The effects of buserelin microparticles on ovarian function in healthy women.

OBJECTIVE: To investigate the tolerance, pharmacokinetics and pharmacodynamics of the microparticle formulation of buserelin, when it was administered subcutaneously. DESIGN: A single-blind, randomised, parallel-group design was used to investigate the duration of suppression of ovarian function associated with doses of 1.8 3.6 and 7.2 mg buserelin administered subcutaneously as microparticles. SETTING: The study was carried out at the Hoechst Research Centre for Clinical Pharmacology, Department of Pharmacology, University of the Orange Free State, Bloemfontein. PATIENTS: Thirty-two health premenopausal female volunteers aged between 19 and 39 years and weighing between 52 and 85 kg completed the study. OUTCOME MEASURES: Serum progesterone and oestradiol concentrations were measured twice weekly until normal ovarian function resumed, i.e. when serum progesterone concentrations increased to at least 8 nmol/l (a sign of ovulation) and oestradiol concentrations increased to values above 300 pmol/l. Serum and urinary concentrations of buserelin were measured at the same times as those of progesterone and oestradiol. RESULTS: Doses of 1.8 3.6 and 7.2 mg elicited anovulation for mean periods of 52, 77 and 113 days and suppressed ovarian production of oestrogen for 19, 38 and 69 days. Resumption of normal ovarian function occurred when serum buserelin concentrations decreased to between 0.03 and 0.05 microgram/ml. The correlation coefficient between dose and duration of anovulation was 0.75; the correlation coefficient between dose and duration of suppression of oestrogen production was 0.76. CONCLUSION: Apart from minor side-effects such as hot flushes, vaginal spotting and acne, the compound was tolerated well. We conclude that a good relationship exists between dose and duration of suppression of ovarian function. Doses of 3.6 - 7.2 mg buserelin should suppress oestrogen production for approximately 6 - 9 weeks and ovulation for 11 - 16 weeks.

Multiple doses of trandolapril do not affect warfarin pharmacodynamics.

OBJECTIVE: The effects of multiple doses of trandolapril (a new angiotensin-converting enzyme inhibitor) on the pharmacodynamics of a single 25 mg dose of warfarin were investigated in 19 men. DESIGN: A double-blind, placebo-controlled cross-over design was used. The study consisted of two periods of 13 days each, during which subjects received either trandolapril 2 mg or placebo once daily according to a randomisation plan. Warfarin was given on day 8 of each of these periods. SETTING: The study was carried out at the Hoechst Research Centre for Clinical Pharmacology, Department of Pharmacology, University of the Orange Free State, Bloemfontein. PATIENTS: Nineteen healthy white men aged between 18 and 28 years and weighing between 65 and 98 kg volunteered for the study. OUTCOME MEASURES: Prothrombin time (PT) and coagulation factors II, VII, IX and X were measured before and sequentially up to 6 days after warfarin administration. Areas under the PT and coagulation factor time curves for warfarin + trandolapril were compared with the corresponding areas for warfarin + placebo. The two treatment combinations were also compared at each measuring time. RESULTS: The point estimate for the ratio of the treatment means of warfarin + trandolapril relative to warfarin + placebo for PT was 97% (90% confidence interval: 90%-103%). The corresponding value for factor VII was 97% (90% confidence interval: 91%-102%). CONCLUSION: The concomitant administration of trandolapril did not affect the pharmacodynamic effects of warfarin.

The effect of fasting on total serum bilirubin concentrations.

Thirty-seven healthy volunteers, 19 of whom had consistently elevated total serum bilirubin (TSB) concentrations, took part in an open, randomised cross-over study to determine the effect of fasting on TSB concentrations. The study comprised of two treatments. During one treatment period volunteers ate a standard supper but fasted for 24 h thereafter. During the other treatment period volunteers ate a standard supper, snacks, breakfast and lunch. TSB concentrations were measured at regular intervals. In both the normal and high bilirubin groups, minimum TSB values were recorded 4 h after the supper. A 24 h fast more than doubled TSB concentration from baseline values in both the normal and high bilirubin groups. A clinically relevant rise in TSB took place after 12 h into the fasting period (TSB of 17.3 mumol l-1 in the fasted group vs 14.0 mumol l-1 in the non-fasted group). When designing a clinical trial, selecting volunteers, or judging the tolerance of a new drug, the rise in TSB caused by fasting must therefore be taken into account, particularly in trials where volunteers or patients fast before entering the study.

Double-blind comparison of the efficacy and safety of trandolapril 2 mg and hydrochlorothiazide 25 mg in patients with mild-to-moderate essential hypertension. Investigator Study Group.

This multicenter international trial recruited 205 patients from 16 investigators. After a 4-week, single-blind placebo run-in, patients were randomized to receive 16 weeks of trandolapril 2 mg/day (68 patients), hydrochlorothiazide (HCTZ) 25 mg/day (68 patients), or the combination (69 patients). Morning predosing supine diastolic blood pressure (DBP) was the primary efficacy measurement. Intention-to-treat analysis showed significant decreases in all three groups in mean (+/- SEM) supine DBP throughout the study, with no significant differences at week 16 between trandolapril (-10.6 +/- 1.3 mm Hg) and HCTZ (-10.9 +/- 1.3 mm Hg). The combination gave a significantly greater reduction than either drug alone (-15.1 +/- 1.13 mm Hg). Blood pressure was normalized in the combination group in 67% of patients, a significantly higher proportion than either trandolapril (63%) or HCTZ (60%; p = 0.04). Each treatment was well tolerated. The incidence of adverse events was similar in all three groups. Trandolapril 2 mg once daily is an effective antihypertensive agent, comparable to HCTZ. Furthermore, the combination of the two drugs was shown to enhance the antihypertensive effect of the two compounds alone.

Lack of interaction between ramipril and simvastatin.

Twenty two healthy males participated in a randomised, placebo-controlled, double blind, cross-over study to investigate the influence of simvastatin on the pharmacokinetics of ramipril and its active metabolite (ramiprilat), and on the ACE-inhibiting effect of ramiprilat. During two study periods, each of 7 days, subjects received daily either simvastatin 20 mg at 19.00 h or placebo; ramipril (5 mg) was given on Day 5 of each of the periods. Plasma concentrations of ramipril and ramiprilat and ACE-activity were measured in sequential blood specimens, and ramipril and ramiprilat concentrations were measured in urine. Blood and urine collections for pharmacokinetic and pharmacodynamic assessment were made up to 72 h after the dose of ramipril. The mean AUC of ramipril for ramipril+placebo (R+P) and ramipril+simvastatin (R+S) was 22.2 and 21.3 ng.h.ml-1, respectively; for ramiprilat the corresponding figures were 61.3 and 57.6 ng.h.ml-1. The urinary excretion of ramipril+metabolites for (R+P) and (R+S) was 25.2 and 24.1% of dose. The maximum percentage inhibition of ACE-activity for (R+P) was 94.6%, and for (R+S) it was 94.1%. It is concluded that concomitant administration of simvastatin and ramipril has no clinically relevant effect on the pharmacokinetics or ACE-inhibition of the latter drug and its metabolites.

Assessing the risk of ovulation in interaction studies of drugs and oral contraceptives.

When certain drugs are taken concomitantly with an oral contraceptive, the efficacy of the contraceptive may be obtunded, and pregnancy may ensue. Since the function of oral contraceptives is to suppress ovulation, the risk of ovulation is an important parameter in clinical studies investigating interactions between drugs and oral contraceptives. The purpose of this paper is to compare a crossover design, and a new study design used for assessing a possible interaction between a drug and an oral contraceptive, and to discuss the statistical issues involved in the planning and evaluation of the results of such studies.

Effect of renal function on the pharmacokinetics and pharmacodynamics of trandolapril.

1. The pharmacokinetics and pharmacodynamics of a single dose of trandolapril, an angiotensin converting enzyme (ACE) inhibitor with an active metabolite, trandolaprilat, which is in part further metabolised prior to renal elimination, were evaluated in 31 subjects with a wide range of renal function (creatinine clearance 4-112 ml min-1 1.73 m-2). 2. The pharmacokinetics of trandolapril were unaffected by differences in renal function. 3. In contrast, there was a close correlation between the renal clearance (0-96 h) of trandolaprilat and creatinine clearance (r = 0.95, P = 0.0001). The maximum plasma concentration of trandolaprilat, and the area under the concentration curve (0-96 h) correlated inversely with creatinine clearance (r = -0.59, P < 0.001; and r = -0.61, P < 0.001 respectively). 4. Significant changes in plasma trandolaprilat concentrations were seen only in patients with creatinine clearances of 30 ml min-1 1.73 m-2 or less, suggesting that a dose reduction in trandolapril might be advisable in severe renal impairment. 5. However, the majority of parameters of ACE inhibition were unrelated to creatinine clearance, although area under the curve for ACE inhibition (0-336 h) showed a weak negative correlation (r = -0.49, P < 0.01). Similarly, weighted mean changes in blood pressure were not influenced by renal function. 6. Therefore, while the pharmacokinetic parameters of trandolaprilat correlated with creatinine clearance, pharmacodynamic measurements (ACE inhibition and blood pressure changes) in general showed no such relationship, indicating that dose adjustment of ACE inhibitors in renal impairment should be based on pharmacokinetic results only in conjunction with pharmacodynamic data.

Recombinant hirudin, a new anticoagulant, has no effect on faecal blood loss.

Hirudin is a selective thrombin inhibitor with strong anticoagulant properties which could elicit gastro-intestinal bleeding. A double-blind cross-over study of the effects of hirudin on gastro-intestinal bleeding was therefore conducted on 12 healthy, consenting males. After labelling erythrocytes with 51Cr and returning them intravenously, stools were collected for 2 days to measure radioactivity and hence baseline faecal blood loss. After injection of hirudin or placebo stools were collected for 3 days. Partial thromboplastin time was measured sequentially after medication with hirudin or placebo. This procedure was repeated after injection of the alternate medication 1 week later. Hirudin was tolerated well. Mean faecal blood loss associated with hirudin was slightly higher than with placebo (1.63 ml vs 1.15 ml over 3 days; 95% confidence interval for the difference between hirudin and placebo was -0.68 to 1.63) but these differences are clinically irrelevant. After hirudin injection PTT was elevated to about twice the baseline values but returned to baseline within 12 h after the last hirudin injection.

The effects of felodipine on the pharmacokinetics of diazepam.

Twelve consenting, caucasian male volunteers participated in a double-blind, randomized, crossover study of the effects of felodipine, a calcium antagonist, on the pharmacokinetics of diazepam. There were two trial periods of 12 days each with a wash-out period of 9 days between them (total duration: 12 + 12 + 9 = 33 days). During the 12-day periods they received either felodipine or placebo each morning under fasting conditions. On day 6 of each of the two 12-day periods, diazepam, 10 mg was injected i.v. 30 minutes after the felodipine/placebo. Diazepam and desmethyldiazepam concentrations were measured in plasma up to 168 hours after the injection. Diazepam plasma concentrations and pharmacokinetic parameters were not affected by the concomitant medication with felodipine. However, the co-administration of felodipine increased desmethyldiazepam plasma concentrations relative to placebo: mean area under the plasma concentration-time curve of 4,910 vs 5,581 ng.h/ml and mean peak concentrations of 40 vs 47 ng/ml. Felodipine might cause a retarded elimination of desmethyldiazepam, possibly by obtruding the formation of oxazepam. The clinical relevance of these findings remains to be elucidated.

Safety, tolerance and pharmacokinetics of cefpirome administered intramuscularly to healthy subjects.

The pharmacokinetics of cefpirome were studied in healthy male subjects following single (0.5, 1.0 and 2.0 g) and multiple (1.0 g every 12 h for 3.5 days) intramuscular injections. High pressure liquid chromatography was used to determine cefpirome concentrations in plasma and urine. Cefpirome was absorbed rapidly, mean peak times were 1.6-2.3 h. Pharmacokinetics were linear over the 0.5 to 2.0 g range with mean total body clearance ranging from 148 to 154 mL/min. The peak plasma concentration and area under the curve increased in a dose proportional manner. The terminal half-life (2 h) was not influenced by dose or duration of dosing. There was no drug accumulation after multiple in administrations. About 70-80% of an administered dose was excreted in the urine as unchanged cefpirome. Cefpirome was well tolerated, slight to moderate pain being reported in less than 30% of the injections.

The pharmacology of recombinant hirudin, a new anticoagulant.

A new anticoagulant, recombinant hirudin, was given to healthy volunteers (5 per test dose) in single intravenous doses of 0.01, 0.02, 0.04, 0.07 and 0.1 mg/kg to study its anticoagulant effects, how it was tolerated and its pharmacokinetics. Hirudin proved to be a potent anticoagulant with important effects on thrombin (increase in thrombin time and partial thromboplastin time). The maximum pharmacodynamic effect was achieved with the 0.07 mg/kg dose, and upwards. All doses of the compound were tolerated without side-effects. The mean elimination half-life is about 1 hour. Mean total clearance and volume of distribution are approximately 190 ml/min and 14 l, respectively. Hirudin obeys first-order pharmacokinetics.

Statistical significance versus clinical relevance. Part II. The use and interpretation of confidence intervals.

Most clinical studies are carried out to estimate some quantity, such as a difference in means or proportions. However, significance testing without controlling the power of the test is not an appropriate tool for this purpose, since practical conclusions are difficult (or even impossible) to formulate. The use of confidence intervals, which provide effective information in this regard, is recommended and illustrated by means of an example. With confidence intervals, it can clearly be stated in what range the population value (difference, proportion, or any other point estimate) is likely to lie. A clinically relevant interpretation can then be made without difficulty.

Statistical significance versus clinical relevance. Part III. Methods for calculating confidence intervals.

Formulae for calculating confidence intervals for different types of studies and conditions are presented. These include means, proportions, difference in means and proportions for paired and unpaired data, more complicated analyses of variance, medians, quantiles, relative risks (odd ratios), standardised ratios and rates, intercepts, slopes and correlation coefficients in regression and correlation analyses, as well as survival proportions calculated in survival analysis. For less frequently used formulae, examples are included.

Statistical significance versus clinical relevance. Part I. The essential role of the power of a statistical test.

When comparing two treatment groups, hypothesis testing is widely used. However, clinical trialists should be more interested in statistical methods which elicit the magnitude of the differences between treatment groups, rather than a simple indication of whether or not the differences are statistically significant. Statistical significance does not necessarily imply clinical relevance. If the true difference between two treatment groups is so small that it is clinically irrelevant, a sample size can be found for which this difference is statistically significant. On the other hand, if the difference between treatment groups is statistically non-significant, it may still be clinically important. The limitations of conventional hypothesis testing of equal true means as such are highlighted. The need to control the power of the test--which takes into account the difference in treatment means which is considered important (clinically relevant) by the researcher--is discussed.

Bio-availability of three formulations of glibenclamide.

Eighteen healthy men participated in a double-blind, randomised, crossover study to compare the bio-availability of three 5 mg formulations of glibenclamide. The products compared were Daonil (Hoechst), Glycomin (Lennon) and Melix (Lagamed). Volunteers received a continuous intravenous infusion of glucose at a rate of 0.25 g/kg/h for 10 hours. Two hours after commencement of this infusion medication was given orally with 200 ml of a 10% (m/v) glucose solution. The subjects also drank 200 ml of the glucose solution hourly for 5 hours after medication. Blood samples were taken up to 22 hours after medication for radio-immunoassay of glibenclamide as well as for measurement of glucose concentrations. The following kinetic variables were calculated; maximum concentration, time to maximum concentration, terminal half-life, areas under the serum concentration-time curves, relative total clearance, total mean time and relative volume of distribution. Daonil and Glycomin were bio-equivalent, but important differences were demonstrated between these two formulations and Melix. This study method necessitates close surveillance of volunteers in order to detect and treat hypoglycaemia.

Effects of HOE 760 (histamine H2-receptor antagonist) on diazepam pharmacokinetics.

A double-blind cross-over study of the effects of HOE 760 (histamine H2-receptor blocker) on diazepam pharmacokinetics was conducted in 12 healthy men. HOE 760 or placebo was given daily for 12 days and, after a wash-out period of 9 days, the alternate medication was given for 12 days. Diazepam 10 mg was given intravenously on day 6 of each of the 12-day periods. Blood was taken up to 1 week after the diazepam injections for assay of diazepam and desmethyldiazepam. The co-administration of HOE 760 did not affect the pharmacokinetics of diazepam and desmethyldiazepam.

The effects of forskolin eye drops on intra-ocular pressure.

Two studies were performed to investigate the effects of forskolin (Hoechst Research) on intra-ocular pressure (IOP). In the first study two 1.0% formulations of forskolin eye drops were compared with placebo in 10 healthy volunteers. Oxybuprocaine eye drops were used for local anaesthesia before measurement of IOP by applanation tonometry. This was followed by instillation of either medication or placebo on a randomised cross-over basis and hourly measurement of IOP. No significant differences were present between the forskolin treatments and placebo. For 6 hours after drug application a definite decrease in IOP relative to base-line values was observed after each of the forskolin treatments as well as after placebo. In a subsequent study only one formulation of 1% forskolin was compared with placebo. Proxymetacaine eye drops were used for local anaesthesia. Forskolin resulted in a significant reduction in IOP relative to placebo. It is concluded that forskolin reduces IOP in healthy volunteers, and that oxybuprocaine reduces IOP in its own right.

Pharmacokinetics of ramipril in the elderly.

Ramipril (HOE 498) is a pro-drug of which the main metabolite (HOE 498 diacid or ramiprilat) is a potent angiotensin converting enzyme inhibitor. Thirteen healthy white volunteers (5 females and 8 males, ages 65 to 76 years) participated in a study to investigate the pharmacokinetics of HOE 498 in the elderly. After administration of 10 mg of HOE 498, sequential urine and serum specimens were obtained for assay of HOE 498 and metabolites (HOE 498-glucuronide, diacid, diacid-glucuronide, diketopiperazine and diketopiperazine acid). Side effects, clinical chemistry and hematology were monitored. HOE 498 reached peak concentrations of 62.4 +/- 23.3 ng/ml in serum after 0.7 +/- 0.3 hours. Serum levels decreased with an apparent half-life of 0.9 +/- 0.4 hours. The diacid was rapidly formed in serum, reaching peak concentrations of 40.6 +/- 14.0 ng/ml after 2.0 +/- 0.6 hours and declining with a half-life of 2.2 +/- 0.5 hours. A prolonged terminal phase of serum concentration versus time curve was observed at concentrations less than 1 ng/ml. The mean recovery of HOE 498 and metabolites in urine, up to 26 hours after administration, was 35 +/- 14% of the dose. The apparent half-lives, calculated from urine parameters, for HOE 498 and the diacid were 2.6 +/- 0.9 and 4.0 +/- 1.1 hours, respectively. The mean peak concentration and half-life of HOE 498 in serum are slightly higher in the elderly than in younger volunteers. Complete urinary collection was not possible, but urinary recovery did not seem different from younger volunteers.