concentrations had returned to background (baseline) values by 48 h post‐ROCC, and therefore were unlikely to still exert pharmacological effects. Furthermore, there was no significant correlation between plasma dexamethasone and cortisol concentrations at either 24 or 48 h post‐ROCC.Discussion: The data suggest that between 24 and 48 h post‐ROCC the patients could be at risk of relative adrenocortical insufficiency as dexamethasone had been substantially cleared from the plasma and cortisol continued to remain below baseline in the majority of patients. The independence of dexamethasone and cortisol concentrations between 24 and 48 h is interesting and would indicate that other regulators are responsible for the prolonged pituitary adrenocortical suppression.Conclusions: Neonates may be at risk of prolonged reduced cortisol secretion after major cardiac surgery via suppression of pituitary ACTH release. The results cannot be dismissed as simple feedback inhibition by prolonged elimination of dexamethasone. Neonates may benefit from supplemental corticosteroids after major cardiac surgery by measurement of plasma cortisol concentrations postoperatively and providing steroid supplementation if required.Acknowledgements: We are grateful to the APA for funding this study, to the biochemistry laboratory at Guy's and St Thomas’ Trust for performing the assays, and to the parents of the patients for allowing them to be included in this study.Reference 1 Humphreys N et al.‘Plasma cortisol concentrations in children in PICU after cardiac surgery: evidence of prolonged suppression in infants under 90 days old’. Abstract presented at PICS ASM, September 2003.

Erythrocytes-Mediated Delivery of Dexamethasone in Steroid-Dependent IBD Patients-A Pilot Uncontrolled Study

Autologous erythrocytes can be used as carriers of drugs, owing to the ability of their membrane to be opened and resealed under appropriate conditions. In this pilot uncontrolled study, we investigated efficacy and safety of dexamethasone-encapsulated erythrocytes in steroid-dependent IBD patients. Ten patients (5 with ulcerative colitis and 5 with Crohn's disease) with steroid dependency ranging from 8 to 60 months were studied. Seven of them were in clinical remission, and the remaining three had mild activity. Eight patients were also under azathioprine or 6-MP for at least 6 months (range 6-24 months), while another two patients were intolerant to both drugs. Fifty milliliters of blood were drawn from each subject; dexamethasone 21-Phosphate (Dex 21-P) was encapsulated into erythrocytes by means of specially designed equipment, and drug-loaded erythrocytes were infused into original donors. The procedure was repeated after 4 and 8 wk, and patients were instructed to withdraw corticosteroids. A mean dose of 5.5+/-2.4 mg Dex 21-P was loaded in the erythrocytes at each treatment. Following re-infusion of loaded erythrocytes, plasma Dexamethasone (Dex) concentrations were detected after as long as 28 days. Steroids were completely withdrawn by the second month. After the third infusion, all patients, including the three with mild active disease, were in clinical remission. ESR levels dropped from 47+/-27 at baseline to 27+/-16 mm/h (p<0.02), and CRP levels from 1.6+/-1.3 to 0.6+/-0.5 mg/dl (p<0.02). After a mean follow-up of 12+/-3 months, six patients relapsed, and the remaining four patients remained in remission. Pre-existing steroid-related adverse effects disappeared during the follow-up. Loading of Dex 21-P in autologous erythrocytes is feasible and safe. The very low dose of Dex released in blood stream was able to maintain patients in clinical remission and allowed steroids withdrawal.

Cortisol and ACTH Response to Oral Dexamethasone in Obesity and Effects of Sex, Body Fat Distribution, and Dexamethasone Concentrations: A Dose-Response Study

There is increasing evidence that the abdominal obesity phenotype may be associated with multiple alterations of the hypothalamic-pituitary-adrenocortical (HPA) axis activity in both sexes. Our hypothesis is that the lack of adequate cortisol suppression after the dexamethasone test may constitute an indirect marker of HPA axis hyperactivity in the presence of the abdominal obesity phenotype. A total of 34 normal-weight (13 men and 21 women) and 87 obese (36 men and 51 women), healthy, nondepressed subjects therefore underwent four different dexamethasone suppression tests randomly performed at varying intervals of at least 1 wk between each test. After a standard overnight 1-mg dexamethasone test, which served as a reference, three other tests were randomly performed at 1-wk intervals by administering 0.0035, 0.0070, and 0.015 mg oral dexamethasone per kilogram of body weight overnight. Blood samples were obtained for cortisol, ACTH, and dexamethasone. Results were analyzed separately in men and women as well as in normal-weight [body mass index (BMI) < or = 25 kg/m(2)] and overweight or obese (BMI > 25 kg/m(2)) subjects. The waist circumference and the waist to hip ratio (WHR) were used as markers of body fat distribution. After the standard 1-mg test, cortisol suppression was greater than 90% in all subjects. However, after each test, obese women had significantly higher values of percent cortisol and percent ACTH suppression than normal-weight women without any difference between obese and normal-weight men. Considering the response to the three variable-dose tests, a clear dose- response pattern (P < 0.001 for trend analysis) in percent cortisol and percent ACTH suppression was found in all subjects. After each test men had significantly higher dexamethasone levels than women, regardless of BMI. However, obese women, but not men, had significantly higher dexamethasone levels after each test than their normal-weight counterpart. Plasma dexamethasone concentrations were dose related (P < 0.001 for trend analysis) in all subjects, but the dose-related increase was significantly higher in normal-weight men than normal-weight women, whereas it was similar in obese subjects of both sexes. Stepwise multiple regression analysis revealed that both percent cortisol and percent ACTH variations were significantly and negatively influenced by dexamethasone levels, as well as by waist circumference values in men, and independently by BMI and waist circumference in women. However, in contrast to what has been found in men, a divergent contribution of BMI and waist circumference was found in women indicating that, with increasing waist values, a smaller suppression of the HPA axis was found with respect to that expected on the basis of BMI values. In conclusion, this study provides data of both physiological and physiopathological relevance. Overall, our data indicated that adjustment of the dexamethasone dose to body weight does not seem to substantially improve the sensitivity of the test, even in obese individuals, particularly when near-maximal doses are administered. However, this study demonstrated a highly significant effect of dexamethasone blood level concentrations on cortisol and ACTH suppression to low-dose dexamethasone tests. In addition, a significant effect of gender on postdexamethasone cortisol concentrations, suppression of the HPA axis, and dexamethasone levels were found, which may be dependent on related differences in both cortisol and dexamethasone metabolism. We showed that pituitary sensitivity to feedback inhibition by dexamethasone is preserved in obesity in both sexes even at low dosages. On the other hand, our data suggest that, at least in women, abdominal fat distribution may partially counteract the progressively greater suppressibility of the HPA axis that would be expected according to increasing BMI.