Finasteride concentrations and prostate cancer risk: results from the Prostate Cancer Prevention Trial

OBJECTIVE

In the Prostate Cancer Prevention Trial (PCPT), finasteride reduced the risk of prostate cancer by 25%, even though high-grade prostate cancer was more common in the finasteride group. However, it remains to be determined whether finasteride concentrations may affect prostate cancer risk. In this study, we examined the association between serum finasteride concentrations and the risk of prostate cancer in the treatment arm of the PCPT and determined factors involved in modifying drug concentrations.

METHODS

Data for this nested case-control study are from the PCPT. Cases were drawn from men with biopsy-proven prostate cancer and matched controls. Finasteride concentrations were measured using a liquid chromatography-mass spectrometry validated assay. The association of serum finasteride concentrations with prostate cancer risk was determined by logistic regression. We also examine whether polymorphisms in the enzyme target and metabolism genes of finasteride are related to drug concentrations using linear regression.

RESULTS AND CONCLUSIONS

Among men with detectable finasteride concentrations, there was no association between finasteride concentrations and prostate cancer risk, low-grade or high-grade, when finasteride concentration was analyzed as a continuous variable or categorized by cutoff points. Since there was no concentration-dependent effect on prostate cancer, any exposure to finasteride intake may reduce prostate cancer risk. Of the twenty-seven SNPs assessed in the enzyme target and metabolism pathway, five SNPs in two genes, CYP3A4 (rs2242480; rs4646437; rs4986910), and CYP3A5 (rs15524; rs776746) were significantly associated with modifying finasteride concentrations. These results suggest that finasteride exposure may reduce prostate cancer risk and finasteride concentrations are affected by genetic variations in genes responsible for altering its metabolism pathway.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00288106.

Pharmacokinetic interaction of finasteride with tamsulosin hydrochloride: an open-label, randomized, 3-period crossover study in healthy Chinese male volunteers

PURPOSE

The primary aim of this study was to evaluate whether there was clinically significant pharmacokinetic (PK) interaction between finasteride and tamsulosin in healthy Chinese male subjects.

METHODS

This was an open-label, randomized, 3-period, crossover study. Subjects received single and multiple doses of 5 mg finasteride alone, single and multiple doses of 0.2 mg tamsulosin hydrochloride sustained-release capsule alone, and single and multiple doses of 5 mg finasteride with 0.2 mg tamsulosin hydrochloride, in an order determined by a computerized randomization schedule. Blood samples were collected up to 48 hours after dosing on study day 1 and up to 24 hours after dosing on study day 9 for determination of plasma concentrations with a validated LC-MS/MS method. Pharmacokinetic parameters were estimated via noncompartmental methods. Tolerability was evaluated by monitoring adverse events, laboratory assays, vital signs, and 12-lead ECG.

FINDINGS

Fifteen subjects were enrolled, and 14 completed the study. The geometric mean ratios (GMRs) (90% CIs) of AUC(τ,ss) and C(max,ss) values of finasteride at steady state between coadministration of finasteride and tamsulosin hydrochloride and finasteride alone were 1.14 (1.05-1.23) and 1.06 (0.99-1.14), respectively. The GMRs (90% CIs) for AUC(0-t) and C(max) values of finasteride for a single dose of coadministration of finasteride and tamsulosin hydrochloride and finasteride alone were 1.02 (0.94-1.11) and 1.06 (1.01-1.11), respectively. The GMRs (90% CIs) for AUC(τ,ss) and C(max,ss) values of tamsulosin at steady-state for coadministration of finasteride and tamsulosin hydrochloride and tamsulosin hydrochloride alone were 1.18 (1.05-1.33) and 1.23 (1.06-1.43), respectively. The GMRs (90% CIs) for AUC(0-t) and C(max) values of tamsulosin for a single dose of coadministration of finasteride and tamsulosin hydrochloride and tamsulosin hydrochloride alone were 1.04 (0.97-1.10) and 1.04 (0.98-1.11), respectively. Statistical analyses confirmed that the 90% CIs for these PK parameters were within the predefined not clinically significant PK drug-drug interaction effect boundaries (0.5-2.0) in this study. If comparing the findings with narrower boundaries (0.8-1.25), the conclusion may not be supportive for tamsulosin hydrochloride. During the study, a total of 4 adverse events were reported in 3 subjects including allergic reaction, abnormal findings on an ECG, a slight increase in alanine aminotransferase, and a positive result on glucose urine test.

IMPLICATIONS

Both finasteride and tamsulosin hydrochloride were well tolerated. Coadministration of finasteride and tamulosin hydrochloride seems unlikely to lead to a clinically significant PK drug-drug interaction, after a single dose and at steady state.

Simultaneous pharmacokinetic and pharmacodynamic analysis of 5α-reductase inhibitors and androgens by liquid chromatography tandem mass spectrometry

Benign prostatic hyperplasia and prostate cancer can be treated with the 5α-reductase inhibitors, finasteride and dutasteride, when pharmacodynamic biomarkers are useful in assessing response. A novel method was developed to measure the substrates and products of 5α-reductases (testosterone, 5α-dihydrotestosterone (DHT), androstenedione) and finasteride and dutasteride simultaneously by liquid chromatography tandem mass spectrometry, using an ABSciex QTRAP(®) 5500, with a Waters Acquity™ UPLC. Analytes were extracted from serum (500 µL) via solid-phase extraction (Oasis(®) HLB), with (13)C3-labelled androgens and d9-finasteride included as internal standards. Analytes were separated on a Kinetex C18 column (150 × 3 mm, 2.6 µm), using a gradient run of 19 min. Temporal resolution of analytes from naturally occurring isomers and mass +2 isotopomers was ensured. Protonated molecular ions were detected in atmospheric pressure chemical ionisation mode and source conditions optimised for DHT, the least abundant analyte. Multiple reaction monitoring was performed as follows: testosterone (m/z 289 → 97), DHT (m/z 291 → 255), androstenedione (m/z 287 → 97), dutasteride (m/z 529 → 461), finasteride (m/z 373 → 317). Validation parameters (intra- and inter-assay precision and accuracy, linearity, limits of quantitation) were within acceptable ranges and biological extracts were stable for 28 days. Finally the method was employed in men treated with finasteride or dutasteride; levels of DHT were lowered by both drugs and furthermore the substrate concentrations increased.

A rapid, simple, specific liquid chromatographic-electrospray mass spectrometry method for the determination of finasteride in human plasma and its application to pharmacokinetic study

A fast, accurate, sensitive, selective and reliable method using reversed-phase high-performance liquid chromatography-mass spectrometry coupling with an electrospray ionization interface was developed and validated for the determination of finasteride in human plasma. After deprotienation with acetonitrile, centrifugation, evaporation to dryness and dissolving in mobile phase, satisfactory separation was achieved on a Hypersil-Keystone C(18) reversed-phase column using a mobile phase consisting of acetonitrile-water (46:54, v/v), 0.1% acetic acid and 0.1% trifluoracetic acid. Carbamazepine (IS) was used as internal standard. This method involved the use of the [M+H](+) ions of finasteride and IS at m/z 373 and 237 with the selective ion monitoring (SIM) mode. The calibration curve was linear in the range of 0.2-120 ng ml(-1). The limit of quantification for finasteride in plasma was 0.2 ng ml(-1) with good accuracy and precision. The intra-assay precision and accuracy were in the range of 2.1-11.2% and -1.3% to 8.5%, respectively. The inter-assay precision and accuracy were in the order of 3.4-12.1% and -1.5% to 11.5%, respectively. The mean sample extract recoveries of the method were higher than 85% and 74% for finasteride and internal standard (IS), respectively. The assay has been successfully used to estimate the pharmacokinetics of finasteride after oral administration of a 5mg tablet of finasteride to 24 healthy volunteers.

[Determination of finasteride in human plasma by HPLC-MS]

AIM

To develop an HPLC-MS assay for determination of finasteride in human plasma and to investigate the bioequivalence in healthy volunteers.

METHODS

After alkalization with sodium hydroxide, plasma was extracted with ethyl acetate and separated using a C18 column with a mobile phase of methanol-water (85:15). LC-ESI-MS was performed in the selected ion monitoring (SIM) mode using target ions at m/z 395 for finasteride and m/z 407 for the IS. The fragmentor voltage was 120 V. A randomized crossover design was performed in 20 healthy volunteers. In the two study periods, a single 10 mg dose of each tablet was administered to each volunteer.

RESULTS

Calibration curves were linear over the range 1-200 micrograms.L-1 (r = 0.9986). The limit of determination for finasteride in plasma was 0.05 microgram.L-1. The recovery of finasteride from plasma was in the range of 85.9%-98.7%. The results of variance analysis and two one-side t-test showed that there was no significant difference between the two formulations in the AUC and Cmax.

CONCLUSION

The assay was proved to be sensitive, accurate and convenient. The two formulations were bioequivalent.

Pharmacokinetic parameters and mechanisms of inhibition of rat type 1 and 2 steroid 5alpha-reductases: determinants for different in vivo activities of GI198745 and finasteride in the rat

The interaction of baculovirus expressed rat steroid 5alpha-reductase types 1 and 2 (r5AR1 and r5AR2) with 17beta-N-(2,5-bis(trifluoromethyl)phenyl)carbamoyl-4-aza-5alpha-androst-1-en-3-one (GI198745) was investigated at pH 7 and 37 degrees. This 5alpha-reductase inhibitor was found previously to be a time-dependent inhibitor of the two human 5alpha-reductase isozymes. In contrast, we demonstrate in the present study that although GI198745 is a potent time-dependent inhibitor of r5AR2, it is a classical rapid-equilibrium inhibitor of r5AR1. This type of behavior with human and rat 5alpha-reductases has been shown for the inhibitor 17beta-(N-tert-butylcarbamoyl)-4-aza-5alpha-androst-1-en-3-one (finasteride), a current therapy for benign prostatic hyperplasia. Inhibition of r5AR1 by GI198745 was competitive with testosterone and followed Michaelis-Menten kinetics with a K(i) value of 0.3 +/- 0.02 nM. Data for the inhibition of r5AR2 by GI198745 were consistent with a two-step mechanism, where K(i) is the dissociation constant for an initial enzyme-inhibitor complex and k(3) is the rate constant for the second slow step. The pseudo-bimolecular rate constant (k(3)/K(i)) for the association of GI198745 with r5AR2 was (2.0 +/- 0.4) x 10(7) M(-1) sec(-1). The high affinity of this inhibitor for r5AR2 was further demonstrated by the inability of the enzyme-inhibitor complex to dissociate after approximately 7 days of dialysis at 4 degrees. Both GI198745 and finasteride appear to inactivate r5AR2 by apparent irreversible modification, but are classical, reversible inhibitors of r5AR1. Therefore, we hypothesize that because of its pharmacokinetic parameters and increased potency against r5AR1, GI198745 is more effective than finasteride in preventing the growth of the rat prostate.

Bioequivalence study of finasteride. Determination in human plasma by high-pressure liquid chromatography coupled to tandem mass spectrometry

Two different finasteride (CAS 98319-26-7) tablet formulations were evaluated for their relative bioavailability (Flaxin tablets 5 mg, as the test formulation vs reference formulation, tablets 5 mg) in 23 healthy male volunteers who received a single 5 mg oral dose of each preparation. The study was open, randomized with a two-period crossover design and a 7-day washout period. Plasma samples were obtained over a 48-h interval. The finasteride concentrations were determined by high-pressure liquid chromatography (HPLC) coupled to tandem mass spectrometry (LC-MS-MS). The analytical method developed has a limit of quantitation (LOQ) of 0.50 ng/ml in plasma. For the quality control the measured concentration was 2.05 +/- 0.14 ng/ml (mean +/- SD, n = 30) with a precision of 6.9% and an accuracy of 2.55% at a concentration of the starting solution of 2.00 ng/ml, while with 20.00 ng/ml starting solution the measured concentrations were 20 +/- 0.80 ng/ml (n = 30) with a precision of 3.81% and an accuracy of 0.09%. From the plasma finasteride concentration vs time curves the following pharmacokinetics parameters were obtained: AUC0-48, AUC0-infinity, Cmax, Cmax/AUC0-48, Ke, elimination half-life and tmax. Geometric mean test/reference formulations individual percent ratio was 95.71 for AUC0-48 h and 88.70% for Cmax. The 90% confidence interval for the geometric mean of the individual ratio test/reference formulations was 95.70-120.20% for AUC0-48 h, 94.60-121.30 for AUC0-infinity and 88.70-108% for Cmax. Since for both Cmax or AUC the 90% Cl values are within the interval proposed by the Food and Drug Administration, the test formulation is bioequivalent to the reference formulation for both the rate and extent of absorption after single dose administration.

Determination of finasteride in human plasma by liquid-liquid extraction and high-performance liquid chromatography

A high-performance liquid chromatographic method for the quantitation of finasteride in human plasma is presented. The method is based on liquid-liquid extraction with hexane-isoamylalcohol (98:2, v/v) and reversed-phase chromatography with spectrophotometric detection at 210 nm. The mobile phase consists of acetonitrile-15 mM potassium dihydrogenphosphate (40:60, v/v). Clobazam is used as the internal standard. The limit of quantitation is 4 ng/ml and the calibration curve is linear up to 300 ng/ml. Within-day and between-day precision expressed by relative standard deviation is less than 5% and inaccuracy does not exceed 8%. The assay was used for pharmacokinetic studies.

Pharmacokinetic interaction between finasteride and terazosin, but not finasteride and doxazosin

The alpha 1-adrenoceptor antagonists doxazosin and terazosin and the 5 alpha-reductase inhibitor finasteride are used in the treatment of benign prostatic hyperplasia. The aim of this study was to assess the potential pharmacokinetic interaction of doxazosin or terazosin when coadministered with finasteride. This was a randomized, placebo-controlled, multi-center study. Ninety healthy men were assigned to one of six treatment groups: doxazosin; doxazosin plus finasteride; terazosin; terazosin plus finasteride; placebo; and placebo plus finasteride. Plasma concentrations, maximum plasma concentration (Cmax), time to maximum concentration (tmax), and area under the plasma concentration-time curve from 0 to 24 hours (AUC0-24) of doxazosin, terazosin, and finasteride were determined. Ratios of Cmax and AUC for doxazosin and terazosin were not significantly altered by coadministration with finasteride. The Cmax and AUC0-24 of finasteride were not significantly altered by coadministration with doxazosin. However, Cmax and AUC0-24 of finasteride were significantly higher after coadministration with terazosin. There is no statistically significant pharmacokinetic interaction between finasteride and doxazosin; however, there is a statistically significant interaction between finasteride and terazosin, which affects the pharmacokinetics of finasteride but not those of terazosin. The clinical significance of this interaction remains to be determined.

Matrix effect in quantitative LC/MS/MS analyses of biological fluids: a method for determination of finasteride in human plasma at picogram per milliliter concentrations

Contrary to common perceptions, the reliability of quantitative assays for the determination of drugs in biological fluids using high-performance liquid chromatography with tandem mass spectrometric (LC/MS/MS) detection methods and the integrity of resulting pharmacokinetic data may not be absolute. Results may be adversely affected by lack of specificity and selectivity due to ion suppression caused by the sample matrix, interferences from metabolites, and "cross-talk" effects. In this paper, an example of the effect of the sample matrix on the determination of finasteride (I) in human plasma is presented. The ion suppression effect was studied by analyzing standards of I injected directly in mobile phase and comparing the response (peak areas) of I and an internal standard (II) with the peak areas of the same analytes spiked before extraction into five different plasma pools and standards spiked into the plasma extracts after extraction. The LC/MS/MS analyses were performed using a turbo ion spray interface (TISP) under chromatographic conditions, characterized by minimal (total run time of 2 min, capacity factors, k' of 1.50 and 1.75 for I and II, respectively) and high retention of the analytes (total run time 6 min, k' of 3.25 and 13.25 for I and II, respectively). The absolute peak areas for I and II in different plasmas were calculated, and the slopes and peak area ratios at all concentrations within the standard curve ranges were compared. When analyses were performed under conditions of minimal HPLC retention, the slope of the standard line for one set of plasma samples was substantially different (about 50% higher) from that from other plasma sources. The precision of the assay, expressed as coefficient of variation (CV, %) was also inadequate and varied from 15 to 30% at all concentrations within the standard curve range. When the same experiments were repeated using high HPLC retention, the slopes from different plasma sources were practically the same, and the CV was improved to 6-14%. By increasing k' and providing more chromatographic retention of analytes, the "unseen" interferences from plasma matrix were mostly separated from analytes, practically eliminating the ion suppression. In addition, by eliminating from plasma extracts a number of endogenous components through more selective extraction, the ion suppression was also minimized. The detailed data and the design of these experiments are presented. In addition, development of a highly sensitive assay for I in human plasma at low picogram per milliliter concentrations using LC/MS/MS with a heated nebulizer (HN) interface, instead of a TISP interface, is described. In this case, the effects of sample matrixes were not observed.

Matrix effect in quantitative LC/MS/MS analyses of biological fluids: a method for determination of finasteride in human plasma at picogram per milliliter concentrations

Contrary to common perceptions, the reliability of quantitative assays for the determination of drugs in biological fluids using high-performance liquid chromatography with tandem mass spectrometric (LC/MS/MS) detection methods and the integrity of resulting pharmacokinetic data may not be absolute. Results may be adversely affected by lack of specificity and selectivity due to ion suppression caused by the sample matrix, interferences from metabolites, and "cross-talk" effects. In this paper, an example of the effect of the sample matrix on the determination of finasteride (I) in human plasma is presented. The ion suppression effect was studied by analyzing standards of I injected directly in mobile phase and comparing the response (peak areas) of I and an internal standard (II) with the peak areas of the same analytes spiked before extraction into five different plasma pools and standards spiked into the plasma extracts after extraction. The LC/MS/MS analyses were performed using a turbo ion spray interface (TISP) under chromatographic conditions, characterized by minimal (total run time of 2 min, capacity factors, k' of 1.50 and 1.75 for I and II, respectively) and high retention of the analytes (total run time 6 min, k' of 3.25 and 13.25 for I and II, respectively). The absolute peak areas for I and II in different plasmas were calculated, and the slopes and peak area ratios at all concentrations within the standard curve ranges were compared. When analyses were performed under conditions of minimal HPLC retention, the slope of the standard line for one set of plasma samples was substantially different (about 50% higher) from that from other plasma sources. The precision of the assay, expressed as coefficient of variation (CV, %) was also inadequate and varied from 15 to 30% at all concentrations within the standard curve range. When the same experiments were repeated using high HPLC retention, the slopes from different plasma sources were practically the same, and the CV was improved to 6-14%. By increasing k' and providing more chromatographic retention of analytes, the "unseen" interferences from plasma matrix were mostly separated from analytes, practically eliminating the ion suppression. In addition, by eliminating from plasma extracts a number of endogenous components through more selective extraction, the ion suppression was also minimized. The detailed data and the design of these experiments are presented. In addition, development of a highly sensitive assay for I in human plasma at low picogram per milliliter concentrations using LC/MS/MS with a heated nebulizer (HN) interface, instead of a TISP interface, is described. In this case, the effects of sample matrixes were not observed.

Finasteride in biological fluids: extraction and separation by a graphitized carbon black cartridge and quantification by high-performance liquid chromatography

A simple, specific and sensitive high-performance liquid chromatographic method has been developed and validated for the determination of finasteride in human plasma. A solid-phase extraction procedure was used to isolate finasteride from the biological matrix before quantitative analysis. The analyte was separated on a Symmetry reversed-phase column using acetonitrile-0.04 M orthophosphoric acid (pH 4.0) as mobile phase and quantified by measuring its UV absorbance at 215 nm. The limit of detection for the analyte was 0.005 microg/ml. 4-Androstene-3,17-dione was used as internal standard. The calibration graph of the method was linear from 0.01 to 3.0 microg/ml of finasteride in human plasma, and the coefficient of variation less than 4.5%. This HPLC procedure is simple, precise and accurate for the determination of finasteride in human plasma.

Effects of finasteride, a type 2 5-alpha reductase inhibitor, on fetal development in the rhesus monkey (Macaca mulatta)

In genetic male fetuses, dihydrotestosterone (DHT) plays an important role in normal prostatic and external genital differentiation. The enzyme steroid 5-alpha reductase (5 alpha R) catalyzes the conversion of testosterone (T) to DHT. The importance of 5 alpha R in sexual differentiation is evident from the study of human genetic males who congenitally lack this enzyme and consequently develop ambiguous genitalia. These individuals are specifically deficient in the type 2 isozyme, whereas the normal type 1 isozyme activity has been found. The purpose of this study was to determine 1) the suitability of the rhesus monkey for testing the safety of 5 alpha R inhibitors when administered during pregnancy and 2) the potential risk of administering a known type 2 5 alpha R inhibitor, finasteride, during the critical period of internal and external genital differentiation in rhesus monkeys. In vitro studies were also performed on selected rhesus monkey tissues to determine the distribution of the 5 alpha R isozymes. Gravid monkeys were treated once daily from gestational days (GD) 20 to 100. Sonographic monitoring was performed during the course of gestation to monitor viability, growth, and organ system development. Detailed fetal evaluations for developmental abnormalities were performed at term (GD 152 +/- 2). A group of 13 pregnant monkeys ("positive control") were given a high oral dose (2 mg/kg/day) of finasteride to demonstrate that inhibiting type 2 5 alpha R results in specific external genital abnormalities in male fetuses. Thirty-two pregnant monkeys were administered an intravenous (i.v.) formulation of finasteride at doses of 8, 80, or 800 ng/day. The highest i.v. dose selected was at least 60-750 times the semen levels of finasteride in man given orally 5 or 1 mg/day, respectively. Seventeen vehicle-control pregnant monkeys were also included. Administration of a high oral dose (2 mg/kg/day) of finasteride resulted in external genital abnormalities characterized by hypospadias, preputial adhesions to the glans, a small underdeveloped scrotum, a small penis, and a prominent midline raphe in male fetuses; however, no developmental abnormalities were seen in female fetuses. Similarly, no abnormalities were observed in either male or female fetuses of mothers given iv doses (8, 80, or 800 ng/day) of finasteride during pregnancy. The in utero sonographic findings in fetuses correlated with the gross findings at term. These studies have shown that external genital abnormalities can be produced in male monkey fetuses when exposed to a high oral dose (2 mg/kg/day) of finasteride, whereas no abnormalities were observed in fetuses exposed to the i.v. formulation of finasteride. Detailed in vitro studies demonstrated that the rhesus monkey also has two 5 alpha R isozymes (types 1 and 2) with a tissue distribution similar to that seen in man and, furthermore, that finasteride is a potent, mechanism-based inhibitor with selectivity for both human and rhesus type 2 5 alpha R. These studies have demonstrated that the monkey is a suitable model for assessing the safety of 5 alpha R inhibitors administered during pregnancy.

Determination of turosteride, a new inhibitor of 5 alpha-reductase, in human plasma by high-performance liquid chromatography with ultraviolet detection

A sensitive and specific HPLC method for the determination of turosteride in human plasma was developed and validated. Turosteride was extracted from plasma with diethyl ether. Further purifications of the fraction extracted were performed sequentially by solid-phase extraction using a CN cartridge and by liquid-liquid partition between n-hexane and acetonitrile. Finally the acetonitrile solution containing the test compound was evaporated to dryness and the residue dissolved in the mobile phase, then injected onto the HPLC system. The chromatographic separation was performed isocratically by a reversed-phase column filled with ODS using a water-acetonitrile-methanol mixture. The eluate was monitored at 210 nm. No peak interfering with that of turosteride was observed when blank human plasma was assayed. Linearity was obtained in the turosteride concentration range of 5-1000 ng/ml plasma. Six calibration curves in plasma prepared and run on six different days showed correlation coefficients higher than 0.99 and good reproducibility of the slope (C.V. = 4.3%). The intra-day precision, evaluated at three concentrations (in the low, mid and high range of the standard curve) and expressed as C.V., ranged from 0.81 to 13.25%. The inter-day precision evaluated at the same concentrations was better than 10.7%. The inter-day accuracy evaluated in the same samples and expressed as the ratio of found/added amount of turosteride ranged from 97.66 to 98.38%. The limit of quantitation was 5 ng/ml plasma. The HPLC method described was successfully employed for the determination of turosteride in plasma samples obtained during a phase I clinical trial with the test compound.

Disposition and metabolism of finasteride in dogs

Finasteride (FIN) is a potent 5 alpha-reductase inhibitor that has shown clinical success in treating men with benign prostatic hyperplasia. In the study of biological effects and metabolism of FIN in animals, the dog serves as the primary modality. This study was conducted to determine the pharmacokinetics and fate of FIN after oral administration of single doses of [14C]FIN to dogs at 10 and 80 mg/kg (N = 2 and 3, respectively), and also after intravenous infusion at 5 mg/kg (N = 2). Plasma, urine, and feces were analyzed for total 14C content. Parent drug and metabolites in plasma and excreta were measured by HPLC/UV/radioassay and identified by NMR spectroscopy and MS, FIN was subject to extensive biotransformation before excretion. Structures were determined for the major metabolites in plasma, urine, and feces. The primary metabolic events for FIN were hydroxylation of the t-butyl side chain to give hydroxymethyl-FIN (metabolite I), which is oxidized further to form the carboxylic acid derivative (metabolite IV), and hydroxylation at positions B alpha and 15. Terminal half-life of FIN after the intravenous dose was 3.4 hr. Plasma clearance and volume of distribution at steady-state were 4.8 ml/min/kg and 1.1 liter/kg. Dogs showed rapid absorption after oral administration of the low dose, with Cmax reached in the 1-2 hr, bioavailability was estimated to be > 90%. After either dosing route, 45% of the plasma radioactivity (as represented by AUC) was parent drug, 43% was metabolite I, and 1% was metabolite IV. After oral administration, the 80 mg/kg dose was absorbed slowly, with the highest levels of radioactivity in plasma reached in 4-30 hr. Average Cmax value for FIN and metabolite I increased in a dose-related, but nonproportional, manner. Compared with the 10 mg/kg dose, it seems the higher dose was reasonably well-absorbed, as indicated by the nearly proportional increase of AUC values of total radioactivity and FIN. Composition of plasma metabolites observed at the 80 mg/kg dose level was similar to that observed previously for the low dose, suggesting that an increase in plasma exposure was effected in dogs receiving FIN at 80 mg/kg in toxicity studies. Most of the administered radioactivity was recovered in feces after all doses. Little of the intravenous and low oral doses, but > 50% of the 80 mg/kg oral dose, was excreted as intact FIN, suggesting that metabolism might have been saturated at the high dose.

High-performance liquid chromatographic determination of finasteride in human plasma using direct injection with column switching

A fully automated column-switching high-performance liquid chromatographic (HPLC) method was developed for the quantification of finasteride [N-(1,1-dimethylethyl)-3-oxo-4-aza-5 alpha-androst-1-ene-17 beta- -carboxamide] in human plasma. Plasma samples were diluted with an equal volume of ethylene glycol-water (40:60, v/v), then the diluted sample (150 microliters) was injected into the HPLC system without clean-up. The analyte was retained on a pretreatment column, whereas plasma proteins and other endogenous components were washed out to waste. The analyte was transferred to the analytical column in the heart-cut mode and then detected at 210 nm. A quantification limit of 1 ng/ml was attained. There was a linear relationship between peak height and drug concentration in plasma in the range 1-50 ng/ml. This method was validated and applied to the assay of plasma samples to characterize pharmacokinetic parameters in clinical studies.

Synthesis of 5,6,6-[2H3]finasteride and quantitative determination of finasteride in human plasma at picogram level by an isotope-dilution mass spectrometric method

Finasteride is a potent inhibitor of the enzyme steroid 5 alpha-reductase now approved as a drug for the treatment of benign prostatic hyperplasia. We describe an original method for the quantitative determination of finasteride at picogram level in human plasma by isotope-dilution gas chromatography mass spectrometry. 5,6,6-[2H3]Finasteride was synthesized with an high ratio of trideuteration (finasteride/[2H3]finasteride = 0.007) allowing its optimal use as internal standard. Plasma samples were purified in a single-step procedure on solid-phase extraction C18 columns with a recovery > or = 90%. Samples were injected in the GC-MS instrument without any derivatization and the minimum detection level of finasteride was 50 pg with a signal-to-noise ratio of 6:1. The coefficients of variation for the 5 and 10 ng/ml (plasma) concentrations were 5.8% and 4%, respectively. The method has been applied to the determination of the plasma pharmacokinetic of finasteride in five male volunteers treated with a single 5-mg dose of the drug, affording kinetic parameters which are in good agreement with the values previously reported with a different methodology. The present method results accurate, specific, sensible and reliable for a routinely determination of finasteride at picogram levels.

Picogram determination of finasteride in human plasma and semen by high-performance liquid chromatography with atmospheric-pressure chemical-ionization tandem mass spectrometry

A method based on high-performance liquid chromatography (HPLC) with atmospheric-pressure positive-ion chemical ionization (APCI)-tandem mass spectrometric (MS-MS) detection for the determination of finasteride (MK-906, I) in human plasma and semen has been developed. The drug and internal standard (II) were extracted from biological matrices using a single solid-phase cyano cartridge. The eluent from the cartridge was injected directly onto the a 33 x 4.6 mm I.D. C18, 3-microns column coupled with a base deactivated C18 20 x 4.6 mm I.D., 5-microns guard column. The column eluate was passed into the corona discharge APCI source by means of a heated nebulizer interface. The analyte and its internal standard were detected using multiple reaction monitoring (MRM) mode for enhanced selectivity and sensitivity. The chromatographic run time was 3 min, and the method had sufficient sensitivity, precision, accuracy and selectivity for the analysis of clinical samples containing finasteride at concentration of 0.2 ng/ml. The assay methodology confirms the versatility of APCI-MS-MS detection, combined with HPLC, for the quantitation of selected drugs in the sub-ng/ml range in biological fluids.

A rapid and specific assay, based on liquid chromatography-atmospheric pressure chemical ionization mass spectrometry, for the determination of MK-434 (a 5 alpha-reductase inhibitor) and its metabolites in plasma

MK-434 is a new 5 alpha-reductase inhibitor. A sensitive and specific assay based on combined liquid chromatography-mass spectrometry (LC-MS) has been developed for the determination of this compound in plasma. The analyte was isolated from plasma by solid-phase extraction on a C18 cartridge. A related substance, L-654,066, was used as the internal standard. Extracts were separated on a 5-cm C18-reversed-phase high performance liquid chromatography column interfaced via the heated nebulizer probe to a corona discharge chemical ionization source. The mass spectrometer was operated in the positive ion MS-MS mode. The method had sufficient sensitivity, precision, accuracy, and selectivity for the analysis of clinical samples containing MK-434 and its two principal metabolites at concentrations in the range 0.5-50 ng ml-1. The chromatographic run time was < 5 min.

Plasma concentrations and effect on testosterone metabolism after single doses of MK-0434, a steroid 5 alpha-reductase inhibitor, in healthy subjects

A four-period, two-panel, single-rising-dose study (0.1-100 mg) was conducted in healthy males to investigate the pharmacodynamics, tolerability and pharmacokinetics of MK-0434, a steroid 5 alpha-reductase inhibitor. MK-0434 was associated with a significant reduction in dihydrotestosterone, which was maximal at 24 h and maintained through 48 h post treatment. The maximum reduction was approximately 50% and occurred at all doses above 5 mg (10, 25, 50 and 100 mg). MK-0434 appeared to have no effect on serum testosterone at these single doses. Rising single doses of MK-0434 were associated with an increase in Cmax and AUC but the changes were less than proportional to dose, most likely due to nonlinear absorption. MK-0434 given in single doses up to 100 mg was without significant adverse effects in healthy male volunteers. In summary, MK-0434 is a well-tolerated, potent, orally active 5 alpha-reductase inhibitor in man.