Preliminary Pharmacokinetic Study Research Articles

Sensitive Determination of Felodipine in Human and Dog Plasma by Use of Liquid–Liquid Extraction and LC–ESI–MS–MS

A sensitive and selective liquid chromatographic method coupled with electrospray ionization tandem mass spectrometry (LC–ESI–MS–MS) has been developed for quantification of felodipine in human and dog plasma. Compounds were separated on a 2.0 mm × 150 mm, 5.0 μm particle, C8 column with 1 m m ammonium acetate–acetonitrile, 20:80, pH 6.0, as mobile phase at a flow rate of 200 μL min−1. Nifedipine was used as internal standard. Plasma samples were extracted with diethyl ether, the centrifuged upper layer was evaporated, the residue was reconstituted with mobile phase, and the reconstituted samples were injected. The analytical column lasted for at least 1000 injections. By use of multiple reaction monitoring (MRM) mode in MS–MS felodipine and nifedipine were detected without severe interference from the human or dog plasma matrix. Felodipine produced a protonated precursor ion ([M + H]+) at m/z 384 and a corresponding product ion at m/z 338. And internal standard (nifedipine) produced a protonated precursor ion ([M + H]+) at m/z 347 and a corresponding product ion at m/z 315. Detection of felodipine in human and dog plasma was accurate and precise, with a limit of quantification of 0.05 ng mL−1. The method has been successfully applied to preliminary pharmacokinetic study of felodipine in human and dog plasma.

16α-Bromo-epiandrosterone therapy modulates experimental feline immunodeficiency virus viremia: initial enhancement leading to long-term suppression

16α-Bromo-epiandrosterone (epiBr), a synthetic derivative of the natural hormone dehyroepiandrosterone (DHEA), was evaluated for its effects on feline immunodeficiency virus (FIV) infection in experimental cats. The rationale for this study was based on the ability of DHEA to significantly reduce the mortality to viral infections in mice. DHEA and epiBr also have demonstrable in vitro anti-viral activity for both HIV-1 and FIV. Preliminary pharmacokinetic studies in cats demonstrated that subcutaneously injected epiBr was rapidly absorbed, completely metabolized, and nontoxic. Metabolites were excreted in both urine and feces, with the latter having the most complex pattern of breakdown products. Cats were then divided into four groups; two groups were infected with FIV and two uninfected. Two groups, one infected and one uninfected were treated on 5 consecutive days of weeks 0, 4, 8, 12 and 16 with epiBr. The remaining two groups were mock treated with the drug vehicle alone. Treatment started 1 week prior to infection and extended for 4 weeks after infection. Cats were observed for 20 weeks post-FIV infection. Infected cats had identical decreases in blood neutrophil and lymphocyte counts following, regardless of whether they were treated with epiBr or vehicle alone. The CD4/CD8 T-cell ratio was decreased following FIV exposure, but was significantly more decreased for the epiBr treated animals from week 2 post-infection onward. CD4+ T cells were decreased in FIV-infected cats treated with epiBr compared to their untreated cohort, while CD8+ T cells tended to be higher in treated animals. FIV infected cats that were treated with epiBr had over one-log higher virus loads at week 2 post-infection than non-epiBr treated cohorts. In spite of this enhanced initial viremia, the subsequent levels of virus in the blood were significantly lower in epiBr treated versus untreated animals. EpiBr treated cats had significantly higher FIV-p24 antibody responses than control cats receiving vehicle alone, although primary and secondary antibody responses to a T-cell dependent non-FIV antigen, keyhole limpet hemocyanin (KLH), were unaffected. EpiBr treatment significantly decreased the expected FIV-induced suppression of IL-12 p40 mRNA levels in peripheral blood mononuclear cells (PBMCs) observed at weeks 4, 5, 8, 9 and 16 post-infection, but had no influence on FIV-induced changes in IL-4, IL-6, IL-10, IFN-γ, MIP-1α and RANTES.

Measurement of piperaquine in plasma by liquid chromatography with ultraviolet absorbance detection

Piperaquine (PQ) is an antimalarial drug enjoying a resurgence of use in combination with an artemisinin derivative because of parasite resistance to standard treatments. Its pharmacokinetic properties have not been characterised. An assay for PQ in plasma was developed using solvent extraction and liquid chromatographic separation on a Waters XTerra™ RP 18 column, with a mobile phase of 7% acetonitrile in water (containing 0.025% trifluoroacetic acid, 0.1% NaCl and 0.008% triethylamine) and UV detection at 340 nm. The assay was linear up to 1000 μg/l. Intra- and inter-day relative standard deviations were <10% (5–500 μg/l) and <21% (5–500 μg/l), respectively. Inter-day limits of quantitation and detection were 5 μg/l and 3 μg/l, respectively. A preliminary pharmacokinetic study in a patient who received 2.56 g of PQ phosphate orally with dihydroartemisinin as four doses over 32 h found an apparent steady-state volume of distribution of 447 l/kg, an apparent oral clearance 0.93 l/h/kg and a terminal half-life of 17.3 days.

Effects of N-acetyl-L-cysteine and glutathione on antioxidant status of human serum and 3T3 fibroblasts.

The effectiveness of several sulfhydryl compounds in the treatment of paraquat intoxication has been previously tested based on their antioxidant ability. However, practical guidelines for their clinical use remain to be determined. As a preliminary pharmacokinetic study on sulfhydryl compounds, we attempted to establish the optimal concentration of N-acetyl-L-cysteine, glutathione, superoxide dismutase, and catalase. We measured the antioxidant effect of these antioxidants in normal pooled plasma and on intracellular reactive oxygen species (ROS) induced by paraquat. N-acetyl-L-cysteine begins to suppress the production of ROS in plasma at concentrations as low as 5 mM, with the suppression being maximal at 40 mM. In the same way, glutathione increased the total antioxidant status in plasma at concentrations of 5-40 mM in a dose-dependent manner. Complete suppression of ROS in plasma induced by exposure to 500 micro M paraquat for 40 min was observed when using 40 mM N-acetyl-L-cysteine and 5 mM glutathione. These concentrations are comparable with 50 units of catalase, which reduced ROS at concentrations of 5-100 units. Further pharmacokinetic study into the systemic administration of these antioxidants is necessary, using effective concentrations of 5-40 mM for both N-acetyl-L-cysteine and glutathione, and 1-50 units of catalase.

Preliminary Pharmacokinetic Study of Different Preparations of Acyclovir with β-Cyclodextrin

Acyclovir has absorption problems, because of its low solubility and/or its saturable absorption mechanism, that take place in the small intestine in a passive, variable, and incomplete manner. The oral bioavailability of acyclovir is thereby affected and reaches only 15-30%. The purpose of this study was to investigate the possibility of increasing the oral availability of acyclovir by forming inclusion complexes of acyclovir with beta-cyclodextrin. Acyclovir, its complex (1:1) with beta-cyclodextrin (acyclovir-beta-cyclodextrin complex), and a 50:50 mixture of acyclovir and the inclusion complex (acyclovir/complex mixture) as an aqueous suspension were administered intraintestinally to male Sprague-Dawley rats in doses equivalent to an acyclovir dose of 75 mg/kg. Sequential samples of plasma were taken by microdialysis. The samples were analyzed by high-performance liquid chromatography with ultraviolet detection. Plasma concentration versus time curves show that the complex and the mixture of acyclovir/complex have a higher bioavailability and a pharmacokinetic profile than that of the drug itself.

P-glycoprotein-mediated efflux of antiepileptic drugs: preliminary studies in mdr1a knockout mice

Evidence suggests that the efflux transporter P-glycoprotein (P-gp) may play a facilitatory role in refractory epilepsy by limiting the brain access of antiepileptic drugs (AEDs). We have conducted a preliminary pharmacokinetic study of seven commonly used AEDs in mdr1a knockout mice, devoid of P-gp at the blood–brain barrier. A parallel group of matched wild-type mice served as controls. AEDs were administered by subcutaneous injection and serum and brain drug concentrations determined at 30, 60, and 240 min post-dosing. The brain–serum concentration ratio for topiramate was higher in mdr1a(−/−) mice than in wild-type controls at all time points investigated. No consistent effects were observed with any other AED investigated. These findings suggest that topiramate may be a substrate for P-gp-mediated transport. Further studies employing a range of model systems are required to substantiate this observation and to address the potential role of drug transporters in refractory epilepsy.

Poly(DL-lactide-co-glycolide) microporous microsphere-based depot formulation of a peptide-like antineoplastic agent

In the present investigation, a poly(DL-co-glycolide) (PLGA)-based, microspheric depot system for bleomycin (BLM) has been formulated, and the same has been evaluated in-vivo in C57BL/6J mice bearing transplantable melanoma B16F1 murine solid tumour. The microparticulate delivery systems were formulated employing a water-in-oil-in-water (W/O/W) emulsion-solvent evaporation technique and characterized in-vitro. The microspheres were injected subcutaneously to form a drug depot at the site of injection in mice bearing experimental tumours and the drug was continuously infused into the systemic circulation with progressive biodegradation. The drug-loaded microspheres exhibited improved pharmacodynamic efficacy, as evidenced by retarded tumour growth kinetics. Preliminary pharmacokinetic studies illustrated controlled release of the drug into the systemic circulation over the study period to exert an anti-neoplastic action. These studies demonstrated the feasibility of employing a PLGA-based microparticulate system as an effective biodegradable, injectable, depot-forming therapeutic system for long-term administration of anti-neoplastic agents.

Piperine in food: Interference in the pharmacokinetics of phenytoin

This study was carried out to explore the effect of piperine-containing food in altering the pharmacokinetics of phenytoin, an anti-epileptic drug with a narrow therapeutic index. A preliminary pharmacokinetic study was carried out in mice by administering phenytoin (10 mg) orally, with or without piperine (0.6 mg). Subsequently, oral pharmacokinetics of phenytoin was carried out in six healthy volunteers in a crossover design. Phenytoin tablet (300 mg) was given 30 minutes after ingestion of a soup (melahu rasam) with or without black pepper. A further study of intavenous pharmacokinetics of phenytoin (1 mg) in rats with or without oral pretreatment with piperine (10 mg) was also conducted. The phenytoin concentration in the serum was analyzed by HPLC. The study showed a significant increase in the kinetic estimates of Ka, AUC(0-10) and AUC(0-infinity) in the piperine-fed mice. Similarly, in human volunteers piperine increased Ka, AUC(0-48), AUC(0-infinity), and delayed elimination of phenytoin. Intravenous phenytoin in the oral piperine-treated rat group showed a significant alteration in the elimination phase indicating its metabolic blockade. The significance of this finding in epileptic patients maintained on phenytoin therapy requires further investigation. This study may also have implications in the case of other drugs having a low therapeutic index.

A preliminary pharmacokinetic study of docetaxel, carboplatin and concurrent radiotherapy for regionally advanced squamous cell carcinoma of the head and neck

This work investigates the pharmacokinetics and toxicity resulting from the concomitant use of low dose carboplatin (CBCA)/docetaxel (DTX) plus concurrent radiotherapy in patients with head and neck cancer. The study comprised 11 patients with stage III–IV head and neck cancer. All patients received 2 Gy radiotherapy daily, 5 fractions per week, up to a planned total of 70 Gy over 7 weeks. CBCA (AUC 0.4 mg/ml, min/day) was also administrated as 20 min i.v. infusion, starting 1 day before the first radiotherapy fraction. CBCA was administered for 5 consecutive days every 2 weeks (weeks 1, 3, 5 and 7). DTX 30 mg/m 2 (1 h i.v. infusion) was given as a single dose on days 10, 24 and 38. CBCA on day 1 and DTX on day 10 were analysed to determine the concentration–time curves during the first 24 h. CBCA C max and C min in 2–5 days and on day 15 and 29, as well as total plasma platinum on days 2, 3, 4, 5, 29 and 43 were also assayed. By calculating the non-compartmental pharmacokinetic parameters of the two drugs from the available plasma concentrations we found in the first week values similar to those reported in the literature as single agents. In contrast, during subsequent weeks (weeks 3 and 5), a significant and progressive increase of platinum levels was observed. So, it could be assumed that after 2 weeks of CBCA and DTX treatment a bias in dose calculation occurred because the linear relationship between creatinine clearance (used to calculate the expected AUC through the Calvert formula) and CBCA clearance was no longer observed.

High-performance liquid chromatographic assays for a second-generation novel oral iron chelator (APCP363) and their application to pharmacokinetic studies in rats

Sensitive and specific HPLC assays for APCP363 in biological matrices (rat plasma, urine and feces) were developed. The recovery of APCP363 ranged from 81.2 to 99.9% in plasma, from 82.1 to 92.8% in urine, and from 65 to 68% in feces. Standard deviations were below 10% for all analyses. The limits of quantitation were 0.1, 10 and 30 μg/ml in plasma, urine and feces, respectively. The HPLC assays, which are the first reports for APCP363 analysis in biological matrices, have been successfully applied to preliminary pharmacokinetic studies in rats. The stool assay is the first non-radiolabeled method for hydroxypyridinones in feces.

COMPARATIVE ANTI-NOCICEPTIVE, ANTI-INFLAMMATORY AND TOXICITY PROFILE OF NIMESULIDE vs NIMESULIDE AND PIPERINE COMBINATION

Piperine is an inhibitor of various hepatic and other enzymes involved in the biotransformation of drugs. Preliminary pharmacokinetic studies conducted by us suggested the increased bioavailability of nimesulide co-administered with piperine. The present study was, thus, conducted to evaluate the antinociceptive, anti-inflammatory and toxicity profile of a new nimesulide–piperine combination administered orally as compared with nimesulide alone. Antinociceptive efficacy was tested using an acetic acid writhing test and tail flick latency test (TFL). The ED50 value of a nimesulide–piperine combination in writhing test was calculated to be significantly lower (1.5 mg kg−1) as compared to (11.2 mg kg−1) of nimesulide alone. The antinociceptive effect was lesser in the tail flick latency test as compared to what was observed in the writhing test indicating the peripheral action of the Non-Steriodal Anti-Inflammatory Drug (NSAID). In carrageenan-induced inflammatory tests, the nimesulide–piperine combination was found to be dose-to-dose superior than nimesulide alone. Acute toxicity studies on mice revealed a reduction in lethal dose (LD50) of the combination (980 mg kg−1) as compared to nimesulide (1500 mg kg−1) alone. Results from the present study suggest a better therapeutic index for the nimesulide–piperine combination indicating that this combination would further reduce the frequency of adverse effects associated with nimesulide alone.

Pyrroloquinoxaline derivatives as high-affinity and selective 5-HT(3) receptor agonists: synthesis, further structure-activity relationships, and biological studies.

The synthesis, pharmacological evaluation, and structure-activity relationships (SARs) of a series of novel pyrroloquinoxalines and heteroaromatic-related derivatives are described. The new pyrroloquinoxaline-related ligands were tested in rat cortex, a tissue expressing high density of 5-HT(3) receptors, and on NG108-15 cells and exhibited IC(50) values in the low nanomolar or subnanomolar range, as measured by the inhibition of [(3)H]zacopride binding. The SAR studies detailed herein delineated a number of structural features required for improving affinity. Some of the ligands were employed as "molecular yardsticks" to probe the spatial dimensions of the lipophilic pockets L1, L2, and L3 in the 5-HT(3) receptor cleft, while the 7-OH pyrroloquinoxaline analogue was designed to investigate hydrogen bonding with a putative receptor site H1 possibly interacting with the serotonin hydroxy group. The most active pyrroloquinoxaline derivatives showed subnanomolar affinity for the 5-HT(3) receptor. In functional studies ([(14)C]guanidinium accumulation test in NG108-15 hybrid cells, in vitro) most of the tested compounds showed clear-cut 5-HT(3) agonist properties, while some others were found to be partial agonists. Several heteroaromatic systems, bearing N-substituted piperazine moieties, have been explored with respect to 5-HT(3) affinity, and novel structural leads for the development of potent and selective central 5-HT(3) receptor agonists have been identified. Preliminary pharmacokinetic studies indicate that these compounds easily cross the blood-brain barrier (BBB) after systemic administration with a brain/plasma ratio between 2 and 20, unless they bear a highly hydrophilic group on the piperazine ring. None of the tested compounds showed in vivo anxiolytic-like activity, but potential analgesic-like properties have been possibly disclosed for this new class of 5-HT(3) receptor agonists.

Liposomal nystatin against experimental pulmonary aspergillosis in persistently neutropenic rabbits: efficacy, safety and non-compartmental pharmacokinetics.

The activity of liposomal nystatin against invasive pulmonary aspergillosis was investigated in persistently neutropenic rabbits. Treatment groups included liposomal nystatin at dosages of 1, 2 and 4 mg/kg/day intravenously, or amphotericin B deoxycholate 1 mg/kg/day administered intravenously after normal saline loading. As compared with untreated controls, liposomal nystatin administered at 2 and 4 mg/kg/day prolonged survival and reduced fungus-mediated tissue injury and excess lung weight at post-mortem in a similar manner to amphotericin B. Although amphotericin B was superior in clearing infected lung tissue, treatment with all regimens of liposomal nystatin led to a significant reduction in pulmonary fungal tissue burden. During treatment, ultrafast CT-scan demonstrated ongoing resolution of pulmonary lesions at 2 and 4 mg/kg/day, but not at 1 mg/kg/day. With the exception of mild increases in blood urea nitrogen (BUN) and serum creatinine values during treatment at 2 and 4 mg/kg/day, which were similar to those found in amphotericin B-treated rabbits, liposomal nystatin was well tolerated. Preliminary pharmacokinetic studies in non-infected animals established linear drug disposition of liposomal nystatin in plasma over the investigated dosage range and peak plasma levels above the MIC for the test strain after multiple daily dosing for 7 days. Liposomal nystatin increased survival and provided reduced tissue injury, effective microbiological clearance and tolerable side effects in experimental pulmonary aspergillosis in persistently neutropenic rabbits, thus providing a rational basis for further investigations in clinical trials.

Preparation, purification, and characterization of a reversibly lipidized desmopressin with potentiated anti-diuretic activity.

. To prepare and characterize a reversibly lipidized dipalmitoyl desmopressin (DPP), and to compare its anti-diuretic efficacy and biodistribution with that of unmodified desmopressin (DDAVP). Dithiothreitol (DTT) was used to reduce the intramolecular disulfide bond in DDAVP, and the reduced DDAVP was treated with a thiopyridine-containing disulfide lipidization reagent, Pal-CPD. The product, DPP, was purified by acid precipitation and, subsequently, by size-exclusion chromatography. Reversed-phase HPLC was used to analyze the purity and to evaluate the hydrophobicity of the product. Mass spectrometry was employed to characterize its molecular structure. The biological activity of DPP was demonstrated by the antidiuretic effects in vasopressin-deficient Brattleboro rats. Preliminary pharmacokinetic and biodistribution studies of intravenously injected DDAVP and DPP were carried out in CF-1 mice. DDAVP was readily reduced by a 2-fold molar excess of DTT at 37 degrees C for 0.5 hr. DPP was formed by the reaction of reduced DDAVP with Pal-CPD. Each DPP molecule contains two palmitic acid moieties, which link to the peptide via two disulfide bonds. After acid precipitation and size-exclusion chromatography, the purity was found to be approximately 95%, and the overall yield was 57%. When DPP was administered subcutaneously to Brattleboro rats, the potency of the anti-diuretic activity of DDAVP was enhanced to more than 250-fold. The plasma concentration of intravenously injected DDAVP in mice decreased rapidly during the first 20 min and followed by a slow elimination rate. However, in DPP administered mice, the plasma concentration actually increased in the first 20 min, followed by a slow elimination with a rate similar to that in DDAVP-injected mice. The regeneration of DDAVP was detected in the plasma of mice treated with DPP. Studies of the organ distribution in mice indicated that the liver retention of DPP was longer than that of DDAVP. On the other hand, the intestinal excretion of DPP was significantly less than that of DDAVP. The 250-fold increase of the anti-diuretic potency in DPP is most likely due to a slow elimination and prolonged tissue retention, together with the regeneration of active DDAVP, in the animals. Our results indicate that reversible lipidization is a simple and effective approach for improving the efficacy of many peptide drugs.

HIGH PRESSURE LIQUID CHROMATOGRAPHIC DETERMINATION OF NITRENDIPINE IN HUMAN PLASMA AFTER SOLID PHASE EXTRACTION

A rapid and sensitive Reversed-Phase High Pressure Liquid Chromatographic (RP-HPLC) method has been developed for the quantitative determination of nitrendipine in human plasma. A Hypersil C18 150×4.6 mm, 5 μm analytical column was used with a mixture of CH3CN-H2O at a volume ratio 50:50 v/v. Detection was performed with a variable wavelength UV-VIS detector at 238 nm. The detection limit was 0.4 ng/mL. Nimodipine was used as internal standard (IS) at a concentration of 12 ng/mL. The statistical evaluation of the method was examined performing intra-day and inter-day calibration. Nitrendipine was extracted from human plasma matrices by Solid Phase Extraction (SPE) technique instead of conventional liquid-liquid extraction methods. Recovery of nitrendipine in spiked samples was 97.75±5.43. The method was applied to a preliminary pharmacokinetic study in which an oral dose of 20 mg of nitrendipine was given to eight healthy volunteers.

High-performance liquid chromatographic assay for a new fasciolicide agent, αBIOF10, in biological fluids

This paper describes a high-performance liquid chromatographic method with ultraviolet absorbance detection at 304 nm for the determination of 6-chloro-5-(1-naphthyloxy)-2-methylthio benzimidazole (αBIOF10) — a new fasciolicide agent — and its sulphoxide (SOαBIOF10), in plasma and urine. It requires 2 ml of biological fluid, an extraction using Sep-Pak cartridges, and methanol for drug elution. Analysis is performed on a μBondapak C 18 (10 μm) column, using methanol–acetonitrile–water (40:30:30, v/v) as the mobile phase. Results showed that the assay is sensitive: 12 ng/ml for αBIOF10 and SOαBIOF10 in plasma and 3.6 ng/ml for both compounds in urine. The response was linear between 0.195 and 12.5 μg/ml. Maximum intra-day coefficient of variation was 5.3%. Recovery obtained was 97.8% for both αBIOF10 and SOαBIOF10. In urine, recovery was 99.6% and 93.1% for αBIOF10 and SOαBIOF10 respectively. The method was used to perform a preliminary pharmacokinetic study in two sheep and was found to be satisfactory.

Determination of pravastatin in human plasma by high-performance liquid chromatography with ultraviolet detection

A sensitive high-performance liquid chromatographic (HPLC) method for the quantitation of the HMG-CoA reductase inhibitor pravastatin in human plasma is described. Sample preparation based on reversed-phase solid-phase extraction using triamcinolone acetonide as internal standard (I.S.). The compounds were separated on C 18 reversed-phase analytical column and then determined by ultraviolet detection. The recovery of pravastatin from plasma was 69.2±6.7% (mean±S.D.). The limit of detection for pravastatin in aqueous solution was 0.4 ng, the limit of quantitation in plasma was 2 ng/ml. In a preliminary pharmacokinetic study with two healthy volunteers the t 1/2 of pravastatin in plasma was found to be 0.8 and 2.3 h.

In vitro characterization of methotrexate loaded poly(lactic-co-glycolic) acid microspheres and antitumor efficacy in Sarcoma-180 mice bearing tumor

Methotrexate (MTX) loaded poly (lactic-co-glycolic) acid (PLGA) microspheres were prepared by emulsion solvent evaporation technique. The mean diameter of the microspheres was affected by the type of emulsion stabilizer, polymer concentration, aqueous and organic phase volume and stirring speed. The in vitro release was triphasic and was dependent on copolymer composition and molecular weight of the polymer. Antitumor efficacy in Sarcoma-180 tumor bearing mice exhibited increased volume doubling time (18 ± 2.7 days) compared to plain subcutaneous injection of methotrexate (8 ± 0.7 days). Preliminary pharmacokinetic studies following subcutaneous administration of MTX loaded PLGA microspheres illustrated the controlled release of the drug. The studies demonstrated the feasibility of employing PLGA as an effective carrier for antineoplastic drug like methotrexate.

Determination of Flavopiridol (L 86 8275) in Rat Serum Using Ion-Pair Reversed-Phase High-Performance Liquid Chromatography

A specific, sensitive, and simple high-performance liquid chromatographic method has been developed for assaying flavopiridol in rat serum for preliminary bioavailability and pharmacokinetic studies. The drug and internal standard were extracted with dichloromethane from serum. After evaporating the solvent, the extract was reconstituted with mobile phase. Chromatography was performed on a 10-μ. Bondapak C18 column (30 cm × 3.9 mm ID), using methanol:water (50:50, v/v) containing 0.05 M ion-pairing reagent PIC B-6 as a mobile phase at a flow rate of 1.1 ml/min, with ultraviolet detection at 278 nm. The drug and internal standard were well resolved from other serum constituents. Due to high sensitivity and reproducibility the method can be adapted very well for assaying flavopiridol in higher animals.

Combined effect of clinically relevant doses of emitefur, a new 5-fluorouracil derivative, and radiation in murine tumours.

We investigated the combined effect of radiation and clinically relevant doses of emitefur (BOF-A2), a newly developed anti-cancer agent consisting of a masked form of 5-fluorouracil (5-FU) and a potent inhibitor of 5-FU degradation, in two types of murine tumours. In preliminary pharmacokinetic studies, the area under the curve for 5-FU in plasma, after administration of 12.5 mg kg-1 and 25 mg kg-1 emitefur in mice, appeared to be similar to that obtained on the first day and that on the seventh day, respectively, after starting administration of 400-600 mg day-1 in humans. These doses (12.5 and 25 mg kg-1) of emitefur were evaluated either alone or in combination with single (15 Gy), five-fraction (4 Gy each) or ten-fraction (2.8 Gy each) irradiation using a tumour growth delay assay for SCCVII tumours and in combination with four-fraction (5 Gy each) irradiation using an in vivo-in vitro assay for EMT6 tumours. The anti-tumour and radiation-enhancing effects of 12.5 mg kg-1 emitefur were not significant in any except the ten-fraction experiment. On the other hand, multiple doses of 25 mg kg-1 emitefur given either alone or in combination with radiation produced marked effects. The mean tumour growth delay time (the time to double in volume for treated tumours minus that for untreated tumours) was 8.1 days for five administrations of 25 mg kg-1 emitefur. 10.4 days for five fractions of 4 Gy and 22.1 days for five treatments with the combination of the two. Thus, the increase in growth delay afforded by this combination was at least additive. The effect of four fractions of 5 Gy with 25 mg kg-1 emitefur in EMT6 tumours was lower than that of four fractions of 7.5 Gy, but the effect of five fractions of 4 Gy with this dose of emitefur in SCCVII tumours was similar to the effect of five fractions of 6 Gy, and the effect of ten fractions of 2.8 Gy with 25 mg kg-1 emitefur was much higher than that of ten fractions of 4.2 Gy. In conclusion, emitefur given either alone or in combination with radiation appears to have a significant anti-tumour effect even at clinically relevant dose levels, although a threshold dose exists between 12.5 and 25 mg kg-1. Further clinical studies of this compound are warranted.