Effects of coadministration of corn oil and ponazuril on serum and cerebrospinal fluid concentrations of ponazuril in horses.

BACKGROUND: Ponazuril is used for the treatment of equine protozoal myeloencephalitis (EPM). Coadministration of ponazuril with oil could result in higher serum and cerebrospinal fluid (CSF) concentrations of ponazuril. HYPOTHESIS: Coadministration of corn oil will result in higher serum and CSF concentrations of ponazuril than when ponazuril is administered alone. ANIMALS: Ten resident university-owned adult horses of either sex and >2 years of age. METHODS: Cohort study. Ponazuril oral paste (5 mg/kg BW; ponazuril treatment group (PON); n = 5), or ponazuril oral paste (5 mg/kg BW; ponazuril and oil treatment group (PONOIL; n = 5) coadministered with 2 oz of corn oil q24h for 21 days. Horses were treated once daily, for 21 days. Blood was collected on days 0, 7, 14, and 21 before dosing. In addition, CSF was collected on days 1, 7, 14, and 21. The concentration of ponazuril was determined in serum and CSF and results compared using repeated measures ANOVA. RESULTS: Coadministration of ponazuril with 2 oz of corn oil resulted in higher concentrations of ponazuril in serum (at steady state) than that found in horses given ponazuril alone (6.2 ± 0.9 mg/L versus 4.5 ± 1.0 mg/L; P = .004) (mean ± 1 SD). Cerebrospinal fluid concentrations of ponazuril were also greater in horses that received ponazuril and oil (0.213 mg/L ± 0.04 versus 0.162 ± 0.04 mg/L) (P = .03). CONCLUSIONS AND CLINICAL IMPORTANCE: Results suggest that coadministration of corn oil with ponazuril might enhance the effectiveness of treatment with ponazuril.

Pharmacokinetics of a low dose and FDA-labeled dose of diclazuril administered orally as a pelleted topdressing in adult horses.

The purpose of this study was to determine the pharmacokinetics of the FDA-approved labeled dose of diclazuril and compare it to a low dose in plasma and CSF in adult horses. During each research period, six healthy adult horses received 0.5 mg/kg of 1.56% diclazuril pellets (Protazil(TM) , Merck Animal Health) compared to the approved labeled dose of 1 mg/kg orally once in two separate phases. A dose of 0.5 mg/kg was calculated to each horse's weight. Blood was then collected immediately before diclazuril administration and then at regular intervals up to a 168 h. After the last blood collection following the single dose at hour 168, a once daily oral dose was administered for the next 10 days to ensure the drug's concentration reached steady-state. To determine the CSF concentration at steady-state, CSF samples were collected after the 9th oral dose. Blood was then collected after the 10th dose and then at regular intervals up to 168 h. A washout period of 4 weeks was allowed before repeating this protocol for the FDA-labeled dose at 1 mg/kg. Plasma and CSF samples were analyzed by high-pressure liquid chromatography. A one-compartment pharmacokinetic model with first-order oral absorption was fitted to the single administration data. Steady-state pharmacokinetics was performed using noncompartmental analysis for steady-state analysis. The mean (standard deviation) concentration of diclazuril in CSF following the low dose was 26 ng/mL (5 ng/mL), while CSF in the FDA-labeled dose was 25 ng/mL (4 ng/mL), P = 0.3750. Substantial accumulation in plasma occurred at steady-state after the 10th dose for both doses. The results of this study show that diclazuril pellets given at the approved label dose and a lower dose both produce similar plasma drug concentrations at steady-state and attain plasma and CSF concentrations known to inhibit Sarcocystis neurona in cell culture.

A double-blind randomized clinical trial in amyotrophic lateral sclerosis using lamotrigine: effects on CSF glutamate, aspartate, branched-chain amino acid levels and clinical parameters.

OBJECTIVES: A study was conducted to examine the effect of lamotrigine (LTG) in amyotrophic lateral sclerosis (ALS). MATERIAL AND METHODS: Patients were entered in a double-blind, placebo-controlled, crossover study. None of the patients were treated with riluzole, which was not approved for treatment of ALS in Sweden when the study started. After randomization, each patient was treated with placebo or LTG 300 mg daily, followed by a washout period and a second treatment period. RESULTS: Thirty patients completed the study and were included in the analysis of the primary outcome, which was measured with clinical scales. The cerebrospinal fluid (CSF) levels of glutamate, aspartate, branched-chain amino acids and LTG were also measured. Changes for glutamate, valine and LTG were found during the progression of the disease. The clinical parameters and the levels of CSF amino acids were similar for the two treatment groups. CONCLUSION: No clinical effect of LTG on ALS progression could be found.

Plasma concentration of topiramate correlates with cerebrospinal fluid concentration.

The authors examined the ratio between the plasma and the cerebrospinal fluid (CSF) concentration of topiramate in 14 adults with epilepsy. Simultaneous trough samples of venous blood and CSF were collected and analyzed as total and unbound concentrations. Concomitant levels were also analyzed of lamotrigine (n = 5) and the relevant oxcarbazepine metabolite, 10-hydroxycarbazepine (n = 3). There was a close correlation between the plasma and the CSF concentration for both the total and unbound concentration of topiramate. The median CSF/plasma ratio of total topiramate was 0.85. The free topiramate concentration in plasma was not different from the free topiramate concentration in CSF. The CSF/plasma ratios showed little variation and were independent of the plasma level for both the total and the unbound levels. The unbound fraction of topiramate was 84% in plasma and 97% in CSF. The CSF concentrations of lamotrigine and 10-hydroxycarbazepine were 50% and 61% of the plasma concentrations, respectively. For topiramate, there is a close correlation between the plasma concentration and the CSF concentration. There does not seem to be a saturable carrier mechanism restricting topiramate transport across the blood-brain barrier. The concentration of topiramate in CSF is equal to the unbound proportion of topiramate in plasma, implying that the delivery of topiramate to the brain occurs via transfer from the unbound plasma pool. Plasma is thus a relevant matrix for therapeutic drug monitoring of topiramate.

Cerebrospinal fluid and serum concentrations of ponazuril in horses.

Ponazuril was administered orally to 10 adult horses at 5 mg/kg body weight, once a day for 28 days. Blood was collected once a week from each horse from Days 0 through 35, daily from Days 35 through 42, and on Day 49. Cerebrospinal fluid (CSF) was also collected once a week from Day 0 through Day 49. Concentrations of ponazuril in the serum and CSF were determined, and pharmacokinetic calculations were performed. Ponazuril was readily absorbed following oral administration; and after 7 days of dosing, the serum concentration was 4.33 +/- 1.10 mg/L, and the mean CSF concentration was 0.162 +/- 0.05 mg/L. Cerebrospinal fluid concentration did not vary during the 28 days of dosing and concentrations declined rapidly after cessation of administration on Day 28. The terminal elimination half-life ofponazuril in serum (using Day 28 to 42 results) was 4.3 +/- 0.6 days. Repeated CSF collections from the atlanto-occipital space did not induce changes in the immunoglobulin G index or albumin quotient. It was concluded that oral administration of ponazuril to healthy horses at 5 mg/kg provided concentrations of ponazuril in the CSF that are presumed to be adequate for the treatment of equine protozoal myeloencephalitis (EPM). These results indicate that this dosage rate should be investigated for efficacy against EPM.

Comparison of serum, cerebrospinal fluid and brain extracellular fluid pharmacokinetics of lamotrigine.

We investigated the rate of penetration into and the intra-relationship between the serum, cerebrospinal fluid (CSF) and regional brain extracellular fluid (bECF) compartments following systemic administration of lamotrigine in rat. The serum pharmacokinetics were biphasic with an initial distribution phase, (half-life approximately 3 h), and then a prolonged elimination phase of over 30 h. The serum pharmacokinetics were linear over the range 10 - 40 mg kg(-1). Using direct sampling of CSF with concomitant serum sampling, the calculated penetration half-time into CSF was 0.42+/-0.15 h. At equilibrium, the CSF to total serum concentration ratio (0.61+/-0.02) was greater than the free to total serum concentration (0.39+/-0.01). Using in vivo recovery corrected microdialysis sampling in frontal cortex and hippocampus with concomitant serum sampling, the calculated penetration half-time of lamotrigine into bECF, 0.51+/-0.11 h, was similar to that for CSF and was not area or dose dependent. At equilibrium, the bECF to total serum concentration ratio (0.40+/-0.04) was similar to the free to total serum concentration (0.39+/-0.01), and did not differ between hippocampus and frontal cortex. The species specific serum kinetics can explain the prolonged action of lamotrigine in rat seizure models. Lamotrigine has a relatively slow penetration into both CSF and bECF compartments compared with antiepileptic drugs used in acute seizures. Furthermore, the free serum drug concentration is not the sole contributor to the CSF compartment, and the CSF concentration is an overestimate of the bECF concentration of lamotrigine.

Analysis of CSF amino acids in young patients with generalised refractory epilepsy during an add-on study with lamotrigine.

The effect of add-on administration of lamotrigine (1-12 mg/kg per day, 2-12 months) on the levels of neurotransmission related amino acids including gamma-aminobutyric acid (GABA), glutamate, aspartate, glycine and antiepileptic drugs (AEDs) in lumbar cerebrospinal fluid (CSF) was studied in 22 children and young adults with generalised therapy resistant epilepsy. Two lumbar punctures were performed, one prior to, and one following a mean of 5 months (2-12 months) of lamotrigine treatment. Lamotrigine decreased seizure incidence and severity in 12 of the 22 patients without influencing CSF GABA, glutamate, aspartate or glycine levels. Lamotrigine did not alter the concentrations of AEDs in CSF or plasma. However, CSF GABA levels were 86% higher in those patients also treated with gamma-vinyl-GABA (vigabatrin, GVG) compared with patients treated with other combinations and this was not altered by co-medication with lamotrigine. The proposed mechanism of action of lamotrigine, namely that it may inhibit glutamate release in the CNS, is not reflected by changes in CSF glutamate levels. The present findings indicate that CSF GABA, glutamate, aspartate and glycine levels may not be useful as in vivo neurochemical markers in young patients responding to the therapeutic dose of lamotrigine used in this study.

Diclazuril in the horse: its identification and detection and preliminary pharmacokinetics.

Diclazuril (4-chlorophenyl [2,6-dichloro-4-(4,5-dihydro-3H-3,5-dioxo-1,2,4-triazin-2-yl)pheny l] acetonitrile), is a benzeneacetonitrile antiprotozoal agent (Janssen Research Compound R 64433) marketed as Clinacox . Diclazuril may have clinical application in the treatment of Equine Protozoal Myeloencephalitis (EPM). To evaluate its bioavailability and preliminary pharmacokinetics in the horse we developed a sensitive quantitative high-pressure liquid chromatography (HPLC) method for diclazuril in equine biological fluids. MS/MS analysis of diclazuril in our HPLC solvent yielded mass spectral data consistent with the presence of diclazuril. After a single oral dose of diclazuril at 2.5 g/450 kg (as 500 g Clinacox), plasma samples from four horses showed good plasma concentrations of diclazuril which peaked at 1.077 +/- 0.174 microg/mL (mean +/- SEM) with an apparent plasma half-life of about 43 h. When this dose of Clinacox was administered daily for 21 days to two horses, mean steady state plasma concentrations of 7-9 microg/mL were attained. Steady-state levels in the CSF ranged between 100 and 250 ng/mL. There was no detectable parent diclazuril in the urine samples of dosed horses by HPLC or by routine postrace thin layer chromatography (TLC). These results show that diclazuril is absorbed after oral administration and attains steady-state concentrations in plasma and CSF. The steady state concentrations attained in CSF are more than sufficient to interfere with Sarcocystis neurona, whose proliferation is reportedly 95% inhibited by concentrations of diclazuril as low as 1 ng/mL. These results are therefore entirely consistent with and support the reported clinical efficacy of diclazuril in the treatment of clinical cases of EPM.

Central nervous system pharmacology of Baker's antifolate (NSC139105) in man.

Radiolabelled Baker's Antifolate (BAF) was administered to 6 patients undergoing surgical resection of intracerebral tumors. Levels of radioactivity in resected tumor and edematous brain adjacent to tumor were generally higher than levels in concurrent plasma samples and were generally comparable to levels in temporalis muscle. Levels in tumor cyst fluid were far lower than concurrent plasma levels and levels in surrounding tumor. Chromatography was performed on tumor from 2 patients and revealed that only a small proportion of the radioactivity represented unchanged BAF. The major metabolite present in tissues was 1 000 times less potent as an inhibitor of dihydrofolate reductase than was BAF. Five patients had cerebrospinal fluid (CSF) sampled following administration of tracer doses of radiolabelled BAF. Radioactivity levels were far lower in CSF than in plasma. Levels of radioactivity in the CSF were also far lower than levels in tumor and brain samples from other patients and were slightly lower than tumor cyst fluid levels. Two patients had CSF collected after they received therapeutic doses of BAF. In these patients, both CSF and plasma were assayed using a dihydrofolate reductase inhibition assay. As with tracer dose studies, CSF concentrations of BAF were substantially lower than were concurrent plasma concentrations. Thus it appears that only very low concentrations of BAF are attainable in human CSF and intracerebral tumor, although a metabolite which is a very weak inhibitor of dihydrofolate reductase attains high concentrations in tumor.

Pharmacology of a new triazine antifolate in mice, rats, dogs, and monkeys.

Triazinate (TZT), a potent inhibitor of dihydrofolate reductase, was selected for detailed investigation to determine its mechanism of selective action as well as its metabolic fate in mice, rats, dogs, and monkeys. The serum disappearance of TZT in normal and tumor-bearing mice was similar, with a rapid tissue equilibration phase and a slower elimination phase. Serum disappearance in normal and tumor-bearing rats was 1.5 to 2.2 hr. Serum disappearance in dogs and monkeys was similar, with half-lives of 3 to 4 and 2 to 4 hr, respectively. Urinary excretion of TZT at 24 hr was only 5 to 6% of the injected dose in mice and rats; in contrast, the dogs excreted 60% of the injected dose in 8 hr. TZT accumulated to comparable degrees in the organs of rats and mice, with progressively lesser concentrations in liver, kidney, spleen, and brain. Dihydrofolate reductase activity became almost undectectable in all tissues studied within 15 min after drug adminsitration. An important difference in drug accumulation was in the ascites cells of tumor-bearing animals: in mice, the drug level was consistently lower in the L1210 cells than in the ascites fluid; in contrast, by 30 min after treatment with TZT the drug level in Walker 256 cells was 10-fold higher than the level in the ascites fluid. No evidence for drug metabolism was found in extracts of urine, feces, or organ tissues from either mice or rats. TZT and two related triazines were studied for their ability to accumulate in the cerbrospinal fluid of dogs after i.v. administration. TZT achieved a cerebrospinal fluid level of approximately 15% of the serum concentration at 1 hr; in contrast, the other two triazines reached maximum cerebrospinal fluid values of 1% at 1 hr.