Pharmacokinetics and tolerance of ciprofloxacin after sequential increasing oral doses.

The pharmacokinetics and safety of orally administered ciprofloxacin (Bay o 9867) were examined in 12 healthy male volunteers who received sequential doses of 250, 500, 750, and 1,000 mg. The individual and mean data were best described by biexponential disposition and elimination, assuming an apparent zero-order rate of absorption. The peak serum concentrations determined from the individual data occurred at approximately 1.5 h after each dose and ranged from 0.42 to 4.2 micrograms/ml; the mean peak concentrations increased in proportion to the dose. The areas under the curve determined from the mean data were also proportional with respect to dose. The mean elimination half-lives calculated from pooled data were 4.1, 4.1, 6.9, and 6.3 h for doses of 250, 500, 750, and 1,000 mg, respectively. Longer half-lives but proportional area-under-the-curve values after the 750- and 1,000-mg doses implied that smaller fractions of ciprofloxacin were absorbed after these doses, although nonlinear kinetics could not be ruled out. The mean serum concentrations 12 and 24 h following each dose were greater than or equal to 0.08 and 0.01 micrograms/ml, respectively. The urinary concentrations ranged from 30 to 500 micrograms/ml for at least 12 h after administration and were greater than or equal to 9 micrograms/ml at 24 h following each dose. The urinary recovery level of unchanged ciprofloxacin over a 24-h period ranged from 28 to 44%. The mean renal clearances for each dose ranged from 300 to 500 ml/min. Ciprofloxacin was well tolerated, and no significant clinical or laboratory abnormalities were observed.     

Norfloxacin disposition after sequentially increasing oral doses.

Single doses of norfloxacin (200, 400, 800, 1,200, and 1,600 mg) or placebo were administered orally at weekly intervals to 14 healthy male volunteers in a double-blind study. Norfloxacin was measured in serum and urine by high-pressure liquid chromatography with UV detection. The concentrations of this drug in serum peaked 1 to 2 h after each dose; the mean peak values for increasing doses were 0.75, 1.58, 2.41, 3.15, and 3.87 micrograms/ml. Mean area under the serum concentration-time curves for the first 12 h after each dose were 3.56, 6.26, 11.4, 16.1, and 19.7 micrograms . h/ml, respectively. The elimination half-life of norfloxacin was about 7 h and was similar for all doses. The concentrations of the drug in urine also peaked 1 to 2 h after dosage; mean peak values for increasing doses were 200, 478, 697, 992, and 1,045 micrograms/ml. Renal clearances approximated 285 ml/min. About 30% of each dose was excreted into urine as unmetabolized norfloxacin. Crystals of the drug were occasionally observed during microscopic examination of freshly voided urine collected after the 1,200- and 1,600-mg doses. Crystalluria was not encountered at lower doses.     

Pharmacokinetics and safety of lomefloxacin following multiple doses

This was a randomized, double-blind, placebo-controlled study comparing the safety and tolerance of 400 mg lomefloxacin, given orally twice daily, to that of placebo administered to eight and four subjects, respectively, for 2 wk. This dose, interval, and duration of dosing were chosen to be identical to the highest anticipated clinical dose for the longest anticipated clinical duration. Subject assessments included ophthalmological examinations performed prior to the study, at midstudy, and after the dosing. No clinically significant differences from baseline were observed for any test result. Analysis of trough plasma concentrations, CMIN, showed that steady state was achieved on Day 4 (Fig. 2). At steady-state, mean plasma concentrations of lomefloxacin ranged from a maximum of 4.86 micrograms/ml to a minimum of 1.47 micrograms/ml. Mean time to maximum plasma concentration on Day 14 was 1.23 hr in the morning and 3.81 hr in the evening. Plasma half-life was approximately 8 hr. Lomefloxacin was well tolerated at 400 mg administered twice daily for 2 wk; plasma concentrations were maintained at a level that is above the MIC of most clinically significant isolates.     

Pharmacokinetics of temafloxacin in humans after single oral doses.

Temafloxacin (A-63004) is a new quinolone antibacterial agent with a broad spectrum of activity against gram-positive and gram-negative aerobes and anaerobes. The pharmacokinetics and metabolism of temafloxacin were determined in healthy volunteers after administration of single oral doses of 100, 200, 400, 600, 800, and 1,000 mg. The corresponding peak concentrations in plasma (mean +/- standard deviation) were 0.98 +/- 0.26, 1.61 +/- 0.57, 2.43 +/- 0.56, 3.87 +/- 0.64, 4.54 +/- 1.03, and 6.67 +/- 0.74 micrograms/ml. The times that elapsed to attain peak levels ranged from 1.25 to 3.5 h. Statistical analyses of parameters related to the extent of absorption and the linearity of the dispositional pharmacokinetics detected no dose-related trends. Study-wide, total clearance (223 ml/min) and renal clearance (125 ml/min) showed low intersubject variability, with coefficients of variation near 20%. The terminal-phase rate constant of 0.090 +/- 0.008 h-1 corresponds to a half-life of 7.7 h. Temafloxacin was excreted mainly in the urine, with 57 +/- 11% of the dose appearing in the urine unchanged. Conjugated temafloxacin, oxidative metabolites, and conjugates thereof were minor components in urine, collectively accounting for 5 to 8% of the dose. Since intravenously dosed dogs eliminated 50% of the dose by nonrenal processes, urinary recoveries approaching two-thirds of the dose in humans were consistent with high, if not quantitative, absorption. Reported adverse events were generally mild, were randomly distributed between temafloxacin- and placebo-treated subjects, and were not dose related.     

Pharmacokinetics of temafloxacin in humans after multiple oral doses.

The multiple-dose pharmacokinetics and tolerance of temafloxacin, a new fluoroquinolone antibacterial agent, were evaluated in healthy volunteers. Temafloxacin was found to be well tolerated when administered orally every 12 h for 7 days at doses of 100, 200, 300, 400, 600, and 800 mg. Steady-state maximum and minimum concentrations in plasma were proportional to dose, averaging slightly over 1.0 and 0.5 microgram/ml/100 mg administered. Analyses of variance found no significant differences among the dosage groups in total apparent clearances (CLT/F), renal clearances (CLR), or nonrenal clearances, which averaged 197, 119, and 78 ml/min, respectively. The half-life increased slightly with dose, averaging 8.4 h overall. The extent of absorption of temafloxacin was quite reproducible, with day-to-day intrasubject variability in minima averaging under 10%. Renal glomerular filtration of unbound drug was the dominant elimination process; however, tubular secretion and reabsorption also appear to occur. Secretion was estimated to account for about 12% of CLT/F during a regimen of 600 mg every 12 h. CLR was relatively constant for urine flow rates above 1 ml/min, but reabsorption appeared to occur under low-flow conditions, resulting in day-versus-night differences in CLR. Intersubject variability in CLT/F over the eightfold range in dosage was only 20%, and 60% of this variance was accounted for by differences in body surface area (or lean body mass), concentration in plasma, and urine flow rate. Overall, it appears that the pharmacokinetics of temafloxacin are essentially linear, reproducible within a subject, and predictable among subjects.     

Pharmacokinetics and tolerability of teicoplanin in healthy volunteers after single increasing doses.

In this double-blind, randomized study, five healthy subjects per group received doses of 15, 20, or 25 mg of teicoplanin per kg of body weight, and one subject per group received a 0.9% NaCl placebo as single intravenous infusion over 30 min. Serial blood samples and urine were collected for 13 days postadministration, and concentrations of teicoplanin were determined by microbiological assay. The pharmacokinetic data were analyzed by noncompartmental and compartmental analyses. Laboratory safety tests, audiometry, and serum creatinine clearance measurements were done prior to day 1 and on days 2 and 14. In the three groups, peak levels at the end of the infusion averaged 194, 197, and 253 mg/liter, respectively. Mean concentrations in plasma 24 h after the administration were 10.5, 13.6, and 19.8 mg/liter, respectively. Mean values of volume of distribution at steady state were 0.80, 0.87, and 0.87 liters/kg, respectively. Terminal half-lives averaged 88, 83, and 92 h. Mean total clearance values were 10.9, 11.0, and 11.3 mg/h/kg, respectively, with renal clearance accounting for 75, 81, and 78%, respectively, of the total. The 13-day cumulative mean urinary recovery ranged from 71 to 78% of the dose within the groups. The pharmacokinetics of teicoplanin appears to be linear in the range of administered doses. Teicoplanin was generally well tolerated. Side effects, appearing in five subjects, were represented by fevers, chills, and skin reactions; these adverse reactions were mild, but one episode of rash necessitated the interruption of infusion, and one episode of chills necessitated treatment with corticosteroids. There was no indication of drug-related modifications of laboratory test results.     

Pharmacokinetics of rufloxacin in healthy volunteers after repeated oral doses.

Rufloxacin is a new broad-spectrum fluoroquinolone antibacterial agent. The pharmacokinetics and safety of rufloxacin were evaluated after repeated oral administration to healthy volunteers. The drug was administered once a day for 6 consecutive days following two different dose schedules. The first group of 11 subjects was given a loading dose of 300 mg on the first day and 150 mg on the subsequent 5 days. The second group of 12 subjects was given a loading dose of 400 mg and 200 mg for 5 days. Serum levels and urine concentrations of rufloxacin were determined by microbiological assay. A simultaneous fit of all data points for each subject was done according to a one-compartment open model. The drug was rapidly absorbed (absorption half-life 17 +/- 6 min in the 300 + 150 mg and 11 +/- 5 min in the 400 + 200 mg dose regimen group) and reached maximal serum concentrations (2.77 +/- 0.24 and 3.62 +/- 0.35 micrograms/ml) 4.2 +/- 0.4 and 4.0 +/- 0.9 h after the first administration. Steady-state serum concentrations (3.19 +/- 0.31 and 4.06 +/- 0.33 micrograms/ml) were reached in 3.7 +/- 0.7 and 4.5 +/- 0.4 days. Elimination half-lives were 29.5 +/- 2.4 and 36.0 +/- 2.8 h. Apparent volumes of distribution were 111 +/- 8 and 136 +/- 16 liters and apparent plasma clearances were 46 +/- 5 and 44 +/- 4 ml/min. Renal clearances were 18 +/- 3 and 17 +/- 2 ml/min.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacokinetics and tolerance of DU-6859a, a new fluoroquinolone, after single and multiple oral doses in healthy volunteers.

The pharmacokinetics and tolerance of DU-6859a, 7-[(7S)-7-amino-5-azaspiro[2,4]heptan-5-yl]-8-chloro-6-fluor o-1-[(1R, 2S)-2-fluoro-1-cyclopropyl]-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid sesquihydrate, were investigated in healthy male Japanese volunteers after single (25, 50, 100, and 200 mg) and multiple (100 mg three times a day for 6 days plus once a day on the 7th day and 50 mg every 12 h for 13 doses) oral doses. DU-6859a was well tolerated at all doses, and all 36 subjects completed the study; mild transient soft stool in five volunteers and mild transient diarrhea in one volunteer on the multiple-dose (100 mg three times a day) study were the only side effects reported. No drug crystals were observed in the urine after the single 200-mg dose and the 100-mg three times a day regimen. DU-6859a was rapidly absorbed in the fasted state. The mean maximum concentration in serum (Cmax) ranged from 0.29 to 1.86 micrograms/ml for the 25- to 200-mg dose, and the mean time to reach Cmax ranged from 1.0 to 1.3 h. The terminal half-life ranged from 4.4 to 5.0 h. The area under the curve increased dose dependently. The serum protein binding of the drug was approximately 50%. The apparent volume of distribution clearly exceeded 1 liter/kg, suggesting good tissue penetration. Within 48 h, the cumulative urinary recovery of unchanged drug amounted to 69 to 74% of the dose administered, while fecal excretion up to 48 h after the 200-mg dose accounted for ca. 3% of the dose. Food intake did not affect the rate and extend of absorption of DU-6859a to a clinically significant extent. During multiple oral dosing, the accumulation of the drug in serum was close to the theoretically predicted values, which indicated that there was virtually no drug accumulation.     

Pharmacokinetics of clarithromycin, a new macrolide, after single ascending oral doses.

The pharmacokinetics and safety of single ascending doses of clarithromycin (6-0-methylerythromycin A) were assessed in a placebo-controlled, double-blind, randomized trial with 39 healthy male volunteers. Subjects were randomized to receive single doses of either placebo or 100, 200, 400, 600, 800, or 1,200 mg of clarithromycin. Blood and urine collections were performed over the 24 h following administration of the test preparation. Biological specimens were analyzed for clarithromycin and 14(R)-hydroxyclarithromycin content by a high-performance liquid chromatographic technique. The pharmacokinetics of clarithromycin appeared to be dose dependent, with terminal disposition half-life ranging from 2.3 to 6.0 h and mean +/- standard deviation area under the concentration-versus-time curve from time 0 to infinity for plasma ranging from 1.67 +/- 0.48 to 3.72 +/- 1.26 mg/liter.h per 100-mg dose over the 100- to 1,200-mg dose range. Similar dose dependency was noted in the pharmacokinetics of the 14(R)-hydroxy metabolite. Mean urinary excretion of clarithromycin and its 14(R)-hydroxy metabolite ranged from 11.5 to 17.5% and 5.3 to 8.8% of the administered dose, respectively. Urinary excretion data and plasma metabolite/parent compound concentration ratio data suggested that capacity-limited formation of the active metabolite may account, at least in part, for the nonlinear pharmacokinetics of clarithromycin. No substantive dose-related trend was observed for the renal clearance of either compound. There were no clinically significant drug-related alterations in laboratory and nonlaboratory safety parameters. In addition, there was no significant difference between placebo and clarithromycin recipients in the incidence or severity of adverse events. Clarithromycin appears to be safe and well tolerated.     

Pharmacokinetics of the bronchodilator tulobuterol in man after repeated oral doses

Plasma levels and elimination half-life of tulobuterol, a new beta-adrenergic agonist, were determined in ten healthy male volunteers after repeated dosing with 2 mg, twice daily, for seven days. Peak plasma levels attained (2.8 +/- 0.8 ng/ml), the time to peak plasma concentration (1.0 +/- 0.3 hr) and the elimination half-life (2.4 +/- 0.4 hr) were generally unchanged from the first to the final study dose. This suggests that tulobuterol does not accumulate in plasma after repeated administration of a dose regimen known to be clinically effective.     

Pharmacokinetics of azithromycin in pediatric patients after oral administration of multiple doses of suspension.

Azithromycin is an azalide antibiotic. On the basis of data in adults, azithromycin appears to have a greater distribution into tissues, a longer elimination half-life, and a lower incidence of adverse effects than the macrolide antibiotic erythromycin. However, little about the pharmacokinetics of azithromycin in children is known. The objective of our study was to characterize the pharmacokinetics of azithromycin after oral administration of multiple doses of suspension to children with streptococcal pharyngitis. Fourteen children (6 to 15 years of age) received a single oral dose of 10 mg of azithromycin per kg of body weight on day 1 followed by single daily doses of 5 mg/kg on days 2 to 5. Each child fasted overnight before receiving the final dose on day 5. Blood samples were collected at 0, 0.5, 1, 2, 4, 6, 8, 12, 24, 48, and 72 h after this last dose. Concentrations of azithromycin in serum were measured by a specific high-performance liquid chromatography-mass spectrometry method. The mean +/- standard deviation for maximum concentration of drug in serum, time to maximum concentration of drug in serum, and area under the curve (0 to 24 h) were 383 +/- 142 ng/ml, 2.4 +/- 1.1 h, and 3,109 +/- 1,033 ng.h/ml, respectively. Concentrations in serum at 0 h (predose) and at 24, 48, and 72 h after the final dose were 67 +/- 31, 64 +/- 24, 41 +/- 17, and 29 +/- 14 ng/ml, respectively. Thus, once-daily administration of azithromycin resulted in sustained systemic exposure to the drug.     

Pharmacokinetics of methotrimeprazine after single and multiple doses.

Concentrations of methotrimeprazine and a metabolite, methotrimeprazine sulfoxide, were measured in plasma after a single intramuscular dose and after single and multiple oral doses of methotrimeprazine. The highest plasma concentrations of methotrimeprazine were found 30 to 90 min after intramuscular injection, and 1 to 3 hr after oral administration. On average 50% of orally administered drug reached the general circulation as unchanged methotrimeprazine. The apparent volume of distribution (Vbeta) was 23 to 42 L/kg body weight, and the biologic half-life, 15 to 30 hr. The sulfoxide could not be traced in plasma after a 25-mg intramuscular dose, but was found in higher plasma concentrations than the unmetabolized drug after single and multiple oral doses. This could be due to oxidation of the drug either in the gastrointestinal lumen or in the intestinal wall, or during its first passage through the liver. The apparent half-life of the sulfoxide was on average 30% shorter than the half-life of methotrimeprazine.     

Pharmacokinetics and tissue penetration of orally administered lomefloxacin.

The pharmacokinetics of the quinolone lomefloxacin were determined following a single 400-mg oral dose given to each of six male volunteers. Concentrations in serum, urine, and cantharidin-induced inflammatory fluid were determined by a microbiological assay. Samples from two volunteers were also assayed by high-performance liquid chromatography. The mean peak level in serum, 4.7 micrograms/ml, was attained within 1 h of administration. The mean elimination half-life from serum was 7 h. Inflammatory fluid was penetrated rapidly, with a mean peak level of 3.5 micrograms/ml occurring after 2.7 h. The mean recovery of lomefloxacin from urine over 48 h was 76% of the administered dose. There was a minor peak on the high-performance liquid chromatography trace, suggesting a small amount of unidentified metabolite. This was present only in urine; no detectable metabolites were found in serum. This study suggests that either once-daily or twice-daily dosage of lomefloxacin should be sufficient to treat urinary or systemic infections, respectively, caused by susceptible pathogens.     

Tolerance and pilot pharmacokinetics of amiflamine after increasing single oral doses in healthy subjects

Oral doses of 1 to 100 mg amiflamine, a new reversible monoamine oxidase type A-selective inhibitor, were given for the first time in humans to six healthy men. No apparent pharmacologic effects were recorded until the 80 mg dose. After 100 mg, one subject developed symptoms indicative of an overdose. Amiflamine is extensively metabolized by two consecutive N-demethylations. The biotransformation patterns in plasma and urine were found to correlate with the debrisoquin metabolic ratio.     

Pharmacokinetics of ofloxacin after parenteral and oral administration.

In 10 volunteers, the pharmacokinetics of ofloxacin [HOE 280, DL 8280; (+/-)-9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7H -pyrido-[1,2,3-de] [1,4]benzoxacine-6-carboxylic acid] was determined after administration of 25, 50, 100, and 200 mg intravenously (30-min infusion) as well as 200 and 400 mg orally. Concentrations in serum and urine were measured by high-pressure liquid chromatography. Concentrations in serum following different parenteral ofloxacin dosages demonstrated dose dependency with long biological half-lives of 231 to 267 min. Pharmacokinetic parameters were calculated on the basis of open two- and three-compartment models, which yielded nearly identical results. High volumes of distribution (1.2 to 1.4 liters/kg of body weight) suggested effective diffusion into the extravascular space. High total and renal clearances indicated primarily renal excretion with additional elimination pathways, such as tubular secretion and extrarenal elimination. After oral administration, absorption was excellent, and the absolute bioavailability following 200 mg of ofloxacin could be calculated at greater than 0.95. Maximal concentrations in serum were attained 1.2 to 1.9 h after dosing; areas under the curve increased in proportion to dose between 200 and 400 mg of oral ofloxacin. The amount of known metabolites (demethyl and N-oxide compounds) excreted in urine reached only 4.3% (intravenously) and 4.0% (orally). Transient headaches in some volunteers were the only side effects registered.     

Pharmacokinetics of ciprofloxacin after oral and parenteral administration.

In 12 fasting volunteers, the pharmacokinetics of ciprofloxacin (Bay o 9867; 1-cyclopropyl-6-fluor-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinoline carbonic acid) were determined after the administration of 50, 100, and 750 mg orally as well as 50 and 100 mg intravenously over 15 min. Serum and urine concentrations were detected with a bioassay. In addition, urine concentrations after a 50-mg dosing were measured by high-pressure liquid chromatography. The serum course of ciprofloxacin could best be described by an open three-compartment model. High volumes of distribution (exceeding 200 liters/100 kg) suggested effective diffusions in the extravascular space. The terminal half-life of ciprofloxacin ranged between 3 and 4 h. High total and renal clearances suggested additional elimination pathways, such as tubular secretion, metabolism, or biliary excretion. After oral administration, absorption was sufficient, and the absolute bioavailability varied between 0.77 and 0.63. Maximal serum concentrations were attained 0.5 to 1 h after dosing; the higher dosage tended towards a delay in absorption. The proportion of the relative amount of metabolites to the total amount of drug excreted in urine increased from 29.7% after intravenous administration to 42.7% after oral dosing, indicating a first-pass effect of the liver. Ciprofloxacin concentrations with a bioassay were 3 to 27% higher than with high-pressure liquid chromatography, which may indicate the presence of biologically active metabolites. No side effects were recorded.     

Pharmacokinetics and tissue penetration of linezolid following multiple oral doses

The pharmacokinetics of multiple-dose linezolid were determined following administration of five 600-mg oral doses given every 12 h to each of six healthy male volunteers. Concentrations of the drug were determined in plasma and inflammatory blister fluid using high-pressure liquid chromatography. A mean peak concentration in plasma of 18.3 microg/ml (standard deviation [SD], 6.0) was attained at a mean time of 0.7 h (SD, 0.3) after the final dose. The penetration into the inflammatory fluid was 104% (SD, 20.7). A mean peak concentration of 16.4 microg/ml (SD, 10.6) was attained in the inflammatory fluid at 3 h (SD, 0.6) after the final dose. The elimination half-life from serum and inflammatory fluid was 4.9 (SD, 1.8) and 5.7 (SD, 1.7) h, respectively. The area under the concentration-time curve in plasma and blister fluid was 140.3 (SD, 73.1) and 155.3 (SD, 80.1) microg x h/ml, respectively. These data suggest that linezolid has good tissue penetration, and we can predict that it will be successful in the treatment of a variety of gram-positive infections.     

Pharmacokinetics of clinafloxacin after single and multiple doses

Clinafloxacin (CI-960) is a potent broad-spectrum, fluoroquinolone antibiotic that has been studied for parenteral and oral administration in patients with serious infections. The objectives of these studies were to examine the pharmacokinetics and safety of clinafloxacin following administration of single and twice-daily intravenous (i.v.) and oral doses to volunteers. Plasma and urine samples were assayed by validated liquid chromatographic methods, and pharmacokinetic parameter values were determined by noncompartmental methods. Safety was evaluated by clinical observation and laboratory tests. Absorption was rapid after oral administration, with maximum concentrations in plasma (C(max)) generally occurring within 2 h. Concentrations in plasma declined biexponentially, with an average terminal half-life of 4 to 6 h after single doses and 5 to 7 h after multiple doses. Increases in C(max) and area under the concentration-time curves (AUC) were generally proportional to the dose. The volume of distribution was much greater than total body water. Approximately 40 to 75% of the clinafloxacin doses were excreted unchanged into urine. Absolute bioavailability of orally administered clinafloxacin was approximately 90% and did not change with increasing dose. Therefore, switching patients from i.v. to oral dosing should achieve similar concentrations in plasma. The tolerability of clinafloxacin was acceptable. No serious adverse events occurred. C(max) values and minimum plasma clinafloxacin concentrations during multiple dosing exceeded MICs for a wide range of organisms.     

Pharmacokinetics of BILR 355 after multiple oral doses coadministered with a low dose of ritonavir

The pharmacokinetics and safety of BILR 355 following oral repeated dosing coadministered with low doses of ritonavir (RTV) were investigated in 12 cohorts of healthy male volunteers with a ratio of 6 to 2 for BILR 355 versus the placebo. BILR 355 was given once a day (QD) coadministered with 100 mg RTV (BILR 355/r) at 5 to 50 mg in a polyethylene glycol solution or at 50 to 250 mg as tablets. BILR 355 tablets were also dosed at 150 mg twice a day (BID) coadministered with 100 mg RTV QD or BID. Following oral dosing, BILR 355 was rapidly absorbed, with the mean time to maximum concentration of drug in serum reached within 1.3 to 5 h and a mean half-life of 16 to 20 h. BILR 355 exhibited an approximately linear pharmacokinetics for doses of 5 to 50 mg when given as a solution; in contrast, when given as tablets, BILR 355 displayed a dose-proportional pharmacokinetics, with a dose range of 50 to 100 mg; from 100 to 150 mg, a slightly downward nonlinear pharmacokinetics occurred. The exposure to BILR 355 was maximized at 150 mg and higher due to a saturated dissolution/absorption process. After oral dosing of BILR 355/r, 150/100 mg BID, the values for the maximum concentration of drug in plasma at steady state, the area under the concentration-time curve from 0 to the dose interval at steady state, and the minimum concentration of drug in serum at steady state were 1,500 ng/ml, 12,500 h·ng/ml, and 570 ng/ml, respectively, providing sufficient suppressive concentration toward human immunodeficiency virus type 1. Based on pharmacokinetic modeling along with the in vitro virologic data, several BILR 355 doses were selected for phase II trials using Monte Carlo simulations. Throughout the study, BILR 355 was safe and well tolerated.