A Phase 1, Open-Label, Pharmacokinetic Trial to Investigate Possible Drug-Drug Interactions Between Clobazam, Stiripentol, or Valproate and Cannabidiol in Healthy Subjects

GW Pharmaceuticals' formulation of highly purified cannabidiol oral solution is approved in the United States for seizures associated with Lennox-Gastaut and Dravet syndromes in patients aged ≥2 years, for which clobazam, stiripentol, and valproate are commonly used antiepileptic drugs. This open-label, fixed-sequence, drug-drug interaction, healthy volunteer trial investigated the impact of cannabidiol on steady-state pharmacokinetics of clobazam (and N-desmethylclobazam), stiripentol, and valproate; the reciprocal effect of clobazam, stiripentol, and valproate on cannabidiol and its major metabolites (7-hydroxy-cannabidiol [7-OH-CBD] and 7-carboxy-cannabidiol [7-COOH-CBD]); and cannabidiol safety and tolerability when coadministered with each antiepileptic drug. Concomitant cannabidiol had little effect on clobazam exposure (maximum concentration [Cmax ] and area under the concentration-time curve [AUC], 1.2-fold), N-desmethylclobazam exposure increased (Cmax and AUC, 3.4-fold), stiripentol exposure increased slightly (Cmax , 1.3-fold; AUC, 1.6-fold), while no clinically relevant effect on valproate exposure was observed. Concomitant clobazam with cannabidiol increased 7-OH-CBD exposure (Cmax , 1.7-fold; AUC, 1.5-fold), without notable 7-COOH-CBD or cannabidiol increases. Stiripentol decreased 7-OH-CBD exposure by 29% and 7-COOH-CBD exposure by 13%. There was no effect of valproate on cannabidiol or its metabolites. Cannabidiol was moderately well tolerated, with similar incidences of adverse events reported when coadministered with clobazam, stiripentol, or valproate. There were no deaths, serious adverse events, pregnancies, or other clinically significant safety findings.

Adipogenic effects of piperlonguminine in 3T3-L1 cells and plasma concentrations of several amide constituents from Piper chaba extracts after treatment of mice

In our previous study, piperlonguminine from the fruit of Piper chaba was reported to promote adipogenesis in 3T3-L1 cells like the peroxisome proliferator-activated receptor-γ (PPARγ) agonist, troglitazone. In the present study, the mode of action of piperlonguminine in cells was examined. Piperlonguminine increased mRNA levels of adiponectin, glucose transporter 4, and fatty acid-binding protein (aP2). It also increased mRNA levels of PPARγ2 but, unlike troglitazone, piperlonguminine did not activate PPARγ directly in a nuclear receptor cofactor assay. Analyses of plasma from mice treated with piperlonguminine, piperine, and retrofractamide A, and an extract of the fruit, showed that concentrations of piperlonguminine were higher than those of piperine and retrofractamide A, and that the "area-under-the-curve" of piperine increased following in vivo administration of the extract.

LC analysis and pharmacokinetic study of synthetic piperlonguminine in rat plasma after oral administration

Only one kind of synthesized alkaloid, piperlonguminine, was used to understand the interference of the other alkaloids in pharmacokinetic study using HPLC/UV in rat plasma after oral administration. Compared with the previous report, it was clarified that mixed alkaloids such as piperine and the other extract from Piper longum Linn did not interfere with the results.

Simultaneous UFLC-ESI-MS/MS determination of piperine and piperlonguminine in rat plasma after oral administration of alkaloids from Piper longum L.: application to pharmacokinetic studies in rats

The alkaloids from Piper longum L. showed protective effects on Parkinson's disease models in our previous study and piperine and piperlonguminine were the two main constituents in the alkaloids. The present study aimed at developing a rapid, sensitive, and accurate UFLC-ESI-MS/MS method and validating it for the simultaneous determination of piperine and piperlonguminine in rat plasma using terfenadine as the internal standard. The analytes and internal standard (IS) were extracted from rat plasma using a simple protein precipitation by adding methanol/acetonitrile (1:1, v/v). A Phenomenex Gemini 3 u C18 column (20 mm × 2.00 mm, 3 μm) was used to separate the analytes and IS using a gradient mode system with a mobile phase consisting of water with 0.1% formic acid (mobile phase A) and acetonitrile with 0.1% formic acid (mobile phase B) at a flow rate of 0.4 mL/min and an operating column temperature of 25°C. The total analytical run time was 4 min. The detection was performed using the positive ion electrospray ionization (ESI) in multiple reaction monitoring (MRM) mode with transitions at m/z 286.1-201.1 for piperine, m/z 274.0-201.1 for piperlonguminine, and m/z 472.4-436.4 for the IS. The calibration curves were both linear (r>0.995) over a concentration range of 1.0 to 1000 ng/mL; the lower limit of quantification (LLOQ) was 1.0 ng/mL for both piperine and piperlonguminine. The intra-day and inter-day precisions (RSD %) were <12.1%, accuracies ranged from 86.6 to 120%, and recoveries ranged from 90.4 to 108%. The analytes were proven stable in the short-term, long-term, and after three freeze-thaw cycles. The method was successfully applied to pharmacokinetic studies of piperine and piperlonguminine in rats after oral administration of alkaloids from P. longum L.

Determination of the active metabolite of prulifloxacin in human plasma by liquid chromatography-tandem mass spectrometry

A liquid chromatographic-tandem mass spectrometric method (LC-MS/MS) for the determination of ulifloxacin, the active metabolite of prulifloxacin, in human plasma is described. After sample preparation by protein precipitation with methanol, ulifloxacin and ofloxacin (internal standard) were chromatographically separated on a C(18) column using a mobile phase consisting of methanol, water and formic acid (70:30:0.2, v/v/v) at a flow rate of 0.5 ml/min and then were detected using MS/MS by monitoring their precursor-to-product ion transitions, m/z 350-->m/z 248 for ulifloxacin and m/z 362-->m/z 261 for ofloxacin, in selected reaction monitoring (SRM) mode. Positive electrospray ionization was used for the ionization process. The linear range was 0.025-5.0 microg/ml for ulifloxacin with a lower limit of quantitation of 0.025 microg/ml. Within- and between-run precision was less than 6.6 and 7.8%, respectively, and accuracy was within 2.0%. The recovery ranged from 92.1 to 98.2% at the concentrations of 0.025, 0.50 and 5.0 microg/ml. Compared with the reported LC method, the present LC-MS/MS method can directly determine the ulifloxacin in human plasma without any need of derivatization. The present method has been successfully used for the pharmacokinetic studies of a prulifloxacin formulation product after oral administration to healthy volunteers.

Short-term safety and pharmacodynamics of amdoxovir in HIV-infected patients

OBJECTIVES

To evaluate the pharmacodynamics and safety of escalating doses of amdoxovir (DAPD) monotherapy administered to treatment-naive and experienced HIV-1-infected patients over 15 days.

DESIGN

Ninety patients with plasma HIV-1 RNA levels between 5000 and 250,000 copies/ml were randomized to DAPD 25, 100, 200, 300 or 500 mg twice daily or 600 mg once daily monotherapy [antiretroviral therapy (ART)-naive and ART-experienced] or to add DAPD 300 or 500 mg twice daily to existing ART. After 15 days of dosing, patients were followed for an additional 7 days.

METHODS

Antiviral activity was compared between treatment arms using log10 HIV-1 RNA based on average area under the curve minus baseline to day 15. Safety and tolerability was analyzed by incidence of grade 1 to 4 clinical and laboratory adverse events.

RESULTS

In ART-naive patients receiving short-term DAPD monotherapy, a median reduction in plasma HIV-1 RNA of 1.5 log10 copies/ml at the highest doses was observed. In ART-experienced patients, the reduction in viral load observed at each dose was less than that observed in treatment-naive patients (reduction of 0.7 log10 at 500 mg twice daily). The incidence of adverse events was similar across groups with the majority of adverse events reported as mild or moderate in severity. Steady-state plasma concentrations of DAPD and dioxolane guanosine followed linear kinetics.

CONCLUSIONS

DAPD was well tolerated and produced antiviral activity in treatment-naive and in some treatment-experienced patients. In ART-experienced patients, the antiviral activity was significant in those with no thymidine-analogue mutations and higher baseline CD4+ cell counts.

Penetration of Orally Administered Prulifloxacin Into Human Lung Tissue

OBJECTIVE

To evaluate the distribution in lung tissue of ulifloxacin, the active metabolite of prulifloxacin, a new once-daily fluoroquinolone administered orally in a single 600mg dose.

DESIGN

Open-label, randomised study.

PATIENTS

Twenty-seven patients (25 males, 2 females; mean age 65.7 years [range 49-79 years]) with a lung neoplasm requiring lobectomy or pneumonectomy.

METHODS

Patients were randomly assigned to five treatment groups and received a single oral dose of prulifloxacin 600mg at 2, 4, 6, 12 or 24 hours preoperatively. During surgery, blood and healthy lung (based on macroscopic appearance) samples were collected at the same time. Ulifloxacin concentrations in plasma and lung tissue were determined by a validated reversed-phase high-performance liquid chromatography assay. Lung tissue ulifloxacin concentrations were adjusted for blood contamination, by measuring haemoglobin in the supernatant of each tissue sample and applying a corrective equation.

RESULTS

Ulifloxacin concentration in lung tissue exceeded plasma concentration at every timepoint. Following administration of prulifloxacin 600mg, the overall mean corrected lung/plasma ratio over the 24-hour period was 6.9 (range 1.2-14.1). When sampling intervals were assessed, the corrected lung/plasma ratios were 7.5 (2 hours after dosing), 6.3 (4 hours), 4.3 (6 hours), 7.0 (12 hours) and 9.2 (24 hours). The mean corrected lung/plasma area under the concentration-time curve ratio was 6.3, demonstrating the ability of the drug to penetrate lung tissue and confirming the high exposure of this target tissue to ulifloxacin. However, the limitation of the lung tissue sampling method and the high interpatient variability should be considered. Over the 24-hour period, the concentrations of ulifloxacin in lung tissue were higher than the minimum inhibitory concentration (MIC) values for pathogens frequently involved in community-acquired respiratory tract infections.

CONCLUSION

Lung tissue penetration data may have a supportive value when considered jointly with MICs and efficacy results. The findings from this lung penetration study could explain the efficacy of once-daily prulifloxacin 600mg observed in clinical trials conducted in patients with exacerbation of chronic bronchitis.

Enzymatic assay for measurement of intracellular DXG triphosphate concentrations in peripheral blood mononuclear cells from human immunodeficiency virus type 1-infected patients

DXG ([2R-cis]-2-amino-1,9-dihydro-9-[2-[hydroxymethyl]-1,3-dioxolan-4-yl]-6H-purin-6-one) and its prodrug DAPD ([2R-cis]-4-[2,6-diamino-9H-purin-9-yl]-1,3-dioxolane-2-methanol; amdoxovir) are novel 2',3'-dideoxynucleosides (ddNs) displaying activity against human immunodeficiency virus type 1 (HIV-1). In this paper, we describe the development of an enzymatic assay for determining the intracellular active metabolite of DXG and DAPD, DXG triphosphate (DXGTP), in peripheral blood mononuclear cells (PBMCs) from HIV-infected patients. The assay involves inhibition of HIV reverse transcriptase (RT), which normally incorporates radiolabeled deoxynucleoside triphosphates (dNTPs) into a synthetic template primer. DXGTP (0.6 pmol) inhibited control product formation with or without a preincubation step. Inhibition was greatest when the template primer was most diluted. DAPDTP inhibited control product formation only at very high levels (50 pmol) and when a preincubation procedure was used. However, reduced template primer stability in assays using preincubation steps, coupled with potential interference by DAPDTP, led to the current assay method for DXGTP being performed without preincubation. Standard DXGTP inhibition curves were constructed. The presence of PBMC extracts or endogenous dGTP did not interfere with the DXGTP assay. Intracellular DXGTP and dGTP concentrations were determined in PBMCs from HIV-infected patients receiving oral DAPD (500 mg b.i.d.). Peak concentrations of DXGTP were obtained 8 h after dosing and were measurable through 48 h postdose. Levels of endogenous dGTP were also determined over 48 h. No direct relationship was observed between concentrations of DXGTP and dGTP. Quantification of DXGTP concentrations in PBMCs from patients receiving a clinically relevant dose of DAPD is possible with this enzymatic assay.

Nutmeg (myristicin) poisoning--report on a fatal case and a series of cases recorded by a poison information centre

In literature, cases of nutmeg abuse have been described repeatedly, but only one fatal case of poisoning was reported [1]. In the present case, myristicin (4 microg/ml) was detected for the first time in the postmortal serum of a 55-year-old woman. Identification was achieved with the aid of UV-VIS spectroscopy and TLC; for quantification, HPLC was used. Because also flunitrazepam (0.072 microg/ml) was found, death had probably been due to the combined toxic effect of both substances. From 1996 to 1998, in a series of cases, seven poisonings with nutmeg were recorded by the Erfurt Poison Information Centre. Even where higher doses (20-80 g of powder) had been ingested, a life-threatening situation was never observed. In one of these cases, a myristicin blood level of 2 microg/ml was measured 8h after ingestion of two to three tablespoonful of nutmeg powder (approx. 14-21 g, or 280-420 mg/kg).

Pharmacokinetics of (-)-beta-D-dioxolane guanine and prodrug (-)-beta-D-2,6-diaminopurine dioxolane in rats and monkeys

(-)-beta-D-Dioxolane guanine (DXG) is a nucleoside analog possessing potent activity against human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2), and hepatitis B virus (HBV) in vitro. Owing to the limited aqueous solubility of DXG, (-)-beta-D-2,6-diaminopurine dioxolane (DAPD), a more water-soluble prodrug of DXG, is being developed for clinical use. The purpose of this study was to characterize the pharmacokinetics of DXG after administration of DXG and DAPD to rats and monkeys. After intravenous administration of DXG, plasma concentrations of the nucleoside declined in a biexponential manner, with a terminal-phase half-life of 0.44 +/- 0.14 hr (mean +/- SD) in rats and 2.3 hr in monkeys. Total clearance of DXG was 4.28 +/- 0.99 liters/hr/kg in rats and 0.72 liters/hr/kg in monkeys. Renal excretion of unchanged DXG accounted for approximately 50% of total clearance in both species. Steady state volume of distribution of DXG was 2.30 liters/kg in rats and 1.19 liters/kg in monkeys. After intravenous administration of DAPD to rats, prodrug concentrations declined with a half-life of 0.37 +/- 0.11 hr. DXG was rapidly generated from DAPD, with approximately 61% of the dose of DAPD being converted to DXG. After administration of DAPD to monkeys, only concentrations of metabolite DXG could be determined owing to rapid conversion of DAPD to DXG during sample collection. The half-lives of DAPD and DXG after intravenous administration determined from urinary excretion data were 0.8 +/- 0.4 and 1.6 +/- 0.2 hr, respectively. Oral bioavailability of DAPD was estimated to be approximately 30%.

Effect of stiripentol dose on phenytoin-induced teratogenesis in a mouse model

PURPOSE

Previous studies have suggested that polytherapy by design may aid in the management of human pregnancies complicated by epilepsy. However, mechanistic parallels must be drawn between the models of teratogenesis and human pregnancies, and doses of the second agent given to minimize side-effects must be justified. This study sought to determine the lowest dosage of stiripentol (STP) protective against phenytoin-induced teratogenesis in a mouse model, and to determine mechanistically if inhibition of oxidative metabolism by STP in vitro decreased production of reactive phenytoin (PHT) metabolites.

METHODS

Pregnant SWV mice were assigned to control or treatment groups of STP alone, PHT alone, or PHT with ascending doses of STP coadministration. Treatments continued from Day 6 to Day 18 of gestation when fetuses were examined for developmental anomalies. [14C]PHT was incubated in mouse liver microsomes with and without NADPH and in the presence or absence of STP or piperonyl butoxide. Covalent binding of [14C] was measured.

RESULTS

There were no dose-related differences in the frequency of fetal malformations per litter among groups treated with STP alone. However, STP (all doses) reduced the frequency of PHT-induced malformations. Covalent binding of [14C]PHT was NADPH-dependent and was inhibited by either piperonyl butoxide or STP.

CONCLUSIONS

The beneficial effects of STP occurred at concentrations below the therapeutic range for its anticonvulsant effects. These results support the concept of polytherapy by design to reduce the risk of teratogenesis associated with PHT.

Application of solid-phase extraction in the method development for determination of SEPA, an acronym for soft enhancement of percutaneous absorption, in human, rat, and rabbit serum using GC-FID method

A new nonaqueous topical minoxidil formulation containing SEPA (2-n-nonyl-1,3-dioxolane) for enhancement of percutaneous absorption was under evaluation. SEPA does not have chromophore for either ultraviolet or fluorescence detection using liquid chromatography and has no functional groups for derivatization. Therefore, a direct gas-chromatographic method with flame-ionization detection (GC-FID) was developed. Owing to the limited detection response of the FID detection, it needs a selective and concentrated extract for GC-FID analysis to improve the assay sensitivity to meet the requirement for pharmacokinetic evaluation after topical application. In addition, SEPA is a very volatile compound. Any extraction procedures involving evaporation will result in a poor recovery. The application of solid-phase extraction (SPE) makes it possible to achieve a selective and a 10-fold concentrated extract with an absolute extraction recovery of approximately 90%, which greatly improved the assay sensitivity. This method involved the extraction of SEPA and the internal standard (2-n-heptyl-1,3-dioxolane) from serum (0.1-1 ml) with 100 microliter of hexane-chloroform (1:1, v:v) using a 50 mg 1.0 ml-1 phenyl SPE column (Varian, Harbor City, CA, USA), followed by direct GC-FID analysis on a fused-silica column chemically bonded with cross-linked methyl silicone gum phase (Hewlett Packard Ultra-1, 12 m x 0.2 mm x 0.33 micron, Avondale, PA, USA). The assay demonstrated a lower limit of quantitation of 2.5 ng ml-1 and a linear range of 2.5 to 250 ng ml-1 with intra- and inter-assay precision and accuracy of < or = 10%.

Quantitative analysis quantitation of 2-n-nonyl-1,3-dioxolane by stable-isotope dilution gas chromatography-mass spectrometry

We report here a quantitative methodology developed for determination of SEPA (2-n-nonyl-1,3-dioxolane) in human serum. The method employed solid-phase extraction of SEPA and internal standard, [13C2]SEPA, from serum followed by gas chromatography-mass spectrometry analysis using EI monitoring m/z 73 and 75. We have investigated the utility of stable isotope dilution gas chromatography-mass spectrometry (GC-MS) for the determination of SEPA concentrations in serum using chemical ionization (positive ion, CI) or electron ionization (EI). The comparison of the specificity and sensitivity between EI and CI indicated that monitoring the m/z 73 ion in EI was superior to monitoring either MH+ or m/z 73 using CI. The method was simple, sensitive and accurate, demonstrating a lower limit of quantitation (LLOQ) of 0.25 ng/ml and intra- and inter-assay accuracy and precision of < or = 7.5%.

Biotransformation and pharmacokinetics of prodrug 9-(beta-D-1,3-dioxolan-4-yl)-2-aminopurine and its antiviral metabolite 9-(beta-D-1,3-dioxolan-4-yl)guanine in mice

9-(beta-D-1,3-Dioxolan-4-yl)guanine (DXG) exhibits potent antiviral activity against human immunodeficiency virus type 1 (HIV-1) and hepatitis B virus (HBV) in vitro. However, since DXG possesses limited aqueous solubility, a more water soluble prodrug of DXG, 9-(beta-D-1,3-dioxolan-4-yl)-2-aminopurine (APD), was synthesized. The purpose of this study was to characterize the pharmacokinetics of APD and its antiviral metabolite DXG in mice. Female NIH-Swiss mice were administered 100 mg/kg APD intravenously or orally. Serum, brain and liver were collected at selected times following prodrug administration and concentrations of APD and DXG were determined by HPLC. APD was efficiently converted to parent nucleoside DXG following both intravenous and oral administration. Biotransformation of APD to DXG likely occurs in the liver and is mediated by xanthine oxidase. Similar pharmacokinetic profiles for DXG were observed following either route of administration in serum, liver and brain. These results demonstrate that APD appears to be a promising prodrug for the delivery of DXG.

High-performance liquid chromatographic determination of (-)-beta-D-2-aminopurine dioxolane and (-)-beta-D-2-amino-6-chloropurine dioxolane, and their metabolite (-)-beta-D-dioxolane guanine in monkey serum, urine and cerebrospinal fluid

(-)-beta-D-2-Aminopurine dioxolane (APD), (-)-beta-D-2-amino-6-chloropurine dioxolane (ACPD) and dioxolane guanine (DXG) are nucleoside analogues possessing potent activity against human immunodeficiency virus (HIV) and hepatitis B virus (HBV) in vitro. APD and ACPD are metabolized in vivo to yield DXG. Reversed-phase HPLC analytical methodologies were developed for the simultaneous determination of APD and DXG, and for ACPD and DXG in monkey serum, urine and cerebrospinal fluid (CSF). 2-Fluoro-2',3'-dideoxyinosine (FDDI) served as the internal standard. The extraction recoveries of the nucleoside analogues from serum samples were similar, averaging approximately 90%. The limit of quantitation of the analytical method for serum samples was 0.1 microg/ml for DXG, and 0.25 microg/ml for APD and ACPD. The intra- and inter-day relative standard deviations for each compound at low, medium and high nucleoside concentrations were less than 9.0%. The accuracy of the assay methods was greater than 90% for prodrugs and parent compound. Similar results were observed with urine and CSF samples. Thus, these methods provide sensitive, accurate and reproducible determination of the prodrugs and parent nucleoside in biological samples.

Pharmacokinetics of prulifloxacin. 1st communication: absorption, distribution and excretion in rats, dogs and monkeys after a single administration

The pharmacokinetics of prulifloxacin ((+/-)-6-fluoro-1-methyl-7-[4-(5-methyl-2-oxo-1,3-dioxolen-4-yl) methyl-1-piperazinyl]-4-oxo-4H-[1,3]thiazeto[3,2-a]quinoline-3-car boxylic acid. CAS 123447-62-1, NM441), a quinolone antibacterial prodrug, was investigated after i.v. (14C-NM394, CAS 112984-60-8) or oral (14C-NM441) administration to rats, dogs and monkeys. 1. 14C-NM441 was absorbed mainly from the upper small intestine and then metabolized to NM394 partly in the intestinal membrane but mainly in the portal blood and liver. Thus NM441 was not detected in the systemic circulation. 2. After i.v. administration of 14C-NM394 (5 mg/kg), the plasma concentration of radioactivity decreased biexponentially, and the elimination half-life in rats, dogs and monkeys was 4.2, 5.8 and 7.0 h, respectively. After oral administration of 14C-NM441 (20 mg/kg), the plasma concentration of radioactivity reached a maximum at 0.7-3.3 h, and thereafter decreased as observed after i.v. administration of 14C-NM394. An effect of food on the absorption of NM441 was found. No clear sex-related differences were observed in the plasma concentration profiles of rats. 3. The concentration of radioactivity in most tissues of rats reached a maximum within 1 h after oral administration of 14C-NM441 and thereafter decreased along with the plasma concentration. At 0.5 h, the radioactivity concentrations were highest in the liver and kidney, moderately high in the spleen, pancreas, lung and mandibular gland and extremely low in the cerebrum and cerebellum. 4. The radioactivity in the excreta collected over a 96-h period was 96-98% of the oral dose (urine, 22-32%; feces, 64-75%) in rats, dogs and monkeys, 35% of the radioactivity administered was excreted in the bile of rats during a 48-h period after oral administration, and only a small portion of the biliary radioactivity was reabsorbed. 5. The proportion of 14C-NM394 that bound to serum proteins in vitro in rats, dogs, monkeys and humans was 41-59% in a concentration range of 0.1-10 micrograms/ml.

Preclinical pharmacokinetics of beta-L-dioxolane-cytidine, a novel anticancer agent, in rats

PURPOSE

beta-L-Dioxolane-cytidine (OddC), a novel L-nucleoside analog with potent cytotoxicity in vitro, appears to be a promising candidate for anticancer therapy. In this study, a high performance liquid chromatography (HPLC) analytical method was developed and the preclinical pharmacokinetics of OddC were characterized in rats.

METHODS

Adult male Sprague Dawley rats were given 10, 25, or 50 mg/kg of OddC both intravenously and orally with a 6-day washout period between doses. Each rat received one dosage level of OddC and the route of administration was assessed by a randomized crossover design. Plasma and urine concentrations were determined by HPLC. Pharmacokinetic parameters were generated by area-moment analysis.

RESULTS

Following intravenous administration, the plasma concentrations of OddC declined rapidly in a biexponential manner with a terminal phase half-life of 1.65 +/- 1.12 h (mean +/- SD). Mean total, renal, and nonrenal clearances were 1.38 +/- 0.62, 0.30 +/- 0.14, and 1.08 +/- 0.59 1/h per kg. Approximately 22% of the administered dose was excreted unchanged in the urine. Thus, nonrenal clearance was the predominant route of elimination of OddC. The steady-state volume of distribution averaged 1.42 +/- 0.66 1/kg, indicating intracellular distribution of OddC. The nucleoside analog was slowly absorbed after oral administration and bioavailability varied greatly between individual rats, averaging 41 +/- 27% when calculated from urinary excretion data and 37 +/- 25% when calculated from plasma OddC concentration data.

CONCLUSION

The pharmacokinetics of OddC in rats were linear over the dose range studied.

Effect of stiripentol on carbamazepine plasma concentration and metabolism in epileptic children

OBJECTIVE

To study the relationship between the plasma concentration of stiripentol (STP), a new antiepileptic drug, and its inhibitory effect on the formation of carbamazepine epoxide (CBZE) in epileptic children treated with carbamazepine (CBZ) either alone or in combination with another antiepileptic drug.

METHODS

Minimum plasma concentration of antiepileptic drugs was measured before initiation of STP therapy (day 0) and on days 28 (STP 60 mg.kg-1.day-1) and 84 (STP 90 mg.kg-1.day-1) by HPLC.

RESULTS

The CBZE/CBZ plasma concentration ratio decreased exponentially with increasing minimum plasma STP concentration (r = 0.80). The asymptote of the curve allowed the calculation of the minimum plasma STP concentration required to obtain the maximum inhibitory effect, i.e. 6.7 mg.l-1.

CONCLUSION

The inhibitory effect of STP on CBZ metabolism expressed as the CBZE/CBZ plasma concentration ratio is dependent on STP plasma concentration, with a maximum effect at an average of 7 mg.l-1. The present data suggest that in order to evaluate the anticonvulsant efficacy of STP as add-on therapy, the minimum plasma STP concentration should be maintained above 7 mg.l-1 and the dosage of CBZ should simultaneously be decreased in steps by more than 50% to minimize the change in CBZ plasma concentration.

High-performance liquid chromatographic determination of (-)-beta-D-2,6-diaminopurine dioxolane and its metabolite, dioxolane guanosine, using ultraviolet and on-line radiochemical detection

(-)-beta-D-2,6-Diaminopurine dioxolane (DAPD) and its metabolite dioxolane guanosine (DXG) have potent activity against hepatitis B virus and HIV, in vitro. A reversed-phase HPLC analytical method using UV and on-line radiochemical detection for the determination of DAPD and DXG in monkey serum and urine is described in this report. Retention times for DXG, DAPD and internal standard (2',3'-didehydro-2'deoxythymidine, D4T) were 5.0, 6.0 and 13.0 min, respectively. The extraction recovery was greater than 97% for DAPD and 94% for DXG. The limit of quantitation for UV detection was 100 ng/ml and 125 ng/ml for DXG and DAPD in monkey serum. The standard curves were linear from 0.1 microgram/ml to 5 micrograms/ml for DXG and 0.125 microgram/ml to 5 micrograms/ml for DAPD. For radiochemical detection, calibration curves of standard solutions of DAPD and DXG were linear in the range of 3500 Bq to 32,000 Bq and 7500 Bq to 60,000 Bq. The intra- and inter-day relative standard deviations were less than 7.2% using UV and less than 8.6% using on-line radiochemical detection. The HPLC method was applied to serum and urine samples collected from a male rhesus monkey that was administered 33.3 mg/kg DAPD with 200 microCi of [3H]DAPD intravenously.

Disposition of stiripentol in the pregnant and non-pregnant female rat

1. The disposition of stiripentol labelled with 14C and 3H on two positions has been studied in the pregnant and non-pregnant female rat after p.o. administration of a 200 mg/kg dose. 2. For both labelled species radioactivity was eliminated mainly in the faeces (69% within 72 h). Urinary excretion was rather low (22% within 72 h). No significant difference was found between the disposition of the two labelled species. 3. For both labelled species concentrations of radioactivity reached a plateau in the plasma and tissues between 1 and 6 h after administration. The liver, fat, mammary gland and adrenal gland were the most extensively-labelled organs. The affinity for the mammary gland was significantly greater in pregnant rats and for the adrenal gland was significantly greater in the non-pregnant rats. The fact that the concentration in the placenta was higher than in the foetus demonstrated that this membrane acts as a barrier for the penetration of the drug in the amniotic fluid. 4. Chromatographic analysis of the faeces and urine showed that an important portion of the dose remained unabsorbed through the gastrointestinal tract. The absorbed fraction undergoes an extensive first-pass metabolism involving mainly the oxidative cleavage of the methylenedioxy ring. Comparison with the results of other work conducted on the non-pregnant rat demonstrated that pregnancy did not affect the disposition and metabolic process.

Phenytoin and/or stiripentol in pregnancy: infant monkey hyperexcitability

A monkey (Macaca fascicularis) model was used to assess infant hyperexcitability after prenatal exposure to phenytoin (PHT, n = 4), stiripentol (STP, n = 5), or PHT + STP (n = 4). Adult female monkeys were equipped with tether systems and stomach catheters so that drug administration could start 1 month before mating and could be continued throughout gestation. During pregnancy, PHT and STP plasma levels were maintained between 4-12 and 4-10 micrograms/ml respectively (for both monotherapy and polytherapy). Infants were separated from mothers at birth and transferred to the University of Washington's (Seattle) Infant Primate Research Laboratory (IPRL) for postnatal care and testing. Data on a hyperexcitability scale were obtained during cognitive testing for visual and cross-modal recognition memory in 13 infant monkeys when they were between 2 weeks and 3 months of age. The data indicated that infants prenatally exposed to PHT, whether alone or in combination with STP, were at increased risk for hyperexcitability (screeching, refusing to attend to stimuli, lack of visual orientation). This was not true of infants prenatally exposed to STP monotherapy (drug group differences, p < 0.05).

In vitro and in vivo investigations of dihydropyridine-based chemical delivery systems for anticonvulsants

A dihydropyridine-based chemical delivery system (CDS), intended to improve drug delivery to the brain, was investigated with a series of analogues of the anticonvulsant striripentol. In vitro experiments demonstrated that the rates of hydrolysis of the corresponding pyridinium conjugates were influenced markedly by small changes in the structure of the drug moiety to be released. Thus, allylic esters were hydrolyzed rapidly to drug in all aqueous media, while the analogous saturated esters and an allylic amide derivative were almost totally stable. The mechanism of hydrolysis, which is particular to this series of CDS conjugates, appeared to occur via ionization to a resonance-stabilized carbocation intermediate. The same CDS compounds were investigated in vivo and compared to the corresponding drugs after intravenous administration. Only those CDS compounds that were found to hydrolyze in vitro released appreciable amounts of drug in vivo. Prolonged release of the drug from the CDS in the brain could be demonstrated for these compounds, but the gain in the ratio of brain-to-plasma AUC when the CDS was administered depended on the innate distribution characteristics of the drug. Thus, the drug D3, which had a high brain-to-plasma AUC ratio, did not show an improvement in this ratio when administered as CDS3. In contrast, stiripentol with a poor brain-to-plasma AUC ratio showed a two- to threefold increase in this ratio when administered as a CDS. These investigations highlight the need for a thorough understanding of the mechanism of drug release and the importance of the pharmacokinetic properties of the drug in designing a carrier system for delivery of drugs to the brain.

Carbamazepine plus stiripentol: is polytherapy by design possible?

To test the idea that the combination of carbamazepine (CBZ) plus stiripentol (STP) is synergistic, an alumina-gel monkey model (N = 4) was used to compare polytherapy electroencephalographic (EEG) effects to those of CBZ monotherapy. The research design included five consecutive phases (2-3 weeks each): baseline, CBZ, CBZ + STP, CBZ, and postdrug baseline. Both drugs were administered in suspension through a chronic gastric catheter every 4 h (to minimize plasma level oscillations). Doses of CBZ were adjusted to maintain CBZ concentration at the same level in the drug periods (except during the initial polytherapy phase, where levels were allowed to increase prior to adjustment). Phased-reversed interictal spikes were manually counted (expressed as a rate per minute). Relative to baseline, CBZ (Cmin = 0.59; Cmax = 2.36 micrograms/ml) increased interictal EEG spikes by an average of 42%. Relative to CBZ monotherapy, the addition of STP (Cmin = 12.02; Cmax = 13.21 micrograms/ml) was associated with an average decrease in spike rate of 39%. This effect was reversible since removal of STP was associated with an increase in spike rate of 66%. The CBZ-epoxide/CBZ ratio decreased from 0.29 to 0.06 when STP was added and increased to 0.30 when STP was removed. The data fit a pharmacodynamic interpretation and suggest that in the case of CBZ + STP the benefits may outweigh the usual disadvantages of polytherapy.

Stiripentol in acute/chronic efficacy tests in monkey model

Acute and chronic efficacy tests of stiripentol (4,4-dimethyl-1-[3,4-(methylenedioxy)-phenyl]-1-penten-3-ol) were conducted in alumina-gel rhesus monkeys. In the acute study (n = 6), discrete serial seizures precipitated by 150 mg/kg of 4-deoxypyridoxine hydrochloride were challenged by intravenous administration of stiripentol and the data compared with those obtained with valproate similarly tested in other monkeys (reported here) and with those from four other standard anticonvulsants (phenytoin, carbamazepine, phenobarbital, and diazepam--data published previously). In the acute challenge (Study 1), stiripentol performed comparably to valproate by delaying the onset of seizures but not eliminating them as did the other four drugs. In two separate chronic studies (at different doses, n = 6 each), stiripentol was given every 4 h by gastric catheter for 4 weeks, preceded and followed by 4 weeks of baseline. In these studies, stiripentol significantly reduced EEG interictal spike rates at mean plasma concentrations from 20 to 27 micrograms/ml in Study 2 and 11 to 14 micrograms/ml in Study 3. From these results, and those evinced in other studies, it appears that stiripentol should be evaluated for absence epilepsy and possible synergistic effects in polytherapy.

Stiripentol kinetics in epilepsy: nonlinearity and interactions

Stiripentol kinetics during oral therapy were assessed in six patients with epilepsy who were receiving other antiepileptic drugs. Steady-state levels at 600, 1200, and 2400 mg/day increased in a nonlinear fashion, indicating Michaelis-Menten kinetics. Oral clearance of stiripentol at 600 mg/day was 41.5 +/- 23.4 l/day/kg (mean +/- SD), greater than that at 1200 mg/day (20.3 +/- 8.8 l/day/kg; P less than 0.05) or 2400 mg/day (8.5 +/- 3.8 l/day/kg; P less than 0.01). The apparent in vivo Michaelis-Menten parameters were determined from three mean steady-state concentrations. The average velocity of conversion of stiripentol to its metabolites (Vm), Michaelis constant (Km), and the ratio Vm/Km were 49.3 +/- 13.1 mg/day/kg, 1.35 +/- 1.08 mg/l, and 50.2 +/- 27.5 l/day/kg. Stiripentol reduced the elimination clearances of concomitant antiepileptic drugs. Phenytoin clearance was reduced in all five subjects who received this drug, from a mean control of 29.5 +/- 13.4 l/day to 18.5 +/- 4.6 l/day at a stiripentol dose of 1200 mg/day (P = 0.05) and to 6.48 +/- 2.59 l/day at 2400 mg/day (P less than 0.01). Stiripentol reduced the clearance of carbamazepine in one subject from a control value of 209 l/day to 128 l/day (1200 mg/day) and 61 l/day (2400 mg/day). Stiripentol reduced phenobarbital clearance in two subjects from 3.8 and 5.1 l/day to 2.3 and 3.4 l/day (2400 mg/day). The Michaelis-Menten kinetics of stiripentol, as well as its interactions with other antiepileptic drugs, have important implications in the designing of controlled clinical trials.

Pharmacokinetics of stiripentol in normal man: evidence of nonlinearity

The pharmacokinetics and metabolism of stiripentol, a new antiepileptic drug, were investigated in normal male subjects after single-dose and multiple-dose administration. Each of six subjects received single doses of 300, 600, and 1200 mg of stiripentol in powder form and another 600 mg in solution. In the multiple-dose study, each of six subjects received a 300-mg dose on day 1 and multiple doses (1200 mg/day) from day 2 to day 8. Five of these six subjects participated also in the single-dose study. Stiripentol and several of its metabolites, namely, stiripentol conjugate, DiOH, P-OH, and M-OH, were analyzed in plasma and urine. After single doses, the elimination curve of stiripentol appeared multiphasic. The oral clearance was 1.3 to 1.8 liter/hr/kg. The average mean residence time was 4 hours. There were no statistically significant differences in clearance or mean residence time among the three doses. However, dose dependence was found in all the four pathways when formation clearances were compared. Only trace amounts of the drug were excreted unchanged in urine. The active metabolite, P-OH, was not detectable in plasma. Stiripentol was very highly bound to plasma proteins in plasma from dosed subjects as well as spiked human plasma (free fraction of 1 per cent). In the multiple-dose study, there was a decrease (nearly eightfold) in oral clearance of stiripentol between day 1 and day 8. The fractions of dose metabolized through conjugation and methylenedioxy ring opening increased 183 and 49 per cent, respectively, but the formation clearances for all the pathways were decreased. These findings suggest that the steady-state plasma level/dose ratio of stiripentol will increase with the daily dose.

[Pharmacokinetic study of 3H-stiripentol in rats (author's transl)]

The radioactive constituents of blood, urine, and bile specimens from Wistar Rats, following intravenous administration of 3H-stiripentol were analyzed, in parallel with samples of: liver, lung, kidneys, testis, heart, brain, cerebellum, and medulla. These investigations yielded the following results: 3H-Stiripentol was quantitatively and rapidly absorbed and metabolized by Wistar rats, due to intense metabolism in the liver. The cerebellum and medulla accumulated radioactivity, which was probably related to the pharmacological effects of this drug.

Influence of probenecid on serum levels and urinary excretion of cinoxacin

Serum levels and urinary excretion of cinoxacin were examined in healthy individuals after a two-step intravenous infusion in the presence and absence of probenecid. After dosing cinoxacin alone, steady-state serum levels were approached in 1 h and were maintained for an additional 2 h with a reduced infusion rate. After probenecid pretreatment, serum levels of cinoxacin continued to increase during 3 h of infusion, reaching levels approximately double those obtained with cinoxacin alone. The mean elimination half-life of cinoxacin from serum was increased from 1.3 to 3.5 h in the presence of probenecid, and renal clearance was significantly reduced, with 46% of dosed drug appearing in 7-h urines of probenecid-treated subjects compared with 68% in subjects receiving cinoxacin alone. Probenecid had no apparent influence on cinoxacin distribution in the body but caused a significant decrease in the rate of cinoxacin extrarenal elimination, possibly due to competition for a common metabolic pathway.

Cinoxacin: pharmacokinetics and the effect of probenecid

Cinoxacin is a new synthetic organic antibacterial compound which has a serum half-life of approximately 1 hour. Most of the drug is eliminated in man by the kidney, primarily as unchanged drug. The renal clearance of cinoxacin is slightly greater than the usually accepted value for the average glomerular filtration rate, which suggests that it is probably filtered and is also secreted by the tubule. Results after pretreatment with probenecid further suggest secretion of the drug.