Impact of tamoxifen on the pharmacokinetics and endocrine effects of the aromatase inhibitor letrozole in postmenopausal women with breast cancer.

This study examined whether the addition of tamoxifen to the treatment regimen of patients with advanced breast cancer being treated with the aromatase inhibitor letrozole led to any pharmacokinetic or pharmacodynamic interaction. Twelve of 17 patients completed the core period of the trial in which 2.5 mg/day letrozole was administered alone for 6 weeks and in combination with 20 mg/day tamoxifen for the subsequent 6 weeks. Patients responding to treatment continued on the combination until progression of disease or any other reason for discontinuation. Plasma levels of letrozole were measured at the end of the 6-week periods of treatment with letrozole alone and the combination and once more between 4 and 8 months on combination therapy. No further measurements were done thereafter. Hormone levels were measured at 2-week intervals throughout the core period. Marked suppression of estradiol, estrone, and estrone sulfate occurred with letrozole treatment, and this was not significantly affected by the addition of tamoxifen. However, plasma levels of letrozole were reduced by a mean 37.6% during combination therapy (P<0.0001), and this reduction persisted after 4-8 months of combination therapy. Letrozole is the first drug to be described in which this pharmacokinetic interaction occurs with tamoxifen. The mechanism is likely to be a consequence of an induction of letrozole-metabolizing enzymes by tamoxifen but was not further addressed in this study. It is possible that the antitumor efficacy of letrozole may be affected. Thus, sequential therapy may be preferable with these two drugs. It is not known whether tamoxifen interacts with other members of this class of drugs or with other drugs in combination.

Pharmacokinetics of terbinafine and five known metabolites in children, after oral administration.

As an extensive study, the pharmacokinetics of terbinafine and five known metabolites have been investigated after single and repeated oral administration to 12 pediatric patients. After single administration of 125 mg terbinafine, four compounds were unconjugated and the hydroxymetabolites appeared in trace amounts as glucuronides. The main metabolites in plasma were unconjugated carboxy compounds. Kinetics of terbinafine and N-desmethylterbinafine metabolite were comparable. The interindividual AUCt variability was similar for terbinafine, N-desmethylterbinafine and carboxyterbinafine. In urine, the major fraction was the hydrophilic unconjugated N-desmethyl-carboxyterbinafine (15%). After repeated administration of 125 mg day(-1), mean trough levels of terbinafine, N-desmethylterbinafine, carboxyterbinafine and N-desmethylhydroxy-terbinafine, and also that of hydroxyterbinafine metabolite were similar, for each compound, on days 21, 42 and 56 denoting that steady state was reached at least on day 21 and no accumulation occurred between days 21 and 56.

The effect of age on the pharmacokinetics of valsartan.

Twelve young (mean age 23 years, range 18-28) and 12 elderly (mean age 76 years, range 65-89) volunteers were given a single oral dose of 80 mg valsartan after an overnight fast. Each group consisted of six male and six female subjects. Mean systemic exposure to valsartan was higher in the elderly when compared with the young (AUC(0-24 h), 52% increase and AUC(0-infinity), 70% increase). Variability, as shown by the coefficient of variation (CV), was larger for the elderly subjects and ANOVA of the log transformed AUC showed a significant difference between the two groups. This difference was largely brought about by five elderly subjects (one male, four females), whose AUC was about 2-fold higher than the rest of the group. For the remaining elderly subjects, plasma valsartan AUC was similar to that observed for the young volunteers. This higher systemic exposure in five of the elderly subjects is not thought to be of clinical relevance when data from the patient population are considered. Other covariates--such as body weight, comedication, creatinine clearance, valsartan kinetics (absorption rate, distribution, and elimination)--did not explain the higher AUC in this subset of the elderly group. Data from the present study were compared with population kinetic data obtained from larger clinical trials including hypertensive patients in all age groups. Using this population approach, there was no difference in the pharmacokinetics of valsartan between male and female patients. Also, a relationship between plasma clearance of valsartan and age was established. The median age of patients in the hypertensive pool was 55 years. For an average 70-year-old patient, plasma clearance of valsartan is predicted to fall by 22% compared with an average 55-year-old. For the population this difference is not sufficient to warrant initial dose adjustment based on age per se. The covariate age, does not completely explain the variability in the pharmacokinetics of valsartan within the general population. The treatment was well tolerated.

Pharmacokinetics of valsartan in patients with liver disease.

OBJECTIVES: Valsartan (CGP 48933), an orally active angiotensin II antagonist, is eliminated mainly by hepatic clearance. To characterize the compound(s) excreted in the bile, biliary excretion of valsartan was investigated by collection of bile after an intravenous dose of valsartan. In addition, to determine the exposure to valsartan when liver function is impaired, a pharmacokinetic study (open, single dose) was performed in patients with mild and moderate impairment of liver function. PATIENTS: Biliary excretion of valsartan (after intravenous administration of 20 mg valsartan) was assessed in a patient who underwent a hepaticojejunostomy with subsequent bile drainage. Exposure to valsartan in patients with mild (n = 6) or moderate (n = 6) impaired liver function (Child's-Pugh classification) and matching (sex, age, and weight) healthy volunteers (n = 12) was studied after oral administration of a single dose of 160 mg valsartan. RESULTS: After intravenous administration, valsartan was eliminated mainly as unchanged drug in the bile. Mean exposure (measured as area under the plasma valsartan concentration-time curve) to valsartan was increased about twofold in both the mild and the moderate groups compared with matched (age, sex, and weight) healthy volunteers. CONCLUSION: These data are consistent with the pharmacokinetics of valsartan in that biliary excretion is the main route of elimination.

Comparative bioavailability of letrozole under fed and fasting conditions in 12 healthy subjects after a 2.5 mg single oral administration.

Letrozole is a new non-steroidal inhibitor of the aromatase enzyme system. It is currently under development for the treatment of postmenopausal women with advanced breast cancer. To investigate the influence of food on the bioavailability of letrozole, 12 healthy male volunteers were treated under fed and fasted conditions with single oral doses of 2.5 mg letrozole in film-coated tablets. Plasma concentration profiles were determined. No significant difference in the extent of absorption (AUC or AUC0-8 h) was observed between the two treatments but the rate of letrozole absorption decreased slightly under fed conditions. However, in view of the half-life of about 2 d this small change in the absorption rate is not considered to be of clinical relevance for treatment with repeated administrations.

Pharmacokinetics of pamidronate disodium in patients with cancer with normal or impaired renal function.

Pamidronate is a second-generation bisphosphonate that undergoes negligible biodegradation and is eliminated exclusively by renal excretions. Nineteen cancer patients were stratified according to baseline creatinine clearance (Clcr): group I, Clcr > 90 mL/min (n = 6); group II, Clcr 61 mL/min to 90 mL/min (n = 6); group III, Clcr 30 mL/min to 60 mL/min (n = 3); group IV, Clcr < 30 mL/min (n = 4). All patients received a single, 90-mg dose of pamidronate disodium administered in a 4-hour intravenous infusion. Plasma and urine samples were collected at intervals up to 36 and 120 hours, respectively, after the start of infusion and were assayed for pamidronate, using validated high-performance liquid chromatography. Pamidronate's pharmacokinetics were characterized by a short distribution phase (2-3 hours) followed by rapid elimination of the drug in urine. Elimination of pamidronate was slower in patients in group IV with a mean +/- standard deviation area under the plasma concentration-time curve (AUC0-36) of 19.0 +/- 4.60 micrograms.hr/mL compared with 8.1 +/- 3.13 micrograms.hr/mL in patients in group I. A linear relationship in Clcr was observed for AUC0-36 (r = 0.67), urinary excretion (r = 0.69), and renal clearance (r = 0.81). Renal clearance was proportional to Clcr for patients in all four renal-function groups. In the treatment of bone metastases of malignancy, successive doses of pamidronate are generally separated by weeks; thus, plasma accumulation in patients with renal impairment is not expected to be clinically relevant. A reduction in dose of pamidronate disodium should not be necessary in cancer patients with renal impairment.

Determination of artemether and its metabolite, dihydroartemisinin, in plasma by high-performance liquid chromatography and electrochemical detection in the reductive mode.

An analytical method for the determination of artemether (A) and its metabolite dihydroartemisinin (DHA) in human plasma has been developed and validated. The method is based on high-performance liquid chromatography (HPLC) and electrochemical detection in the reductive mode. A, DHA and artemisinin, the internal standard (I.S.), were extracted from plasma (1 ml) with 1-chlorobutane-isooctane (55:45, v/v). The solvent was transferred, evaporated to dryness under nitrogen and the residue dissolved in 600 microliters of water-ethyl alcohol (50:50, v/v). Chromatography was performed on a Nova-Pak CN, 4 microns analytical column (150 mm x 3.9 mm I.D.) at 35 degrees C. The mobile phase consisted of pH 5 acetate-acetonitrile (85:15, v/v) at a flow-rate of 1 ml/min. The analytes were detected by electrochemical detection in the reductive mode at a potential of -1.0 V. Intra-day accuracy and precision were assessed from the relative recoveries (found concentration in % of the nominal value) of spiked samples analysed on the same day (concentration range 10.9 to 202 ng/ml of A and 11.2 to 206 ng/ml of DHA in plasma). The mean recoveries over the entire concentration range were from 96 to 100% for A with C.V. from 6 to 13%, from 92% to 100% for DHA (alpha-tautomer) with C.V. from 4 to 16%. For A, the mean recovery was 96% at the limit of quantitation (LOQ) of 10.9 ng/ml with a C.V. of 13%. For DHA, the mean recovery was 100% at the LOQ of 11.2 ng/ml with a C.V. of 16%.

Pharmacokinetic and pharmacodynamic interaction of single doses of valsartan and atenolol.

OBJECTIVE: Valsartan (V), a specific inhibitor of the angiotensin II receptor subtype, AT1, has been developed for treatment of hypertension. Combination therapy with a beta-adrenoceptor blocking agent might be considered in cases with insufficient efficacy of V alone. Therefore, an interaction trial was performed to evaluate the effects of co-administration of V on the pharmacokinetics of atenolol (A), and vice versa, and to monitor the pharmacodynamic response of plasma angiotensin II (ANG II) concentrations and plasma renin activity (PRA), as well as of heart rate and blood pressure, under resting and exercise conditions. METHODS: Twelve healthy, normotensive, male volunteers aged 23-46 years were treated with single doses of either 160 mg V or 100 mg A alone, or with both drugs in combination (V + A) according to a three-period crossover design. Plasma concentrations of V and A were determined using HPLC with fluorimetric and UV detection, respectively, and concentration-time profiles were established over 24 h. Plasma ANG II concentrations and PRA were monitored using specific radioimmunoassays. Heart rate and blood pressure were measured at rest and during exercise on a cycle ergometer at a workload of 2.5 W/kg-1. RESULTS: For V, mean AUC and Cmax were slightly higher when A was co-administered, the ratios of log transformed values being 1.13 and 1.22 for AUC(0-inf) and Cmax, respectively. For A, mean AUC and Cmax were slightly lower when the drug was given in combination with V. The ratios of log-transformed values in this case were 0.90 and 0.92, respectively. The sharp increase in plasma ANG II concentrations and PRA, induced by administration of V, was significantly attenuated when the drug was combined with A. In the first 12 h after drug intake, heart rate and systolic blood pressure at rest were significantly decreased when V and A were co-administered compared with treatment with V alone. V given alone did not influence heart rate or systolic blood pressure during exercise, whereas A alone and V + A led to a significant reduction in those variables. Adverse experiences reported after A and V + A could be explained by the high degree of beta-adrenoceptor blockade resulting from the administration of A. CONCLUSIONS: Co-administration of single doses of V and A does not modify the pharmacokinetics of the two drugs to a clinically relevant degree. With respect to pharmacodynamics, a single dose of A attenuates the increase in plasma ANG II and PRA in response to a single dose of V, and V has no effect on the hemodynamic response to exercise. The combined treatment with single doses of 160 mg V and 100 mg A has some additive effects on resting blood pressure in healthy, normotensive subjects.

Simultaneous determination of imipramine and its metabolite desipramine in human plasma by capillary gas chromatography with mass-selective detection.

An analytical method for the simultaneous determination of imipramine (IMI) and its N-desmethyl metabolite, desipramine (DIMI) in human plasma by capillary gas chromatography-mass selective detection (GC-MS), with D4-imipramine (D4-IMI) and D4-desipramine (D4-DIMI) as internal standards, was developed and validated. After addition of the internal standards, the compounds were extracted from plasma at basic pH into n-heptane-isoamyl alcohol (99:1, v/v), back-extracted into acidic aqueous solution and re-extracted at basic pH into toluene. Desipramine and D4-desipramine were converted into their pentafluoropropionyl derivatives. The compounds were determined by gas chromatography using a mass selective detector at m/z 234 for IMI, m/z 238 for D4-IMI, m/z 412 for DIMI and m/z 416 for D4-DIMI. The method was applied to clinical samples.

Absolute bioavailability of letrozole in healthy postmenopausal women.

Letrozole is a new non-steroidal inhibitor of the aromatase enzyme system. It is currently under development for the treatment of postmenopausal women with advanced breast cancer. Absolute bioavailability of letrozole when given orally as one 2.5 mg film-coated tablet in comparison to the same dose given intravenously as a bolus injection was studied in 12 healthy postmenopausal women. Letrozole absolute systemic bioavailability after p.o. administration was 99.9 +/- 16.3%. Elimination of letrozole was slow. Total-body clearance of letrozole from plasma after i.v. administration was low (2.21 L h-1). The calculated distribution volume at steady state (1.87 L kg-1) suggests a rather high tissue distribution. Biotransformation of letrozole is the main elimination mechanism with the glucuronide conjugate of the secondary alcohol metabolite being the predominant species found in urine. The two study treatments were tolerated equally well.

Quantitative determination of norethisterone acetate in human plasma by capillary gas chromatography with mass-selective detection.

An analytical method for the determination of norethisterone acetate (NETA) in human plasma by capillary gas chromatography-mass-selective detection (GC-MS), with testosterone acetate as internal standard, was developed and validated. After addition of the internal standard, the compounds were extracted from plasma at basic pH into diethyl ether-dichloromethane (3:2, v/v), which was then evaporated to dryness. The compounds were converted into their pentafluoropropionyl derivatives which were determined by gas chromatography using a mass selective detector at m/z 486 for NETA and m/z 476 for the internal standard. Intra-day and inter-day accuracy and precision were found suitable over the range of concentrations between 0.10 to 10 ng/ml. The method was applied to clinical samples.

High-performance liquid chromatography of the aromatase inhibitor, letrozole, and its metabolite in biological fluids with automated liquid-solid extraction and fluorescence detection.

An analytical method for the determination of letrozole (CGS 20,267) in plasma and of letrozole and its metabolite, CGP 44,645, in urine is described. Automated liquid-solid extraction of compounds from plasma and urine was performed on disposable 100-mg C8 columns using the ASPEC system. The separation was achieved on an ODS Hypersil C18 column using acetonitrile-phosphate buffer, pH 7, as the mobile phase at a flow-rate of 1.5 ml/min. A fluorescence detector was used for the quantitation. The excitation and emission wavelengths were 230 and 295 nm, respectively. The limits of quantitation (LOQ) of letrozole in plasma and in urine were 1.40 nmol/l (0.4 ng/ml) and 2.80 nmol/l, respectively. The respective mean recoveries and coefficient of variation (C.V.) were 96.5% (9.8%) in plasma and 104% (7.7%) in urine. The LOQ of CGP 44645 in urine was 8.54 nmol/l (2 ng/ml). The mean recovery was 108% (6.3%). The compounds were well separated from co-extracted endogenous components and no interferences were observed at the retention times of compounds. The sensitivity of this method for letrozole in plasma should be sufficient for kinetic studies in humans with single doses of 0.5 mg and possibly less.

Bioequivalence assessment: a pharmaceutical industry perspective.

Various aspects of bioequivalence are investigated in this paper. Some aspects dealing with bioequivalence studies conducted either during the development of the drug or after its marketing will be presented and discussed: Bioequivalence of highly variable drugs with the associated problem of widening the acceptance range or alternative solutions. Bioequivalence for the final market image. Bioequivalence for investigating the food effect. Bioequivalence in special population such as children, non Caucasian population. Bioequivalence based on in vitro data or literature. New approaches in bioequivalence interpretation. Bioequivalence and analytical methods which are not sensitive or specific enough.

Simultaneous determination of isosorbide dinitrate and its mononitrate metabolites in human plasma by capillary gas chromatography with electron-capture detection.

A method for the simultaneous determination of isosorbide dinitrate (ISDN) and its mononitrate metabolites (2- and 5-ISMN) in human plasma by capillary gas chromatography with electron-capture detection was developed. Two internal standards were used: isomannide dinitrate (IMDN) for the determination of ISDN and isomannide mononitrate (IMMN) for the determinations of 2- and 5-ISMN. After addition of the internal standards, the compounds were isolated from plasma by solid-liquid extraction. They were determined by gas chromatography using an electron-capture detector. The reproducibility and accuracy of the method were found suitable in the range of concentrations 2.5-83 ng/ml for ISDN, 2.6-208 ng/ml for 2-ISMN and 2.3-1010 ng/ml for 5-ISMN. The limit of quantitation (LOQ) was about 2.5 ng/ml for each compound. The method was applied to clinical samples.

Simultaneous determination of norethisterone and six metabolites in human plasma by capillary gas chromatography with mass-selective detection.

A method for the simultaneous determination of norethisterone (NET) and six metabolites in human plasma by capillary gas chromatography-mass-selective detection (GC-MS) is described. The compounds are determined in plasma after enzymatic hydrolysis. After addition of norgestrel as the internal standard, the compounds are extracted from plasma at pH 5 using an Extrelut column and elution with dichloromethane. After evaporation, the compounds are converted into bistrimethylsilyl derivatives which are determined by gas chromatography using a mass-selective detector at m/z 429 for the two dihydro-NET (5 beta-NET and 5 alpha-NET), m/z 431 for the four tetrahydro-NET (3 alpha,5 alpha-NET, 3 beta,5 beta-NET and 3 beta,5 alpha-NET), m/z 442 for NET and m/z 456 for the internal standard. The reproducibility and accuracy of the method were found suitable over the range of concentrations between 0.50 and 8 ng/ml for NET, and metabolites except for 5 alpha-dihydro-NET (between 1 and 8 ng/ml). The method was applied to clinical samples.

Stereospecific high-performance liquid chromatographic determination of an S(-)-benzopyran methyl ester derivative (CGP 50 068), its (-)-carboxylic acid metabolite (CGP 55 461) and the related (+)-enantiomer (CGP 54 228) in human and dog plasma.

The simultaneous determination of CGP 50 068, S(-)-enantiomer (I), its (-)-carboxylic acid metabolite CGP 55 461 (II) and the related (+)-enantiomer CGP 54 228 (III) by stereospecific high-performance liquid chromatography, in human plasma, is described. The three compounds and racemic acebutolol, used as internal standard, were isolated from plasma by liquid-solid extraction on disposable C18 columns. The resolution and determination of I and the two carboxylic acid enantiomers were achieved by direct chromatography using a Chiral-AGP column refrigerated at 5 degrees C. The mobile phase was tetrabutylammonium iodide in a pH 7 phosphate buffer solution used at a constant flow-rate of 0.5 ml/min. The UV detection wavelength was set at 270 nm. The reproducibility and accuracy of the method were found to be suitable over the concentration range 0.56-28.0 mumol/l for II and III and 2.0-26.7 mumol/l for I.

Renal and endocrine effects of flosulide, after single and repeated administration to healthy volunteers.

UNLABELLED: Two double-blind, placebo-controlled, balanced cross-over studies were carried out successively in 8 male normotensive volunteers to investigate the acute and chronic effects of two doses of a novel non-steroidal anti-inflammatory drug flosulide (5 mg b.d. and 25 mg b.d.), on the renin-angiotensin-aldosterone system, linking this to changes in the urinary excretion of prostaglandins. Plasma renin and aldosterone were determined on Days 2 and 9, with the subject supine, after 1 h of rest in the sitting position following 1 h of walking, and 3 h after oral intake of 40 mg furosemide, also in the sitting position. Twenty-four hour urine samples were collected on Days 1 and 8 for the measurement of the electrolytes, aldosterone pH1 and the urinary prostaglandins PGE2, PGF2 alpha, 6-keto-PGF1 alpha and TxB2. RESULTS: After the first day of treatment with 25 mg b.d. flosulide, the increase in body weight was close to significance (0.86 vs -0.08 kg with placebo). A dose- and time-dependent decrease in both active and inactive plasma renin were observed, whereas the fall in plasma and urinary aldosterone was statistically significant only after the higher dose of flosulide. These changes in the renin-angiotensin-aldosterone system were observed in the absence of oedema. Two out of eight volunteers experienced a strong and immediate reduction in the excretion of prostaglandins but overall the two doses tested did not produce a statistically significant inhibition in renal prostaglandins, especially following repeated dosing. The inhibitory effect of flosulide on renal prostaglandin synthesis was found to be less pronounced after repeated treatment, as documented on Day 9 by the lower inhibition of 6-keto-PGF1 alpha and TxB2. CONCLUSION: These two studies in normal volunteers, in spite of some methodological limitations, were helpful in order to select doses of flosulide which should be effective and safe in patients during Phase II trials, by examining the inhibitory effect of the drug on renin synthesis and renal prostaglandin synthesis.

Percutaneous absorption of diclofenac in healthy volunteers after single and repeated topical application of diclofenac Emulgel.

The percutaneous absorption of diclofenac was studied in ten healthy volunteers treated with Emulgel containing 1.16% diclofenac diethylammonium for 8 d as follows: a single application of 5 g Emulgel on days 1 and 8, and two applications d-1 on days 2-7. Plasma concentration profiles of unchanged diclofenac and urinary concentrations of total diclofenac and metabolites (sum of free and conjugated) were determined. High inter-individual variations in plasma and urine data were recorded, due probably to the permeability and the hydration of the skin. Steady state was reached after 2 d of twice-daily administration. Plasma concentrations were low but remained in the range 10-50 nmol L-1 over the full day for most of the subjects, indicating prolonged absorption from the application site.

The absence of a pharmacokinetic interaction between aspirin and the angiotensin-converting enzyme inhibitor benazepril in healthy volunteers.

Potential effects of the coadministration of single doses of aspirin (325 mg) and of benazepril hydrochloride (20 mg) on the pharmacokinetics and the metabolism of these two drugs were evaluated in 12 healthy subjects. Plasma concentration profiles of benazepril, its active metabolite benazeprilat, and total salicylic acid were determined together with urinary excretion of benazeprilat, salicylic acid, salicyluric acid, and salicylate glucuronides. Almost superimposable plasma profiles of benazepril, benazeprilat, and total salicylic acid were achieved with the drugs given alone and concomitantly. The coadministration of benazepril hydrochloride and aspirin did not modify the pharmacokinetics or the metabolism of the two drugs.

Development, application and comparison of an enzyme immunoassay and a high-performance liquid chromatography method for the determination of the aromatase inhibitor CGS 20,267 in biological fluids.

CGS 20,267 is a new potent and selective, nonsteroidal, oral aromatase inhibitor. For its determination in human plasma and urine, an enzyme immunoassay (EIA) and an HPLC method were developed. The EIA showed good precision and accuracy (intra- and interassay variation between 3.0 and 17.7%, recoveries between 81 and 106%) and a quantitation limit of 0.7 nmol/L. A strong cross reactivity of the antibodies with the hydroxy metabolite of CGS 20,267 (CGP 44,645) was observed. The HPLC method showed a quantitation limit in plasma of 28 and 34 nmol/L for CGS 20,267 and CGP 44,645, respectively. For urine, concentrations down to 180 nmol/L (CGS 20,267) and 210 nmol/L (CGP 44,645) could be measured. A cross check between EIA and HPLC on plasma samples from healthy male volunteers or breast cancer patients treated orally with CGS 20,267 revealed an excellent correlation (slope = 0.934, intercept = 26, r = 0.991). However, the EIA measurements of urine samples yielded 3-25 times higher concentrations than those obtained by HPLC. Further, HPLC analysis revealed the presence of CGS 20,267 and cross-reacting metabolites in urine but not in plasma. Therefore, the EIA can only be used for the determination of CGS 20,267 in plasma samples.