BIOPHARMACEUTICS & DRUG DISPOSITION, VOL. 12, 577-582 (1991)
SINGLE ORAL DOSE PHARMACOKINETICS AND COMPARATIVE BIOAVAILABILITY OF DANAZOL IN HUMANS w. D. HOOPER, M. J.
EADIE AND R. G . DICKINSON*
Department of Medicine, The University of Queensland, Clinical Sciences Building, Royal Brisbane Hospital, Herston. Queensland 4029, Australia
ABSTRACT A comparative bioavailability study was conducted with two capsule formulations of danazol (200 mg) in 16 healthy adult male volunteers. Fasting subjects received single doses (400 mg) of each formulation on separate occasions 1 week apart. Blood samples were drawn at specified times up to 32 h after the dose and danazol concentrations in plasma were determined by a specific and sensitive HPLC method. The results for one subject were excluded as outlier values. The data from the other 15 subjects showed small differences, which did not achieve statistical significancebetween the formulations with respect to C,,,,,, TPakand AUCo-,. The mean elimination half-life for danazol was 9 4 4 f S D 2.74 h and the mean apparent total body clearance was 710fSD 2161 h-I. These data differed from previously published results, probably as a result of the more sensitive and specific assay method used in the present work. It is likely that a high proportion of the oral dose of danazol is eliminated by presystemic metabolism. KEY WORDS
Danazol
Pharmacokinetics Bioavailability
Presystemicelimination
INTRODUCTION Danazol (17-a-pregna-2,4-dien-20-yno[2,3-d]isoxazol-l7-01) is a synthetic hormone structurally related to testosterone and ethisterone. The compound has multiple biological effects, and consequently has found diverse clinical applications. Its major uses in the management of gynaecological disorders have been reviewed in a recent symposium.' Although the drug has been in clinical use for almost 20 years, there is very little published information on its disposition and pharmacokinetics in humans. This paucity of pharmacokinetic data results largely from unavailability until recently of satisfactory methods for the analysis of danazol in plasma a t clinically relevant concentrations. The first published method was a radioligand binding assay,* which had reasonable sensitivity but poor specificity. Subsequently a radioimmunoassay which offered a lower limit of measurement of
* Addressee for correspondence. 0142-278219 1/080577-O6$05.00 0 1991 by John Wiley & Sons, Ltd.
Received 4 January 1991 Revised 3 April 1991
578
W. D. HOOPER, M. J . EADIE AND R. G . DICKINSON
29 ngml-I was de~cribed.~ This was subsequently refined4 to give a detection limit of 1-2 ng ml-l, but the potential remained for interference, particularly from related steroids and metabolites. An early high performance liquid chromatographic (HPLC) method was applied only to assay of danazol in pharmaceutical preparation^.^ However two independent groups published very similar HPLC methods almost simultaneously in 1987.6.7Both methods were demonstrated to be adequate for the conduct of single dose pharmacokinetic studies in humans. We have conducted a comparative bioavailability study with two formulations of danazol and the results are presented here primarily to document, for the first time in a comprehensive way, the pharmacokinetics of this important drug following single oral doses in healthy volunteers.
MATERIALS AND METHODS Study Design
The study was conducted according to a balanced crossover design in 16 subjects, each of whom received single doses of two capsule formulations of danazol on two occasions 1 week apart. The investigational protocol received the prior approval of the University of Queensland Medical Research Ethics Committee and all volunteers gave written informed consent to participate. Subjects
Sixteen healthy young adult males participated in the study. Their ages ranged from 18-26 years (mean 22.3 SD 1.9 years) and body weights from 56-83 kg (mean 69.1 f SD 8.3 kg). All had normal values for parameters included in standard screening tests for blood chemistry and haematology, which were conducted both prior to and at the completion of the study. Formulations studied
The formulations used in this study were Winthrop Laboratories capsules (Danocrine@)containing 200 mg danazol (Batch Number CD 0632) and Alphapharm capsules (Danzol@),also containing 200 mg danazol (Batch Number 030488). Capsules from both batches assayed by HPLC (using a Waters Novapak C t 8cartridge in a radial compression module, mobile phase 75 per cent methanol, 25 per cent water (v/v) at 2 ml min-', UV detection at 286 nm) gave mean danazol contents of 203.4 mg (Winthrop) and 203.7 mg (Alphapharm). Dissolution profiles (obtained in phosphate buffer pH 7.2 containing 1 per cent oxamin, one capsule per flask, U.S.P. Apparatus I1 at 50 revmin-I) were found to be similar.
DANAZOL
579
Clinical protocol
Subjects were enrolled in the study and randomly assigned to two groups of eight. On day 1, eight subjects received each danazol preparation and all subjects received the alternate preparation on day 8. Doses (2 x 200 mg capsules) were taken with water (100 ml) at approximately 8 am following an overnight fast. Fasting continued for 4 h after drug administration. Venous blood samples (10 ml) were collected via indwelling cannulas before dosing and at the following times (h) post-dose: 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0, 2.5, 3, 4, 5, 6, 8, 10, 12. Further samples were obtained by separate venepuncture at 24 and 32 h. Actual sampling times were recorded to the nearest minute and were used in all pharmacokinetic calculations. Immediately after drawing, blood samples were transferred to tubes containing lithium heparin (125 IU) and the plasma was separated and frozen (-20") within 60 min of drawing. Drug assay
Danazol was assayed by the HPLC method which was published previously from this laboratory.' Briefly, the drug and internal standard (quazepam) were extracted from plasma with hexane, which was then evaporated under a stream of air. The residue was taken up in HPLC mobile phase (68 per cent v/v acetonitrilelwater) and chromatography was performed on a Waters C18 Novapak cartridge contained in a Waters RCM-100 radial compression module. The column effluent was monitored at 287 nm, using a Waters Lambda-Max 481 UV-visible spectrometer, and danazol was quantified in terms of peak height ratios. The assay method was formally validated and shown to provide excellent linearity, accuracy, and precision over the concentration range 2-200 ng ml-I for danazol in plasma. Quality control samples were assayed with the plasma samples from the subjects in this study, and on the basis of these the method was shown to be accurate to within f8.8 per cent at longml-', f4.8 per cent at 50 ngml-I and f4.1 per cent at 200 ngml-', while the precision (R.S.D. per cent) at these same three concentrations was 12.2 per cent, 5.5 per cent and 3.9 per cent, respectively. Pharmacokinetic and statistical analyses
The maximum plasma danazol concentration (Cmm)and the time at which this occurred (Tpak)were read directly from the tabulated concentration vs time results. The terminal elimination rate constant (k,) was determined by the model-independent method of computing by regression analysis the slope of the approximately log-linear terminal elimination phase. Elimination half-life (t,J was In 2/k,. AUCo-, was the sum of AUCo-t (obtained by trapezoidal rule, where t was the time at which danazol was last measurable in plasma) and AUC,-, (obtained as CJk,). Apparent total body clearance (CWF) was calculated from the expression DOSE/AUCo- -.
5 80
W. D. HOOPER, M. J . EADlE AND R . G . DICKINSON
C,,, and AUCo-, for the two formulations were compared by analysis of variance and calculation of confidence intervals. Tpeakwas compared by the non-parametric Wilcoxon paired data test. RESULTS AND DISCUSSION The C,,, values for danazol following 400 mg oral doses ranged from 34.1 to 170ngml-' for the Alphapharm formulation, and from 30.8 to 143ngml-' for the Winthrop formulation in 15 of the subjects. Subject 7 on one occasion only (Alphapharm dose) gave a C,,, value of 31 1 ngml-' which was more than three standard deviations outside the mean of values for that formulation, and more than four standard deviations from the grand mean (n = 32). This result was therefore treated as an outlier, and data for this subject were excluded from further analysis. The presumption was that this outlier value was more likely to be a consequence of a perturbation in the physiological status of the subject on this occasion, rather than of the formulation per se. Minor changes in physiology ( e g blood pressure, hepatic blood flow, gastrointestinal motility) are well known to exert major effects on the absorption of drugs with a high extraction ratio.8
8o
r
C
0
04 I
0
I
I
4
I
I
8
I
, , 12
I
16
I
I
20
I
I
24
,
I
28
,
, 32
Time after Dosing (hours) Figure 1. Mean ( n = 15) plasma concentration-time profiles for danazol following a 400 mg oral dose of Alphapharm (closed circles) or Winthrop (open circles) formulation to healthy male subjects. Bars represent one standard error.
58 1
DANAZOL
The mean plasma concentration-time curves for the two formulations in 15 subjects are shown in Figure 1. While the curves do differ slightly, especially in the vicinity of the C,,, values, the differences are not great in relation to the variances in the data sets. The significance of these differences between formulations is better appreciated from the pharmacokinetic data given in Table 1. The C,,, values were not significantly different (ANOVA; a = 0.05; p = 0.541), and the 90 per cent confidence interval for the ratio of mean C,,, values (AlphaphamdWinthrop) was 0-90-1.22. Similarly the TFakvalues were not statistically significantly different (Wilcoxon test), and their ratio had a 90 per cent confidence interval of 0.52-1.10. The AUCo-, values were not significantly different (ANOVA; a = 0.05;p = 0.395) and the 90 per cent confidence interval for their ratio of means was 0.93-1.21. Thus, in relation to these three important parameters, we concluded that the two formulations were not significantly different. Table 1. Pharmacokinetic parameters for danazol after administering a 400 mg oral dose to healthy males* Parameter, units Cmax,
ng m1-l
Tpeak,
AUC,,, ng.h ml-' t, h CL/F, 1 h-'
Formulation administered Alphapharm Winthrop 73.6 f36.6 2-00 f 1.29 636 f 238 9.17 f2.15 693 f 218
69.6 f29.9 2.47 f 1.62 601 f 181 9.70 f 3.29 727 f221
*Mean*SD,n= 15.
Although these studies were conducted as a comparative bioavailability trial, their major value is in documenting, for the first time with a sensitive and specific chromatographic assay method, the single dose pharmacokinetics of danazol. There was an early report9 on the pharmacokinetics of danazol showing mean C,,, values of about 80 ng ml-' following a single oral 400 mg dose to ten healthy female volunteers. The mean elimination half-life was given as 4.5 h, but the drug was undetectable after 8 h. These studies were performed with a radioligand binding assay,2 the lower limit of quantification of which was stated as 19 ng ml-l. However later workers used a radioimmun~assay~ which was claimed to have improved specificity and a limit of detection of 2ngml-' and found a mean half-life of 29 h in 24 healthy females.'O The mean half-life in the present study in healthy males was found to be 9.44*SD 2.74 h (mean of 15 subjects on two occasions); individual values in this study ranged from 5.0 to 18.2 h. While these present studies relate to healthy adult males, and the possibility of a gender-related difference in elimination cannot be discounted, our results suggest that the previously published elimination data for females should be called into question. It seems
582
W . D. HOOPER. M . J . EADIE AND R . G. DICKINSON
possible that the reported mean half-life of 4.5 h9 was not obtained from the true terminal phase (since no data were obtained after 8 h), and that the value of 29 h10may have been erroneously high as a result of non-specific radioimmunoassay in which metabolites interfered. We did not study female volunteers, as we received advice that the Medical Research Ethics Committee would be reluctant to approve such studies. The apparent total body clearance values (overall mean 710 fSD 216 1h-I) obtained in the present study indicate the likelihood of extensive presystemic elimination. This would be completely consistent with the early studies in rats and monkeys? which showed that the peak level of intact danazol in plasma represented less than 2 per cent of the total administered radioactive dose. If the extraction ratio in humans does exceed 0.9, the comments made above in relation to the outlier result seem completely plausible. Clearly a more detailed documentation of the hepatic extraction would require a parenteral formulation of danazol, which is not available at present. Another question which was not addressed in the present study, but which might be important with a drug whose oral clearance is so high, is the possible effects of food on its absorption. In summary, this study in adult male volunteers sheds new light on the single dose pharmacokinetics of danazol, and suggests further studies which should be conducted in order to document adequately the clinical pharmacokinetics of this important but hitherto poorly studied drug. In particular there is a requirement for study of the pharmacokinetics of danazol in females receiving the drug therapeutically, since we cannot be certain that the present findings in male volunteers will apply to the population to whom the drug is usually administered. ACKNOWLEDGEMENTS The authors wish to thank Alphapharm Pty. Ltd for financial support of these studies and for conducting the capsule assays and dissolution studies. Drs D. K. Moses, G. K. Herkes and M. L. Bullpitt assisted with the recruitment of volunteers and with the blood sample collections. REFERENCES I. 2. 3. 4. 5. 6. 7. 8. 9. 10.
J. Reproduct. Med., 35 (1) (suppl) (1990). J. E. Creange and G. 0.Potts, Steroids, 23,411 (1974). T. A. Williams, J . Edelson and R. W. Ross, Steroids, 31, 205 (1978). J. E. Peterson, M. E. King, W. F. Banks, J. F. Baker, A. F. Jensen, R. W. Ross, S. Clemans and J . Edelson, J. Pharm Sci. 67, 1425 (1978). R . T. Sane, M. Chakraborty, V. G. Nayak and B. L. Chauhan, J. Chromatogr., 358,448 (1986). G. A. Nygard, L. J . Lovett, G. R. Erdmann and S. K . W. Khalil, J. Chromutogr.,415,438 (1987). W. D. Hooper, G. R. Cannell and R . G. Dickinson, J. Chromutogr.,416,347 (1987). S. M. Pond and T. N. Tozer, Clin. Pharmacokinef.,9, 1 (1984). C. Davison, W. Banks and A. Fritz, Arch. Int. Phurmarodyn. Ther., 221,294 (1976). G. 0.Potts, H. P. Schane and J . Edelson, Drugs, 19,321 (1980).
SINGLE ORAL DOSE PHARMACOKINETICS AND COMPARATIVE BIOAVAILABILITY OF DANAZOL IN HUMANS w. D. HOOPER, M. J.
EADIE AND R. G . DICKINSON*
Department of Medicine, The University of Queensland, Clinical Sciences Building, Royal Brisbane Hospital, Herston. Queensland 4029, Australia
ABSTRACT A comparative bioavailability study was conducted with two capsule formulations of danazol (200 mg) in 16 healthy adult male volunteers. Fasting subjects received single doses (400 mg) of each formulation on separate occasions 1 week apart. Blood samples were drawn at specified times up to 32 h after the dose and danazol concentrations in plasma were determined by a specific and sensitive HPLC method. The results for one subject were excluded as outlier values. The data from the other 15 subjects showed small differences, which did not achieve statistical significancebetween the formulations with respect to C,,,,,, TPakand AUCo-,. The mean elimination half-life for danazol was 9 4 4 f S D 2.74 h and the mean apparent total body clearance was 710fSD 2161 h-I. These data differed from previously published results, probably as a result of the more sensitive and specific assay method used in the present work. It is likely that a high proportion of the oral dose of danazol is eliminated by presystemic metabolism. KEY WORDS
Danazol
Pharmacokinetics Bioavailability
Presystemicelimination
INTRODUCTION Danazol (17-a-pregna-2,4-dien-20-yno[2,3-d]isoxazol-l7-01) is a synthetic hormone structurally related to testosterone and ethisterone. The compound has multiple biological effects, and consequently has found diverse clinical applications. Its major uses in the management of gynaecological disorders have been reviewed in a recent symposium.' Although the drug has been in clinical use for almost 20 years, there is very little published information on its disposition and pharmacokinetics in humans. This paucity of pharmacokinetic data results largely from unavailability until recently of satisfactory methods for the analysis of danazol in plasma a t clinically relevant concentrations. The first published method was a radioligand binding assay,* which had reasonable sensitivity but poor specificity. Subsequently a radioimmunoassay which offered a lower limit of measurement of
* Addressee for correspondence. 0142-278219 1/080577-O6$05.00 0 1991 by John Wiley & Sons, Ltd.
Received 4 January 1991 Revised 3 April 1991
578
W. D. HOOPER, M. J . EADIE AND R. G . DICKINSON
29 ngml-I was de~cribed.~ This was subsequently refined4 to give a detection limit of 1-2 ng ml-l, but the potential remained for interference, particularly from related steroids and metabolites. An early high performance liquid chromatographic (HPLC) method was applied only to assay of danazol in pharmaceutical preparation^.^ However two independent groups published very similar HPLC methods almost simultaneously in 1987.6.7Both methods were demonstrated to be adequate for the conduct of single dose pharmacokinetic studies in humans. We have conducted a comparative bioavailability study with two formulations of danazol and the results are presented here primarily to document, for the first time in a comprehensive way, the pharmacokinetics of this important drug following single oral doses in healthy volunteers.
MATERIALS AND METHODS Study Design
The study was conducted according to a balanced crossover design in 16 subjects, each of whom received single doses of two capsule formulations of danazol on two occasions 1 week apart. The investigational protocol received the prior approval of the University of Queensland Medical Research Ethics Committee and all volunteers gave written informed consent to participate. Subjects
Sixteen healthy young adult males participated in the study. Their ages ranged from 18-26 years (mean 22.3 SD 1.9 years) and body weights from 56-83 kg (mean 69.1 f SD 8.3 kg). All had normal values for parameters included in standard screening tests for blood chemistry and haematology, which were conducted both prior to and at the completion of the study. Formulations studied
The formulations used in this study were Winthrop Laboratories capsules (Danocrine@)containing 200 mg danazol (Batch Number CD 0632) and Alphapharm capsules (Danzol@),also containing 200 mg danazol (Batch Number 030488). Capsules from both batches assayed by HPLC (using a Waters Novapak C t 8cartridge in a radial compression module, mobile phase 75 per cent methanol, 25 per cent water (v/v) at 2 ml min-', UV detection at 286 nm) gave mean danazol contents of 203.4 mg (Winthrop) and 203.7 mg (Alphapharm). Dissolution profiles (obtained in phosphate buffer pH 7.2 containing 1 per cent oxamin, one capsule per flask, U.S.P. Apparatus I1 at 50 revmin-I) were found to be similar.
DANAZOL
579
Clinical protocol
Subjects were enrolled in the study and randomly assigned to two groups of eight. On day 1, eight subjects received each danazol preparation and all subjects received the alternate preparation on day 8. Doses (2 x 200 mg capsules) were taken with water (100 ml) at approximately 8 am following an overnight fast. Fasting continued for 4 h after drug administration. Venous blood samples (10 ml) were collected via indwelling cannulas before dosing and at the following times (h) post-dose: 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, 2.0, 2.5, 3, 4, 5, 6, 8, 10, 12. Further samples were obtained by separate venepuncture at 24 and 32 h. Actual sampling times were recorded to the nearest minute and were used in all pharmacokinetic calculations. Immediately after drawing, blood samples were transferred to tubes containing lithium heparin (125 IU) and the plasma was separated and frozen (-20") within 60 min of drawing. Drug assay
Danazol was assayed by the HPLC method which was published previously from this laboratory.' Briefly, the drug and internal standard (quazepam) were extracted from plasma with hexane, which was then evaporated under a stream of air. The residue was taken up in HPLC mobile phase (68 per cent v/v acetonitrilelwater) and chromatography was performed on a Waters C18 Novapak cartridge contained in a Waters RCM-100 radial compression module. The column effluent was monitored at 287 nm, using a Waters Lambda-Max 481 UV-visible spectrometer, and danazol was quantified in terms of peak height ratios. The assay method was formally validated and shown to provide excellent linearity, accuracy, and precision over the concentration range 2-200 ng ml-I for danazol in plasma. Quality control samples were assayed with the plasma samples from the subjects in this study, and on the basis of these the method was shown to be accurate to within f8.8 per cent at longml-', f4.8 per cent at 50 ngml-I and f4.1 per cent at 200 ngml-', while the precision (R.S.D. per cent) at these same three concentrations was 12.2 per cent, 5.5 per cent and 3.9 per cent, respectively. Pharmacokinetic and statistical analyses
The maximum plasma danazol concentration (Cmm)and the time at which this occurred (Tpak)were read directly from the tabulated concentration vs time results. The terminal elimination rate constant (k,) was determined by the model-independent method of computing by regression analysis the slope of the approximately log-linear terminal elimination phase. Elimination half-life (t,J was In 2/k,. AUCo-, was the sum of AUCo-t (obtained by trapezoidal rule, where t was the time at which danazol was last measurable in plasma) and AUC,-, (obtained as CJk,). Apparent total body clearance (CWF) was calculated from the expression DOSE/AUCo- -.
5 80
W. D. HOOPER, M. J . EADlE AND R . G . DICKINSON
C,,, and AUCo-, for the two formulations were compared by analysis of variance and calculation of confidence intervals. Tpeakwas compared by the non-parametric Wilcoxon paired data test. RESULTS AND DISCUSSION The C,,, values for danazol following 400 mg oral doses ranged from 34.1 to 170ngml-' for the Alphapharm formulation, and from 30.8 to 143ngml-' for the Winthrop formulation in 15 of the subjects. Subject 7 on one occasion only (Alphapharm dose) gave a C,,, value of 31 1 ngml-' which was more than three standard deviations outside the mean of values for that formulation, and more than four standard deviations from the grand mean (n = 32). This result was therefore treated as an outlier, and data for this subject were excluded from further analysis. The presumption was that this outlier value was more likely to be a consequence of a perturbation in the physiological status of the subject on this occasion, rather than of the formulation per se. Minor changes in physiology ( e g blood pressure, hepatic blood flow, gastrointestinal motility) are well known to exert major effects on the absorption of drugs with a high extraction ratio.8
8o
r
C
0
04 I
0
I
I
4
I
I
8
I
, , 12
I
16
I
I
20
I
I
24
,
I
28
,
, 32
Time after Dosing (hours) Figure 1. Mean ( n = 15) plasma concentration-time profiles for danazol following a 400 mg oral dose of Alphapharm (closed circles) or Winthrop (open circles) formulation to healthy male subjects. Bars represent one standard error.
58 1
DANAZOL
The mean plasma concentration-time curves for the two formulations in 15 subjects are shown in Figure 1. While the curves do differ slightly, especially in the vicinity of the C,,, values, the differences are not great in relation to the variances in the data sets. The significance of these differences between formulations is better appreciated from the pharmacokinetic data given in Table 1. The C,,, values were not significantly different (ANOVA; a = 0.05; p = 0.541), and the 90 per cent confidence interval for the ratio of mean C,,, values (AlphaphamdWinthrop) was 0-90-1.22. Similarly the TFakvalues were not statistically significantly different (Wilcoxon test), and their ratio had a 90 per cent confidence interval of 0.52-1.10. The AUCo-, values were not significantly different (ANOVA; a = 0.05;p = 0.395) and the 90 per cent confidence interval for their ratio of means was 0.93-1.21. Thus, in relation to these three important parameters, we concluded that the two formulations were not significantly different. Table 1. Pharmacokinetic parameters for danazol after administering a 400 mg oral dose to healthy males* Parameter, units Cmax,
ng m1-l
Tpeak,
AUC,,, ng.h ml-' t, h CL/F, 1 h-'
Formulation administered Alphapharm Winthrop 73.6 f36.6 2-00 f 1.29 636 f 238 9.17 f2.15 693 f 218
69.6 f29.9 2.47 f 1.62 601 f 181 9.70 f 3.29 727 f221
*Mean*SD,n= 15.
Although these studies were conducted as a comparative bioavailability trial, their major value is in documenting, for the first time with a sensitive and specific chromatographic assay method, the single dose pharmacokinetics of danazol. There was an early report9 on the pharmacokinetics of danazol showing mean C,,, values of about 80 ng ml-' following a single oral 400 mg dose to ten healthy female volunteers. The mean elimination half-life was given as 4.5 h, but the drug was undetectable after 8 h. These studies were performed with a radioligand binding assay,2 the lower limit of quantification of which was stated as 19 ng ml-l. However later workers used a radioimmun~assay~ which was claimed to have improved specificity and a limit of detection of 2ngml-' and found a mean half-life of 29 h in 24 healthy females.'O The mean half-life in the present study in healthy males was found to be 9.44*SD 2.74 h (mean of 15 subjects on two occasions); individual values in this study ranged from 5.0 to 18.2 h. While these present studies relate to healthy adult males, and the possibility of a gender-related difference in elimination cannot be discounted, our results suggest that the previously published elimination data for females should be called into question. It seems
582
W . D. HOOPER. M . J . EADIE AND R . G. DICKINSON
possible that the reported mean half-life of 4.5 h9 was not obtained from the true terminal phase (since no data were obtained after 8 h), and that the value of 29 h10may have been erroneously high as a result of non-specific radioimmunoassay in which metabolites interfered. We did not study female volunteers, as we received advice that the Medical Research Ethics Committee would be reluctant to approve such studies. The apparent total body clearance values (overall mean 710 fSD 216 1h-I) obtained in the present study indicate the likelihood of extensive presystemic elimination. This would be completely consistent with the early studies in rats and monkeys? which showed that the peak level of intact danazol in plasma represented less than 2 per cent of the total administered radioactive dose. If the extraction ratio in humans does exceed 0.9, the comments made above in relation to the outlier result seem completely plausible. Clearly a more detailed documentation of the hepatic extraction would require a parenteral formulation of danazol, which is not available at present. Another question which was not addressed in the present study, but which might be important with a drug whose oral clearance is so high, is the possible effects of food on its absorption. In summary, this study in adult male volunteers sheds new light on the single dose pharmacokinetics of danazol, and suggests further studies which should be conducted in order to document adequately the clinical pharmacokinetics of this important but hitherto poorly studied drug. In particular there is a requirement for study of the pharmacokinetics of danazol in females receiving the drug therapeutically, since we cannot be certain that the present findings in male volunteers will apply to the population to whom the drug is usually administered. ACKNOWLEDGEMENTS The authors wish to thank Alphapharm Pty. Ltd for financial support of these studies and for conducting the capsule assays and dissolution studies. Drs D. K. Moses, G. K. Herkes and M. L. Bullpitt assisted with the recruitment of volunteers and with the blood sample collections. REFERENCES I. 2. 3. 4. 5. 6. 7. 8. 9. 10.
J. Reproduct. Med., 35 (1) (suppl) (1990). J. E. Creange and G. 0.Potts, Steroids, 23,411 (1974). T. A. Williams, J . Edelson and R. W. Ross, Steroids, 31, 205 (1978). J. E. Peterson, M. E. King, W. F. Banks, J. F. Baker, A. F. Jensen, R. W. Ross, S. Clemans and J . Edelson, J. Pharm Sci. 67, 1425 (1978). R . T. Sane, M. Chakraborty, V. G. Nayak and B. L. Chauhan, J. Chromatogr., 358,448 (1986). G. A. Nygard, L. J . Lovett, G. R. Erdmann and S. K . W. Khalil, J. Chromutogr.,415,438 (1987). W. D. Hooper, G. R. Cannell and R . G. Dickinson, J. Chromutogr.,416,347 (1987). S. M. Pond and T. N. Tozer, Clin. Pharmacokinef.,9, 1 (1984). C. Davison, W. Banks and A. Fritz, Arch. Int. Phurmarodyn. Ther., 221,294 (1976). G. 0.Potts, H. P. Schane and J . Edelson, Drugs, 19,321 (1980).
