Direct measurement of BDP and 17-BMP in bronchial and peripheral lung tissue after inhalation of HFA- vs CFC-driven aerosols

Indirect assessments have shown a superior lung deposition of HFA-BDP (Ventolair/Qvar) compared to CFC-BDP (Aerobec). The aim of this study was to assess the concentrations of BDP and its metabolite 17-BMP in airways and peripheral tissue from resected lung specimens after inhalation of these BDP formulations. Immediately prior to surgery for lung cancer, 10 patients inhaled 1000 microg of either CFC-BDP (n = 5) or HFA-BDP (n = 5) Mouthwash was collected after inhalation, and serum before, during, and after surgery. There was no significant difference between CFC and HFA in the concentration of 17-BMP in bronchi (median, 4365 vs 4121 pg/g tissue). After CFC, concentrations of 17-BMP were lower in peripheral tissue (1424 vs 2089 pg/g; ANCOVA, p = 0.001) and in serum taken immediately after inhalation (688 vs 1219 pg/ml, p < 0.01). Furthermore, the CFC group showed a higher concentration of BDP in the mouthwash (17,660 vs 1320 ng/ml, p < 0.05), but the concentration of 17-BMP was lower (452 vs 1028 ng/ml, n.s.). These findings indicate a predominantly peripheral deposition of HFA-BDP, in line with previous data. They also provide evidence for a faster uptake and metabolism of HFA-BDP, probably because BDP is dissolved in HFA and has a smaller particle size distribution than the CFC suspensions.

Influence of particle size on lung deposition and pharmacokinetics of beclomethasone dipropionate in children

We set out to evaluate lung deposition, systemic availability, and basic pharmacokinetic parameters of beclomethasone dipropionate (BDP) in children with chronic asthma. Plasma levels of BDP, 17 and 21 beclomethasone monopropionate (17-BMP and 21-BMP), and beclomethasone were measured after an intravenous infusion of 60 microg BDP and after inhalation of A) 100 microg HFA-BDP, B) 200 microg HFA-BDP, C) 200 microg HFA-BDP after ingestion of charcoal to block gastrointestinal (GI) absorption of drug, and D) 400 microg CFC-BDP. A breath-actuated pMDI (Autohaler) was used for HFA inhalations, and a pMDI with a large volume spacer (Volumatic) for CFC inhalations. Treatments A-D were given in a randomized, cross-over design. Fourteen patients aged 10-14 years completed all 5 study days. The mean systemic bioavailabilities in percent of dose leaving the canister valve (ex-valve) were 70% (100 HFA), 74% (200 HFA), 60% (200 HFA + charcoal), and 27% (400 microg CFC). After HFA treatment, 82% of the systemically available dose was absorbed through the lungs, and 18% from the gastrointestinal tract. The estimated bioavailability of BDP from the GI tract was 68%. BDP was metabolized to 17-BMP within minutes. Mean steady-state volume of distribution of 17-BMP was 84 L, and the mean terminal half-life (T((1/2))) after the four inhalations was 2.7 hr (range, 2.2-3.7 hr). Mean T((1/2)) and clearance after i.v. administration were 1.7 hr and 0.9 L/min, respectively. The HFA Autohaler delivers approximately three times as much BDP to the intrapulmonary airways as a CFC-pMDI with a large volume spacer.

Commentary on the FDA draft guidance for bioequivalence studies for nasal aerosols and nasal sprays for local action: an industry view

In June 1999, the Food and Drug Administration issued draft guidance for bioequivalence studies for nasal aerosols and nasal sprays for local action. The purpose of this opinion paper is to highlight the need for a balanced scientific debate before this guidance is used by underscoring the areas in the document that are in opposition to prevailing scientific understanding.

Tumour necrosis factor-alpha production in human alveolar macrophages: modulation by inhaled corticosteroid

Using an ex vivo alveolar macrophage model, the hypothesis that inhaled preparations of corticosteroids might have important anti-inflammatory effects on cells of the peripheral airway was tested. The tumour necrosis factor (TNF)-alpha-inducing potential of three glycolipid preparations from nonpathogenic (arabinofuranasyl lipoarabinomannan (LAM (Ara-LAM)) and virulent (mannase LAM (ManLAM)) mycobacteria and Gram-negative bacteria (lipopolysaccharide (LPS)), in primary alveolar macrophage preparations was investigated. A novel inhaled chlorofluorocarbon (CFC)-free preparation of beclomethasone dipropionate (hydrofluoroalkane 134a (HFA)-BDP) with increased peripheral lung deposition was investigated for its ability to modulate glycolipidinduced TNF-alpha production by human alveolar macrophages, in comparison with a CFC-containing preparation and placebo. Compared to the basal TNF-alpha bioactivity of 0.72 ng x mL-1 (geometric mean), the TNF-alpha bioactivity in the macrophage preparation increased following incubation with LPS (138 ng x mL-1, p<0.001), AraLAM (12.6 ng-mL-1, p<0.001) and ManLAM (1.42 ng x mL-1, p=0.02). HFA-BDP, administered in vivo, significantly reduced LPS- and ManLAM-induced TNF-alpha production by alveolar macrophages cultured ex vivo. No change in glycolipid-induced TNF-alpha production was observed following in vivo administration of CFC-BDP or HFA-placebo. This is the first demonstration of an immunomodulatory effect on alveolar cells of corticosteroid delivered via metered dose inhaler. The present findings suggest that alveolar deposition of beclomethasone dipropionate is capable of modulating the inflammatory potential of the alveolar macrophage population.

Pharmacokinetic differences between chlorofluorocarbon and chlorofluorocarbon-free metered dose inhalers of beclomethasone dipropionate in adult asthmatics

We have compared the serum pharmacokinetics of the metabolites of beclomethasone dipropionate after inhalation from chlorofluorocarbon (CFC) and hydrofluoroalkane HFA-134a (HFA) formulations in asthmatic patients. Twenty-three patients completed this open-label, randomized, single-dose, three-period crossover study. Each patient received in separate periods 200 microg or 400 microg HFA-beclomethasone dipropionate, or 400 microg CFC-beclomethasone dipropionate. Venous blood samples were collected over 24 h for the determination of beclomethasone esters and beclomethasone in the serum. Significant differences in pharmacokinetics following HFA- and CFC-beclomethasone dipropionate were observed. Following a 400 microg beclomethasone dipropionate dose, the HFA formulation gave mean maximum concentrations (Cmax) and area under the curve (AUC) values of beclomethasone esters of 1153 pg mL(-1) and 4328 pg h mL(-1), respectively, and beclomethasone Cmax and AUC values of 69 pg mL(-1) and 682 pg h mL(-1), respectively. These values were approximately 2-3-fold those seen with the CFC formulation (beclomethasone esters Cmax and AUC of 380 pg mL(-1) and 1764 pg h mL(-1), respectively; beclomethasone Cmax and AUC of 41 pg ml(-1) and 366 pg h mL(-1), respectively). Beclomethasone esters, the major component of beclomethasone dipropionate in the serum, peaked significantly earlier for the HFA formulation (0.8 h) than for the CFC formulation (2 h). Tests for dose proportionality of beclomethasone esters pharmacokinetics following HFA-beclomethasone dipropionate showed that the two hydrofluoroalkane strengths were proportional. The more rapid and greater efficiency of systemic drug delivery of the HFA formulation compared with the CFC formulation can be explained if most of each inhalation from CFC-beclomethasone dipropionate is swallowed and absorbed orally, whereas most of each inhalation from HFA-beclomethasone dipropionate is absorbed through the lungs. There is a need for comprehensive dose-response efficacy trials, with the use of the steep portion of the dose-response relationship, to evaluate the significance of these pharmacokinetic differences.

Adrenal effects and pharmacokinetics of CFC-free beclomethasone dipropionate: a 14-day dose-response study

Since equivalent efficacy is achieved with lower doses of the reformulated beclomethasone dipropionate in the chlorofluorocarbon (CFC)-free propellant HFA-134a (HFA) than with the original CFC-beclomethasone dipropionate formulation, it is possible the HFA-beclomethasone dipropionate may have less safety concerns than the CFC formulation. Despite its chronic use, the steady-state pharmacokinetics of beclomethasone dipropionate has never been studied before. This double-blind study examined adrenal effects and pharmacokinetics after 14 days of dosing with HFA-beclomethasone dipropionate. Forty-three steroid-naïve asthmatic patients were randomised into 5 parallel groups and dosed every 12 h for 14 days with: HFA-placebo; 200, 400 or 800 microg day(-1) HFA-beclomethasone dipropionate; or 800 microg day(-1) CFC-beclomethasone dipropionate. After two weeks of dosing, the 24-h urinary free cortisol of all but one patient remained within the normal range, showing that all doses were well tolerated from a systemic safety perspective. The active HFA-beclomethasone dipropionate treatment groups showed a dose-related fall in 24-h urinary free cortisol. Total-beclomethasone (beclomethasone dipropionate and metabolites) pharmacokinetics after either the first dose of HFA-beclomethasone dipropionate or CFC-beclomethasone dipropionate were not substantially affected by subsequent doses. The extent of drug absorption from 800 microg day(-1) HFA-beclomethasone dipropionate and CFC-beclomethasone dipropionate was in the ratio of 1.7 : 1. A non-linear correlation between 24-h urinary free cortisol and the pharmacokinetic parameters was observed, reflecting smaller changes in 24-h urinary free cortisol than in pharmacokinetics as the dose was increased. No clinically meaningful change in the pharmacokinetics of beclomethasone dipropionate plus metabolites was seen on multiple dosing. The greater systemic availability of HFA-beclomethasone dipropionate was still associated with adrenal effects comparable with that of the CFC formulation at the same dose.

Beclomethasone relative availability of oral versus inhaled beclomethasone dipropionate from an HFA-134A metered dose inhaler

3M has formulated a new chlorofluorocarbon-free (CFC-free) beclomethasone dipropionate (BDP) metered-dose inhaler (MDI) with the use of the propellant HFA-134a (HFA). Lung deposition studies demonstrated that the HFA BDP MDI delivers to the lungs approximately 56% of the BDP dose (ex-adaptor), a substantially higher percentage than the 5-30% delivered by conventional CFC BDP MDIs. As new sensitive bioanalytical methods are becoming available to quantitate systemic levels of inhaled corticosteroids, pharmacokinetic evaluations are emerging as sensitive and reproducible methods that can be used as a complement to the data obtained from lung deposition studies to assess and compare the performance of MDIs. The present study was designed to determine the beclomethasone (BOH) availability of oral BDP relative to inhaled HFA BDP as a first step to alloy MDI product comparisons in the future. Forty mild asthmatic patients completed this open-label, randomized, single-dose, two-period crossover study. Each patient received an oral dose of BDP (0.2, 0.5, 1, 2 or 5 mg) in one period and an inhaled dose of BDP (0.2 or 0.8 mg) in the other period, with four patients allocated to each of ten different treatment sequences. The BOH availability of orally administered BDP was approximately 40% relative to inhaled HFA BDP. In addition, the fraction of an oral dose that reaches the systemic circulation was estimated from the 40% relative availability and previous lung deposition data to be 0.26. These estimated pharmacokinetic parameters will be used in the future to further characterize the pharmacokinetics of inhaled BDP and to compare the performance of different MDI products.

Effect of changing the fine particle mass of inhaled beclomethasone dipropionate on intrapulmonary deposition and pharmacokinetics

Reformulation of beclomethasone dipropionate (BDP) in the chlorofluorocarbon (CFC)-free propellant hydrofluoroalkane-134a (HFA) gave the opportunity to produce a solution formulation that provides a greater total mass of fine drug particles than the current CFC suspension metered dose inhaler (MDI). The HFA-BDP MDI was studied in three pharmacokinetic trials in asthmatic patients. Serum levels of BDP plus metabolites [total beclomethasone (total BOH) assay] were used to test whether the increased fine particle mass of HFA-BDP would result in improved intrapulmonary deposition and subsequent differences in serum profiles. Serum levels, maximum serum concentrations and area under the serum concentration-time curves of total BOH following both single and multiple doses of HFA-BDP were similar to those obtained with approximately twice the dose of CFC-BDP. The observed lower bioavailability of CFC-BDP compared with HFA-BDP could be explained if most of each inhaled dose from the CFC-BDP MDI was swallowed and absorbed from the gastrointestinal tract, while most of each inhaled dose from the HFA-BDP MDI was absorbed from the lungs. Deposition studies have confirmed this explanation. These results suggest that asthmatic patients can be treated with lower total daily doses of drug from HFA-BDP extrafine aerosol than from CFC-BDP.

Pharmacokinetics and dose proportionality of beclomethasone from three strengths of a CFC-free beclomethasone dipropionate metered-dose inhaler

As part of a development program to offer alternatives to chlorofluorocarbon (CFC) containing metered-dose inhalers, beclomethasone dipropionate has been formulated in a CFC-free system at three strengths: 50, 100, and 200 micrograms/actuation ex valve. To measure serum levels and dose proportionality of the beclomethasone derived from beclomethasone dipropionate, 13 mild to moderate asthmatic patients received a single dose of eight inhalations from each strength according to a double-blind crossover design. Seven patients were studied over 4 h and six patients over 12 h. For the total doses of 400, 800, and 1600 micrograms studied over 12 h, Cmax and AUC increased in a ratio of 1:1.8:3.1. A good correlation was seen between the fine-particle mass delivered and the in vivo performance of the three strengths. From a clinical point of view, the predictable increases in serum levels with an increase in dose will permit the clinician to effectively titrate a patient with this product.

Comparative serum estradiol profiles from a new once-a-week transdermal estradiol patch and a twice-a-week transdermal estradiol patch

Two identical open-label, randomized crossover studies were conducted to compare serum estradiol profiles from the new 12.5- and 25-cm2 once-a-week adhesive patches with those from the 10- and 20-cm2 commercially available twice-a-week Estraderm patches when applied as directed during a 1-week patch-wear period. Both studies were conducted in healthy postmenopausal women; serum estradiol levels were determined by gas chromatography/mass spectroscopy (GC/MS). Although both sizes of both patch treatments produced mean serum estradiol levels in the therapeutic range, the once-a-week patch provided more constant mean levels, avoiding large peak-to-trough fluctuations. As expected, the differences in mean serum estradiol concentrations between the two patch treatments occurred during the second application of the twice-a-week patch. Based on these results, the once-a-week drug in adhesive patch appears to be an acceptable means of hormone replacement therapy.

Twenty-eight-day double-blind safety study of an HFA-134a inhalation aerosol system in healthy subjects

A 28-day double-blind parallel group study has been conducted to compare the safety and tolerability of HFA-134a, a chlorofluorocarbon-free propellant in a pressurized metered-dose inhaler (MDI A), with a chlorofluorocarbon propellant (MDI C). Sixteen subjects were randomly assigned to receive one of the two MDIs, either four inhalations four times per day for 14 days or eight inhalations four times a day for 14 days, and were then crossed over to the alternative exposure regime with the same propellant for the next 14-day period. No clinically significant changes occurred in blood pressure, heart rate, electrocardiograms, pulmonary function (FEV1, FVC, FEF25-75%), haematology or serum chemistry. One subject in the MDI A group had elevated eosinophil counts throughout the study; there were no other remarkable clinical laboratory data. Fifty six adverse events were related to the study propellants; 34 of these occurred in the MDI C group and 22 in the MDI A group. For each adverse event no statistically significant differences were detected between propellant systems or between exposure levels. The most frequent adverse event was headache, which was reported by four subjects with each propellant system. Blood samples for HFA-134a in the MDI A group were collected on day 28 to measure systemic absorption. Blood levels of HFA-134a were detected in all subjects given this propellant within 1 min post-exposure, and these levels decreased to one-tenth of the original value by 18 min after the start of exposure. The safety and tolerability of an HFA-134a chlorofluorocarbon-free system was demonstrated over 28 days of exposure in healthy subjects. These negative results are clinically important because they indicate it will be safe to proceed with the study of this chlorofluorocarbon-free system in asthmatic patients.

Systemic concentrations of salbutamol and HFA-134a after inhalation of salbutamol sulfate in a chlorofluorocarbon-free system

The objective of this study was to determine if salbutamol was absorbed from a new salbutamol sulfate chlorofluorocarbon (CFC)-free metered-dose inhaler (MDI). Measurement of HFA-134a, the CFC-free propellant, was included to provide proof of delivery of this MDI. Eight healthy men received two inhalations (90 micrograms salbutamol base equivalents per inhalation ex adapter) from the CFC-free inhaler (MDI A) in period 1 and from a reference CFC inhaler (MDI V) in period 2. Eight postdose samples were collected for the determination of salbutamol serum levels over a 4-h period. Salbutamol levels were not quantifiable in most samples. Four subjects given MDI A and two given MDI V had a few transient salbutamol levels, which occurred in the first hour after dosing, within a narrow range of 1-2 ng/ml and close to the lower limit of detection (1 ng/ml). No pharmacokinetic analyses were possible. Blood samples were also collected after MDI A for propellant quantitation. HFA-134a levels were seen in all subjects, verifying absorption. We conclude that the transient salbutamol serum levels can be attributed to the two-inhalation dose and not to either propellant system.

Acute safety of the CFC-free propellant HFA-134a from a pressurized metered dose inhaler

The acute safety of the alternative chlorofluorocarbon-free (CFC-free) propellant HFA-134a from a pressurized metered-dose inhaler (MDI) was assessed in 12 healthy male subjects according to a double-blind, randomized, crossover design. On each of three consecutive days, cumulative doses of 1,2,4,8 and 16 inhalations were administered 30 min apart from one of three MDIs. The three MDIs contained either the HFA-134a CFC-free system without drug (HFA-Placebo), the CFC-free system with salbutamol sulphate (HFA-Salbutamol), or a conventional CFC propellant mixture without drug (CFC-Placebo). Pulmonary function (FEV1, FEF25-75%), cardiovascular performance (heart rate and blood pressure), objective tremor measurements and serum potassium were measured after each incremental dose. Similar responses for pulmonary function, cardiovascular performance, tremor and serum potassium were observed between the HFA-Placebo and CFC-Placebo groups. No statistically significant difference was seen in change from baseline of any parameter between the two propellant systems. The administration of HFA-Salbutamol produced statistically significant dose-related increases in heart rate, systolic blood pressure and tremor and a significant dose-related decrease in serum potassium; these responses were expected based on cumulative doses of active drug. Blood samples for HFA-134a analysis were collected to measure systemic absorption of this propellant. Levels of HFA-134a between 200 and 700 ng.ml-1 were detected in all subjects given the CFC-free system. This study shows that acute inhalation of HFA-134a in a CFC-free system is as safe as a CFC propellant system. Salbutamol sulphate in the CFC-free system can be delivered in a dose-linear fashion, without any noticeable change in the safety profile of active drug.

Determination of the chlorofluorocarbon substitute 1,1,1,2-tetrafluoroethane (HFA-134a) in human and animal blood using gas chromatography with headspace analysis

A gas chromatographic procedure with headspace analysis and flame-ionization detection is described for the determination of the chlorofluorocarbon substitute 1,1,1,2-tetrafluoroethane (HFA-134a). A 0.5-2 ml sample of heparinized whole blood from a laboratory animal or human is added directly into a presealed headspace vial from which an equivalent volume of air has been removed. The internal standard 1,1,2,2-tetrafluoroethane is added and the sample frozen until analysis. Chromatographic separation is achieved using a PoraPlot Q porous-layer capillary column. The analytical range is 5.8-3298 ng/ml when 2-ml human blood samples are used. The concentration range of the calibration curve can be easily adapted to accommodate the concentrations expected in either pharmacokinetic or toxicokinetic studies. Automation of the assay permits the maximum number of samples to be processed in a day.

Dynamic monitoring of total-body absorption by 19F NMR spectroscopy: one hour ventilation of HFA-134a in male and female rats

Six male and six female Sprague-Dawley rats were ventilated head-only for 1 h on a 15% atmosphere of 1,1,1,2-tetrafluoroethane (HFA-134a) in air in a magnetic resonance imaging spectrometer. Results from these dynamic 19F NMR studies suggest that a steady-state in vivo concentration of HFA-134a was approached at approximately 25 min into the exposure. Quantitative integration analysis using an external standard estimated this plateau to be 58.3 +/- 11.9 mg of absorbed HFA-134a per rat. The HFA-134a 19F NMR signal disappeared rapidly following removal of the test atmosphere, with an elimination half-life of 4.6 +/- 0.6 min in the male rats and 4.9 +/- 1.5 min in the female rats. The data suggest that there was no statistical difference between the sexes in amount absorbed or in elimination half-lives.

Comparative pharmacokinetics of morning and evening doses of once-a-day theophylline capsules

The objective of this study was to determine if the theophylline diurnal variation that has been observed primarily between morning and evening doses of twice-a-day products could be overcome by a once-a-day formulation. Eighteen healthy, nonsmoking, adult male subjects were given 900-mg theophylline doses as three 300-mg once-a-day theophylline capsules in the morning or evening for 5 days in a single-blind fashion. Matching placebo capsules were administered midway between each dose of active drug. Predose theophylline serum levels on day 3-6 were statistically equivalent within each treatment, indicating that approximate steady-state conditions were achieved by day 3. Mean serum level profiles over the 24-h interval following the active dose on day 5 were almost superimposable for the morning and evening treatments. All pharmacokinetic parameters were equivalent between the treatments, except for the time to peak serum level (Tmax), which was significantly shorter for the morning dose. Given the flatness of the serum level curves for both treatments, the Tmax difference was judged to be clinically unimportant. A small peak-trough level fluctuation of about 50% was seen with each treatment. We conclude that by designing a dose form in which drug release was the rate-limiting step in drug absorption, the diurnal variation commonly associated with theophylline formulations may be eliminated.

Kinetics of absorption of a new once-a-day formulation of theophylline in the presence and absence of food

Two three-way crossover studies were done to characterize the drug release characteristics of Monospan (3M Pharmaceuticals, St. Paul, MN) capsules, a new once-a-day theophylline formulation. In the first study, 22 healthy males received single 450-mg doses of Monospan in the presence and absence of a high-fat breakfast; the same dose of Somophyllin (Fisons, Rochester, NY) immediate-release liquid was given to fasted subjects as a reference. The second study involved 29 healthy males given a single dose of 900 mg of Monospan in the presence and absence of the same high-fat meal; Theo-24 (G. D. Searle and Co., Skokie, IL) capsules were given to fasted subjects as a reference. The results of both studies showed that food did not affect the absorption of theophylline from Monospan; peak concentration, to and area under the serum concentration-time curve were all unchanged. The absorption rates were similar with both strengths and dietary conditions and showed that theophylline was absorbed slowly from Monospan at a constant rate (approximately 3.2%/h) over 24 h. Absorption continued past 24 h, and the extent of absorption from Monospan compared with that from each reference averaged 88% or higher. A good correlation (r > 0.980) was observed for Monospan between the amount absorbed in vivo and the amount released in the in vitro dissolution test, a result that demonstrates the precise rate control of Monospan. We conclude that Monospan is a suitable once-a-day formulation that can be taken without regard to food.

Effect of food on salsalate absorption

To assess the effect of food on salsalate absorption, single 1500-mg oral doses of salsalate were administered to 17 men under fasted and fed conditions according to a randomized open-label crossover design. A 7-day washout separated treatment periods. Blood samples were drawn throughout the 48-h period following dose administration and the resulting plasma samples assayed by high-performance liquid chromatography (HPLC) for unchanged drug, salsalate, and the major metabolite, salicylic acid. When results for the fasted and fed treatments were compared, no significant differences were observed in the pharmacokinetic parameters for the major metabolite salicylic acid or in the extent of absorption of unchanged drug; however, the rate of salsalate absorption was affected. Although the time-to-peak for salsalate was significantly delayed by approximately 1 h in the presence of food, the peak level was not significantly affected. The lack of difference between the two treatments for the therapeutic moiety, salicylic acid, indicates a lack of a significant food effect on single doses of salsalate.

Transdermal nitroglycerin systems: methods for comparison

A number of transdermal nitroglycerin delivery systems are able to maintain a constant plasma level of nitroglycerin for up to 24 hours, even though the drug's elimination half-life is only a few minutes. Unfortunately, wide variations in plasma drug levels reported in studies of transdermal delivery systems can make plasma level comparisons between products inappropriate and misleading. Other measures of clinical performance include adhesive properties and patient preference. In one adhesion study, Minitran demonstrated superior adhesive properties when compared with Transderm-Nitro, Nitro-Dur II, and a medical reference tape. In patient preference studies involving several hundred patients with angina pectoris, patients consistently selected Minitran over Transderm-Nitro or Nitro-Dur II, citing patch size, shape, ease of application, comfort, better patch adhesion, and reduced instances of skin irritation.

Drug release rates from four sizes of a new transdermal nitroglycerin adhesive patch

This study was conducted to determine the amount of nitroglycerin released from transdermal nitroglycerin patches of four different sizes: 3.3 cm2, 6.7 cm2, 13.3 cm2, and 20 cm2. Thirty healthy men received a single 24-hour application of each patch size according to a randomized, open-label, four-period crossover design. A 24-hour interval separated each treatment period. The total amount of nitroglycerin released by the four patches was proportional to size. All four patch sizes released nitroglycerin at a comparable rate. The mean overall 24-hour release rate of 0.76 mg/cm2 was similar to the release rate of 0.75 mg/cm2/24 hr observed in a previous study. Adverse experiences common to nitroglycerin administration were reported for all patch sizes, with headache, light-headedness, and nausea reported most frequently.

Pharmacokinetic properties of sustained-release theophylline (Theolair-SR) in relation to timing of doses after low-fat meals

Pharmacodynamic and pharmacokinetic properties of sustained-release anyhdrous theophylline (Theolair-SR) were similar when doses were given either immediately after or two hours after low-fat meals in children with moderate asthma requiring daily theophylline maintenance. Asthma and pulmonary function values were maintained and approached values for healthy subjects during both treatment regimens.

Performance of a new transdermal nitroglycerin adhesive patch formulation

This two-period crossover study in 24 healthy men compared the transdermal absorption of nitroglycerin from a new 20-cm2 nitroglycerin adhesive transdermal patch applied for a single 24-hour period (q24hr) with that from one inch of 2% nitroglycerin ointment applied over a 50-cm2 area every eight hours (q8hr) during a single 24-hour period. The observed differences in pharmacokinetic parameters were expected, based on product design (q24hr vs q8hr) and surface area (20 cm2 vs 50 cm2); however, when corrected for surface area, the mean plasma AUC ratios indicated that the patch delivered about 1.5 times more drug than the ointment. The patch delivery of nitroglycerin was confirmed by patch residual results, which indicated nitroglycerin was released at a rate of 0.75 mg/cm2/24 hrs. The patch exhibited good skin adhesion throughout the 24-hour application period.

Steady-state evaluation of two controlled-release theophylline preparations in children

The absorption profiles of Theolair-SR and Theo-Dur were studied in 23 asthmatic children (mean age 11 years). A 250-mg dose of each product was administered twice a day until steady state was attained (mean, 8 days). Both products maintained adequate theophylline levels over 12 hours, although Theolair-SR gave significantly higher serum levels and a 19% greater extent of theophylline absorption. The mean Cmax-Cmin was also significantly greater for Theolair-SR. Both products should be considered comparable for practical use.

Disposition of radiolabeled flumequine in rat and dog

Single doses of 14C-flumequine (a urinary tract antibacterial) were given to rats and dogs. Unchanged drug accounted for more than 80% of the drug in plasma of rats but only 25-50% in plasma of dogs. Although only a small percentage of the dose was excreted in the urine of each species as unchanged drug, a wide differentiation in the urinary metabolite profiles was observed. No significant tissue retention was seen in rats or dogs.

Salsalate kinetics in patients with chronic renal failure undergoing hemodialysis

A 1500 mg dose of salsalate (SSA) was given to five patients undergoing chronic hemodialysis on an interdialytic day and again before dialysis. Compared with control subjects, patients undergoing dialysis had a lower peak plasma SSA level (17 +/- 3 vs. 45 +/- 2 micrograms/ml; P less than 0.01) that occurred slightly later. In contrast, plasma salicylic acid (SA), the active SSA metabolite, had a similar but later peak level that remained substantially higher. Therefore, the AUC for SA was increased by 50% and the SA t1/2 was prolonged in the patients receiving dialysis (8.1 +/- 0.7 vs 3.8 +/- 0.2 hours; P less than 0.01). During a single treatment, dialysis clearance reduced plasma SA levels, removed 18% of total body SA, and returned the SA t1/2 to nearly normal. Because the elimination of SA is impaired in patients undergoing dialysis, the interdialytic SSA dosage should be reduced. Hemodialysis improves SA kinetics and may be followed by a normal SSA replacement dose. However, periodic monitoring of plasma SA levels is recommended when SSA dosing is begun in patients receiving dialysis.

Effects of salsalate (nonacetylated salicylate) and aspirin on serum prostaglandins in humans

Prostaglandin E2 (PGE2), thromboxane B2 (TXB2), and salicylic acid were measured in blood samples from 10 healthy men after administration of antiinflammatory doses of aspirin (3.9 g/day) or salsalate (3.0 g/day). Each medication was given for 3 days, followed by an observation period of 13 days. Plasma salicylate concentrations were slightly, but generally insignificantly, higher during aspirin dosing, although both drugs produced salicylic acid levels in the antiinflammatory range. Serum levels of PGE2 and TXB2, which reflected synthesis of cyclo-oxygenase products by platelets, were minimally affected by salsalate but profoundly suppressed by aspirin. When medication was discontinued, the effects of salsalate on serum PGE2 and TXB2 were readily reversible within 36 h, whereas the recovery from aspirin was still incomplete after 13 days of observation. These results indicate that the two orally administered salicylates have differential effects on prostaglandin synthesis in platelets and may also differ in their therapeutic and adverse effects.

Plasma and urine levels of flumequine and 7-hydroxyflumequine following single and multiple oral dosing

Plasma and urine concentrations of flumequine and its microbiologically active metabolite, 7-hydroxyflumequine, were determined in healthy subjects following single oral doses of 400, 800, and 1200 mg of flumequine, and following multiple oral doses of 800 mg given four-times daily. After administration of the single oral doses, antimicrobial levels in plasma and urine were rapidly attained, were proportional to the dose given, and were maintained for 12 to 24 h. The multiple dosage regimen yielded antimicrobial levels in both plasma and urine that were several-fold higher than the levels required to inhibit the growth of susceptible bacteria. Following both the single and multiple dose regimens, the plasma elimination half-life of flumequine was about 7h. The excretion of 7-hydroxyflumequine in the urine contributed significantly to the antimicrobial activity.

Determination of flumequine and a hydroxy metabolite in biological fluids by high-pressure liquid chromatographic, fluorometric, and microbiological methods

A sensitive and specific high-pressure liquid chromatographic method is described for the determination of the antibacterial drug flumequine and a major metabolite, 7-hydroxyflumequine, in human plasma and urine. The assay was linear over a concentration range of 1 to 120 micrograms/ml for both compounds. This method is compared with fluorometric and microbiological assays for flumequine. These latter methods did not differentiate between flumequine and any fluorescent or antimicrobiologically active metabolites. However, because essentially all drug in the plasma was found to be flumequine in radiolabeled studies, levels of unchanged drug in the plasma could be quantitated by either high-pressure liquid chromatography or fluorometry. Although only high-pressure liquid chromatography was able to specifically measure flumequine in the urine, the antimicrobial activity of the urine, which is more therapeutically relevant due to antimicrobially active metabolites, could be quantitated by either the fluorometric or the microbiological assay.

Salicylic acid plasma levels following multiple doses of Norgesic Forte and aspirin

Plasma salicyclic acid levels from the recommended multiple dose regimen of Norgesic Forte (orphenadrine citrate, aspirin, and caffeine) were compared to those from an equivalent multiple dose regimen of aspirin alone in 24 volunteers. The drugs were administered double-blind so that side effects could also be compared. No statistically significant differences were found between Norgesic Forte and aspirin in peak or trough levels, time to peak level, area under the curve, or mean steady-state level of salicylic acid. Mean steady-state levels averaged 154 +/- 46 (+/- SD) and 152 +/- 49 micrograms/ml on days 5 and 10 following Norgesic Forte versus 161 +/- 49 and 154 +/- 47 micrograms/ml following aspirin. Thus, the aspirin in Norgesic Forte provides an anti-inflammatory amount of salicylic acid equivalent to that of plain aspirin. There was no evidence that the combination of orphenadrine citrate, caffeine, and aspirin in Norgesic Forte caused increased or unusual side effects compared with aspirin alone.

Absorption, biotransformation, and pharmacokinetics of salicylsalicylic acid in humans

The absorption, biotransformation, and pharmacokinetics of the antiinflammatory drug salicylsalicylic acid (SSA) were studied. Healthy adult males received 1000 mg SSA and 1300 mg aspirin according to a crossover design either as a single oral dose (12 subjects) or three times a day for five days (4 subjects). A newly developed, high-pressure liquid chromatographic assay permitted selective, direct measurement of SSA in the presence of high concentrations of salicylic acid, one of its metabolites. Following a single dose, SSA was promptly absorbed (mean time to peak level 1.5 hour) and was eliminated from plasma with a mean half-life of 1.1 hour. Less than 1 per cent was excreted in the urine as unchanged SSA. SSA did not accumulate in the plasma during multiple dosing. Plasma levels of salicylic acid following single and multiple doses of SSA indicate that SSA is extensively hydrolyzed to salicylic acid in the body. The slightly lower levels of salicylic acid after SSA than after aspirin may reflect direct biotransformation of some of the SSA to an SSA conjugate, without hydrolysis to salicylic acid.

High-pressure liquid chromatographic determination of salicylsalicylic acid, aspirin, and salicylic acid in human plasma and urine

A high-pressure liquid chromatographic method was developed for the separation and quantitation of salicylsalicylic acid (I), aspirin (II), and salicylic acid (III) in human plasma and urine. The method for plasma involves the selective extraction of I--III and an internal standard, alpha-phenylcinnamic acid, into methylene chloride from acidified plasma, followed by evaporation of the organic phase and dissolution of the residue in methanol. A 25-microliter aliquot is analyzed on a reversed-phase column with UV detection. Urine is treated similarly with hexane as the extracting solvent. If 300 nm is used as the monitoring wavelength, the assays of I and III are linear over the concentration range of 1--150 microgram/ml in both plasma and urine. If 280 nm is used as the monitoring wavelength, II can be quantitated along with I and III; however, detector sensitivities of I and III are two to three times greater at 300 nm. The accuracy and precision of the methods for I--III are adequate for clinical pharmacokinetic studies. Following therapeutic doses of I in humans, the method was applied successfully to the determination of I and III in plasma and urine.

Physiologically based pharmacokinetic model for digoxin disposition in dogs and its preliminary application to humans

A physiologically based pharmacokinetic model for digoxin disposition developed in the rat was modified to account for the interspecies differences in tissue-to-plasma digoxin concentration ratios and applied to the dog. The model provided a quantitative assessment of the time course of digoxin concentrations in dog plasma, various tissues, and urine. It also predicted the effect of renal failure on digoxin pharmacokinetics in the dog. An attempt to scale the dog model to humans by simply considering differences in organ volumes, organ flow rates, and digoxin clearances was partially successful. Good predictions of plasma digoxin concentration and urinary digoxin excretion after a single dose and of steady-state plasma, heart, and skeletal muscle digoxin concentrations were obtained. However, the model predicted considerably higher kidney digoxin concentrations than are actually found. Although the model adequately characterized the time course of digoxin concentrations in patients with moderate renal impairment, it provided a relatively poor fit to that observed in anuric patients.

Physiologically based pharmacokinetic model for digoxin distribution and elimination in the rat

A plasma flow rate-limited pharmacokinetic model was developed to describe the distribution of digoxin to the heart, liver, kidneys, skeletal muscle, and GI tract in the rat. The model also provides for renal, hepatic (metabolic and biliary), and GI clearance as well as for biliary and GI secretion and GI reabsorption of digoxin. Predicted concentrations of digoxin in the heart, liver, skeletal muscle, and plasma were consistent with experimental observations in conscious rats after an intravenous dose. The model was extended to describe digoxin concentrations in the plasma of bile duct-ligated rats and ureter-ligated rats, simply by modifying appropriate clearance parameters. Excellent agreement was obtained between predicted and observed urinary excretion rates of digoxin for 12 hr after in intravenous dose to normal and bile duct-ligated rats.

Influence of cholestasis on drug elimination: pharmacokinetics

A two-compartment model representing the body and the GI tract, with elimination occurring in each compartment, was used to study, in theory, the influence of impaired biliary excretion on drug disposition. The results suggest that cholestasis can either increase or decrease a drug's half-life, depending upon the relative values of the two elimination rate constants, In all cases, however, impaired biliary excretion reduced the initial elimination of drug from the body and increased the half-life of the alpha-phase of drug disposition.

Pharmacokinetics of digoxin in the rat

Previous studies on the pharmacokinetics of 3H-digoxin in the rat have been based on total radioactivity in the plasma, even though the drug is extensively metabolized in this species. A comparison of total radioactivity vs. unchanged drug in rat plasma after administration of 3H-digoxin clearly showed the need to separate digoxin from its metabolites. The pharmacokinetics of digoxin were therefore examined using solvent extraction and thin-layer chromatography to isolate unchanged drug. Digoxin levels after a 1 mg/kg iv dose were measured in the plasma and urine of adult male rats in which the bile duct or the ureters had been ligated, as well as in sham-operated controls. In all cases, digoxin concentrations were best described by a two-compartment open model. Digoxin was rapidly eliminated from the plasma of controls, with a half-life of 2.5 hr, a volume of distribution of 3.6 liter/kg, and a renal clearance somewhat lower than the glomerular filtration rate. No significant change in these parameters was observed in rats with bile duct ligation. The total body clearance of 5.77 ml/min in the controls was reduced by only 10% in the bile duct-ligated rats. In animals with bilateral ureter ligation, the body clearance was reduced by 30% and the plasma half-life of digoxin was increased to 4 hr, although no significant change in the apparent volume of distribution was noted. Approximately 60% of the total body clearance was unaffected by bile duct and ureter ligations, and was assumed to be due to biotransformation. Biliary excretion was found to be important for digoxigenin bisdigitoxoside, inasmuch as rats with bile duct ligation showed elevated metabolite levels in the plasma as well as a 3-fold increase in renal excretion of the bisglycoside.

Transport of L-4-azaleucine in Escherichia coli

The uptake of L-4-azaleucine was examined in Escherichia coli K-12 strains to determine the systems that serve for its accumulation. L-4=Azaleucine in radio-labeled form was synthesized and resolved by the action of hog kidney N-acylamino-acid amidohydrolase (EC 3.5.1.B) on the racemic alpha-N-acetyl derivative of DL-[dimethyl-14C]4-azaleucine. L-4-Azaleucine is taken up in E. coli by energy-dependent processes that are sensitive to changes in the pH and to inhibition by leucine and the aromatic amino acids. Although a single set of kinetic parameters was obtained by kinetic experiments, other evidence indicates that transport systems for both the aromatic and the branched-chain amino acids serve for azaleucine. Azaleucine uptake in strain EO317, with a mutation leading to derepression and constitutive expression of branched-chain amino acid (LIV) transport and binding proteins, was not repressed by growth with leucine as it was in parental strain EO300. Lesions in the aromatic amino acid transport system, aroP, also led to changes in the regulation of azaleucine uptake activity when cells were grown on phenylalanine. Experiments on the specificity of azaleucine uptake and exchange experiments with leucine and phenylalanine support the hypothesis that both LIV and aroP systems transport azaleucine. The ability of external azaleucine to exchange rapidly with intracellular leucine may be an important contributor to azaleucine toxicity. We conclude from these and other studies that at least four other process may affect azaleucine sensitivity: the level of branched-chain amino acid biosynthetic enzymes; the level of leucine, isoleucine, and valine transport systems; the level of the aromatic amino acid, aroP, uptake system; and, possibly, the ability of the cell to racemize D and L amino acids. The relative importance of these processes in azaleucine sensitivity under various conditions is not known precisely.