An evaluation of human ADME and mass balance studies using regular or low doses of radiocarbon.

There has been increased interest in conducting human absorption, distribution, metabolism, and excretion (ADME) studies with low doses (up to 0.1 MBq) as opposed to regular doses (1.85-3.7 MBq) of radiocarbon (14 C). This is due to the fact that low-dose human ADME studies may be conducted without dosimetry calculations and will lead to lower human radiation exposure. Here, we sought to compare the outcomes of low-dose versus regular-dose human ADME studies in healthy volunteers. Forty oral human ADME studies conducted at PRA were surveyed, among which 12 were low-dose studies. The fraction of drug material absorbed was 67% ± 7% in the regular-dose studies (data for 13 studies) versus 39% ± 16% in the low-dose studies (data for 5 studies). The average total recovery of 14 C in excreta was 93% ± 5% for regular-dose studies, and 21 of 28 such studies showed recoveries more than 90%. For low-dose studies, average total recovery was 89% ± 9%, and 6 of 12 studies showed recoveries more than 90%. Metabolite profiling was successful in all cases reported (13 regular-dose studies and 5 low-dose studies). There was no obvious relationship between the total recoveries of 14 C in excreta and the proportion of 14 C excreted in feces, or between the total recoveries and the plasma elimination half-lives for parent or total 14 C, neither in the low-dose nor the regular-dose studies. A significant correlation was found between the fraction absorbed and the recovery in feces in the low-dose but not in the regular-dose studies, and no correlation was found between the fractions absorbed and the total recoveries in both types of studies. Low-dose studies were more often conducted on drugs that had a plasma elimination half-life of parent drug more than 100 hours (5 of 12 studies) than regular-dose studies (1 of 26 studies). We conclude that both low-dose as well as regular-dose human ADME studies provide adequate data to support decision making for further drug development.

Excretion and metabolism of desogestrel in healthy postmenopausal women.

The metabolism of desogestrel (13-ethyl-11-methylene-18,19-dinor-17alpha-pregn-4-en-20-yn-17-ol), a progestagen used in oral contraceptives and hormone replacement therapy, was studied in vivo after a single oral administration of 150 microg [14C]-labeled desogestrel and 30 microg ethinylestradiol under steady state conditions to healthy postmenopausal women. After this oral administration, desogestrel was extensively metabolized. The dosed radioactivity was predominantly ( approximately 60%) excreted via urine, while about 35% was excreted via the feces. Desogestrel was metabolized mainly at the C3-, C5-, C6- and C13-CH(2)CH(3) positions. At the C3-position, the 3-keto moiety was found and in addition, 3beta-hydroxy and 3alpha-hydroxy groups were observed in combination with a reduced Delta(4)-double bond (5alpha-H). Hydroxy groups were introduced at the C6- (6beta-OH), the C13-ethyl (C13-CH(2)CH(2)OH) and possibly the C15- (15alpha-OH) position of desogestrel. Conjugation of the 3alpha-hydroxy moiety with sulfonic acid and conjugation with glucuronic acid were also major metabolic routes found for desogestrel in postmenopausal women. The 3-keto metabolite of desogestrel (the biologically active metabolite) was the major compound present in plasma at least up to 24 h after administration of the radioactive dose. Species comparison of the metabolic routes of desogestrel after oral administration indicates that in rats and dogs desogestrel is also mainly metabolized at the C3-position, similar to what is now found for postmenopausal women. Most other metabolic routes of desogestrel were found to differ between species. Finally, major metabolic routes found in the present study in postmenopausal women are in line with outcome of previous in vitro metabolism studies with human liver tissue (microsomes and postmitochondrial liver fractions) and intestinal mucosa.

Inhibitory effect of telmisartan on the blood pressure response to angiotensin II challenge.

Telmisartan is a new angiotensin receptor antagonist possessing potent, selective, and insurmountable inhibitory activity specific to the angiotensin II type 1 (AT 1 ) receptor. The current study was performed to determine the inhibition of the angiotensin II pressor response by telmisartan in 48 healthy volunteers challenged with hypertension-inducing doses of i.v. angiotensin II. Subjects were challenged with this dose of angiotensin II at intervals between 0.25 and 48 h after double-blind single-dose oral administration of telmisartan 20 mg (n = 12), 40 mg (n = 12), or 80 mg (n = 12) or placebo (n = 12) in parallel groups. Diastolic and systolic blood pressure and pulse rate were recorded continuously using a servophotoplethysmograph. Urine samples were collected during the study for urinalysis. Tolerability of telmisartan, in comparison with placebo, was also monitored throughout the study. Telmisartan 20-80 mg dose dependently inhibited the increase in diastolic and systolic blood pressure induced by angiotensin II. Telmisartan 40 mg produced 80.1% maximum inhibition, and with 80 mg 89.6% maximum inhibition of diastolic blood pressure was achieved. Inhibition was apparent after 0.3-1.1 h and was still observed 48 h after administration for all telmisartan doses. The inhibitory effect of telmisartan 20, 40, and 80 mg, 48 h after dosing was significantly greater than that of placebo. A > 25% inhibition of the angiotensin II response on diastolic blood pressure was detected until 26.9, 35.4, and 40.5 h, respectively, after telmisartan 20 mg, 40 mg, and 80 mg. Anti-clockwise hysteresis was observed, indicating a delay and longer persistence of effect than to be expected from the plasma concentration-time course. The slow dissociation of telmisartan from the receptor probably contributed to this hysteresis. The incidence of adverse events was comparable in telmisartan-and placebo-treated subjects and was not dose dependent. In conclusion, telmisartan 40 mg provides rapid-onset, well-tolerated, and near-maximal inhibition of angiotensin II-induced hypertension, with maintenance of the inhibitory effect for 48 h.

Anticoagulant pharmacodynamics of tinzaparin following 175 iu/kg subcutaneous administration to healthy volunteers.

Tinzaparin, a sodium salt of a low-molecular-weight heparin (LMWH) produced via heparinase digestion, is used for the treatment of deep vein thrombosis (DVT) and pulmonary embolism in conjunction with warfarin for the prevention of DVT in patients undergoing hip or knee replacement surgery, and as an anticoagulant in hemodialysis circuits. Its average molecular weight ranges between 5500 and 7500 daltons (Da); the percentage of chains with molecular weight lower than 2000 Da is not more than 10% in the marketed tinzaparin formulation. While this fraction is generally considered pharmacologically inactive, this has never been evaluated in vivo. The importance of the < 2000 Da fraction on the anticoagulant pharmacodynamics of tinzaparin assessed by anti-Xa and anti-IIa activity was studied in a two-way crossover trial. In this trial, 30 healthy volunteers received a single 175 IU/kg subcutaneous administration of tinzaparin containing approximately 3.5% of the < 2000 Da fraction and a tinzaparin-like LMWH containing 18.3% of the < 2000 Da fraction. The anti-Xa/anti-IIa ratios of the drug substances were comparable at 1.5 and 1.7 for tinzaparin and the tinzaparin-like LMWH, respectively. Both formulations were safe and well tolerated. Mean maximum plasma anti-Xa activity (A(max)) was approximately 0.818 IU/ml at 4 h following tinzaparin injection. Mean maximum plasma anti-IIa activity was 0.308 IU/ml at 5 h postdose. Intersubject variation was lower (< 18% for both anti-Xa and anti-IIa metrics) than in previous fixed-dose administration studies. There was no correlation between anti-Xa or anti-IIa AUC or A(max) and bodyweight in the present study supporting the weight-adjusted dosing regimen. Individual anti-Xa and anti-IIa profiles following the single 175 IU/kg subcutaneous administration of the tinzaparin-like LMWH were similar to that obtained with tinzaparin. Based on average equivalence criteria, the two LMWH preparations were determined to be bioequivalent using either anti-Xa or anti-IIa activity as biomarkers. The calculated intrasubject variabilities were low (< 14% for anti-Xa activity and < 18% for anti-IIa activity) yielding little evidence for a significant Subject x Formulation interaction. In summary, anti-Xa and anti-IIa activity following a single subcutaneous administration of tinzaparin 175 IU/kg to healthy volunteers yielded activity consistent with targeted therapeutic levels derived from previous trials in adult DVT patients. Weight-based dosing for the treatment of DVT appears rational based on the reduction in anti-Xa and anti-IIa variability consistent with the recommendation derived from earlier fixed-dose pharmacokinetic studies. Furthermore, differences in the percentage of molecules in the < 2000 Da molecular weight fraction of tinzaparin do not translate into differences in anti-Xa and anti-IIa activity in vivo.

Steady-state pharmacodynamics and pharmacokinetics of warfarin in the presence and absence of telmisartan in healthy male volunteers.

The effects of multiple-dose telmisartan on the steady-state pharmacodynamics and pharmacokinetics of warfarin were assessed in 12 healthy young males in an open-label, single-period study conducted over 30 days. Subjects received loading doses of oral once-daily warfarin on days 1 to 5, which were individually adjusted at days 6 and/or 9 to attain stable predose prothrombin time values (INRpre) of between 1.2 and 1.8 by the end of medication phase 1 (day 14). From days 15 to 24 (medication phase 2), subjects received oral once-daily telmisartan 120 mg in addition to individualized oral doses of once-daily warfarin. On days 25 to 31 (medication phase 3), oral once-daily warfarin was again administered alone at individualized doses. Under steady-state conditions, INRpre remained unchanged during medication phases 1, 2, and 3. The difference between phases 1 and 3 was -0.04 (95% confidence interval [CI]: -0.7 to 0.10) and between phases 2 and 1 was 0.03 (95% CI: -0.11 to 0.10). Mean trough plasma warfarin concentrations (Cpre) were stable during medication with warfarin alone but showed a small, although statistically significant, decrease during the combined-medication phase. The point estimate of the ratio of phase 2/phase 1 was 0.89 (95% CI: 0.84 to 0.95). The decrease in Cpre did not result in decreased anticoagulation. This suggests that the extent of pharmacokinetic interaction between telmisartan and warfarin is limited, and since telmisartan had no effect on INRpre and the concomitant medication was well tolerated, there is no evidence for a clinically relevant interaction between telmisartan and warfarin.

The effect of telmisartan on the steady-state pharmacokinetics of digoxin in healthy male volunteers.

A multiple-dose, open-label, two-period, crossover randomized study was conducted in 12 healthy male volunteers to investigate the effect of multiple-dose telmisartan on the steady-state pharmacokinetics of digoxin. On day 1 of a 7-day medication period, subjects received a loading dose of digoxin 0.5 mg in the morning, followed by an evening dose of digoxin 0.25 mg, either alone or together with telmisartan 120 mg administered in the morning. On the subsequent 6 days, either digoxin 0.25 mg or digoxin 0.25 mg together with telmisartan 120 mg was administered once daily in the morning. Each 7-day medication period was separated by a washout period of > or = 14 days. A steady-state plasma concentration-time profile was assessed for digoxin during each period and for telmisartan during the period with the combined treatment. Multiple-dose telmisartan administered with digoxin resulted in higher serum digoxin concentrations than those observed after digoxin given alone. Geometric mean AUC144-168, Cmax, and Cmin values for digoxin when given in combination with telmisartan were higher by 22%, 50%, and 13%, respectively, compared with values when given alone. However, the 90% confidence interval for the geometric mean of Cmin was within the predefined 80% to 125% range of no interaction. During combination medication, digoxin tmax was shorter and Cmax/AUC144-168 increased, suggesting that the rise in digoxin Cmax may be due to more rapid drug absorption. Study medications were well tolerated, with the incidence, nature, and intensity of adverse events being similar during both medication periods. Also, no changes in vital signs or clinical laboratory tests were observed during the study. Although there was some evidence for a pharmacokinetic interaction between digoxin and telmisartan found in this study, the safety and tolerability of digoxin were unaffected by concurrent administration of telmisartan in the study population. Since any symptoms of overdose are related only to steady state and not peak concentrations and due to the fact that there was a lack of effect on serum trough levels of digoxin in this study, it is unlikely that the findings have any clinical relevance. The magnitude of increase in digoxin concentrations is comparable with increases observed with administration of calcium antagonists, carvedilol, ACE inhibitors such as captopril, and antiarrhythmic drugs such as amiodarone, quinidine, and propafenone. Monitoring of serum digoxin concentrations should be considered when patients first receive telmisartan and in the event of any changes in telmisartan dose.

Absorption, metabolism and excretion of a single oral dose of (14)C-repaglinide during repaglinide multiple dosing.

OBJECTIVE: The present study was designed to assess the disposition of (14)C-repaglinide in whole blood, plasma, urine and faeces, and to measure the total recovery of drug-related material in urine and faeces after a single 2-mg oral dose of (14)C-repaglinide during multiple dosing. METHODS: In this single-centre, open-label, phase-I trial, six healthy male volunteers received 2 mg of the prandial glucose regulator, repaglinide, four times daily for 13 days, 15 min before meals. On the morning of day 7, breakfast was omitted and the dose was given as an oral solution containing 2 mg of (14)C-repaglinide. RESULTS: After oral dosing, a mean peak plasma concentration of repaglinide of 27.74 ng. ml(-1) (range: 16.84-36.65 ng. ml(-1)) was observed with a time to peak concentration of 0.5 h. Approximately 20% of repaglinide and its associated metabolites were distributed into red blood cells. No measurable (14)C-radioactivity was present in whole blood samples 6 h after dosing. Within 96 h of dosing with (14)C-repaglinide, 90% of the administered dose appeared in the faeces and 8% was excreted in urine. In the plasma, the major compound was repaglinide (61%). In the urine, the major metabolites were unidentified polar compounds, the aromatic amine (M(1)) (24%), and the dicarboxylic acid (M(2)) (22%). In the faeces, the major metabolite was M(2) (66% of administered dose). Therefore, repaglinide was excreted predominantly as metabolites and the major in vivo metabolite of repaglinide in humans was M(2). During regular dosing for 6 days, the morning plasma trough levels of repaglinide were, with very few exceptions, almost always too low to measure, indicating the absence of accumulation at this dose of 2 mg four times daily. Repaglinide was well tolerated, and there were no episodes of hypoglycaemia. CONCLUSION: After oral dosing with repaglinide, the mean peak plasma concentration was rapidly attained and, thereafter, plasma concentrations decreased promptly. The major route of excretion was via the faeces. These properties make repaglinide a suitable insulin secretagogue for all patients with type-2 diabetes who retain sufficient beta-cell function.

The absolute bioavailability and effect of food on the pharmacokinetics of zolmitriptan in healthy volunteers.

AIMS: Zolmitriptan (Zomig (formerly 311C90)) is a novel 5-HT1B/1D receptor agonist developed for the acute oral treatment of migraine. A highly sensitive LCMS-MS assay has been developed which allows quantification of plasma concentrations of zolmitriptan and its active metabolite, 183C91, after therapeutic doses. Two studies using this assay method were conducted to investigate the pharmacokinetics, including absolute bioavailability, of 2.5 and 5 mg oral doses of zolmitriptan in men and women, the dose-proportionality of 2.5, 5 and 10 mg doses and the effect of food on the pharmacokinetics of a 5 mg oral dose. METHODS: Two randomized, balanced, open-label, 4-period crossover studies were conducted in a total of 32 healthy volunteers. The first study determined the absolute bioavailability of 2.5 and 5 mg doses of zolmitriptan and compared the pharmacokinetics in men and women. The second study examined the dose-proportionality in pharmacokinetics after fasting doses of 2.5, 5 and 10 mg, and the effect of food on a 5 mg dose. Blood pressure, heart rate, ECG, clinical chemistry, haematology and adverse events were also monitored. RESULTS: The mean (s.d.) absolute oral bioavailability was 0.41 (0.14 and 0.40) 0.09 after 2.5 mg and 0.48+/-0.14 and 0.36+/-0.07 after 5 mg in women and men, respectively. Without adjustment for bodyweight, plasma concentrations of zolmitriptan, but not 183C91, were higher in women than men. Mean (+/-s.d.) AUC was 32.7+/-10.1 and 60.2+/-26.8 ng ml(-1) h after 5 mg in men and women, respectively (95% CI for ratio 0.43-0.77). After 2.5 mg mean (+/-s.d.) AUC was 18.4+/-5.4 and 23.1+/-9.9 ng ml(-1) h in men and women, respectively (95% CI for ratio 0.61-1.09). However, these differences were of no clinical significance. Cmax and AUC of oral zolmitriptan were dose-proportional and there was a 13 and 16% fall in mean zolmitriptan Cmax and AUC, respectively, when administered after food. Adverse effects were minor, predominantly mild and transient, and there were no clinically significant effects on ECG, blood pressure, or laboratory parameters. CONCLUSIONS: At therapeutic doses zolmitriptan has good oral bioavailability in healthy volunteers and has dose-proportional pharmacokinetics that are not affected by food to any clinically relevant extent.

Pharmacokinetics of [14C]-labelled Losigamone and enantiomers after oral administration to healthy subjects.

Losigamone ((+/-)-(R*,S*)-5-(2-chlorophenylhydroxymethyl)-4-methoxy-2 (5H)-furanone; AO-33) is a new potential antiepileptic drug undergoing clinical development. In a crossover study, 200 mg [14C]-labelled Losigamone, as well as 100 mg of each of the unlabelled enantiomers, was administered to 5 healthy volunteers as an oral suspension. The objectives of the study were to determine the mode of elimination, the excretion balance, metabolic profile, the in vitro and in vivo binding to plasma proteins and the pharmacokinetics of both enantiomers in plasma. From the plasma concentration-time profiles of [14C]-radioactivity and unchanged Losigamone it can be concluded that the absorption of Losigamone occurs very rapidly and the plasma concentration of the parent compound versus total radioactivity was consistently about 40%. An overall recovery of total radioactivity of about 97% with 85% in urine and 12% in faeces was found. Protein binding was 50%. Losigamone was extensively metabolized, with only traces of unchanged drug found in urine. The predominant metabolic pathways are hydroxylation and conjugation. After administration of the pure enantiomers, significant differences in pharmacokinetics were observed. The mean oral clearance of the (-)-enantiomer was 1863 ml/min and of the (+)-enantiomer was 171 ml/min. There was no chiral inversion after administration of the enantiomers.

Pharmacokinetic drug interaction studies with candesartan cilexetil.

The aim of this series of studies was to determine the potential for pharmacokinetic interaction between candesartan (administered orally as the prodrug candesartan cilexetil) and hydrochlorothiazide (HCTZ), nifedipine, glibenclamide, warfarin, digoxin or the components of an oral contraceptive formulation. All studies were performed in healthy volunteers using randomised, crossover or add-on study designs. Candesartan cilexetil was administered orally at doses of 8, 12 or 16 mg. The pharmacokinetic parameters were determined for comparator agents and candesartan following administration of each agent alone or in combination. There were no changes in the drug plasma concentrations of nifedipine, glibenclamide, digoxin or oral contraceptives when co-administered with candesartan cilexetil. Co-administration of candesartan cilexetil caused a slight but significant decrease in the AUC of HCTZ. However, the 90% confidence intervals (CI) for AUC ratios for HCTZ when co-administered with candesartan cilexetil were within the defined limits of bioequivalence. Candesartan cilexetil produced a 7% decrease in trough plasma warfarin concentration but this had no effect on prothrombin time. Co-administration of candesartan cilexetil with HCTZ produced a statistically significant increase in the bioavailability and Cmax values for candesartan (18% and 25%, respectively). However, this increase is not considered to be clinically relevant. No other co-administered drug (nifedipine, glibenclamide, digoxin, oral contraceptive) affected the pharmacokinetic parameters of candesartan. Candesartan cilexetil was well tolerated both alone and in combination with the other agents.

The cognitive, subjective, and physical effects of a ginkgo biloba/panax ginseng combination in healthy volunteers with neurasthenic complaints.

We evaluated the effects of a Ginkgo biloba/ginseng combination on cognitive function in this 90-day, double-blind, placebo-controlled, parallel-group study. Sixty-four healthy volunteers (aged 40 to 65 years), selected on the basis of fulfilling the ICD-10 F48.0 criteria for neurasthenia, were assigned randomly to four equal dosing groups, receiving 80, 160, or 320 mg of the combination b.i.d. or placebo. Assessments were performed on the day before dosing, and again at Days 1, 30, and 90 at 1 hour after the morning dose and 1 hour after the afternoon dose. The assessments included the Cognitive Drug Research (CDR) computerized assessment system, the Vienna Determination Unit, cycle ergometry, and various questionnaires. The treatments were well tolerated by all volunteers. On Day 90 at 1 hour post morning dosing, dose-related improvements were seen on the CDR tests, the 320 mg dose being significantly superior to placebo. These effects, however, were reversed 1 hour after the afternoon dose, possibly suggesting that a longer inter-dosing interval would be preferable. The 80-mg dose produced a significant benefit on the ergometry assessment of heart rate at maximum load. There were also several supporting changes from other assessments, including an advantage of 320 mg over placebo on the global score from the Symptom Checklist-90-revised (SCL-90-R) at Day 90.

Doubling time and hCG score for the early diagnosis of ectopic pregnancy in asymptomatic women.

In a group of 20 asymptomatic women at increased risk for ectopic pregnancy, serum analyses were conducted prospectively early in pregnancy (amenorrhea less than or equal to 45 days) at 2-4-day intervals, to examine the rate of increase in hCG values. The initial serum hCG level, which was determined at the time of the first transvaginal ultrasound examination, was below the discriminatory zone of 1000 IU/l (2nd International Standard). In 8 out of the 9 women who were ultimately diagnosed as having an ectopic pregnancy, the increase in hCG progressed only slowly, with a doubling time exceeding 2.2 days. This slow hCG increase occurred in 2 out of the 11 women who were ultimately diagnosed as having an intra-uterine pregnancy; both women subsequently had an early spontaneous abortion. When Lindblom's hCG score was applied retrospectively to distinguish between intra-uterine and ectopic pregnancies, the hCG increase in all the ectopic pregnancies was below 190 IU/l per day and in 10 of the 11 women with an intra-uterine pregnancy above 190 IU/l per day. A slower rate of increase was observed in only one woman with an intra-uterine pregnancy; she had a spontaneous abortion. The doubling time of hCG and the hCG score are useful diagnostic aids in cases where transvaginal ultrasound has not (yet) given a definite answer regarding the presence of an intra-uterine pregnancy.

B-Z transition in methylated DNA. A quantum-chemical study.

On the basis of modified neglect of differential overlap (MNDO) quantum-chemical calculations on nucleoside systems, we describe the effect of methylation on the energies calculated for the rotation around the glycosidic C(1')-N bond. We found a high anti-syn activation energy in the case of the pyrimidine nucleosides C and m5C, whereas for the purine nucleosides G, m6G, m7G and m8G only moderate anti-syn energetic barriers were calculated. This result is consistent with the experimentally observed preference for d(G-C)2, d(G-C)3 and d(G-m5C)3 duplexes to adopt Z-DNA structures, in which the syn conformation of guanine is favoured. Enhanced anti-syn activation energy with respect to the unmethylated derivative was calculated in the cases of m5C and m8G. This result is rationalized on the basis of steric and electronic factors. In addition, an increased stabilization of the syn conformer due to selective methylation of guanine was calculated. The data obtained are in good correspondence with the experimentally observed B-Z transition in synthetic methylated DNA duplexes with alternating dC-dG sequence. Our work concerning the initiating step in the B-Z transition which involves rotation around the C(4')-C(5') bond induced by P(V) trigonal bipyramidal intermediates, is discussed. In combination with the rotation around the glycosidic C(1')-N bond, it can be shown that the phosphate within the dpC structure is selectively activated.