Vivian A. John

Pharmacokinetic Characterisation of Transdermal Delivery Systems

SummaryThe key aspects of the pharmacokinetics of transdermal delivery systems including time lag, steady-state plasma levels and decline phase are illustrated in this review. The 7 currently marketed transdermal systems [nitroglycerin (glyceryl trinitrate), estradiol, clonidine, fentanyl, nicotine, scopolamine (hyoscine) and estradiol/norethisterone acetate] are discussed, as are systems in development.Single-dose absolute bioavailability studies characterise the period of onset, the steady-state plateau and the declining phase, and typify transdermal delivery. More complex temporal profiles result from interactions with enhancers or removal of the system before steady-state conditions are achieved. Clinically these systems are used to achieve multiple peak serum estradiol concentrations after application of transdermal estradiol, and an initial peak systemic concentration of testosterone after application of transdermal testosterone. Multiple-dose, dose proportionality and skin site bioequivalence studies are needed for the full pharmacokinetic characterisation of a transdermal delivery system.The relationship of system design to variability is discussed. Although the data are limited, population factors, cutaneous metabolism and tolerance all appear to influence the disposition of drugs administered transdermally. For example, the route of delivery influences which nitroglycerin metabolite predominates. Futhermore, as a result of tolerance to nitrates, a transdermal delivery system must be removed for 8 to 12 hours for optimal effect.Therefore, transdermal delivery systems, designed on the basis of pharmacokinetic principles and concentration-effect relationships, have the potential to provide optimal therapy for the treatment of some conditions.

Gastrointestinal transit of a solid indigestible capsule as measured by radiotelemetry and dual gamma scintigraphy

The objectives of the present study were to evaluate gastric and small bowel transit times of an indigestible solid matrix and to characterize the specific changes in intraluminal pH as a function of transit time through the gastrointestinal tract. Particular attention was paid to the lag time at the ileocecal junction. A Heidelberg capsule (HC), labeled with 10 µCi Indium-111, was given orally to six healthy male subjects 15 min after oral ingestion of 100 µCi of 99mTc-sulfur colloid as a liquid fatty meal (4 ml/kg). Intraluminal pH was monitored continuously via the HC. Gastric and small bowel transit of the radionuclides was monitored via external scintigraphy at 0.5-hr intervals. Gastric residence times (GRT) of the HC ranged from 2.8 to 4.8 hr, with a mean (±SD) of 3.6 ± 0.8 hr. These values were independent of the individuals weight, height, or body surface area. Small bowel transit times of the HC ranged from 2.8 to >5.5 hr, which were consistent with the reported values of 3 to 5 hr. The lag times of the HC at ileocecal junction ranged from 0.8 to >2.5 hr. The presence of the lag times at the ileocecal junction in all subjects confirmed that it acts as a valve or sphincter. Mouth-to-cecum transit times of the HC occurred within 9.0 hr in 50% of the subjects. In general, following a sharp rise upon pyloric passage of HC the pH dropped slightly but then increased linearly throughout the small intestine. The mean duodenal pH was 5.8 ± 0.8 and the pH at the ileocecal junction ranged from 6.5 to 8.5, with a mean of 7.3 ± 0.7. Passage through the ileocecal junction was associated with a 0.5- to 1.0-unit rise in pH in three subjects who exhibited passage of the HC into the large bowel within the study period. The present data may have implications in the designing of more effective dosage forms with specific delivery to proximal or distal small bowel regions.

Effectiveness of Alora estradiol matrix transdermal delivery system in improving lumbar bone mineral density in healthy, postmenopausal women.

ObjectiveTo determine the lowest effective dose of an estradiol (E2) matrix-type transdermal delivery system (EMTDS; Alora) for preventing bone loss in postmenopausal women. DesignThis double-blind, double-dummy, randomized, placebo-controlled, multicenter study enrolled 355 nonosteoporotic postmenopausal women who had been hysterectomized with or without oophorectomy at least 12 months earlier. Participants were randomly assigned to one of three doses of the EMTDS (0.025, 0.05, or 0.075 mg/day) or placebo administered twice weekly. Lumbar bone mineral density (LBMD) was measured by dual-energy x-ray absorptiometry at screening and after 1 and 2 years of treatment. Safety was assessed at regularly scheduled visits. ResultsEMTDS provided statistically significant and clinically meaningful changes in LBMD relative to placebo. At 2 years, LBMD declined from baseline by 0.59% in the placebo group, but it increased from baseline by 1.65% (p = 0.0065), 4.08% (p = 0.0001), and 4.82% (p = 0.0001) in the EMTDS 0.025, 0.05, and 0.075 mg/day groups, respectively. The corresponding responder rates (defined as no change or increase in LBMD at endpoint) were 39.7% for placebo, 59.6%, 79.3%, and 83.9% in the EMTDS 0.025, 0.05, and 0.075 mg/day groups, respectively. Mean serum E2 concentrations were proportional to the dose of the E2 transdermal system and did not accumulate over the course of the study. Adverse events were generally comparable across treatment groups, with the majority being mild or moderate in severity and unrelated to study medication. Mammogram findings and other safety assessments were also comparable across groups and did not reveal any safety concerns with 2-y transdermal E2 treatment. ConclusionsThe EMTDS (Alora) administered twice weekly improves lumbar bone mineral density in healthy postmenopausal women, with the benefit of treatment evident by 1 year. The lowest effective dose is 0.025 mg/day.

Application of Radiotelemetric Technique in Evaluating Diclofenac Sodium Absorption After Oral Administration of Various Dosage Forms in Healthy Volunteers

A radiotelemetric technique with the Heidelberg capsule (HC) was used to improve the quality of data generated in a bioavailability study involving an enteric-coated (EC) formulation. Further, changes in plasma levels of the drug from other dosage forms were related to changes in the pH environment as determined by the HC. Eight healthy male subjects received the following treatments, 15 min after a light breakfast, according to a randomized, four-way crossover design: (A) HC and 75 mg of a diclofenac sodium aqueous buffered solution; (B) HC and one 75-mg Voltaren EC tablet; (C) HC and one 100-mg Voltaren slow-release (SR) tablet; and (D) HC alone. Each treatment was separated by a 1-week washout period. Two additional subjects subsequently received Treatment B only. Multiple peaks were observed in the drug plasma level–time profiles for the buffered aqueous solution which, in all cases, occurred before gastric emptying of the HC. The multiple peaks were not observed for the Voltaren SR tablet, but a variable absorption lag time occurred which coincided with the gastric residence time of the SR tablet. For the EC tablet the variability of individual plasma level–time profiles was drastically reduced when the time after dosing was adjusted to coincide with gastric emptying of the HC. Finally, the lag time between gastric emptying of the EC tablet and the onset of drug absorption was consistently at 1 hr for all subjects. This lag time was longer than the in vitro disintegration or dissolution times measured under USP conditions.

Pharmacokinetics of Multiple Daily Transdermal Doses of Nicotine in Healthy Smokers

The plasma concentration–time profiles and pharmacokinetics were characterized for nicotine and its major metabolite, cotinine, after multiple daily application of a nicotine user-activated transdermal therapeutic system (UATTS) to nine healthy smokers. The volunteers abstained from smoking 24 hr prior to and during the course of the study. A 10-cm2 system (designed to deliver 75 µg/cm2/hr) was applied every 24 hr for 5 days, with serial blood samples taken on Days 1 and 5 and after system removal on Day 5. Generally, the nicotine UATTS was well tolerated. Predose nicotine concentrations on Days 3 to 5 indicated that steady state was reached by Day 3. The nicotine pharmacokinetic parameters for Day 1 and Day 5 were similar: the mean (SD) AUC(0-24) values for Days 1 and 5 were 271.7 (50.7) and 311.7 (55.0) ng · hr/ml, the mean (SD) Cmax values were 16.3 (2.6) and 16.8 (2.9) ng/ml, and the median (range) Tmax values on Days 1 and 5 were 12 (9–24) hr and 12 (0–24) hr, respectively. There was only slight or no accumulation of nicotine after multiple dosing as indicated by the Day 5 to Day 1 AUC and Cmax ratios of 1.15 (0.09) and 0.98 (0.06), respectively. Overall, the UATTS system maintained relatively constant plasma nicotine concentrations and is suitable for once-daily application.

Pharmacokinetic and pharmacodynamic studies of single oral doses of metoprolol in normal volunteers

SummaryThe effects of three orally administered doses of metoprolol, a betaj adrenoceptor antagonist, on resting blood pressures, resting pulse rates and heart rates during maximum exercise have been compared with those of placebo in six healthy male volunteers.The differences in blood pressures and pulse rates at rest were small and only statistically significant at isolated time points during the 24 hours study period. The reduction in exercise heart rates reached maximum values at 1.5 to 2 hours after drug administration and thereafter increased linearly with time. The zero-order rate constants for this process were similar for each of the three doses investigated.The mean durations of beta blockade after oral administration of 50, 100 and 200 mg. were 13.2, 16.9 and 19.2 hours, respectively. An apparent linear relationship between exercise heart rate and logarithm of the drug concentration in plasma was observed for each dose studied.The relationship between area under the plasma concentration curve and dose is statistically compatible with a linear function in the range 50 to 200 mg. The actual areas, however, suggest the possibility of an increased bioavailability for the higher dose.The significance of these results is discussed in relation to the possible use of a single daily dosage regimen in the treatment of angina pectoris and hypertension.

Nitroglycerin Absorption from Transdermal Systems: Formulation Effects and Metabolite Concentrations

We recently compared plasma concentrations of nitroglycerin and its two dinitrate metabolites in 16 healthy male subjects after application of two controlled-release transdermal formulations of the drug. Analysis of the resulting plasma concentration–time curves indicated that the two formulations did not produce equivalent concentrations of parent drug or either of the dinitrate metabolites during the initial period of dosing. In addition, both formulations produced concentrations of the two dinitrate metabolites that exceeded the concentration of the parent drug by severalfold. Even if the pharmacologic effect of the dinitrate metabolites is low compared to that of nitroglycerin, these higher concentrations may contribute to the effect of nitroglycerin. Scrutiny of the ratio of 1,2-glyceryl dinitrate to 1,3-glyceryl dinitrate in the 16 subjects confirmed previous observations that preferential formation of the 1,2-glycerol dinitrate metabolite may occur depending on the route of administration. This ratio may thus be indicative of the bioavailability of nitroglycerin following transdermal application. Additional data suggesting racial differences in nitroglycerin absorption after transdermal application are presented.

Intra- and Inter-Subject Variabilities of CGP 33101 after Replicate Single Oral Doses of Two 200-mg Tablets and 400-mg Suspension

AbstractPurpose. The purpose of this study was to use a replicate designed trial to assess the overall, intra- and inter-subject variabilities in pharmacokinetic parameters of CGP 33101 after oral administration of tablets relative to that of powder suspended in water, and to determine the relative proportion of the intra-subject variance to the overall variability. Methods. Sixteen healthy subjects were randomly assigned to four groups to receive tablets and suspension twice in four different treatment sequences. The plasma concentration-time profile of CGP 33101 was characterized in terms of Cmax, Tmax, and AUC. Bioavailability of tablets relative to suspension and intra- and inter-subject variability were assessed by statistical analysis. Results and Conclusions. The overall variabilities in absorption kinetics of CGP 33101 in healthy subjects were small with CVs of the population mean values for AUC and Cmax less than 26% for both tablets and suspension. Contribution of intra-subject variability to the overall variability was also small (~20%). Both the overall and intra-subject variabilities of AUC and Cmax after suspension were larger than after the tablets. However, the differences in variability between tablets and suspension were not statistically significant (p > 0.05). The tablet formulation was bioequivalent to suspension in terms of rate and extent of absorption based on 90% conventional confidence intervals (for AUC and Cmax) and Wilcoxon rank-sum test (for Tmax).

Site-Differential Gastrointestinal Absorption of Benazepril Hydrochloride in Healthy Volunteers

The absorption of benazepril-HCl (BZPH), an orally active angiotensin-converting enzyme (ACE) inhibitor, in various regions of the gastrointestinal (GI) tract was investigated using an intestinal intubation technique. Thirteen subjects completed this single-dose, three-phase sequential crossover study. The drug (20 mg) was administered either as a 4-hr colonic infusion (COLON) or as a small intestinal infusion (SI) in the first two phases and as an oral bolus solution (ORAL) in the third phase, with a 2-week washout between each treatment. Serial plasma and urine samples were collected for up to 4 days after dosing. BZPH and its active metabolite benazeprilat (BZPL) were determined using a gas chromatography/mass spectrometry method. BZPH was absorbed rapidly into the bloodstream (Tmax = 0.5 hr after ORAL). Absorption was also rapid for SI, with a postinfusion half-life (0.57 hr) nearly identical to that for ORAL (0.59 hr). The absorption rate after COLON was much slower (lower Cmax and longer Tmax) compared to that after SI, and the apparent half-life (1.7 hr) was prolonged. SI delivered 90%, whereas COLON delivered 23%, of the drug into the systematic circulation as compared to ORAL. BZPL was rapidly formed upon drug absorption. The metabolite-to-drug AUC ratios were comparable for SI and ORAL (8.9 vs 9.7), indicating that first-pass metabolism of BZPH was neither saturable nor input rate dependent. The metabolite-to-drug AUC ratio was reduced for COLON (5.0), indicating that the mechanism of absorption of BZPH in the colon may be different than that after SI and ORAL. Urinary recovery data were consistent with plasma data. It can be concluded that COLON delivered a smaller amount of drug at a slower absorption rate to the body than either SI or ORAL.

Double-masked, multicenter study of an estradiol matrix transdermal delivery system (Alora™) versus placebo in postmenopausal women experiencing menopausal symptoms

This 12-week, double-masked, double-dummy, randomized, parallel-group study compared the efficacy and safety of an estradiol matrix transdermal delivery system (Alora) in two strengths (50-microgram/d estradiol and 100-microgram/d estradiol) with placebo in postmenopausal women who were experiencing at least 60 moderate-to-severe hot flushes per week. In 273 postmenopausal women, the reduction in the frequency of moderate-to-severe hot flushes was significantly better than placebo within 2 weeks of initiating therapy in the 100-microgram/d group and within 3 weeks of initiating therapy in the 50-microgram/d group. The reduction in hot flushes for both active treatment groups remained significantly different from placebo throughout the 12-week trial. Improvement in vaginal cytology profile (maturation index) was observed in both active treatment groups. Serum estradiol concentrations were elevated to early-to mid-follicular levels, in proportion to dose, and the estradiol/estrone ratio remained within the expected premenopausal range. The incidence of estrogen-related side effects was modest but greater in the active treatment groups than in the placebo group: Breast pain was reported in 4.5% of the patients in the 50-microgram/d group, 5.3% of patients in the 100-microgram/d group, and none of the patients in the placebo group. Breakthrough bleeding occurred in 3.4% of women in the 50-microgram/d group, 20.2% of women in the 100-microgram/d group, and 4.4% of women in the placebo group. Only 3 (1.1%) patients terminated treatment because of skin reactions. This study demonstrates that this estradiol matrix transdermal delivery system is effective in the treatment of menopausal symptoms, while providing the skin tolerability desired by patients.