Simultaneous determination of the five HIV-protease inhibitors: amprenavir, indinavir, nelfinavir, ritonavir, and saquinavir in human plasma by solid-phase extraction and column liquid chromatography.

A sensitive and selective liquid chromatographic assay has been developed for the determination of the five protease inhibitors currently approved by the Food and Drug Administration (FDA) (amprenavir, indinavir, nelfinavir, ritonavir, and saquinavir) in a single run. Pretreatment of a 1-mL plasma sample spiked with internal standard was made by a solid-phase extraction procedure using a polymeric reversed-phase sorbent. Liquid chromatography was performed using a narrowbore C18 reversed-phase column and gradient elution. A double ultraviolet detection at 265 nm (amprenavir) and at 210 nm (indinavir, nelfinavir, ritonavir, saquinavir and internal standard) was used. Calibration curves were linear in the range 25-10000 ng/mL and the assay has been validated over the range 25-5000 ng/mL. Average accuracy at four concentrations was in the range of 100.5-104.2% and 96.9-100.5% for within-day and between-day, respectively. The coefficients of variation were less than 10%. Mean absolute recoveries varied from 85.4% (ritonavir) to 98.8% (saquinavir). No metabolite of the protease inhibitors was found to coelute with the drugs of interest or with the internal standard. At this time, among the tested drugs, especially all the presently licensed nucleoside and nonnucleoside reverse transcriptase inhibitors that can be used in combination with the protease inhibitors, none was found to interfere with the assay. This method is now in use in the authors' laboratory for the therapeutic monitoring of the HIV-protease inhibitors.

Pharmacokinetic and pharmacodynamic drug interactions between digoxin and macrogol 4000, a laxative polymer, in healthy volunteers.

AIMS: The aim of this study was to examine the bioequivalence between a single oral dose of digoxin administered alone and with a coadministration of macrogol 4000 (a laxative polymer) in 18 healthy volunteers. METHODS: This was an open, randomised, two-way cross-over study, with a single dose oral administration of 0.5 mg digoxin administered alone or in combination with macrogol 4000, 20 g day-1 during 8 days. Pharmacokinetics of digoxin, heart rate and PR ECG interval at rest were assessed. RESULTS: Macrogol 4000 coadministration was associated with a 30% decrease of digoxin AUC and a 40% decrease in its Cmax (P<0.05). Digoxin tmax and t1/2,z were not significantly altered. Heart rate and PR interval did not differ during the two therapeutic sequences, digoxin alone and digoxin in combination. CONCLUSIONS: Macrogol 4000 coadministration interacts with single-dose digoxin pharmacokinetics. This is most likely due to a reduction of the intestinal absorption of digoxin. However, there was no consequence of this interaction on heart rate and AV conduction.

Improved sensitivity of digoxin assay by modification of the EMIT 2000 method.

A modified EMIT 2000 digoxin assay was developed on the Cobas Mira plus analyzer for the determination of very low plasma concentrations of the drug. The major modifications were a higher plasma volume withdrawn during the analysis step and calibration curves constructed in the range 0-2 ng/ml using calibrators made up with biological matrix. Assays were controlled with an internal, four-level quality control (targets: 0.15; 0.60; 1.70; 2.70 ng/mL). The within-day and day-to-day mean observed values +/- SD (n = 10) of these quality controls were 0.14 +/- 0.02 and 0.15 +/- 0.02 ng/mL; 0.57 +/- 0.01 and 0.64 +/- 0.03 ng/mL; 1.55 +/- 0.06 and 1.62 +/- 0.04 ng/mL, 2.82 +/- 0.09 and 2.82 +/- 0.12 ng/mL, respectively. The detection and the quantification limits were 0.02 and 0.08 ng/mL, respectively. No significant difference was observed between digoxin plasma concentrations measured by the original and the modified EMIT 2000 digoxin assay in 25 plasma specimens, ranging from 0.4 to 3.0 ng/mL, from patients receiving the drug. This modified digoxin EMIT 2000 assay was subsequently used to study digoxin pharmacokinetics after each of 18 healthy volunteers was administered a single 0.5 mg oral dose. The pharmacokinetic parameters found in this study were in accordance with the literature in healthy subjects, using radioimmunoassay (RIA) for digoxin plasma concentration determinations. In conclusion, the lower limit of quantification of this modified EMIT 2000 digoxin assay is similar to that of RIA and can serve as a valuable screen for digoxin pharmacokinetic interactions studies.

Determination of acyclovir in plasma by solid-phase extraction and column liquid chromatography.

After oral administration, valacyclovir, the L-valyl ester of acyclovir, converts to the antiherpes virus drug, acyclovir. The bioavailability of acyclovir after valacyclovir administration is between 3- to 4.5-fold higher than that achieved after oral acyclovir administration. Therefore, despite the drug's short terminal half-life (3 hours), acyclovir plasma concentrations obtained after oral administration of the prodrug offer a more convenient dosage regimen in patients with herpes zoster than that required after acyclovir administration. Acyclovir is also used for viral infection prophylaxis in patients with hematologic disorders and in those who have undergone solid organ transplantation. We have described a simple and selective liquid chromatographic method for the determination of acyclovir in plasma using a new polymeric reversed-phase sorbent for solid-phase extraction. A mean acyclovir absolute recovery of 90% was found after elution of the drug from the cartridge with the mobile phase. This procedure allowed us to measure 62.5 ng/mL of acyclovir with an acceptable precision using a plasma volume of 250 microL, and no drug was found to interfere with the assay. This method is suitable for the therapeutic monitoring of acyclovir in patients who have been given a wide variety of coadministered drugs.

Epoxyethane-/ethynesulfonamides with antifilarial activities. Degradation kinetics and inhibitory effect on filarial malate dehydrogenase and lactate dehydrogenase.

Some epoxyethane-/ethynesulfonamides had shown strong filaricidal activity with inconstant reproducibility as a result of a lack of stability in aqueous solution. The degradation in hydroxylic and aprotic solutions of two epoxyethanesulfonamides and one ethynesulfonamide was investigated using TLC, HPLC, GC and mass spectrometry. For both epoxydes, the degradation rate followed first-order kinetics and was more rapid in hydroxylic than in aprotic solutions. The degradation increased with the temperature whereas it was not modified with and without light exposure. Four kinds of degradation products were found: the first one involved the oxidation of the epoxyde bond, the second the breaking of the N-S bond, the third a desulfonation product and the fourth was not identified. In contrast, the stability of ethynesulfonamide was better than those of epoxyethanesulfonamide. These results suggest that epoxyethanesulfonamides should be kept at +4 degrees C before being injected to animals during the study of biological activity. Since epoxyde compounds are known to have inhibitory effects on parasite energy metabolism enzymes, the compunds were evaluated on two major filarial enzymes: lactate dehydrogenase (LDH) and cytoplasmic malate dehydrogenase (MDH). Both epoxyethanesulfonamides showed only a slight inhibitory effect on filarial LDH and MDH confirming the evidence that the main mode of action of these compounds remains to discover. Moreover, ethynesulfonamide and the degradation products of both epoxyethane-sulfonamides had no effect on LDH and MDH.

Tissue distribution and metabolism in rat of an ethynesulphonamide with filaricidal activity.

1. The tissue distribution and metabolism of a new filaricidal agent P903 (N-[(2-phenylethynyl)sulfonyl]morpholine) were studied in rat. 2. After s.c. administration of 14C and 13C P903, the Tmax in the blood was observed on day 2. Elimination was slow and > 95% was bound to protein. Radioactivity was distributed in the whole organism but particularly in erythrocytes and the lymphatic channel. Four days later, > 60% of the radioactivity was excreted in urine and faeces at equal amounts and 15% remained at the injection point. 3. In all biological fluids tested no P903 was found but only its metabolites. 4. One principal metabolite, the N-[(2-phenyloxo-2-ethane) sulphonyl] morpholine or oxosulphonamide was identified in blood, urine and faeces as compared with the reference compound by GC/MS and NMR. This latter molecule was detected following hydrolysis by hydrochloric acid but not with beta glucuronidase/sulphatase. 5. Unconjugated and conjugated oxosulphonamide represented > 85% of the radioactivity at all times tested in blood but only 38 and 35% respectively of urinary and faecal radioactivity on day 1 after the administration of the labelled drug. 6. Thus, P903 is rapidly converted to a reactive metabolite, probably an oxirene, which is then conjugated with endogenous components to form conjugated oxosulphonamide and an unknown metabolite. The role of this reactive metabolite in antifilarial activity seems to be very important in understanding the mechanism of action of P903.

New antifilarial agents. 1. Epoxy sulfonamides and ethynesulfonamides.

Two series of 2-substituted 1,2-epoxyethanesulfonamides 2 and ethynesulfonamides 5 were synthesized and evaluated for their antifilarial activity. The trans epoxides 2T were stereospecifically prepared by a Darzens reaction between aldehydes and halomethanesulfonamides. The cis isomers 2c were obtained from ethynesulfonamides 5 by semihydrogenation followed by KOCl epoxidation. 2-Substituted ethynesulfonamides 5 were synthesized from appropriate trans-ethenesulfonamides by a bromination/dehydrobromination sequence. These products, as well as several synthetic intermediates, were evaluated for antifilarial activity against Molinema dessetae either in vivo in its natural host, the rodent Proechimys oris, or in vitro by a new test using cultures of the infective larvae. Most of the epoxides 2T and acetylenic derivatives 5 bearing a 2-aryl substituent were active in vitro. Among these compounds, four epoxides 2T and one acetylenic derivative 5 showed marked macrofilaricidal activity in vivo without any microfilaricidal activity. The differences between the in vivo and in vitro results may be due, in part, to the low chemical stability of the epoxy sulfonamides 2T. Despite this limitation, the activities observed in this reliable animal model suggest further development and testing of both series 2T and 5 as macrofilaricides.