Pharmacokinetics of recombinant human interferon-alpha 2a combined with 5-fluorouracil in patients with advanced colorectal carcinoma.

We evaluated the pharmacokinetics of 5-fluorouracil (5-FU) combined with recombinant human interferon (IFN)-alpha 2a in 10 previously untreated patients with advanced colorectal carcinoma. 5-FU was administered as a continuous i.v. infusion, 750 mg/m2/day for 5 days during week 1. One s.c. injection of IFN-alpha 2a, 9 x 10(6) IU, was administered during week 2. Beginning with week 3, a continuous i.v. infusion of 5-FU 750 mg/m2/day for 5 days was administered in combination with IFN-alpha 2a, 9 x 10(6) IU s.c. three times per week. The combination of 5-FU and IFN-alpha 2a was continued every other week until either 3 months after complete remission or tumor progression. No grade 4 toxicity was observed. Granulocytopenia (two patients), leukopenia (one patient), thrombocytopenia (one patient), stomatitis (two patients), fatigue (one patient) and hand-foot syndrome (one patient) were the major (grade 3) toxic reactions encountered. Overall, one complete and six partial responses were noted. The results of the paired t-test showed no statistically significant differences between the means of the two treatments, 5-FU and 5-FU plus IFN-alpha 2a, with respect to the steady-state plasma concentration, area under the concentration-time curve, total body clearance, or steady-state volume of distribution of 5-FU, or the serum concentration of IFN. We conclude that 5-FU and IFN-alpha 2a do not interact pharmacokinetically at the doses and schedules in the regimen studied.

An evaluation of the integration of pharmacokinetic and pharmacodynamic principles in clinical drug development. Experience within Hoffmann La Roche.

The integration of pharmacokinetic and pharmacodynamic principles into drug development has been proposed as a way of making it more rational and efficient. The use of these principles in drug development to make scientific and strategic decisions is defined as the 'pharmacokinetic-pharmacodynamic guided approach to drug development'. The objectives of this survey were: (i) to assess the extent the pharmacokinetic-pharmacodynamic guided approach to drug development has been used in a large multinational pharmaceutical company: (ii) to evaluate the impact of pharmacokinetic and/or pharmacodynamic results on clinical drug development; and (iii) to identify factors which prevented the full application of the pharmacokinetic-pharmacodynamic guided approach. This was done by looking at 18 projects in the current development portfolio at Hoffman La Roche and evaluating the use of this approach by interviewing the responsible clinical pharmacologist using a standardised questionnaire. (i) Benefits from using the pharmacokinetic-pharmacodynamic guided approach were reported in every project, independent of development phase and therapeutic area. This approach was more extensively used in the recent projects. The selection of dosages in clinical studies was found to be the most important application of pharmacokinetic-pharmacodynamic results in terms of an impact on drug development. (ii) Time savings, up to several months, could be quantified in 8 projects during the entry-into-man studies and in 6 projects during the phase II or III studies. In 4 projects, 1 clinical study was avoided. (iii) The most important scientific factor preventing the full application of the approach was the lack of knowledge on the predictive value of the pharmacodynamic or surrogate marker for effect (6 projects). The results of the survey have shown that the use of the pharmacokinetic-pharmacodynamic guided approach has contributed to making clinical drug development more rational and more efficient. Opportunities to apply the pharmacokinetic-pharmacodynamic approach should be identified in each project and a project specific strategy for the pharmacokinetic-pharmacodynamic guided approach should be defined during phase 0 of drug development.

Negligible systemic absorption of topical isotretinoin cream: implications for teratogenicity.

The objective of the study was to assess the extent of systemic exposure of retinoic acid metabolites after excessive application of 0.1% isotretinoin cream in patients with photodamaged skin. This was a single-center, open-label, noncomparative, multiple-dose study of isotretinoin cream. Eighteen female patients with photodamaged skin received a 10 g topical application of isotretinoin cream once daily to a surface area of approximately 2,300 cm2 for 42 days. The patients were not allowed to have high vitamin A-containing foods, vitamin A supplements, or concomitant medications during the entire study period. Plasma levels of four retinoic acids (isotretinoin, tretinoin, 4-oxo-isotretinoin, and 4-oxo-tretinoin) were evaluated after 42 days of isotretinoin application and compared with baseline (pretreatment) levels. The mean area under the curve (AUC) in plasma increased by 48% (+/-SE 9.2) and 77% (+/-13) from the 24-hour pretreatment baseline level for isotretinoin and 4-oxo-isotretinoin, respectively, after treatment with excessive amounts of isotretinoin cream, suggesting systemic absorption of isotretinoin cream. This increase in systemic exposure of retinoic acids was less than that reported earlier after the U.S. recommended daily allowance of 5,000 i.u. of vitamin A supplementation (isotretinoin 141 +/- 19% and 4-oxo-isotretinoin 171 +/- 27%). The minimal systemic availability of isotretinoin cream compared with the U.S. recommended daily allowance for vitamin A supplements provides reasonable evidence for lack of its potential teratogenic risk.

Antimalarial activity in crude extracts of Malawian medicinal plants.

Aqueous and organic fractions from Cassia abbreviata, Senna petersiana (both Caesalpiniaceae) and Azanza garckeana (Malvaceae) were tested for in-vitro antimalarial activity against the multi-drug-resistant, Vietnam-Smith strain of Plasmodium falciparum; VI/S. Both roots and leaves from these Malawian medicinal plants were investigated. High activity, with a median inhibitory concentration < 3 micrograms/ml, was seen in the organic fractions of C. abbreviata and S. petersiana, the two species most commonly cited by traditional healers in an ethnobotanical investigation of Malawian antimalarials. Extracts of A. garckeana showed weaker activity. Biologically active compounds have thus been detected within species of the family Caesalpiniaceae. Ethnobotanical investigation appears to be useful in identifying plants with antimalarial activity.

Use of an indirect pharmacodynamic stimulation model of MX protein induction to compare in vivo activity of interferon alfa-2a and a polyethylene glycol-modified derivative in healthy subjects.

Interferon alfa-2a was chemically modified by the covalent attachment of a polyethylene glycol (PEG) moiety to enhance its circulating half-life and to reduce its immunogenicity. A comparative evaluation of the pharmacokinetics of the PEG-modified interferon alfa-2a showed a greater than twofold increase in the circulating half-life as a result of this chemical modification. An indirect physiologic response model was developed to characterize the time course of the MX protein response after subcutaneous administration of single ascending doses of either interferon alfa-2a or PEG-interferon alfa-2a in healthy volunteers. Analysis of the pharmacokinetic-pharmacodynamic relationship suggested that the PEG-modified interferon alfa-2a could not be administered less than twice weekly and therefore offered little therapeutic advantage over its unmodified counterpart, which is administered three times weekly. These results were consistent with findings in phase II trials. This study substantiates the usefulness of pharmacodynamic modeling as a tool for the development of dose recommendations and for the early selection of drug candidates in the drug development process.

The effect of orlistat, an inhibitor of dietary fat absorption, on the pharmacokinetics of beta-carotene in healthy volunteers.

To assess the influence of orlistat, a lipase inhibitor, on the absorption of beta-carotene, an open-label, parallel, placebo-controlled, randomized, two-way crossover study was performed in 48 healthy volunteers between the ages of 19 and 58 years. Each subject received a single oral dose of 0, 30, 60, or 120 mg beta-carotene (12 subjects per dose level) on the fourth day of treatment with orlistat (120 mg) or placebo 3 times a day for 6 days. The treatments were separated by a washout period of at least 5 weeks. Serial blood samples were collected before and at appropriate intervals after administration of beta-carotene to determine plasma concentrations of unchanged beta-carotene. Short-term (3 to 6 days) treatment with orlistat did not alter endogenous profiles of beta-carotene in plasma. When beta-carotene was given during orlistat treatment, its absorption was reduced by approximately one-third. This reduction was consistent for all three dose levels of beta-carotene studied; however, the results for the 30-mg dose level were subject to greater variability, particularly for area under the concentration-time curve (AUC). It was concluded that two thirds of a supplemental dose of beta-carotene will be absorbed during orlistat treatment; this may be sufficient to achieve physiologic levels of beta-carotene with an appropriate dose of beta-carotene, should supplementation be needed in obese patients who have developed beta-carotene deficiency during therapy with orlistat.

Review of limited systemic absorption of orlistat, a lipase inhibitor, in healthy human volunteers.

Orlistat, a lipase inhibitor, acts locally in the gastrointestinal tract. Systemic absorption is not required for its efficacy, but knowledge of the extent of its systemic absorption is important for its safe use in obese patients, the intended target population. Pharmacokinetic screening was carried out by monitoring plasma concentrations of unchanged orlistat in 25 phase 1 studies (including two mass balance studies) in normal and obese healthy volunteers. The results of these studies indicate an extremely low degree of systemic absorption for orlistat when administered with a hypocaloric, well-balanced diet with 20% to 30% of calories derived from fat (50-80 gm). To further characterize the pharmacokinetics and excretion pathways of orlistat, two mass balance studies using 14C-labeled orlistat were conducted. After oral dosing of radiolabeled orlistat with a fatty meal (28-30 gm fat), almost the entire dose was recovered from fecal samples; little was found in plasma and urine. It is concluded that systemic absorption of orlistat is negligible; at a clinically efficacious dose level, orlistat is unlikely to produce systemic lipase inhibition.

Simultaneous modeling of the pharmacokinetics and pharmacodynamics of midazolam and diazepam.

The pharmacokinetics and pharmacodynamics of midazolam and diazepam were compared after intravenous infusions of 0.03 and 0.07 mg/kg midazolam and 0.1 and 0.2 mg/kg diazepam on four separate occasions in 12 healthy male subjects in a randomized four-way crossover design. The Digit Symbol Substitution Test (DSST) was used as a measure of drug effect. Subjects performed three practice tests before dosing to account for any effects caused by familiarization ("learning curve") with the testing procedure. Pharmacokinetic and pharmacodynamic data were simultaneously fitted to a semiparametric model. In this model, a pharmacokinetic model related dose to plasma concentrations, a link model related plasma concentrations to the concentration at the effect site, and a pharmacodynamic model related the effect site concentration to the observed effect. The plasma-effect site equilibrium half-life was approximately 2 1/2 times longer for midazolam than for diazepam, which is in good agreement with previously published data. Based on the estimated effect site concentration at which half of the maximal effect was reached, midazolam had approximately a sixfold greater intrinsic potency than diazepam. This difference in potency was also observed in a previous study that used transformed electroencephalographic (EEG) data to assess pharmacodynamic activity. The findings reported here with a clinically relevant pharmacodynamic marker (DSST) confirm the utility of surrogate drug effect measures such as EEG. This work also shows the feasibility of conducting pharmacokinetic pharmacodynamic analysis during the drug development process.

The influence of orlistat on the pharmacokinetics and pharmacodynamics of glyburide in healthy volunteers.

To assess the influence of orlistat on the pharmacokinetics and pharmacodynamics (the blood glucose-lowering effect) of glyburide, an open-label, placebo-controlled, randomized, two-way crossover study was done in 12 healthy male volunteers. Each subject received single 5-mg oral doses of glyburide (Micronase; The Upjohn Company, Kalamazoo, MI) on the fifth day of treatment with placebo (treatment A) and 80-mg orlistat (treatment B) three times a day for 4 1/3 days; the two treatments were separated by a five-day washout period. Serial blood samples were collected before and at appropriate intervals after each glyburide dose to determine plasma concentrations and blood glucose levels. Values of Cmax and AUC of glyburide showed an equality of the two treatments by the analysis of variance. There was an apparent correlation between blood glucose level and the logarithm of plasma glyburide concentration; this relationship appeared to not be altered when glyburide was administered with orlistat. In conclusion, orlistat administered at doses of 80-mg three times daily does not significantly alter the pharmacokinetics and blood glucose-lowering effect of a single 5-mg oral dose of glyburide in healthy volunteers.

The pharmacokinetic-pharmacodynamic (Digit Symbol Substitution Test) relationship of flumazenil in a midazolam steady-state model in healthy volunteers.

To characterize the plasma concentration-effect relationship of flumazenil in the presence of a predefined midazolam level, a double-blind, placebo-controlled, randomized two-way crossover study was conducted in nine healthy male subjects. After reaching a criterion level of midazolam-induced depression of the Digit Symbol Substitution Test (DSST), volunteers received a dose of flumazenil (1.0 mg) or placebo over 1 minute, with the infusion of midazolam continued. Blood samples were collected, simultaneously with the DSST assessment, at predetermined intervals and were assayed for flumazenil and/or midazolam plasma concentrations. Pharmacokinetic-pharmacodynamic modeling techniques were used to estimate the equilibration rate constant (keo) between plasma concentration and effect for flumazenil; a sigmoidal maximum-effect model was used to relate the DSST score to the flumazenil plasma concentration. Flumazenil exhibited a rapid onset (the half-life of equilibration between drug concentration in the blood and drug effect was 3.3 minutes) and short duration of action (the flumazenil plasma concentration causing half-maximal effect was 7.4 ng/ml, which was reached about 1 hour after dosing). The results of this study also show the competitive nature of flumazenil as a midazolam antagonist.

Retrospective population-based analysis of the dose-response (fecal fat excretion) relationship of orlistat in normal and obese volunteers.

Orlistat, an inhibitor of gastrointestinal lipases, limits the absorption of ingested fat and could become a potential treatment for obesity. This analysis was performed to elucidate the relationship between orlistat dose and intensity of inhibition of dietary fat absorption (assessed by measuring fecal fat excretion). In 11 phase I double-blind, placebo-controlled, parallel-group randomized studies, a total of 171 subjects received oral daily doses that ranged from 30 to 1200 mg orlistat or matching placebo three times a day for 9 to 10 days. The results of the daily mean fecal fat excretion percentage (relative to ingested fat) were correlated to the orlistat daily dose. A simple maximum-effect model that included a basal value was used to fit the dose-response relationship for all evaluable subjects. The mean maximum percentage of ingested fat excreted in the feces was approximately 32% during orlistat administration compared with 5% during placebo administration. The orlistat daily dose that produced 50% of the maximum effect was 98 mg/day. The model-fitting suggests the existence of a steep portion of the dose-response curve up to approximately 400 mg/day, with a subsequent tendency to plateau at higher doses. Such an analysis was instrumental in identifying appropriate doses to be used in therapeutic trials for weight loss in obese patients.

High clearance of (S)-warfarin in a warfarin-resistant subject.

A 30 year old black male required a 60 mg daily dose of warfarin to elicit a therapeutic anticoagulant response (normal warfarin dose 2.5-10 mg day-1; maximum 15 mg day-1). Hereditary warfarin resistance was suspected after compliance, diet, concurrent medication and any gastrointestinal disorder were eliminated as contributory causes. The disposition of vitamin K and vitamin K epoxide was examined in the propositus, his two sisters and 13 control black male subjects. Each subject was given an i.v. bolus dose (5 mg) of vitamin K prior to and after 2 weeks of warfarin therapy (5 mg day-1). The oral clearances of (S)- and (R)-warfarin were also measured in each subject during the last day of warfarin therapy. The mean (+/- s.d.) systemic clearance of vitamin K was similar in all subjects before (114 +/- 35 ml min-1) and after (112 +/- 40 ml min-1) warfarin therapy. The mean (+/- s.d.) AUC value for vitamin K epoxide was increased by warfarin treatment (6.5 +/- 5.4 micrograms ml-1 min before and 139 +/- 78 micrograms ml-1 min after) in all subjects. In the propositus, the oral clearance of (S)-warfarin (14.5 ml min-1) and the clearance ratio for (S)/(R)warfarin (2.6) differed by more than 7 standard deviations from the control group (4.3 +/- 1.1 ml min-1 and 1.2 +/- 0.2, respectively). In one sister of the propositus, the stereoselective disposition of warfarin was comparable with that of her brother ((S)-warfarin clearance = 16.2 ml min-1; and (S)/(R)-warfarin clearance ratio = 2.7).

Pharmacokinetics of Ro 23-9424, a dual-action cephalosporin, in animals.

Ro 23-9424 is a dual-action cephalosporin with an aminothiazolylmethoxyimino-type side chain at the 7 position and fleroxacin esterified at the 3' position. The new compound has broad and potent antibacterial activity in vitro and in vivo, reflecting contributions from both the beta-lactam moiety and the quinolone moiety. In animals, the ester bond potentially could be hydrolyzed enzymatically or nonenzymatically, to yield the active metabolites desacetylcefotaxime and fleroxacin. The extent to which Ro 23-9424 acts in vivo as a true dual-action cephalosporin, or acts as a combination of active metabolites, is therefore a function of its pharmacokinetic properties. To investigate these properties, Ro 23-9424 was administered as a single intravenous dose of 20 mg/kg of body weight to mice, rats, dogs, and baboons. Timed plasma samples were assayed by an ion-paired high-pressure liquid chromatography method that allowed detection of both intact Ro 23-9424 and fleroxacin. The pharmacokinetic parameters of Ro 23-9424 were similar to published results for cefotaxime, while concentrations of fleroxacin in plasma were low and fairly constant (about 1 to 3 micrograms/ml) in all species, suggesting that excretion of the intact molecule is a major route of elimination for Ro 23-9424, as it is for cefotaxime. For technical reasons, urinary recovery of Ro 23-9424 was not quantitated, but intact Ro 23-9424 was found in high concentrations (greater than 400 micrograms/ml) in mouse urine aspirated directly from the bladder. In all species, low concentrations of free fleroxacin in plasma persisted after the elimination of Ro 23-9424 was complete, but fleroxacin did not accumulate unduly in a 14-day multiple-dose experiment in baboons. Thus, it seems likely that the activity seen in vivo is primarily due to intact Ro 23-9424, although the low levels of free fleroxacin may also have some therapeutic significance.

Synthesis and mechanisms of decomposition of some cephalosporin prodrugs.

The delta-3 and delta-2 methyl esters of cefazolin were synthesized. The kinetics and mechanisms of degradation of the methyl esters and the delta-3 and delta-2 isomers of pivaloyloxymethyl prodrug esters of the new cephalosporin ceftetrame (Ro 19-5247) were investigated in buffer systems and in human plasma in vitro. The major hydrolytic products of all the delta-3 and delta-2 esters were the inactive delta-2 cephalosporin free acids. The following reaction scheme describes the in vitro hydrolysis of these compounds: [formula: see text]. In addition, there was evidence of opening of the beta-lactam ring to form cephalosporoic acid when the methyl ester of cefazolin was studied in human plasma and in the presence of penicillinase. For the methyl esters, the processes represented by k12, k21, and k20 were operative in buffers; in human plasma, the processes represented by k12, k21, and k20 were operative in addition to cephalosporoic acid formation. For the isomers of the cephalosporin prodrug ester Ro 19-5248 only k12 and k20 were operative in buffers; in human plasma all pathways were operative and there was no evidence of cephalosporoic acid formation. In all cases, the processes represented by k12, k21, and k20 were subject to general and/or specific base catalysis.

Lack of probenecid effect on nonrenal excretion of ceftriaxone in anephric patients.

Probenecid has been shown to decrease renal and biliary excretion of organic acids. In a randomized crossover study, the effect of coadministered probenecid on nonrenal excretion of ceftriaxone was studied in six functionally anephric patients in whom ceftriaxone is eliminated exclusively by nonrenal or presumably by biliary excretion. Each patient received 0.5 g IV ceftriaxone without and with probenecid (0.5 g at 10 and 2 hours prior to ceftriaxone and 0.5 g q12h X 3 doses post ceftriaxone). Serial blood samples were collected over 48 hours and plasma analyzed for ceftriaxone by high performance liquid chromatography (HPLC). Pharmacokinetic analysis was based on a model-independent approach. Probenecid did not significantly affect the disposition of ceftriaxone in this study, thus suggesting that nonrenal excretion of ceftriaxone is not inhibited by probenecid.

The pharmacokinetics of midazolam in patients with congestive heart failure.

The disposition of midazolam was investigated in six patients with congestive heart failure (CHF) and six age- and weight-matched healthy subjects by administering two single doses of the drug (3.75 mg i.v. and 7.5 mg p.o.) separated by 1 week. Serial blood samples were collected for 24 h after each dose and plasma was assayed for midazolam by GC-MS. In the CHF patients, the elimination half-life was prolonged (4 to 4.5 vs less than 3 h), the systemic clearance was lowered (376 vs 551 ml min-1) and the peak plasma drug concentration after the p.o. dose was higher (76 vs 42 ng ml-1). The systemic availability (45 vs 41%), the steady state volume of distribution (111 vs 108 l) and the time of peak plasma drug concentration after the p.o. dose (0.9 vs 0.9 h) were unchanged. The predominant effect of CHF was on the clearance of midazolam which was decreased by 30%. The drug was well tolerated and did not cause any adverse effects.

Increased volume of distribution prolongs midazolam half-life.

It has recently been shown by several investigators that the half-life (t1/2) of midazolam is prolonged (greater than 7 h) in a small proportion of the population. One group has inferred that this subpopulation represents a group of slow metabolizers of midazolam to alpha-OH-midazolam. Others disagree and postulate that there is an increase in the volume of distribution (V) resulting in a prolonged t1/2. This controversy led us to report experience from 90 subjects and patients where t1/2, V, and clearance (CL) were determined by both model-dependent and -independent pharmacokinetic analysis. We found a 5.6% (5 of 90) incidence of prolonged t1/2, similar to that previously reported. V was clearly increased without a decrease in CL in the five subjects with prolonged t1/2. Thus, the prolonged t1/2 is secondary to an increase in V and not a result of alterations in CL and metabolism.

Potencies of ceftriaxone and cefotaxime in a single chamber pharmacokinetic system simulating their in vivo half-lives.

Ceftriaxone and cefotaxime are third-generation cephalosporins with similar in vitro potencies and spectra. However, previous studies have shown that ceftriaxone had superior in vivo activity (mouse PD50 values greater than or equal to 2-fold lower) compared to cefotaxime in 23 of 46 tested enterobacteriaceae. This superior activity was thought to be due to ceftriaxone's 5- to 8-fold longer half-life. The relationship between half-life (ceftriax-one 6 h, cefotaxime 1 h) and potency was examined by following bacterial kill curves in a single chamber, open-ended perfusion model over an 8-hour period. Both antibiotics were compared for efficacy at both half-lives against four gram-negative bacteria. For two of the bacterial strains antibiotic potency differences in the perfusion model were determined largely by pharmacokinetics. For the other two strains intrinsic bacterial and antibiotic properties were of prime importance.