Human Jejunal Permeability of Two Polar Drugs: Cimetidine and Ranitidine

Purpose . To determine the human jejunal permeability of cimetidine and ranitidine using a regional jejunal perfusion approach, and to integrate such determinations with previous efforts to establish a baseline correlation between permeability and fraction dose absorbed in humans for soluble drugs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41484/1/11095_2004_Article_302739.pd

Plasma concentrations of 25-hydroxyvitamin D among Jordanians: Effect of biological and habitual factors on vitamin D status

<p>Abstract</p> <p>Background</p> <p>Vitamin D is cutaneously synthesized following sun exposure (vitamin D₃) as well as it is derived from dietary intake (vitamin D₃and D₂). Vitamin D₂and D₃are metabolized in the liver to 25-hydroxyvitamin D (25(OH)D). This metabolite is considered the functional indicator of vitamin D stores in humans. Since Jordan latitude is 31°N, cutaneous synthesis of vitamin D₃should be sufficient all year round. However, many indications reveal that it is not the case. Thus, this study was conducted to determine the 25(OH)D status among Jordanians.</p> <p>Methods</p> <p>Three hundred healthy volunteers were enrolled in a cross sectional study; 201 females and 99 males. 25(OH)D and calcium concentrations were measured by enzyme linked immunosorbent assay and spectroscopy techniques, respectively. All participants filled a study questionnaire that covered age, sex, height, weight, diet, and dress style for females. Females were divided according to their dress style: Western style, Hijab (all body parts are covered except the face and hands), and Niqab (all body parts are covered including face and hands).</p> <p>Results</p> <p>The average plasma 25(OH)D levels in males and females were 44.5 ± 10.0 nmol/l and 31.1 ± 12.0 nmol/l, respectively. However, when female 25(OH)D levels were categorized according to dress styles, the averages became 40.3, 31.3 and 28.5 nmol/l for the Western style, Hijab and Niqab groups, respectively. These 25(OH)D levels were significantly less than those of males (p < 0.05, 0.001, 0.001, respectively). In addition, the plasma 25(OH)D levels of the Western style group was significantly higher than those of Hijab and Niqab groups (p < 0.001). Furthermore, dairy consumption in males was a positive significant factor in vitamin D status. Even though calcium concentrations were within the reference range, the Hijab and Niqab-dressed females have significantly less plasma calcium levels than males (p < 0.01).</p> <p>Conclusions</p> <p>Very low plasma 25(OH)D levels in females wearing Hijab or Niqab are highly attributed to low sunlight or UVB exposure. In addition, most of males (76%) and Western style dressed females (90%) have 25(OH)D concentrations below the international recommended values (50 nmol/l), suggesting that although sun exposure should be enough, other factors do play a role in these low concentrations. These findings emphasize the importance of vitamin D supplementation especially among conservatively dressed females, and determining if single nucleotide polymorphisms of the genes involved in vitamin D metabolism do exist among Jordanians.</p

Comparative assessment of saliva and plasma for drug bioavailability and bioequivalence studies in humans

Aims: To study the pharmacokinetics of selected drugs in plasma and saliva matrixes in healthy human volunteers, and to suggest using non-invasive saliva sampling instead of plasma as a surrogate in bioavailability and bioequivalence (BA/BE) studies. Methods: Four different pilot BA/BE studies were done in 12–18 healthy humans. Saliva and plasma samples were collected for 3–5 half life values of metformin, tolterodine, rosuvastatin, and paracetamol after oral dosing. Saliva and plasma samples were assayed using LC-MSMS, and then pharmacokinetic parameters were calculated by non-compartmental analysis using Kinetica program. Effective intestinal permeability (Peff) values were also optimized to predict the actual average plasma profile of each drug by Nelder-Mead algorithm of the Parameter Estimation module using SimCYP program. Results: All studied drugs showed salivary excretion with strong correlation coefficients between saliva and plasma concentrations. The optimized Peff ranged 1.44–68.3 × 10−4 cm/s for the drugs under investigation. Saliva/plasma concentrations ratios ranged 0.17–1.5. Inter and intra individual variability of primary pharmacokinetic parameters in saliva matrix was either close to or higher than plasma matrix. This requires larger sample size in saliva studies for some drugs. Conclusion: Our results suggest that there is a potential in BA/BE studies for saliva to be considered as a surrogate for plasma concentration, which goes along with drug regulations. The use of saliva instead of plasma in such studies makes them non-invasive, easy and with a lower clinical burden

Effect of Replicate Design on Drug Variability and Bioequivalence in Humans

International audienceThe purpose of this study is to investigate the effect of using replicate design on the intra/inter subject variability and bioequivalence of drugs in healthy volunteers. Model drugs used for analysis were amoxicillin/clavulanic acid combination. 24 healthy subjects participated in this study using 4-phase replicate cross over design. Individual disposition kinetic parameters of areas under plasma concentrations (AUC 0-t) and maximum concentration (C max) were calculated by non-compartmental analysis using Kinetica program V 4.2 using all phases. The 90 % confidence intervals for log-transformed AUC 0-t and C max were calculated for phases I & II; then for phases I, II and III; and for phases I, II, III and IV respectively. The intra and inter-subject variability values did not show a trend to decrease by the increase in phases included in analysis in both drugs and for both parameters. In addition, the 90 % confidence intervals for log-transformed AUC 0-t and C max passed the 80-125 % limit range in both drugs for all phase combinations, even though C max variability was shown high for clavulanic acid. However, individual bioequivalence was shown for AUC and not shown for C max of both drugs. These results suggest not using replicate design as an approach to show the high inter/intra subject variability of highly variable drugs and hence justify wider acceptance limits of 75-133 % as recommended by the draft EMEA guideline. Literature information about drug high variability should be adequate to justify using wider acceptance limits of 75-133%