Limited Intestinal Absorption Research Articles

Enhancing Oral Delivery of Biologics: A Non-Competitive and Cross-Reactive Anti-Leptin Receptor Nanofitin Demonstrates a Gut-Crossing Capacity in an Ex Vivo Porcine Intestinal Model.

Biotherapeutics exhibit high efficacy in targeted therapy, but their oral delivery is impeded by the harsh conditions of the gastrointestinal (GI) tract and limited intestinal absorption. This article presents a strategy to overcome the challenges of poor intestinal permeability by using a protein shuttle that specifically binds to an intestinal target, the leptin receptor (LepR), and exploiting its capacity to perform a receptor-mediated transport. Our proof-of-concept study focuses on the characterization and transport of robust affinity proteins, known as Nanofitins, across an ex vivo porcine intestinal model. We describe the potential to deliver biologically active molecules across the mucosa by fusing them with the Nanofitin 1-F08 targeting the LepR. This particular Nanofitin was selected for its absence of competition with leptin, its cross-reactivity with LepR from human, mouse, and pig hosts, and its shuttle capability associated with its ability to induce a receptor-mediated transport. This study paves the way for future in vivo demonstration of a safe and efficient oral-to-systemic delivery of targeted therapies.

Recent Advances in Doxorubicin Formulation to Enhance Pharmacokinetics and Tumor Targeting.

Doxorubicin (DOX), a widely used drug in cancer chemotherapy, induces cell death via multiple intracellular interactions, generating reactive oxygen species and DNA-adducted configurations that induce apoptosis, topoisomerase II inhibition, and histone eviction. Despite its wide therapeutic efficacy in solid tumors, DOX often induces drug resistance and cardiotoxicity. It shows limited intestinal absorption because of low paracellular permeability and P-glycoprotein (P-gp)-mediated efflux. We reviewed various parenteral DOX formulations, such as liposomes, polymeric micelles, polymeric nanoparticles, and polymer-drug conjugates, under clinical use or trials to increase its therapeutic efficacy. To improve the bioavailability of DOX in intravenous and oral cancer treatment, studies have proposed a pH- or redox-sensitive and receptor-targeted system for overcoming DOX resistance and increasing therapeutic efficacy without causing DOX-induced toxicity. Multifunctional formulations of DOX with mucoadhesiveness and increased intestinal permeability through tight-junction modulation and P-gp inhibition have also been used as orally bioavailable DOX in the preclinical stage. The increasing trends of developing oral formulations from intravenous formulations, the application of mucoadhesive technology, permeation-enhancing technology, and pharmacokinetic modulation with functional excipients might facilitate the further development of oral DOX.

Investigation of the effect of verapamil on the regional absorption of sofosbuvir from rabbit intestine in situ.

Sofosbuvir, a nucleotide antiviral drug, is a Biopharmaceutics Classification System (BCS) class III prodrug suffering from limited intestinal absorption due to its high hydrophilicity and low intestinal permeability. This research aims to investigate the luminal stability of Sofosbuvir, the influence of anatomical site on its intestinal absorption and the effects of verapamil on such absorption. The study utilized in situ rabbit intestinal perfusion technique to examine absorption of Sofosbuvir from duodenum, jejunum, ileum and ascending colon. This was conducted both with and without verapamil. The luminal stability study showed that Sofosbuvir was subjected to premature degradation with varying fractions degraded from the different intestinal segments. The in situ perfusion data showed incomplete absorption of Sofosbuvir from small and large intestinal segments. The recorded values of the absorptive clearance per unit length (Pe.A/L) of Sofosbuvir were 0.026, 0.0075, 0.0026, & 0.054ml/min.cm for duodenum, jejunum, ileum, and ascending colon, respectively. The Pe.A/L values were ordered as colon > duodenum > jejunum > ileum. This is the opposite rank of P-gp content in the different intestinal segments. The recorded values of the length required for complete Sofosbuvir absorption (L95%) were 29.58, 128.47, 949.2 and, 13.63cm for duodenum, jejunum, ileum, and ascending colon, respectively. Co-perfusion with verapamil significantly increased Pe.A/L and reduced the L95% of Sofosbuvir from both jejunum and ileum (P-value < 0.05). The results indicated that the absorptive clearance of Sofosbuvir was site dependent and associated with the content of P-glycoprotein, in addition to the expected drug interactions that can occur in polymedicated hepatitis C virus (HCV) infected patients.

A liposome-micelle-hybrid (LMH) oral delivery system for poorly water-soluble drugs: Enhancing solubilisation and intestinal transport

A novel liposome-micelle-hybrid (LMH) carrier system was developed as a superior oral drug delivery platform compared to conventional liposome or micelle formulations. The optimal LMH system was engineered by encapsulating TPGS micelles in the aqueous core of liposomes and its efficacy for oral delivery was demonstrated using lovastatin (LOV) as a model poorly soluble drug with P-gp (permeability glycoprotein) limited intestinal absorption. LOV-LMH was characterised as unilamellar, spherical vesicles encapsulating micellar structures within the interior aqueous core and showing an average diameter below 200 nm. LMH demonstrated enhanced drug loading, water apparent solubility and extended/controlled release of LOV compared to conventional liposomes and micelles. LMH exhibited enhanced LOV absorption and transportation in a Caco-2 cell monolayer model of the intestine by inhibiting the P-gp transporter system compared to free LOV. The LMH system is a promising novel oral delivery approach for enhancing bioavailability of poorly water-soluble drugs, especially those presenting P-gp effluxes limited absorption.

D-glucose elicits significant increase in the oral bioavailability of model BCS class III drugs in the rabbit

BCS class III drugs suffer from limited intestinal absorption due to high hydrophilicity and low intestinal permeability. This research was undertaken in order to examine the effect of enhancing the net water influx in the gastrointestinal tract on the oral absorption of ranitidine HCl, atenolol, and acyclovir sodium as model BCS class III drugs using 2-way parallel pharmacokinetic study in the rabbit. The in vivo study involved oral administration of each drug in a hypo-osmolar aqueous solution as a control group. The second group (test group) involved administration of the same drugs in a hypo-osmolar solution containing 80 mM d-glucose and 30 mM NaCl. Serial plasma samples were obtained from the marginal ear vein at predetermined time intervals after drug administration. The AUC and Cmax of the three drugs were increased significantly in the presence of d-glucose. This increase was associated with significant delay in the Tmax. The results indicated that the oral bioavailability of ranitidine HCl, atenolol, and acyclovir sodium had been significantly enhanced in the presence of d-glucose. Thus, d-glucose coadministration can be used as a new approach to increase the intestinal permeability of BCS class III drugs.

Cinnamic Acid and Its Derivatives: Mechanisms for Prevention and Management of Diabetes and Its Complications.

With recent insight into the development of dietary supplements and functional foods, search of effective phytochemical compounds and their mechanisms involved in prevention and management of diabetes and its complications are now being assessed. Cinnamic acid and its derivatives occur naturally in high levels of plant-based foods. Among various biological activities, cinnamic acid and its derivatives are associated with a beneficial influence on diabetes and its complications. The aim of the review is to summarize the potential mechanisms of these compounds for prevention and management of diabetes and its complications. Based on several in vitro studies and animal models, cinnamic acid and its derivatives act on different mechanism of actions, including stimulation of insulin secretion, improvement of pancreatic β-cell functionality, inhibition of hepatic gluconeogenesis, enhanced glucose uptake, increased insulin signaling pathway, delay of carbohydrate digestion and glucose absorption, and inhibition of protein glycation and insulin fibrillation. However, due to the limited intestinal absorption being a result of low bioavailability of cinnamic acid and its derivatives, current improvement efforts with entrapping into solid and liquid particles are highlighted. Further human clinical studies are needed to clarify the effects of cinnamic acid and its derivatives in diabetic patients.

Thiamine et encéphalopathie de Gayet-Wernicke : quelles règles de prescription ?

Background and aimWernicke's encephalopathy (WE) is a medical emergency. The objective of this paper is to systematically review the literature published over the past 15 years pertaining to prophylactic and curative treatment of WE with thiamine. MethodsA systematic literature search was performed using Medline to include all studies published between January 1, 2000 and December 31, 2015. ResultsOf the 316 abstracts identified, 20 met the final inclusion criteria. The evidence on the use of prophylactic thiamine was quite heterogeneous. The use of thiamine in this context largely depended on the evaluation of an individual's risk of developing WE. Use of prophylactic thiamine in low-risk patients is not universally indicated. When prescribed in this sub-population, the oral route is suggested but may be insufficient owing to its limited intestinal absorption and the high risk of non-compliance. High-risk patients need parenteral treatment with a recommended posology of 250 mg daily for 3 to 5 days. Intramuscular route is preferred in the outpatient setting, whereas intravenous route is suggested for inpatients. In cases where the diagnosis of WE is suspected or confirmed, a curative treatment with high-dose IV thiamine is justified. The evidence widely accepted in the literature is much clearer in this condition, with treatment regimens consisting of 500 mg IV 3 times daily for 3 to 5 days, followed by 250 mg IV daily for a minimum of 3 to 5 additional days. ConclusionThe literature does indicate that thiamine should be prescribed at high dosages, with the parenteral routes indicated in hospital settings and in high-risk patients. Based on the current literature review, we suggest treatment algorithms guiding thiamine prescription for WE.

Opinion Paper: Nanotechnology: A Successful Approach to Improve Oral Bioavailability of Phytochemicals.

Abstract Phytochemicals have gained significant recognition for their potential therapeutic uses against a variety of human diseases. However, the poor water solubility, limited intestinal absorption and low water stability of phytochemicals generally prevent from achieving a high oral bioavailability and even detectable plasma levels of the parent compound. Dose escalation is not always a solution to address limited oral bioavailability, and may increase the risk of adverse events, most frequently in the gastrointestinal system [1]. Low water solubility is a common reason for the limited bioavailability of drug candidates because passing through the unstirred aqueous layer on the surface of the intestinal epithelium is a pre-requisite for the intestinal absorption of compounds. It has been estimated that over 40 % of the drugs being identified through combinatorial screening programs are poorly soluble in water [2]. Therefore, formulation improvement into highly stable, water-soluble and orally bioavailable forms is regarded as a prerequisite for the clinical application of phytochemicals. Nanotechnology has emerged as an efficient tool to address the problems regarding solubility, stability and oral bioavailability of phytochemicals [3]. Several nano-sized delivery systems have been utilized to enhance the physicochemical properties of phytochemicals. Characteristics of the most common biocompatible and biodegradable nanoparticulate systems used for the delivery of natural products are summarized in Table 1. Nanoparticulate delivery systems confer a number of advantages, including facilitated transport of incorporated phytochemicals across the biological barriers, enhanced bioavailability of poorly water-soluble phytochemicals, targeted delivery of phytochemicals, protection of sensitive compounds from biological and environmental degradation, and controlled release [4]. Some famous examples of nanoformulated phytochemicals are shown in Table 2 [5-7]. Furthermore, many nanomaterials are being studied in clinical trials or have been approved by the Food and Drug Administration to be used in humans. Liposomal daunorubicin (Daunoxome®; described in patents EP0004467 and US20070286897) and albumin-bound paclitaxel (Abraxane®, described in patents WO2014105644 and WO2008057562) are two breakthrough examples of successful formulation of natural products using nanotechnology-based approaches. Table 2 summarizes some pharmacologically important phytochemicals with optimized nanoformulations [8, 9]. Curcumin is another important anti-cancer and cardioprotective phytopharmaceutical [10-12] for which various nanoformulations have been developed [12], as described in patents WO2013108270 and EP2349237. While nanotechnology offers promising solutions for the formulation of phytochemicals, some challenges still remain to be overcome before developing any nanoparticulate system to be used in clinical practice. These considerations include potential long-term toxicity of nanoparticles, non-specific uptake into cells, off-target biodistribution and tissue accumulation, and costly and complicated manufacturing process of some nanocomposites particularly in the targeted forms [8]. In spite of these challenges, biocompatible and biodegradable nanocarriers are increasingly finding applications in pharmaceutical and nutraceutical industries. Future investigations should address long-term safety issues of nanomaterials particularly when used repeatedly for chronic diseases.

Emulsion-based colloidal nanosystems for oral delivery of doxorubicin: Improved intestinal paracellular absorption and alleviated cardiotoxicity

We have previously reported that the limited intestinal absorption via the paracellular pathway may be the primary cause of the low oral bioavailability of doxorubicin (DOX). In this study, we have formulated medium chain glycerides-based colloidal nanosystems to enhance the intestinal paracellular absorption of DOX and reduce its cardiotoxicity. The DOX formulations prepared by the construction of pseudo-ternary phase diagram were characterized in terms of their droplet size distribution, viscosity, drug loading, and drug release. Further evaluation was conducted by an in vitro Caco-2 transport study as well as in situ/in vivo intestinal absorption, bioavailability and toxicity studies. Compared with DOX solution, these formulations enhanced the absorptive transport of DOX across Caco-2 cell monolayers at least partly due to the paracellular-enhancing effects of their lipidic components. Moreover, the in situ intestinal absorption and in vivo oral bioavailability of DOX in rats were markedly enhanced. In addition, no discernible damage was observed in the rat jejunum after oral administration of these DOX formulations while the cardiac toxicity was significantly reduced when compared with intravenous DOX solution. Taken together, the medium chain glycerides-based colloidal nanosystems prepared in this study represent a potentially effective oral delivery system for DOX.

Preclinical pharmacokinetic characterization of 2-(4-(4-(5-(2-phenyl-5-(trifluoromethyl)oxazole-4-carboxamido)-1H-benzo[d]imidazol-2-yl)phenyl)cyclohexyl) acetic acid, a novel DGAT-1 inhibitor

1. A novel diacylglyceride acyltransferase-1 (DGAT-1) inhibitor, 2-(4-(4-(5-(2-phenyl-5-(trifluoromethyl) oxazole-4-carboxamido)-1H-benzo[d]imidazol-2-yl)phenyl)cyclohexyl) acetic acid (KR-69232), was synthesized for a potential therapeutic use against several metabolic disorders, such as obesity, insulin resistance, and type II diabetes, characterized by excessive triglycerides (TGs) in the blood.2. The half-lives against phase I metabolism were measured as 75.3 ± 20.9 min and over 120 min in rat and human liver microsomes, respectively. In Caco-2 cell monolayers, extremely low permeability (<0.13 × 10−6 cm/s) was seen in the absorptive direction, predicting limited intestinal absorption of KR-69232. This compound was highly bound to rat and human plasma proteins (>99.8%).3. With the intravenous administration of KR-69232 in rats (1, 2, and 5 mg/kg), non-linear kinetics were observed at the highest dose, with significantly higher systemic clearance, higher volume of distribution, and lower dose-normalized AUC. Following oral administration, it exhibited low bioavailability (<10%) and was absorbed slowly (Tmax, 3.8–5.2 h) over the dose range. We also confirmed that considerable KR-69232 remained in the intestine at Tmax, demonstrating its limited absorption into the systemic circulation.

The limited intestinal absorption via paracellular pathway is responsible for the low oral bioavailability of doxorubicin

1. Doxorubicin exhibited dose-independent pharmacokinetics after intravenous (5–20 mg/kg) and oral (20–100 mg/kg) administration to rats. Nearly all (82.1–99.7%) of the orally administered doxorubicin remained unabsorbed, and the hepatic first-pass extraction ratio and oral bioavailability of doxorubicin were approximately 0.5% and 1%, respectively. Based on these results, it is likely that the primary factor responsible for the low oral bioavailability of doxorubicin is the limited intestinal absorption, rather than the CYP3A4-mediated first-pass metabolism.2. Moreover, the in vitro transport and cellular uptake studies using Caco-2 cell monolayers have revealed that doxorubicin crosses the intestinal epithelium primarily via the paracellular pathway (accounting for 85.6% of the overall absorptive transport) probably due to its physicochemical properties (hydrophilic cation; pKa = 9.67, log P = −0.5). These results suggest that P-glycoprotein (P-gp)-mediated efflux activity does not play a significant role in limiting the intestinal absorption of doxorubicin, attenuating the absorptive transport by only 5.56–13.2%.3. Taken together, the present study demonstrated that the limited and paracellular intestinal absorption of doxorubicin was a major factor responsible for its low oral bioavailability, restricting the role of CYP3A4-mediated first-pass metabolism and P-gp-mediated efflux.

Characterization of efflux transport of the PDE5 inhibitors, vardenafil and sildenafil

We aimed to characterize the efflux transport properties of vardenafil and sildenafil, and to compare the kinetics of these compounds via efflux transporters such as P-gp, BCRP and MRP2. We measured the basal-to-apical and apical-to-basal transport of vardenafil and sildenafil within the concentration range of 1-100 µm using MDCKII cells overexpressing P-gp, BCRP and MRP2, and Caco-2 cells. Vardenafil had a much greater basal-to-apical than apical-to-basal transport rate in MDCKII cells overexpressing P-gp, BCRP and MRP2. Sildenafil showed P-gp- and BCRP-mediated efflux transport, but did not seem to be pumped out via MRP2 transporters. Consequently, the absorptive transport of vardenafil and sildenafil in Caco-2 cells increased linearly over the concentration range of 1-100 µm, whereas the secretory transport of these drugs was saturable and inhibited by the presence of specific inhibitors of P-gp and BCRP. MK571, a representative MRP2 inhibitor, inhibited the basal-to-apical transport of vardenafil, but not of sildenafil. The involvement of P-gp, BCRP and MRP2 for vardenafil and the involvement of P-gp and BCRP for sildenafil in the secretory transport with linear absorptive transport may contribute to the limited intestinal absorption of these drugs.

Recent developments in clopidogrel pharmacology and their relation to clinical outcomes

Oral antiplatelet therapy with clopidogrel and aspirin is an important and widely prescribed strategy to prevent ischemic events in patients with cardiovascular diseases. However, the occurrence of thrombotic events including stent thrombosis is still high (> 10%). Current practice guidelines are mainly based on large-scale trials focusing on clinical endpoints and ‘one size fits all’ strategies of treating all patients with the same clopidogrel doses. Pharmacodynamic studies have demonstrated that the latter strategy is associated with wide response variability where a substantial percentage of patients show nonresponsivenes. Translational research studies have established the relation between clopidogrel nonresponsivenes or high on-treatment platelet reactivity to adverse clinical events, thereby establishing clopidogrel nonresponsivenes as an important emerging clinical entity. Clopidogrel response variability is primarily a pharmacokinetic phenomenon associated with insufficient active metabolite generation that is secondary to i) limited intestinal absorption affected by an ABCB1 gene polymorphism; ii) functional variability in P450 isoenzyme activity; and iii) a genetic polymorphism of CYP450 isoenzymes. Personalized antiplatelet treatment with higher clopidogrel doses in selected patients or with newer more potent P2Y12 receptor blockers based on individual platelet function measurement can overcome some of the limitations of current clopidogrel treatment.

Bioaccumulation of anthropogenic contaminants by detritivorous fish in the Río de la Plata estuary: 2-Polychlorinated biphenyls

The temporal variability and bioaccumulation dynamics of individual PCBs were studied in a detritivorous fish (Sábalo: Prochilodus lineatus) collected from 1999 to 2005 in the polluted Buenos Aires coastal area. Fish muscles contain high concentrations of total PCBs (11 ± 7.2, 4.6 ± 3.4 or 19 ± 13 μg g −1, dry, fresh and lipid weight, respectively) reflecting chronic bioaccumulation from sewage-industrial particulates. On a temporal basis, lipid normalized PCBs concentrations peaked by the end of 2001–2002 coincident with the rainiest period over the last four decades and shortly after PCB prohibition in the country, reflecting massive discharges to the coastal ecosystem. PCB composition in fish muscles show a prevailing contribution of hexachlorobiphenyls (35 ± 4.2%), followed by hepta (23 ± 3.0%), penta (20 ± 3.6%), tri-tetra (16 ± 4.8%) and minor proportions of octa-decachlorobiphenyls (5.7 ± 3.1%) similar to an Aroclor 1242–1254–1260 1:2:4 mixture. During 2001–2002 maxima fish showed an enrichment in tri-tetrachlorobiphenyls (∼1242–1254–1260 1:1:1 mixture) denoting a fresher signature. Fish/settling material lipid-organic carbon accumulation factors (BSAFs: 2.4–46, average: 21 ± 10) plotted against k ow showed a parabolic trend (BSAFs = −0.38 log k ow 2 + 5.16 log k ow −15.85; R 2 = 0.46) maximizing at hexa, hepta and octachlorobiphenyl 203 with reduced bioaccumulation of a few hepta (170, 191) and most octa-decachlorobihenyls suggesting limited intestinal absorption.

Physicochemical and biopharmaceutical characterization of BTA-243, a diacidic drug with low oral bioavailability

This investigation has examined possible causes of the poor bioavailability of the beta 3-adrenoceptor agonist BTA-243. The aqueous solubility of BTA-243 is pH dependent with a solubility minimum at pH 1.5. However, the dissolution rate of the disodium salt of BTA-243 is similar at both pH 2.0 and 7.4 indicating that dissolution rate is unlikely to be the controlling factor in the absorption of BTA-243. The apparent permeability coefficient of BTA-243 across Caco-2 monolayers at pH 6 was lower than that of mannitol and therefore the epithelial permeability of the molecule in vivo is predicted to be very low and potentially bioavailability limiting. Apparent permeability coefficients were not dependent on BTA-243 concentration over the concentration range 0.5 to 12 mM, indicating that epithelial transport is unlikely to occur via a saturable mechanism. They were of similar magnitude in both directions across the monolayers, indicative of no significant effluxing of BTA-243 by components of the cell membrane. Apparent octanol/water distribution coefficients increased with decrease of pH between 2 and 6; the relatively low values at pH 4 and 6 suggest that the limited intestinal absorption predicted in vivo will occur predominantly via paracellular passive diffusion. Everted gut sac experiments performed at pH 2.0 and 6.8 suggest that at pH 2.0 a significant proportion of the BTA-243 transport occurs via the transcellular route confirming that the ionization state of the BTA-243 molecule influences the route and rate of epithelial permeability.

Bisphosphonates in prostate carcinoma.

The majority of the patients with advanced prostate carcinoma have painful skeletal metastases, which are responsible for significant skeletal morbidity and disability. Most of these metastases are osteosclerotic, but it has been shown that the abnormal osteoblastic bone formation within metastases is preceded by osteoclastic activation, which appears to be associated with bone pain. This provides the rationale for using bisphosphonates, which are powerful and selective inhibitors of osteoclastic bone resorption. Several bisphosphonates have been shown to be clinically useful for the treatment of several conditions characterized by abnormal osteoclastic bone resorption, including Paget's disease, primary hyperparathyroidism, myelomatosis, and skeletal metastases. Its efficacy in relieving pain in patients with skeletal metastases due to prostate carcinoma has been confirmed in a few studies. The bisphosphonate clodronate was extensively investigated in the study unit. When infused intravenously i.v. (300 mg/day) relief of bone pain become appreciable within 3 days, sometimes preceded by a transient pain flare. These clinical results are very consistent and the residual pain usually is of extraosseous origin. Thus, with regard to pain of strictly bone origin, unresponsive patients are quite rare. Oral administration also is effective, but due to its limited intestinal absorption the effective dose is on the order of 1600-3200 mg/day. These doses usually are well tolerated, but they may be a problem for severely ill patients. Furthermore, the efficacy of treatment becomes apparent only after a few days. Thus, oral clodronate usually is adopted as a continuation of an i.v. course. The duration of the i.v. therapy should be individualized, but usually the more prolonged the treatment the longer the duration of the effect. For practical reasons, clodronate is infused daily for 5 days (Monday-Friday) and the treatment course is repeated at the time of any significant recurrence. The oral continuation prevents or delays the recurrence of bone pain in most patients, but in some patients this therapy has to be integrated occasionally with i.v. infusion. The duration of the effect for the same bioavailable dose is somewhat related to the degree of malignancy of the primary tumor. In an uncontrolled study, the author also evaluated the effectiveness of alendronate given either i.v. or orally. A single infusion of 5 mg alendronate i.v. produces roughly the symptomatic effect of 5 i.v. infusions of 300 mg clodronate. Alendronate, 40 mg orally/day, was effective in reducing bone pain in 11 of 12 patients with bone metastases due to prostate carcinoma but who were not confined to bed. In some patients with prostate carcinoma and a diffuse metastatic invasion of the skeleton, there is indirect biochemical and histologic evidence of osteomalacia. This can be aggravated by bisphosphonate administration because of the transient striking prevalence of osteoblastic activity over bone resorption, which also occasionally causes the appearance of symptomatic hypocalcemia. Therefore, the use of large oral supplements of calcium is recommended, particularly at the start of therapy. It is conceivable that these calcium supplements also may be able to improve the final clinical outcome of the bisphosphonate therapy. In conclusion, administration of large doses of bisphosphonates is one of the most cost-effective palliation treatments for patients with prostate carcinoma with bone metastases, both as first-line therapy and in the long term. With appropriate doses, a large proportion of patients can be maintained free of bone pain until death. Studies of the ability of lower doses to prevent skeletal morbidity in patients without metastases or with asymptomatic bone lesions are warranted.

Vitamin C supplementation and fear-reduction in Japanese quail: short-term cumulative effects.

1. Fear-related behaviour was measured in individually-housed Japanese quail which had received either untreated drinking water (UDW) or a vitamin C solution (ascorbyl-2-polyphosphate, APP, 1 g L-ascorbic acid/1 for 1 or 4 d. Behavioural tests were carried out at 24 or 27 d of age. Water consumption was measured daily and plasma ascorbic acid (AA) content was assayed after differential treatment for 1 or 4 d. 2. The quail in the APP treatment groups drank significantly more than did those receiving untreated drinking water. 3. Supplementation with APP raised plasma AA concentrations substantially above those found in UDW quail. The lower AA concentrations found after APP treatment for 4 d rather than one may have reflected either inter-assay variation or limited intestinal absorption following excess ingestion. 4. Quail treated with APP showed less home-cage avoidance of a novel object and shorter tonic immobility fear reactions than did the UDW birds. The UDW quail showed remarkably similar avoidance and TI scores on test days 1 and 4. Conversely, continued treatment with APP further reduced avoidance scores but, although TI durations fell slightly with continued treatment there were no significant day effects. 5. It was concluded that APP supplementation can reduce underlying fearfulness but that it may not be necessary to continue treatment for longer than 24 h immediately prior to a known frightening event.

Differential pulse polarographic assay procedure and in vitro biopharmaceutical properties of dipotassium clorazepate.

A differential pulse polarographic (DPP) assay was developed to measure the stability kinetics of dipotassium clorazepate at 37°C in various aqueous buffers and in whole blood, and to characterize its transfer across the everted intestinal sac preparation. Employing a differential extraction procedure along with DPP, it was possible to quantify dipotassium clorazepate and desmethyldiazepam, its major degradation product, and qualitatively identify a minor degradation product, 2-amino-5-chlorobenzophenone. The in vitro stability data indicate that the rate of degradation decreases with an increase in pH, with relatively instantaneous breakdown below pH 4 and relative stability at pH 7.4. Permeability across the everted sac preparation at pH 1.5 reflects instantaneous degradation and transfer of the degradation product, desmethyldiazepam. At pH 7.4, negligible desmethyldiazepam is formed and transferred across the sac preparation. In addition, the permeability profile of intact dipotassium clorazepate suggests a potential for permeability rate limited intestinal absorption. Overall, the data suggest that if dipotassium clorazepate is administered so that it bypasses the more favorable acidic pH environment for biodegradation, one should anticipate variable absorption, physiological disposition, and clinical profiles as a function of route of administration and dosage form.

Comparison of Ampicillin and Hetacillin Pharmacokinetics in Man

The pharmacokinetics of oral and intravenous doses of ampicillin were studied when ampicillin was given directly and as its inactive precursor, hetacillin. The two compounds were assayed separately in plasma using an electrophoresis-bioautography method. Plasma concentration and urinary excretion rates of ampicillin after direct intravenous injection and after hetacillin administration were computer fitted using a two-compartment open model. Hetacillin hydrolyzed rapidly and completely to ampicillin with an in vito half-life of 11 ± 2min. in eight human subjects. No differences were found in the distribution rate and volume constants, elimination rates and clearance parameters, and urinary recovery of ampicillin when it was given either as intravenous ampicillin or intravenous hetacillin. The major effect of intravenous hetacillin is that early plasma, urine, and peripheral compartment levels of ampicillin resemble those from a rapid absorption process, with a peak plasma concentration found at about 0.5hr. Limited bioavailability studies in eight fasting subjects showed 32% absorption from ampicillin capsules, while 38 and 42% absorption values from hetacillin capsules were found in four fasting and four nonfasting subjects, respectively. The primary rationale for clinical use of ampicillin precursors is, in general, the improvement of the limited intestinal absorption of the antibiotic as well as increasing the stability of ampicillin in aqueous solutions.

Phenolsulfonphthalein (PSP) in Assessment of Renal Function

Since the first report 1 of the rapid excretion of phenolsulfonphthalein (PSP) or phenol red by the kidney, PSP has been used widely to assess renal function, without serious mishap. 2 Use of the intravenous route and earlier measurement of excretion (starting at 15 minutes) have enhanced the value of the test. The mechanism of tubular excretion of PSP has been reviewed. 3 Its maximal excretory rate in man is about 36 mg/min/1.73 sq m; 50% to 60% is extracted by the kidney in one circulation, and clearance averages 400 ml/min. 4 Glomerular filtration is small compared with the amount secreted by active tubular transport. Ordinarily about 2% to 3% is excreted into the bile and limited intestinal absorption occurs. 5 Binding to albumin in vivo appears much less than the 80% suggested by studies in vitro, and some PSP appears to enter cells other than kidney, liver, and intestine.