Coadministration of naproxen and low-dose methotrexate in patients with rheumatoid arthritis

Fifteen patients (30 to 78 years of age) with diagnoses of rheumatoid arthritis were administered oral and intravenous methotrexate (15 mg), alone or with concomitant naproxen (1000 mg/day). Serial blood samples and urine were collected for 24 hours after the dose of methotrexate and were assayed for methotrexate by a specific radioenzymatic method. In twelve patients who completed the study, methotrexate systemic clearance was not statistically different with naproxen (103.3 +/- 35.0 ml/min) versus without naproxen (113.4 +/- 48.3 ml/min; p = 0.37). Oral clearance of methotrexate was not statistically different with naproxen (161.7 +/- 55.0 ml/min) versus without naproxen (176.7 +/- 68.3 ml/min; p = 0.14). Likewise, there was not a significant difference in methotrexate renal clearance or plasma protein binding with or without naproxen. No toxicity was observed when patients received methotrexate alone or with naproxen. This study indicates that concomitant naproxen does not abruptly alter the disposition of low-dose methotrexate in patients with rheumatoid arthritis who have normal renal function.     

A radioreceptor assay for propranolol and 4-hydroxypropranolol

A radioreceptor assay for the measurement of propranolol and 4-hydroxypropranolol levels in plasma is described. Maximum sensitivity for propranolol was 1.2 +/- 0.15 ng/ml and for 4-hydroxypropranolol 4.2 +/- 0.4 ng/ml. Interassay and intra-assay variations for both were under 10%. Modifications in the radioreceptor assay permitted the measurements of total beta-adrenergic blocking activity and the separate contributions of parent drug and metabolite. When 4-hydroxypropranolol was stabilized, a composite level of total beta-adrenergic blocking activity in plasma was obtained. When the 4-hydroxy metabolite was oxidized, only the stable parent drug was detected. The difference in values between measurements made under these conditions was equivalent to the amount of 4-hydroxypropranolol in the sample. The radioreceptor assay was also used to measure the amount of free propranolol and 4-hydroxypropranolol. Under identical experimental conditions, more 4-hydroxypropranolol than propranolol circulated in the free form. These observations establish the feasibility of adapting the radioreceptor assay for propranolol to the measurement of total beta-adrenergic blocking activity and its components in plasma as well as to the measurement of free drug and metabolite levels.     

Distinct Pharmacokinetic Profile and Safety of a Fixed‐Dose Tablet of Sumatriptan and Naproxen Sodium for the Acute Treatment of Migraine

(Headache 2010;50:357‐373) Objective.— To describe the pharmacokinetic and safety profiles of sumatriptan 85 mg formulated with RT Technology (RT) and naproxen sodium 500 mg in a fixed‐dose combination tablet (sumatriptan/naproxen sodium) that targets both serotonergic dysmodulation and inflammation in migraine. Methods.— Six open‐label, crossover studies were conducted in healthy volunteers (Studies 1, 2, 3, 4, 5) or patients with migraine (Study 6). Results.— Consistently across studies, naproxen administered as a component of sumatriptan/naproxen sodium demonstrated a delayed‐release profile similar to that of an enteric‐coated product. Naproxen from the combination tablet showed a delayed time to peak plasma concentration and lower peak plasma concentration while exposures (area under the plasma concentration–time curve) were similar. The peak plasma concentration for naproxen was approximately 36% lower and the time to peak plasma concentration approximately 4 hours later when naproxen was administered as sumatriptan/naproxen sodium compared with a single naproxen sodium 550 mg tablet. Sumatriptan peak plasma concentration and area under the plasma concentration–time curve after administration of sumatriptan/naproxen sodium (containing sumatriptan 85 mg) were comparable to those after administration of a commercially available sumatriptan 100 mg (RT) tablet. Sumatriptan time to peak plasma concentration occurred, on average, 30 minutes earlier with sumatriptan/naproxen sodium compared with sumatriptan 100 mg (RT). No clinically significant differences between sumatriptan/naproxen sodium and sumatriptan tablets 100 mg (RT) were identified with respect to electrocardiograms, blood pressure, or heart rate. In addition, food had no significant effect on the bioavailability of naproxen or sumatriptan after administration of sumatriptan/naproxen sodium but slightly delayed the time to peak plasma concentration of sumatriptan by approximately 40 minutes. The pharmacokinetics of sumatriptan and naproxen did not differ according to whether sumatriptan/naproxen sodium was administered during a migraine attack or a migraine‐free period. The pharmacokinetics of 2 sumatriptan/naproxen sodium tablets administered 2 hours apart were consistent with the pharmacokinetic predictions from a single dose of the combination tablet. The adverse‐event profile of the sumatriptan/naproxen sodium combination tablet did not appear to differ from that of the individual components of the same or similar dosage strengths administered alone or in combination. In addition, the incidence of adverse events with 2 sumatriptan/naproxen sodium tablets administered 2 hours apart was lower than that with the single dose. Conclusion.— The combination tablet of sumatriptan/naproxen sodium has unique pharmacokinetic properties. The rapid absorption of sumatriptan with the delayed‐release properties of naproxen sodium from sumatriptan/naproxen sodium might contribute to its therapeutic advantage over monotherapy with either component. No clinically meaningful effects of food, administration during a migraine attack, or administration of a second tablet (2 hours after initial dose) on the pharmacokinetics or safety of sumatriptan/naproxen sodium were observed.     

Use of High-Pressure Liquid Chromatography to Determine Plasma Levels of Metronidazole and Metabolites After Intravenous Administration

A rapid and sensitive high-pressure liquid chromatography assay for metronidazole and its two principle metabolites, 1-(2-hydroxyethyl-2-hydroxymethyl)-5-nitro-imidazole [hydroxy metabolite] and 1-acetic acid-2-methyl-5-metronidazole [acid metabolite], was developed. The retention times observed were 5.7, 3.3, and 4.5 min, respectively. A reverse-phase muC(18) Bondapak column using a solvent system of methanol, acetonitrile, and 0.005 M pH 4 potassium dihydrogen phosphate (4:3:93, vol/vol) was used to achieve separation of the three compounds. Patients receiving metronidazole therapy were given a loading dose of 13.6 mg of drug per kg intravenously over 1 h, followed by a maintenance dose of 1.43 mg/kg per h. The range of metronidazole concentrations observed was 6.8 to 47.5 mug/ml. These levels are well above the minimal inhibitory concentrations of most clinically significant anaerobic bacteria including Bacteroides fragilis. Little of the acid metabolite was observed in the plasma. The concentration of hydroxy metabolite ranged from 1.6 to 16 mug/ml. The latter may represent an additional source of antimicrobial activity since the hydroxy metabolite has approximately 30% the biological activity of metronidazole.     

Evaluation of the in vivo effect of naproxen on zidovudine pharmacokinetics in patients infected with human immunodeficiency virus.

OBJECTIVE: To determine if therapeutic doses of naproxen affect the in vivo disposition of zidovudine. METHODS: This was designed as a randomized, two-period, two-treatment, crossover study. The patients were 12 men infected with human immunodeficiency virus who had acquired immunodeficiency syndrome (AIDS) or AIDS-related complex. On two separate occasions 14 days apart, patients received either zidovudine alone (200 mg every 4 hours while awake) or zidovudine (200 mg every 4 hours while awake) and naproxen (500 mg every 12 hours for 4 days). On the morning of the fifth day, each patient received the final dose of each regimen and blood and urine were serially collected for 8 hours. Pharmacokinetic parameters (area under the serum concentration-time curve [AUC], maximum plasma concentration, terminal half-life, renal clearance, and urinary recovery) were assessed for zidovudine and its glucuronide metabolite. MAIN RESULTS: Naproxen had no significant effect (< 10% difference between treatment means, p > 0.15, ANOVA) on the above pharmacokinetic parameters for both zidovudine and its metabolite. Although the power of the study to detect these small differences was < 80% at the 5% significance level, differences ranging from 12.6% for AUC to 38.8% for urinary recovery could be detected with 80% power. CONCLUSION: Therapeutic doses of naproxen do not significantly affect the pharmacokinetic disposition of zidovudine.     

Radioligand receptor assay for 25-hydroxyvitamin D2/D3 and 1 alpha, 25-dihydroxyvitamin D2/D3.

A competitive protein binding assay for measurement of the plasma concentration of 1 alpha, 25-dihydroxyvitamin D3 [1alpha, 25-(OH)2D3] has been extended to include the immediate precursor of this hormone, 25-hydroxyvitamin D3 (25-OHD3). In addition, the assay system is capable of measuring the two metabolic products of ergocalciferol, namely. 25-hydroxyvitamin D2 (25-OHD2) and 1alpha, 25-dihydroxyvitamin D2 [1alpha, 25-(OH)2D2]. The target tissue assay system consists of a high affinity cytosol receptor protein that binds the vitamin D metabolites and a limited number of acceptor sites on the nuclear chromatin. By utilizing a series of chromatographic purification steps, a single plasma sample can be assayed for any of the four vitamin D metabolites either individually or combined. Therefore, the assay procedure allows for both the quantitative and qualitative assessment of the total active vitamin D level in a given plasma sample. To show that the binding assay was capable of measuring 1alpha, 25-(OH)2D2 as well as 1alpha, 25 (OH)2D3, two groups of rats were raised. One group, supplemented with vitamin D3, produced assayable material that represented 1alpha, 25-(OH)2D3. The other group, fed only vitamin D2 in the diet, yielded plasma containing only 1alpha, 25-(OH)2D2 as the hormonal form of the vitamin. The circulating concentrations of the two active sterols were nearly identical (15 ng/100 ml) in both groups, indicating that the competitive binding assay can be used to measure both hormonal forms in plasma. In a separate experiment, 1alpha, 25-(OH)2D2 was generated in an in vitro kidney homogenate system using 25-OHD2 as substrate. Comparison of this sterol with 1alpha, 25-(OH)2D3 in the assay system showed very similar binding curves; the D2 form was slightly less efficient (77%). Comparison of the respective 25-hydroxy forms (25-OHD2 vs. 25-OHD3) at concentrations 500-fold that of 1alpha, 25-(OH)2D3, again suggested that the binding of the D2 metabolite was slightly less efficient (71%). Finally, the assay was employed to measure the total active vitamin D metabolite pools in the plasma of normal subjects and patients with varying degrees of hypervitaminosis D. The normal plasma levels of 25-OHD and 1alpha, 25-(OH)2D measured in Tucson adults were 25-40 ng/ml and 2.1-4.5 ng/100 ml, respectively. Both sterols were predominately (greater than 90%) in the form of vitamin D3 metabolites in this environment. Typical cases of hypervitaminosis D exhibited approximately a 15-fold increase in the plasma 25-OHD concentration, and a dramatic changeover to virtually all metabolites existing in the form of D2 vitamins. In contrast, the circulating concentration of 1alpha, 25-(OH)2D was not substantially enhanced in vitamin D-intoxicated patients. We therefore conclude that hypervitaminosis D is not a result of abnormal plasma levels of 1alpha, 25-(OH)2D but may be cuased by an excessive circulating concentration of 25-OHD.     

Nanogram-range determination of plasma imipramine by gas-liquid chromatography using a selective nitrogen/phosphorus detector

A sensitive and specific gas chromatographic method for the quantitative determination of plasma concentrations resulting from a single normal therapeutic dose of imipramine has been developed and is descriged. After extraction into a mixture of n-heptane/isoamyl alcohol (98.5:1.5), imipramine is well separated from its main metabolite, desmethylimipramine, and both compounds are detected using a selective detector operating in the N/P mode. The procedure permits the rapid routine quantitative analysis of relatively small plasma volumes (1-2 ml) containing as little as 1-2 ng of imipramine. No interference from the biological matrix is apparent. The suitability of the method for the analysis of biological samples was tested by studying the time of course of imipramine plasma concentrations in normal human volunteers, after administration of a single therapeutic dose.     

A sensitive fluorescence assay for quantitation of fludarabine and metabolites in biological fluids

Rapid and quantitative dephosphorylation of the new anticancer nucleotide analogue fludarabine phosphate to its nucleoside 9-β-D-arabinofuranosyl-2-fIuoroadenine (F-ara-A) renders this metabolite the target for pharmacologic investigations. At clinically effective doses of fludarabine phosphate (18–30 mg/m² per day) comprehensive pharmacokinetic analysis of F-ara-A has been limited by the sensitivity of UV based HPLC assays. To address this problem we developed a sensitive test based on the condensation of F-ara-A with chloroacetaldehyde to form the fluorescent derivative, arabinosyl-1, N⁶-etheno-isoguanine. Combined with a solid-phase extraction step prior to derivatization and separation of the reaction products by reverse-phase HPLC, this assay had a quantitation limit of 2 pmol F-ara-A per ml plasma. Slightly modified, the system was also applicable to urine specimens, with a quantitation limit of 1 nmol F-ara-A per ml urine.     

Assay of vitamins D2 and D3, and 25-hydroxyvitamins D2 and D3 in human plasma by high-performance liquid chromatography.

I describe a new assay that is capable of measuring vitamin D2, vitamin D3, 25-hydroxyvitamin D2, and 25-hydroxyvitamin D3 in 2 ml of plasma or serum. Plasma is extracted by the Bligh and Dyer technique [Can. J. Biochem. Physiol. 37, 911 (1959)], the lipid component is fractionated by two high-performance liquid-chromatographic systems based upon adsorption and reversed-phase chromatography, and each of the four vitamin D metabolites is measured by its absorbance at 254 nm. The method has a sensitivity limit of 0.5 mug/liter of plasma. The identity of metabolite peaks was confirmed by mass spectrometry, ultraviolet absorption spectrophotometry, and rechromatography, and there was good correlation (r=0.84) between plasma 25-hydroxyvitamin D as measured by the present method and by a protein binding assay developed in our laboratory. Mean concentrations of vitamin D and 25-hydroxyvitamin D in normal adults (n=25) in December were 2.2 +/- 1.1 (SD) and 16 +/- 3.9 (SD) mug/liter, respectively. 25-Hyroxyvitamin D2 made up 31% of the total 25-hydroxyvitamin D. Patients receiving pharmacological doses of vitamin D had values for vitamin D and 25-hydroxyvitamin D that were 10- to 100-fold normal. This method provides a rapid, reliable physico-chemical assay that appears to have advantages over existing protein binding assays and can be used to measure circulating vitamin D.     

Hydrolysis of [Leu]enkephalin by chick plasma in vitro

The in vitro hydrolysis of [Leu]enkephalin added to plasma collected from 2-day-old chicks was studied with two different techniques: thin-layer chromatography separation of intact [3H]-[Leu]enkephalin from its [3H]-Tyr-containing metabolites and high-performance liquid chromatography-electrochemical detection assay of [Leu]enkephalin disappearance and Tyr-containing metabolite accumulation. The radiometric assay evaluated enkephalin hydrolysis at close to presumed physiological concentrations of this peptide, whereas the liquid chromatography assay necessitated 100-fold higher peptide concentrations to achieve adequate sensitivity. Similar results were obtained with both techniques. We found that the in vitro hydrolysis of [Leu]enkephalin is more rapid in chick plasma (half-life, 0.7-1 min) than in rat (half-life, 2-2.5 min) or mouse (half-life, 9-14 min) plasma. Comparison of the rate of enkephalin hydrolysis and pattern of metabolite accumulation in the absence vs. the presence of various peptidase inhibitors suggested that a bestatin-sensitive aminopeptidase, probably aminopeptidase M, is the primary enzyme responsible for the hydrolysis of enkephalin by chick plasma, and that less than 1% of the total hydrolysis of [Leu]-enkephalin by chick plasma is attributable to dipeptidyl carboxy-peptidase activity. This pattern of enzyme activities differs from that which we identified previously in rat and mouse plasma.