Pharmacokinetic study of human immunodeficiency virus protease inhibitors used in combination with amprenavir.

In an open-label, randomized, multicenter, multiple-dose pharmacokinetic study, we determined the steady-state pharmacokinetics of amprenavir with and without coadministration of indinavir, nelfinavir, or saquinavir soft gel formulation in 31 human immunodeficiency virus type 1-infected subjects. The results indicated that amprenavir plasma concentrations were decreased by saquinavir soft gel capsule (by 32% for area under the concentration-time curve at steady state [AUC(ss)] and 37% for peak plasma concentration at steady state [C(max,ss)]) and increased by indinavir (33% for AUC(ss)). Nelfinavir significantly increased amprenavir minimum drug concentration at steady state (by 189%) but did not affect amprenavir AUC(ss) or C(max,ss). Nelfinavir and saquinavir steady-state pharmacokinetics were unchanged by coadministration with amprenavir compared with the historical monotherapy data. Concentrations of indinavir, coadministered with amprenavir, in plasma decreased in both single-dose and steady-state evaluations. The changes in amprenavir steady-state pharmacokinetic parameters, relative to those for amprenavir alone, were not consistent among protease inhibitors, nor were the changes consistent with potential interactions in CYP3A4 metabolism or P-glycoprotein transport. No dose adjustment of either protease inhibitor in any of the combinations studied is needed.

Pharmacokinetics and safety of amprenavir and ritonavir following multiple-dose, co-administration to healthy volunteers.

OBJECTIVE: To evaluate the safety and pharmacokinetic interaction between amprenavir (APV) and ritonavir (RTV). METHODS: Three open-label, randomized, two-sequence, multiple-dose studies having the same design (7 days of APV or RTV alone followed by 7 days of both drugs together) used 450 or 900 mg APV with 100 or 300 mg RTV every 12 h with pharmacokinetic assessments on days 7 and 14. Safety was monitored as clinical adverse events (AEs) and laboratory abnormalities. RESULTS: Relative to APV alone, RTV co-administration resulted in a 3.3- to 4-fold and 10.84 to 14.25-fold increase in the geometric least-square (GLS) mean area under the plasma concentration--time curve (AUC(tau,ss)) and minimum concentration (C(min,ss)), respectively. APV 900 mg with RTV 100 mg resulted in a 2.09-fold and 6.85-fold increase in the GLS mean AUC(tau,ss) and C(min,ss), respectively. On day 14, the geometric mean (95% confidence interval) for 450 mg APV AUC(tau,ss) (micro x h/mL) was 23.49 (19.32--28.57) with 300 mg RTV and 35.42 (30.46--44.42) with 100 microg RTV, and for the 900 mg APV with 100 mg RTV 47.11 (39.47--61.24). The 450 mg APV C(min,ss) (microg/ml) were 1.32 (1.05--1.67) and 2.01 (1.70--2.61), and 2.47 (2.08--3.32) for 900 mg APV. The most common AEs were mild and included diarrhea, nausea/vomiting, oral parasthesias, and rash. The triglyceride and cholesterol increased significantly from RTV exposure. CONCLUSION: Adding RTV to APV resulted in clinically and statistically significant increases in APV AUC and C(min) with variable effects on maximum concentration. The two RTV doses had similar effects on APV but AEs were more frequent with 300 mg RTV.

Metabolic disposition and pharmacokinetics of [14C]-amprenavir, a human immunodeficiency virus type 1 (HIV-1) protease inhibitor, administered as a single oral dose to healthy male subjects.

The objective of this study was to determine the metabolic profile, routes of elimination, and total recovery of amprenavir and its metabolites after a single oral dose of [14C]-amprenavir. Six healthy male subjects each received a single oral 630 mg dose of amprenavir containing 95.76 microCi of [14C]-amprenavir in this Phase I mass balance study. The metabolic disposition of amprenavir was determined through analyses of radiocarbon in whole blood, plasma, urine, and stool samples, collected for a period of 10 to 17 days postdosing. Cerebral spinal fluid (CSF) sampling was conducted on day 1. The ratio of unchanged amprenavir AUC0-->infinity to plasma radiocarbon was 27%, suggesting that most of the radiocarbon was metabolites. The median total recovery of the administered dose of radiocarbon was 89% (range: 66%-93%), with 75% (range: 56%-80%) recovered in the feces and 14% (range: 10%-17%) in the urine. Most of the recovered radiocarbon in the feces and urine was excreted within 240 and 48 hours postdose, respectively. Of the 75% of the radiocarbon dose recovered in the feces, 62% was identified as a metabolite resulting from dioxidation of the tetrahydrofuran ring (GW549445X) and 32% as a metabolite resulting from subsequent oxidation of the p-aniline sulfonate group (GW549444X). Unchanged amprenavir was below the limit of quantitation in feces and urine. Therefore, approximately 94% of the dose excreted in the feces was accounted for by these two metabolites. Concentrations of radiocarbon in the CSF were below the limit of quantitation in 5 of 6 subjects sampled. In summary, oral amprenavir is extensively metabolized in humans, with concentrations of unchanged drug below the limits of quantitation in urine and feces. The majority (75%) of administered radiocarbon was excreted in feces.

In vivo effect of alpha(1)-acid glycoprotein on pharmacokinetics of amprenavir, a human immunodeficiency virus protease inhibitor.

Observations from early clinical pharmacology studies of amprenavir, an inhibitor of human immunodeficiency virus type 1 (HIV-1) protease that is highly bound to human plasma proteins (approximately 90%), showed the single-dose pharmacokinetics of amprenavir to be variable between and within individuals. A cross-study analysis of various demographic, laboratory, and clinical covariates was therefore performed. Differences in amprenavir pharmacokinetics could be due to variable concentrations in alpha(1)-acid glycoprotein (AAG), the predominant plasma protein to which amprenavir binds. Therefore, AAG was considered an important factor to study since the literature suggested that AAG levels vary by race, age, and weight and following trauma or infection, including HIV disease. Pooled data from three single-dose studies analyzed by stepwise linear regression indicated that AAG concentrations significantly correlated with age and race and that only AAG concentrations were a significant predictor of amprenavir apparent total clearance (CL/F). A significant inverse linear relationship was found between AAG and amprenavir CL/F. Compared to white subjects, black subjects had significantly lower AAG concentrations and therefore significantly higher amprenavir CL/F. Although AAG has a significant influence on the variability of total drug pharmacokinetics, unbound, or free, drug concentrations are not affected by AAG concentrations. Incorrect conclusions could be drawn on the pharmacokinetics of highly protein-bound drugs if AAG concentration is not included in the analysis.

Pharmacokinetic Interaction between amprenavir and rifabutin or rifampin in healthy males.

The objective of this study was to determine if there is a pharmacokinetic interaction when amprenavir is given with rifabutin or rifampin and to determine the effects of these drugs on the erythromycin breath test (ERMBT). Twenty-four healthy male subjects were randomized to one of two cohorts. All subjects received amprenavir (1,200 mg twice a day) for 4 days, followed by a 7-day washout period, followed by either rifabutin (300 mg once a day [QD]) (cohort 1) or rifampin (600 mg QD) (cohort 2) for 14 days. Cohort 1 then received amprenavir plus rifabutin for 10 days, and cohort 2 received amprenavir plus rifampin for 4 days. Serial plasma and urine samples for measurement of amprenavir, rifabutin, and rifampin and their 25-O-desacetyl metabolites, were measured by high-performance liquid chromatography. Rifabutin did not significantly affect amprenavir's pharmacokinetics. Amprenavir significantly increased the area under the curve at steady state (AUC(ss)) of rifabutin by 2.93-fold and the AUC(ss) of 25-O-desacetylrifabutin by 13.3-fold. Rifampin significantly decreased the AUC(ss) of amprenavir by 82%, but amprenavir had no effect on rifampin pharmacokinetics. Amprenavir decreased the results of the ERMBT by 83%. The results of the ERMBT after 2 weeks of rifabutin and rifampin therapy were increased 187 and 156%, respectively. Amprenavir plus rifampin was well tolerated. Amprenavir plus rifabutin was poorly tolerated, and 5 of 11 subjects discontinued therapy. Rifampin markedly increases the metabolic clearance of amprenavir, and coadministration is contraindicated. Amprenavir significantly decreases clearance of rifabutin and 25-O-desacetylrifabutin, and the combination is poorly tolerated. Amprenavir inhibits the ERMBT, and rifampin and rifabutin are equipotent inducers of the ERMBT.

Pharmacokinetic and pharmacodynamic study of the human immunodeficiency virus protease inhibitor amprenavir after multiple oral dosing.

In a dose-ranging study of amprenavir (formerly 141W94), an inhibitor of the protease enzyme of human immunodeficiency virus (HIV) type 1, single-dose and steady-state pharmacokinetic parameters were estimated from plasma samples collected on day 1 and during week 3, respectively. Amprenavir was administered on either a twice-daily (b.i.d.) or three-times-daily dosage schedule to 62 HIV-infected adults, 59 of whom had pharmacokinetic data. Log-log regression analysis (the power model) revealed that the steady-state area under the curve (AUC(ss)) and the maximum, minimum, and average concentrations at steady state (C(max,ss), C(min,ss), and C(avg,ss), respectively) increased in a dose-proportional manner over the 300- to 1,200-mg dose range. Steady-state clearance was dose independent. AUC(ss)/AUC(0-->infinity) decreased linearly with dose and correlated significantly with treatment-associated decreases in alpha(1)-acid glycoprotein. After 3 weeks, the dose of 1,200 mg b.i. d. provided a median amprenavir C(min,ss) (0.280 microg/ml) that was higher than the median in vitro 50% inhibitory concentration for clinical HIV isolates (0.023 microg/ml), even after adjustment for protein binding. The median amprenavir C(min,ss) was also greater than the estimated in vivo trough concentration calculated to yield 90% of the maximum antiviral effect (0.228 microg/ml) over 4 weeks. A pharmacodynamic analysis of the relationship between steady-state pharmacokinetic parameters and safety revealed headache and oral numbness to be the only side effects significantly associated with C(max). The pharmacodynamic relationship defined in this study supports the use of 1,200 mg b.i.d. as the approved dose of amprenavir.

Single-dose pharmacokinetics of amprenavir, a human immunodeficiency virus type 1 protease inhibitor, in subjects with normal or impaired hepatic function.

Amprenavir (141W94) is extensively metabolized by P450 cytochromes, specifically, CYP3A4. Because hepatic insufficiency reduces P450-mediated metabolism, the concentrations in plasma of drugs metabolized through this pathway are often increased in subjects with liver disease. Following administration of a single, oral dose of 600 mg of amprenavir, pharmacokinetic parameters were determined for 10 subjects with severe cirrhosis, 10 subjects with moderate cirrhosis, and 10 healthy volunteers. Model-independent methods for determining the area under the plasma concentration-time curve (AUC) from time zero to infinity (AUC(0-infinity)) showed an increase in amprenavir AUC(0-infinity) of 2.5-fold in the group with moderate cirrhosis and 4.5-fold in the group with severe cirrhosis compared with that in the control group of healthy volunteers (P < 0.05). AUC(0-infinity) was linearly related to the severity of liver disease, as assessed by the Child-Pugh score. Of the laboratory data used to calculate the Child-Pugh score, only the mean total bilirubin concentration showed a significant relationship with AUC(0-infinity). The relationship between the total bilirubin concentration and the AUC(0-infinity) of amprenavir was well characterized by a simple E(max) model, suggesting that the total bilirubin concentration may be a useful parameter for predicting the amprenavir AUC in subjects with hepatic insufficiency. Finally, the sera of cirrhotic subjects showed significant decreases in the levels of alpha(1)-acid glycoprotein, the primary plasma binding protein for amprenavir. On the basis of the results of this study, for an exposure equivalent to a clinical dose of 1,200 mg twice daily in subjects without cirrhosis, subjects with Child-Pugh scores of 5 to 8 should receive a twice-daily 450-mg dose of amprenavir, and subjects with Child-Pugh scores of 9 to 15 should receive a twice-daily 300-mg dose of amprenavir.

Pharmacokinetic interaction between amprenavir and clarithromycin in healthy male volunteers.

The P450 enzyme, CYP3A4, extensively metabolizes both amprenavir and clarithromycin. To determine if an interaction exists when these two drugs are coadministered, the pharmacokinetics of amprenavir and clarithromycin were investigated in healthy adult male volunteers. This was a Phase I, open-label, randomized, balanced, multiple-dose, three-period crossover study. Fourteen subjects received the following three regimens: amprenavir, 1,200 mg twice daily over 4 days (seven doses); clarithromycin, 500 mg twice daily over 4 days (seven doses); and the combination of the above regimens over 4 days (seven doses of each drug). Twelve subjects completed all treatments and the follow-up period. The erythromycin breath test (ERMBT) was administered at baseline, 2 h after the final dose of each of the three regimens and at the first follow-up visit. Coadministration of clarithromycin and amprenavir significantly increased the mean amprenavir AUC(ss), C(max,ss), and C(min,ss) by 18, 15, and 39%, respectively. Amprenavir had no significant effect on the AUC(ss) of clarithromycin, but the median T(max,ss)for clarithromycin increased by 2.0 h, renal clearance increased by 34%, and the AUC(ss) for 14-(R)-hydroxyclarithromycin decreased by 35% when it was given with amprenavir. Amprenavir and clarithromycin reduced the ERMBT result by 85 and 67%, respectively, and by 87% when the two drugs were coadministered. The baseline ERMBT value did not correlate with clearance of amprenavir or clarithromycin. A pharmacokinetic interaction occurs when amprenavir and clarithromycin are coadministered, but the effects are not likely to be clinically important, and coadministration does not require a dosage adjustment for either drug.

Pharmacokinetic interaction between ketoconazole and amprenavir after single doses in healthy men.

STUDY OBJECTIVE: To determine the effects of coadministration of amprenavir and ketoconazole on the pharmacokinetics of both drugs, and to assess the utility of the erythromycin breath test (ERMBT) to predict and explain these effects. DESIGN: Open-label, randomized, balanced, single-dose, three-period crossover study. SETTING: University research center. SUBJECTS: Twelve healthy men. INTERVENTION: Subjects received amprenavir 1200 mg, ketoconazole 400 mg, and amprenavir 1200 mg plus ketoconazole 400 mg. Each treatment was separated by 14 days. MEASUREMENTS AND MAIN RESULTS: Serial plasma samples for amprenavir and ketoconazole concentrations were measured by high-performance liquid chromatography. Coadministration of the drugs increased amprenavir area under the curve extrapolated to infinity (AUCinfinity) by 31% and reduced its maximum concentration (Cmax) by 16%. Amprenavir increased the AUCinfinity of ketoconazole by 44% and increased the drug's half-life and Cmax by 23% and 19%, respectively. Both agents resulted in substantial inhibition of ERMBT. CONCLUSION: Coadministration of ketoconazole and amprenavir results in a statistically significant increase in AUC for both agents, but the changes are not likely to be clinically important.

Safety and pharmacokinetics of amprenavir (141W94), a human immunodeficiency virus (HIV) type 1 protease inhibitor, following oral administration of single doses to HIV-infected adults.

We conducted a double-blind, placebo-controlled, parallel, dose-escalation trial to evaluate the pharmacokinetics and safety of single, oral doses of amprenavir (141W94; formerly VX-478), a potent inhibitor of human immunodeficiency virus (HIV) type 1 protease, administered as hard gelatin capsules in 12 HIV-infected subjects. The doses of amprenavir evaluated were 150, 300, 600, 900, and 1,200 mg. Amprenavir was rapidly absorbed, with the time to maximum concentration occurring within 1 to 2 h after dosing. On the basis of power model analysis, the increase in the maximum concentration of amprenavir in plasma (Cmax) was less than dose proportional, and the increase in the area under the concentration-time curve from time zero to infinity (AUC0-infinity) was greater than dose proportional; mean slopes (with 90% confidence intervals) were 1.25 (1.16 to 1.35) and 0.78 (0.78 to 0.86) for AUC0-infinity and Cmax, respectively. Amprenavir was eliminated slowly, with a terminal-phase half-life of 8 h. A second study was conducted to determine the bioavailability of the hard gelatin capsule relative to that of a subsequently developed soft gelatin capsule. The capsules were bioequivalent in terms of AUC0-infinity but not in terms of Cmax; geometric-least-squares means ratios (with 90% confidence intervals) were 1.03 (0.92 to 1.14) and 1.25 (1.03 to 1. 53) for AUC0-infinity and Cmax, respectively. Administration of soft gelatin capsules of amprenavir with a high-fat breakfast resulted in a 14% decrease in the mean AUC0-infinity (from 9.58 to 8.26 microg. h/ml), which is not likely to be clinically significant. The most common adverse events related to amprenavir were headache, nausea, and hypesthesia. Amprenavir appears to be safe and well tolerated over the dose range of 150 to 1200 mg. On the basis of the present single-dose studies, amprenavir is an HIV protease inhibitor with favorable absorption and clearance pharmacokinetics that are only minimally affected by administration with food.

Efficacy and pharmacokinetics of atovaquone and proguanil in children with multidrug-resistant Plasmodium falciparum malaria.

A trial was conducted in 32 Thai children with uncomplicated multidrug-resistant falciparum malaria to assess the efficacy, safety and pharmacokinetics of atovaquone and proguanil; plasma concentrations of atovaquone, proguanil and its metabolite, cycloguanil, were measured in a subset of 9 children. The children received atovaquone (17 mg/kg/d for 3 d) plus proguanil (7 mg/kg/d for 3 d). Twenty-six children who had only Plasmodium falciparum infection and remained in hospital for 28 d were assessed for drug efficacy. The combination regimen produced a cure rate of 100%. Parasite and fever clearance times were 47 h (range 8-75) and 50 h (range 7-111), respectively. Atovaquone and proguanil were rapidly absorbed, with median time to peak concentrations of 6 h (range 6-24) and 6 h (range 6-12), respectively. Peak concentrations of cycloguanil were achieved between 6 and 12 h (median 6) after administration of proguanil. Mean peak plasma concentration of atovaquone on day 3 was 5.1 micrograms/mL (SD = 2.1). The day 3 mean peak plasma concentration of proguanil was 306 ng/mL (SD = 108) compared with 44.3 ng/mL (SD = 27.3) for cycloguanil. Mean values for the AUC (area under plasma concentration-time curve) were 161.8 micrograms/mL.h (SD = 126.9) for atovaquone, 4646 ng/mL.h (SD = 1226) for proguanil, and 787 ng/mL.h (SD = 397) for cycloguanil. Terminal elimination half-lives of atovaquone, proguanil and cycloguanil were estimated as 31.8 h (SD = 8.9), 14.9 h (SD = 3.3) and 14.6 h (SD = 2.6), respectively. No major adverse effect was attributable to the study drugs. Atovaquone/proguanil combination is safe and highly effective, and should be especially valuable for treatment of multidrug-resistant falciparum malaria.

In vitro antiviral activity of 141W94 (VX-478) in combination with other antiretroviral agents.

141W94 (VX-478) is a novel HIV-1 protease inhibitor with an IC50 of 0.08 microM against HIV-1 (strain IIIB) and a mean IC50 of 0.012 microM against six HIV clinical isolates. 141W94 was synergistic on the basis of isobologram analysis with each of the following reverse transcriptase inhibitors: AZT, 935U83, 524W91, 1592U89 and ddl, 141W94 was also synergistic with saquinavir and additive with either indinavir or ritonavir. Resistance to 141W94 has been reported in vitro passage experiments. The binding of 141W94 to human alpha 1-acid glycoprotein was relatively weak (Kd = 4 microM) and the off-rate for the drug is very fast (> or = 100 s-1). Only a 2-fold reduction of in vitro antiviral activity was observed in the presence of 45% human plasma. No serious drug associated adverse experiences were reported in a Phase I placebo-controlled, single-dose escalation, pharmacokinetic and safety study. The average concentration of 141W94 at 8 and 12 h after single doses of 900 and 1200 mg, respectively, was in excess of 10 times the IC50. As 141W94 is synergistic with a variety of anti-HIV-1 agents and exhibits a unique cross resistance profile compared to other protease inhibitors, 141W94 is considered a good candidate for combination therapy.

Acousto-optic cyclostationary signal processing.

Cyclostationary signal-processing techniques implemented by means of acousto-optics are considered. Cyclic-processing methods are reviewed and motivated, such as the cyclic correlation and the cyclic spectrum. It is shown that the cyclic correlation can be computed at cycle frequencies of interest by use of one-dimensional time-integrating correlators in additive or multiplicative configurations. Detection of cycle frequencies is briefly considered, and a one-dimensional acousto-optic spectrum-analysis approach is described that is effective for amplitude-modulated signals. The problem of computing the two-dimensional cyclic correlation for all cycle frequencies and lags is then considered. This is accomplished by means of an acousto-optic triple-product processor configured in a manner similar to that used for ambiguity-function generation. The cyclic spectrum can be obtained in a postprocessing step by Fourier transformation of the cyclic correlation in one dimension. Higher-order extensions of the cyclic correlation are also discussed, and it is shown how a two-dimensional slice of the three-dimensional cyclic triple correlation can be computed by use of an acousto-optic four-product processor.

Prolonged, but not diminished, zidovudine absorption induced by a high-fat breakfast.

STUDY OBJECTIVE: To determine the effect of a high-fat breakfast on single-dose, zidovudine (ZDV) pharmacokinetics. DESIGN: Open-label, randomized, crossover study. PATIENTS: Eighteen asymptomatic subjects (12 men, 6 women) infected with the human immunodeficiency virus (mean CD4 cell counts of 512 +/- 178/mm3). INTERVENTIONS: Subjects received single 100-mg oral doses of ZDV as follows: after an 8-hour fast (treatment A), with a high-fat breakfast (treatment B), and 3 hours after a high-fat breakfast (treatment C). MEASUREMENTS AND MAIN RESULTS: The high-fat breakfast significantly reduced the mean (coefficient of variation) maximum plasma concentration (Cmax) from 806 (55%) ng/ml with treatment A to 341 (47%) and 424 (42%) ng/ml with treatments B and C, respectively. The time to Cmax was significantly prolonged from 0.68 (30%) hours with treatment A to 1.7 (54%) and 1.3 (42%) hours with treatments B and C, respectively. Area under the plasma ZDV concentration-time curve (AUC) was not statistically different across the study treatments. Men had significantly lower (35%) renal clearances of both ZDV and its glucuronide metabolite than women. CONCLUSIONS: When ZDV was given either with or 3 hours after a high-fat breakfast, its absorption was prolonged and Cmax was reduced relative to fasting. However, systemic exposure, as indicated by AUC, was unchanged.

Pharmacokinetics of methamphetamine self-administered to human subjects by smoking S-(+)-methamphetamine hydrochloride.

S-(+)-methamphetamine hydrochloride ("ice") is abused by smoking (inhaling the vapors of the material). Male human volunteers inhaled the drug from a pipe heated at 300 degrees-305 degrees C for an average inhaled dose of 21.8 +/- 0.3 (SE) mg. The same volunteers were given an intravenous injection of 15.5 mg of S-(+)-methamphetamine hydrochloride. Methamphetamine and its metabolite amphetamine were analyzed in plasma, saliva, and urine by gas chromatography. The bioavailability of smoked methamphetamine was 90.3 +/- 10.4%. (Oral bioavailability calculated from this study and a previous one was 67.2 +/- 3.1%). The geometric mean plasma half-life was 11.1 hr for smoked methamphetamine and 12.2 hr for the intravenous drug. These values agreed with urinary excretion rate data. The volume of distribution in the elimination phase was 3.24 +/- 0.36 liter/kg for the smoked dose and 3.73 +/- 0.59 liter/kg for the intravenous dose. The mean residence times were 11.5 +/- 0.5 hr and 11.3 +/- 1.74 hr for the two routes. Metabolic clearance represented 58 and 55%, respectively, of the total clearance. Significant amounts of the drug (37-45% of the nominal dose) were excreted in urine as methamphetamine and lesser amounts (7% of the nominal molar dose) as amphetamine. Renal clearance was equivalent for the two routes. Methamphetamine concentrations in plasma after inhalation showed a plateau. A model involving both a fast and a slow input function fit the data from 4 of the 6 subjects and indicated a terminal elimination rate that agreed with results from model-independent pharmacokinetic calculations. The drug caused significant subjective and cardiovascular effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of oral methamphetamine and effects of repeated daily dosing in humans.

The pharmacokinetics of orally administered S-(+)-methamphetamine-d3 were investigated in human male volunteers before and after a 13-day course of a slow release form of S-methamphetamine hydrochloride. A one-compartment pharmacokinetic model incorporating a lag time fits the data best. The average elimination half-life was 10.1 hr (range of 6.4-15.1 hr). There were no statistically significant differences in pharmacokinetic parameters when a low dose (0.125 mg/kg) was given before and after the 13-day oral regimen. When a higher challenge dose (0.250 mg/kg) was used, the maximum plasma concentration of methamphetamine-d3 was slightly but significantly greater when the test dose was given at the end of the oral dosing period than when it was given at the beginning. Although minor differences in pharmacokinetics occur after subchronic treatment with low doses of methamphetamine, their result would be to increase plasma concentration of the drug. Therefore, development of pharmacodynamic tolerance to methamphetamine could not be explained on the grounds of a change in pharmacokinetics.

X-ray-induced specific-locus mutations in the ad-3 region of two-component heterokaryons of Neurospora crassa. XI. Heterozygous effects of gene/point mutations of genotype ad-3A or ad-3B.

Previous studies on X-ray-induced irreparable adenine-3 mutants (designated ad-3IR), induced in heterokaryon 12 of Neurospora crassa, showed that they were not recessive, and that they demonstrated heterozygous effects in terms of markedly reduced linear growth rates as compared with a wild-type control (de Serres, 1965, 1988). Homology tests on X-ray-induced irreparable mutants showed that they map, in the main part, as a series of overlapping multilocus deletions that extend both proximally and distally into the immediately adjacent genetic regions, as well as into the 'X' region (a region of unknown, but essential, function) between ad-3A and ad-3B (de Serres, 1969, 1989a). Studies on a larger sample of X-ray-induced multilocus deletion mutations of genotype (ad-3A)IR or (ad-3B)IR (de Serres et al., 1992) demonstrated that heterozygous effects are allele specific and that there was no correlation with genotype, radiation dose or complementation map position. Furthermore, the heterozygous effects of multilocus deletions in the ad-3 region can be modified genetically and biochemically (de Serres and Miller, 1988). In the present paper, the heterozygous effects of X-ray-induced gene/point mutations of genotype ad-3AR or ad-3BR, induced in heterokaryon 12 (Webber and de Serres, 1965; de Serres, 1988, 1989a), were determined. The studies presented in this paper show that 8.1% (3/37) of X-ray-induced ad-3AR mutations exhibit heterozygous effects in terms of reduced linear growth rates in forced dikaryons with a gene/point mutant at the ad-3B locus, and 10.8% (4/37) in forced dikaryons with a multilocus deletion mutation covering the ad-3B locus. In addition, 24.3% (9/37) of ad-3AR mutations exhibit heterozygous effects in terms of enhanced linear growth rates in forced dikaryons with a gene/point mutant at the ad-3B locus. Similar studies with X-ray-induced ad-3BR mutations showed that 54.9% (28/51) exhibit heterozygous effects in terms of reduced growth rates in forced dikaryons with a gene/point mutant at the ad-3A locus and 100.0% (48/48) in forced dikaryons with a multilocus deletion covering the ad-3A locus. These studies have also shown that about a 13-fold higher percentage of X-ray-induced multiple-locus mutations of genotype ad-3AR + RLCL have heterozygous effects resulting in reduced growth rates than X-ray-induced single-locus mutations of genotype ad-3AR. The overall data base on X-ray-induced ad-3 gene/point mutations in the present studies demonstrates that heterozygous effects are allele specific, genotype specific, and locus specific.(ABSTRACT TRUNCATED AT 400 WORDS)

X-ray-induced specific-locus mutations in the ad-3 region of two-component heterokaryons of Neurospora crassa. X. Heterozygous effects of multilocus deletion mutations of genotype ad-3A or ad-3B.

Previous studies on X-ray-induced irreparable adenine-3 mutations (designated [ad-3]IR), induced in heterokaryon 12 of Neurospora crassa, demonstrated that they were not recessive and exhibited heterozygous effects in terms of markedly reduced linear growth rates (de Serres, 1965). Complementation tests with a series of tester strains carrying multilocus deletion mutations in the ad-3 and immediately adjacent genetic regions demonstrated that X-ray-induced irreparable mutations map, in the main part, as a series of overlapping multilocus deletion mutations that extend both proximally and distally into the immediately adjacent genetic regions, as well as into the 'X' region (a region of unknown, but essential function) between ad-3A and ad-3B (de Serres, 1968, 1989). Further studies (de Serres and Miller, 1988) have shown that the heterozygous effects of multilocus deletion mutations in the ad-3 region can be modified genetically and biochemically. In the present paper, the heterozygous effects of X-ray-induced multilocus deletion mutations of genotype ad-3A or ad-3B, induced in heterokaryon 12 (Webber and de Serres, 1965; de Serres, 1988, 1989), have been determined. These data show that 57.7% (15/26) of X-ray-induced multilocus deletion mutations covering the ad-3A locus have heterozygous effects, in terms of reduced linear growth rates, in forced dikaryons with a gene/point mutant at the ad-3B locus and 80.0% (20/25) in forced dikaryons with a multilocus deletion mutation covering the ad-3B locus. In addition, 35.1% (20/57) of X-ray-induced multilocus deletion mutations covering the ad-3B locus have heterozygous effects in forced dikaryons with a gene/point mutant at the ad-3A locus, and 100.0% (35/35) in forced dikaryons with a multilocus deletion mutation covering the ad-3A locus. These results demonstrate that the dominant or recessive characteristics of X-ray-induced specific-locus mutations resulting from multilocus deletion mutations are allele specific.

ENU mutagenesis in the mouse electrophoretic specific-locus test, 1. Dose-response relationship of electrophoretically-detected mutations arising from mouse spermatogonia treated with ethylnitrosourea.

The mouse electrophoretic specific-locus test for induced germ-cell mutations, was used to determine the response of spermatogonial stem cells to a series of doses of the germ cell mutagen N-ethyl-N-nitrosourea (ENU). Male DBA/2J and C57B1/6J mice were treated with doses of 50, 100, 200 or 250 mg/kg ENU and their progeny screened for electrophoretically-detectable mutations at 32 separate loci. As expected, increasing doses of ENU led to increasing mutant frequencies. The differences in mutant frequencies between treated DBA/2J and C57B1/6J males were not statistically significant.

Drug level monitoring in a double-blind multicenter trial: false-positive zidovudine measurements in AIDS clinical trials group protocol 019.

Twenty-three different laboratories using four different assay methods reported zidovudine (ZDV; azidothymidine) measurements in a double-blind trial of ZDV for asymptomatic human immunodeficiency virus-infected patients (AIDS Clinical Trials Group Protocol 019). The risk of false-positive ZDV measurements was defined with coded specimens containing no ZDV in a quality control testing program. This testing identified six problem laboratories which reported ZDV levels of greater than or equal to 100 ng/ml for specimens with no ZDV; all of these laboratories used high-performance liquid chromatography. These six laboratories reported a disproportionately high fraction of positive assays for subjects randomized to the placebo group (31% for these 6 laboratories versus 4% for the other 17 laboratories; P less than 0.0001). The high number of false-positive ZDV results reported by these six laboratories suggested that many of the positive results that they reported for patient specimens were also false-positive results. This hypothesis was examined by retesting specimens from patients in the placebo group that had been reported as positive by these laboratories. Ninety percent (19 of 21) of these specimens were negative on retesting at the reference laboratory. These results confirm the hypothesis; they demonstrate the need for quality control testing to avoid the misinterpretation of multicenter trials because of incorrect laboratory data.