Nelfinavir Plasma Concentrations Research Articles

Monitoring therapy

Monitoring therapy

Assessment of the bioequivalence of two nelfinavir tablet formulations under fed and fasted conditions in healthy subjects

This study was designed to assess the bioequivalence between the commercial 250 mg nelfinavir tablet and the new 625 mg nelfinavir tablet (Roche) which was developed to reduce the daily pill burden for patients from 10 to 4 tablets in a nelfinavir 1250 mg twice daily regimen. A total of 52 healthy male subjects were enrolled in this randomized four-period crossover study to receive single oral doses of 1250 mg nelfinavir administered as five commercial 250 mg tablets (reference formulation) and as two new 625 mg tablets (test formulation). Each of the two formulations were taken after an overnight fast and immediately after intake of a standard breakfast (820 kcal) on separate occasions. Blood samples were collected pre-dose and at appropriate intervals after drug administration. Plasma concentrations of nelfinavir and its main metabolite M8 were assayed by a validated LC-MS/ MS assay and the pharmacokinetics of nelfinavir and M8 were derived using standard non-compartmental analysis. The primary parameters for bioequivalence testing were the logarithmically transformed AUC(0-inf) and C(max) of nelfinavir taken from 50 subjects who completed all four treatments. Bioequivalence was accepted if the 90% confidence interval (CI) was contained entirely in the equivalence region (80%, 125%). In the fed state, this criterion was met for AUC (effect ratio = 95%; CI = 87%, 103%) and Cmax (effect ratio = 101%; CI = 94%, 109%) and bioequivalence of the two treatments could be concluded. In the fasted state, AUC clearly failed to meet the bioequivalence criteria (effect ratio = 73%; CI = 59%, 90%) and Cmax was borderline outside the lower acceptance region (effect ratio = 97%; CI = 79.6%, 118%). Therefore, bioequivalence could not be concluded under fasted condition. Food increased the systemic exposure to nelfinavir (as reflected by comparison of the logarithmically transformed AUC(0-inf) values under fed and fasted conditions) by six- and eight-fold after dosing with the 250 mg and the 625 mg tablet, respectively. Bioequivalence of the new 625 mg nelfinavir tablet relative to the commercial 250 mg tablet, at a dose of 1250 mg, was confirmed in the fed state but not under fasted conditions. As nelfinavir is recommended to be taken with food, the new tablet is well-suited to decrease the daily pill burden for patients on a nelfinavir twice daily regimen and to enhance patient's compliance and adherence.

Simultaneous genotyping of seven single-nucleotide polymorphisms in the MDR1 gene by single-tube multiplex minisequencing.

Responses to different drugs can vary widely among different individuals as a result of genetic variations in drug-metabolizing enzymes, transporters, receptors, and/or other cofactors. The multidrug resistance 1 (MDR1) transporter, a well-characterized member of the ATP-binding cassette superfamily, was shown to efflux a wide variety of structurally and functionally unrelated drugs, including anticancer, antiarrhythmic, antidepressant, antipsychotic, and antiviral agents. The pharmacogenetics of the MDR1 multidrug transporter have recently received much scientific attention. Several single-nucleotide polymorphisms (SNPs) have been identified in the MDR1 gene; some occur only in specific ethnic groups, whereas others occur in all ethnic groups but at significantly different allele frequencies among the different races [see Ref. (1) and references therein]. Nonetheless, the functional significance of these SNPs remains unclear. Various functional associations, some paradoxical, have been observed between the synonymous SNP (exon 26 3435C→T) and MDR1 protein expression and plasma drug concentrations (2)(3)(4)(5), drug-induced side effects (6), and drug response (7). The SNP exon 26 3435T allele has been associated with lower MDR1 expression in the duodenum (2), leukocytes (5), and placental tissues (8), leading to lower rhodamine efflux (5) and increased plasma digoxin concentrations (2). In addition, early-onset Parkinson patients have higher frequency of the SNP exon 26 3435T allele compared with late-onset patients or unaffected controls (9). However, although this same allele has been associated with lower MDR1 expression in peripheral blood mononuclear cells and better response to HIV-1 drugs, it has also been associated with lower plasma concentrations of nelfinavir (7). Additionally, the SNP exon 26 3435T allele has been associated with an increased risk of nortriptyline-induced postural hypertension, although blood concentrations of nortriptyline in these individuals were not significantly different from those in individuals carrying the C allele (6). Furthermore, no association has been demonstrated between the …

Effects of nelfinavir and its M8 metabolite on lymphocyte P-glycoprotein activity during antiretroviral therapy.

The efflux pump P-glycoprotein decreases drug penetration into cells and tissues. To determine whether nelfinavir or its metabolites inhibit P-glycoprotein in lymphocytes from a healthy volunteer, whole blood cells from human immunodeficiency virus-negative donors were incubated either in human plasma to which nelfinavir or its M8 metabolite were added ex vivo or in plasma from human immunodeficiency virus-positive patients receiving nelfinavir. The 50% P-glycoprotein inhibitory concentrations of purified nelfinavir and M8 were 10.9 micromol/L and 29.5 micromol/L, respectively, for CD4(+) T cells and 19.3 micromol/L and >48 micromol/L, respectively, for CD8(+) T cells. Significant inhibitory activity was present in plasma from 27 of 46 patients (59%) receiving nelfinavir. Plasma nelfinavir concentrations correlated with percent inhibition on CD4(+) (rho = 0.85, P <.0001) and CD8(+) (rho = 0.83, P <.0001) T cells. The M8 concentrations correlated weakly with both inhibition and nelfinavir concentrations. On the basis of our findings in lymphocytes from a healthy volunteer exposed to plasma from human immunodeficiency virus-positive patients, we believe it is likely that CD4(+) and CD8(+) lymphocytes in patients receiving nelfinavir as therapy for human immunodeficiency virus may have P-glycoprotein inhibited by plasma concentrations of nelfinavir.

Diurnal variation of plasma protease inhibitor concentrations

Diurnal variation in plasma concentrations of nelfinavir and ritonavir has previously been described. Plasma concentrations of 29 pharmaco-kinetic profiles with indinavir, amprenavir and saquinavir were evaluated, and a statistically significant median difference of 57.6% was found between morning and evening, with the morning C through being higher than the evening C through . Consequently, a change in dosing intervals might result in more balanced plasma protease inhibitor concentrations, thereby decreasing toxicity and the risk of virological failure.

Determination of nelfinavir free drug concentrations in plasma by equilibrium dialysis and liquid chromatography/tandem mass spectrometry: important factors for method optimization

A method was developed and validated for measuring the free fraction of nelfinavir in plasma employing equilibrium dialysis for the separation of free (unbound) drug and liquid chromatography/tandem mass spectrometry for quantitation. Nelfinavir, widely used to treat HIV infection, is a highly bound HIV protease inhibitor with the fraction bound in plasma being greater than 98%. Thus variations in the free fraction may be clinically important when interpreting total drug concentrations. Optimization of the method was carried out considering the influence of sample matrix and physicochemical and absorptive properties of nelfinavir. Nelfinavir free fraction averaged 0.41±0.094, 0.43±0.087 and 0.41±0.063% at nelfinavir plasma concentrations of 1000, 2000 and 3000 ng/ml, respectively. Free nelfinavir concentrations were underestimated with this assay by ∼25% because of unavoidable losses to adsorption. However, the adsorptive loss was reproducible and consistent across the concentration range of the assay. Within-day and between-day precisions ranged from 6.0 to 9.4% and 15.2 to 27.3%, respectively. The lower limit of quantitation of the unbound concentration of nelfinavir was 1.0 ng/ml, permitting analysis of samples with total concentrations of nelfinavir in plasma that are ≥400 ng/ml. This developed method proves reproducible and sensitive and its application to patient plasma samples is also reported.

Efavirenz, Nelfinavir, and Stavudine Rescue Combination Therapy in HIV-1–Positive Patients Heavily Pretreated With Nucleoside Analogues and Protease Inhibitors

Summary: Tolerability, activity, and pharmacokinetic parameters of a combination therapy with efavirenz (EFV), nelfinavir (NFV), and stavudine (d4T) were evaluated in this study. Forty-seven HIV-1-infected study subjects, naive to NFV and nonnucleoside reverse transcriptase inhibitors (NNRTIs), who had experienced virologic failure while being treated with combination antiretroviral therapies including protease inhibitors (PIs), were enrolled. At baseline, HIV-1 viral load in plasma was 4.8 log10, CD4+ count was 204 cells/μl (both mean values); patients had received a mean of 3.1 different treatments (range, 2-5 treatments). Study medications were generally well tolerated; 7 of 47 patients (14.8%) were dropped from the study because of related drug toxicity. At week 24, mean plasma viral load (pVL) was reduced by 1.9 log10, with mean CD4+ count increased to 324 cells/μl (±59% from baseline); pVL was below the limit of detection (500 copies/ml) in 46.1% of patients. An extended follow-up study was performed at 12 months. Results showed a reduction of 1.7 log10 in pVL from basal values that was consistent with values observed at months 3 and 6. A history of previous use of PIs represented a negative prognostic marker. Sequencing analysis, performed in a subset of patients, showed the presence of multiple point mutations associated with PI resistance. Pharmacokinetic analysis demonstrated a marked interindividual variability in NFV plasma concentrations, producing in 4 of 18 patients (22%) trough concentrations lower than minimum effective concentration. In pretreated patients, further studies are needed to characterize the pharmacokinetic factors that affect response to therapy and the association of these results with the 95% inhibitory concentration (IC95) determined by phenotyping.