Dissolution rate and transit times of technetium-99m DTPA-labeled tablets.

In this study we demonstrate that the dissolution rate and gastroduodeno-cecal transit time of radiolabeled tablets of theophylline can be determined in vivo using technetium-99m (99mTc). Six healthy male volunteers ingested a tablet containing 300 mg of theophylline mixed with 3.7 MBq of [99mTc]DTPA. Anterior and posterior scintigraphic views of the abdomen were collected serially over 8 hr, after which a 200-ml solution containing 37 MBq of [99mTc] pertechnetate was ingested in order to visualize the contours of the stomach. The in vivo activity contained in the tablet was calculated from the scintigraphic views after correction of background activity, radioactive decay, and depth attenuation. The dissolution rate of [99mTc] DTPA was also measured in vitro and compared with the dissolution rate of theophylline. The results showed close dissolution rates between [99mTc]DTPA and theophylline in vivo (T1/2 184 min and 176 min, respectively), and a faster early dissolution rate of [99mTc]DTPA in vitro (T1/2 92 min versus 156 min for theophylline). The mean gastroduodenal and duodenocecal times were 72 +/- 25 min (m +/- s.d.) and 245 +/- 15 min, respectively. Scintigraphic imaging of labeled formulations with 99mTc present useful applications in pharmaceutics and pharmacology.

The influence of food on the bioavailability of a slow release theophylline preparation.

Food-induced changes in the absorption of Theostat 300, a controlled release formulation of theophylline, have been studied in healthy volunteers. This open, randomised, 3-way, single-dose study involved 12 volunteers who received the drug either while fasting, or with a standardised low-fat (10g), or high-fat (60g) breakfast. Each subject was studied over a 3-week period, with 3 separate days of oral treatment and a 7-day washout period between treatments. The results showed no differences in AUC0-24 and tmax values between the 3 kinds of diet. The only differences observed concerned absorption. Food intake increased Cmax values by 20%. The steady-state peak concentration obtained by means of simulated plasma levels was not influenced by food intake. This slight food-drug interaction of Theostat 300 seemed to be of no clinical significance.

A new method of dissolution in vitro, the "Bio-Dis" apparatus: comparison with the rotating bottle method and in vitro: in vivo correlations.

The aim was to study a new method of dissolution in vitro, the "Bio-Dis" apparatus, and to compare it with the classical rotating bottle method. Several theophylline controlled-release drug dosage forms were studied. Dissolution testing was performed in increasing pH in standard conditions and after treatment with peanut oil in order to simulate high fat meals and to correlate the in vitro percent dissolved with the in vivo results obtained. The in vivo study was carried out on three groups of healthy volunteers receiving each dosage form in a randomized order just before a high fat breakfast or in the fasting state. The in vitro percent dissolved obtained was compared with those published results obtained with rotating bottles. A linear relationship was established between these results. From the in vivo absorbed percentages calculated according to the Wagner-Nelson method, a linear relation was found between the in vivo percent absorbed and the in vitro percent dissolved in the different conditions. The relationships observed are similar for all the forms under both conditions. The "Bio-Dis" offers advantages over the rotating bottle method. The study reported allows this dissolution apparatus to be proposed as an alternative to the rotating bottle apparatus.

French and/or European perspectives on biopharmaceutical characterization of drug dosage forms.

In order to bring definitions of drug dosage forms up to date, it was necessary for the French Pharmacopoeia to propose assays allowing the quality control of the dosage forms to be based on the kinetics of drug release in vitro. Currently, five examples can be cited of dosage forms that can be characterized by release in vitro. (1) Oral solid dosage forms--for tablets, all the parameters of powders before compression (e.g., flowability, tableting properties) are being studied in addition to the dissolution tests, (2) Rectal dosage forms--the disintegration test of suppositories will be discarded and a new dissolution test using a special flow-through cell is now being studied. (3) Inhalations--since particle diameter is the most important factor for inhalation activity, a method has been developed to give the correct answer to this question. (4) Modified release drug dosage forms--these have been defined separately from the conventional forms. For the peroral route, they are: (i) accelerated release drug dosage forms, (ii) sustained release drug dosage forms and (iii) delayed release drug dosage forms. To emphasize the differences in the release kinetics, use of the paddle method, well known in the USP, and the flow-through cell has been suggested and described in the European Pharmacopoeia. Some associations and/or in vitro-in vivo correlations have increased the interest in the last method. (5) Transdermal delivery systems--these are defined separately from plaster and sticking-plaster. The use of a cell method was suggested to study the drug release and some comparisons between different techniques are presented.

The formulation of drug for ocular administration.

The different barriers that slow the penetration of active ingredients administered by the ocular route are described, and some novel dosage forms designed for this route are discussed. Both precorneal and corneal factors considerably restrict ocular penetration. The low bioavailability of classical ophthalmic dosage forms can be improved by several approaches, particularly by increasing the time the active ingredients remain in contact with the eye tissues. The new dosage forms are reviewed according to their type and their drug release mechanisms. The characteristics, advantages, and limitations of each are outlined. The potential of these dosage forms can be expected to enhance development. They offer prolonged effectiveness, reproducibility, fewer unwanted side effects, and improved tolerance.

Insolubilization test of sodium chondroitin sulphate with a view to its use as colonic carrier of drugs.

Several studies have been devoted to cross-linked sodium chondroitin sulphate (SCS), in the context of numerous strategies attempting to target the colon for the absorption or the therapeutic action of a drug. SCS, a glycosaminoglycan presenting a specific degradation in the colon, is in fact soluble in water and its use as drug carrier at such a distance from the digestive tube necessitates its hydrophobisation. One method described in the literature consists in manufacturing a three-dimensional network by cross-linking with bifunctional compounds. However, all the structural characterisations carried out on the products resulting from the catalysed treatments of SCS with diaminoalkanes demonstrate that there are no cross-linking bridges between the polymer chains. Moreover, treated SCS-based tablets containing theophylline as model drug lead in vitro to dissolution profiles which are identical to those obtained with the non-treated SCS. We were therefore unable to find the announced results using the method described.

The ideal drug delivery system: a look into the future.

In the very near future, the CFC manufacturers are going to be obliged to stop their production as a result of the "Montreal protocole on substances that deplete the ozone layer". The replacement of these propellants by other fluorinated ones will be possible as soon as their lack of toxicity has been demonstrated. Other substitution substances like haliphatic hydrocarbons (butane, propane) or compressed air generated by the device system itself or the user himself are also under development. The pulverisation can also be obtained by the pressure of a classical propellant onto an aluminum or plastic bag. The dispersion is achieved by means of a regulator which is positioned into the valve. The hand-operated spray pumps with or without compression will also allow the obtention of very small particles though the delivered doses are reduced. However, as few of the new devices have metered valves, they are not yet suitable for pulmonary administration.

Influence of food on the disposition of the antidiabetic drug metformin in diabetic patients at steady-state.

The effect of food on the bioavailability of the antidiabetic drug metformin (Glucophage, Lipha Laboratories) was investigated in patients at steady-state. Seventeen diabetic patients (5 males and 12 females) treated with a long-term metformin therapy received their morning dose after an overnight fasting or after each of four types of breakfast: low protein, low fat, low carbohydrate or standard. Mean (+/- SD) and median areas under the serum concentration curves (AUC), maximum concentrations (Cmax) and time to reach the Cmax (Tmax) were calculated. Compared to fasting conditions, AUC and Cmax for metformin were bioequivalent after the four types of breakfast except the low fat (high carbohydrate) diet which had results slightly reduced (90% CI = [0.76-0.90]). The intraindividual variability was calculated and found to be lower than the interindividual variability.

Influence of food on glycemia, insulin, C-peptide and glucagon levels in diabetic patients treated with antidiabetic metformin at steady-state.

Seventeen diabetic patients (5 males and 12 females) treated with long-term metformin therapy received their morning dose after an overnight fast or after one of four types of breakfast: low protein, low fat, low carbohydrate or standard. Mean (+/- SD) and median areas under the serum concentration curves (AUC), maximum concentrations (Cmax) and time to reach the maximum concentrations (tmax) were calculated for the major biological parameters (glycemia, C-peptide, insulin and glucagon levels). None of the diets were bioequivalent to the fasting condition and only the low carbohydrate diet gave comparable results. A strong relationship was found between the carbohydrate intake (in g) and the AUC of the various markers except glucagon.

Peroral absorption of cefroxadine in patients within the first day after severe trauma: comparison to cefroxadine pharmacokinetics in fasted, healthy volunteers.

Peroral absorption of cefroxadine given to 7 24-h fasted trauma patients by nasogastric tube within the first day of admission was compared to that obtained in fasted healthy volunteers. The trauma patients exhibited significantly lower Cmax and reduced AUC. Even though rate and extent of bioavailability cannot be determined from these two different population groups since the total clearance must be assumed to be different in patients and healthy subjects, a reduced bioavailability is assumed based on pathophysiologic reflections.

Comparison of continuous, constant rate enteral tube feeding in supine patients to bolus food intake in ambulatory, healthy subjects regarding bioavailability of perorally administered cefroxadine.

Stabilized, bedridden, inactive trauma patients on enteral nutrition via continuous, constant rate tube feeding (2 different formulas) were given a single dose of cefroxadine p.o. There were no differences in the pharmacokinetic parameters between the groups on different enteral nutrition. These patients were compared to cefroxadine absorption in ambulatory healthy subjects after a standardized meal (bolus-fed). The mean residence time was significantly longer in the patients, and the extent of absorption was slightly reduced with one enteral nutrition formulation and significantly reduced with the other. The other pharmacokinetic parameters were not significantly different. The difference is believed to be caused by reduction in splanchnic blood flow in the immobilized patients, weakening of migrating motor complex due to tube feeding and the lower temperature (4 degrees C) of enteral nutrition.

In vivo-in vitro correlation of salbutamol release from a controlled release osmotic pump delivery system.

The drug release of salbutamol from a controlled release (osmotic pump) tablet was determined in vitro by four different dissolution apparatuses. From published in vivo data, percent of drug absorbed and percent of drug released in vivo were estimated. The highest correlation was obtained between percentage released in vitro versus percentage released in vivo using polynomial regression.

Development of absorption furosemide prodrugs: synthesis, in vitro and in vivo evaluation.

Six acyloxymethyl esters of Furosemide were synthesized and the structures were determined by chemical and spectroscopic methods. Lipophilicity parameters were analysed by high performance liquid chromatography (HPLC). Hydrolysis performances in human plasma and intestinal fluids anticipate their properties as absorption prodrugs of Furosemide. A bioavailability study carried out with 8 male Wistar rats with one of the synthesized prodrug (acetyloxymethyl 4-chloro-N-furfuryl-5-sulfamoylanthranilate) showed a greater absorption in relation to Furosemide. The percentages of mean urinary recovery of Furosemide for the prodrug and for the standard solution of the drug were 20.84 and 14.36 respectively. The doses were 10 mg/Kg in Furosemide. The analytical determinations of Furosemide in biological fluids were done by HPLC.

Pharmacokinetic data processed by microcomputer for the formulation of optimal drug dosage form.

Microcomputers have been used in pharmacokinetics for several years, but their use in the area of formulation is a new application. By using appropriate data on the drug, the dosage form required and its mechanism of absorption and clearance, microcomputers can systematize and speed-up formulation, simplify manufacturing processes and, through simulated models and plasma level predictions, reduce the number of bioavailability studies needed.

Pharmacokinetics of cefotaxime and its desacetyl metabolite in plasma and in cerebrospinal fluid.

The aim of the study was to investigate the pharmacokinetic modelling of Cefotaxime (CTX) and its main metabolite Desacetyl Cefotaxime (DCTX) which has a less antibacterial activity than the CTX. After intravenous administration of 1g of CTX to 26 patients, the plasma concentrations determined by HPLC showed that the pharmacokinetics of CTX and transformation to DCTX can be described with an open five-compartment model. The implications of this are discussed from the clinical point of view.

Average parameters in bioavailability studies: an application to slow-release amitriptyline formulation.

In order to assess the extent and the rate of absorption in bioavailability studies, area under the curve (AUC), experimental maximum concentration (Cmax) and experimental time to reach Cmax (Tmax), are used. But when slow-release formulations are considered, the drug concentration-time curves usually show multiple peaks, and it is difficult to compute a Cmax and Tmax value. In case a Cmax value is computed, important variability in this parameter results in high values in the residual variance of the ANOVA test. So in order to decrease the high variability, average parameters: average concentration (Cav), average maximum concentration (Cmax,av) and Cmax,av x 100/Cav (%Cmax,av), are proposed. These new parameters were applied in a bioavailability study of slow-release amitriptyline formulation.

Bioinversion of ibuprofen enantiomers after administration in dogs: estimation of a novel index.

This study compares the pharmacokinetics and bioinversion of two chemical forms of ibuprofen administered intravenously or orally. Dogs were given the free acid form of the S(+) isomer p.o. or i.v., or the racemate, as the free acid or sodium salt, p.o., in a cross-over design. The main kinetic parameters were calculated and formation and bioinversion curves plotted. The values of Cmax, Tmax and AUC were higher for the S(+) isomer. The percentage bioinversion averaged between 35-70% according to the form. This study proposes a new index for the calculation of bioinversion, independently of any i.v. administration, and confirms its self-limiting nature.

[Comparative study of pharmacokinetics and effects on urinary secretion of electrolytes of furosemide and furosemide-amiloride in healthy subjects]. / Etude comparative chez le sujet sain de la pharmacocinétique et des effets sur l'excrétion urinaire d'électrolytes du furosémide et de l'association furosémide-amiloride.

A randomized cross over study was carried out in 12 healthy volunteers to investigate simultaneously the pharmacokinetics and the effects on urinary volume and electrolyte excretion after administration of single doses of 40 mg frusemide and a combination tablet containing both 40 mg frusemide and 5 mg amiloride. From a statistical analysis of plasma levels of frusemide and amiloride measured by HPLC methodology, no significant difference between the reference drug alone, frusemide, and the combination tablets was observed in mean peak plasma levels, mean times to peak or mean areas under the plasma concentration-time curves (AUC). Frusemide and the combination tablet both produced a rapid and powerful diuresis in the 0-2 hours postdose period and did not differ significantly in urine output at any time point. However a difference in natriuretic activity was observed between frusemide and the combination with the latter producing a significantly greater sodium excretion in the 0 to 2 hours period (p less than 0.05). Potassium retaining activity throughout the 24 hours was marked after the administration of the combination, the potassium excretion being significantly less (p less than 0.05) than either control of frusemide alone. There was also a significant correlation between plasma levels of frusemide and the time course of urine and electrolyte excretion in healthy subjects.

[Transdermal therapeutic methods]. / Les thérapeutiques transdermiques.

Percutaneous absorption has now been largely demonstrated and is defined as the passage of a molecule applied to the skin from the external environment to the blood. This phenomenon takes place in two main steps: penetration and actual absorption. Percutaneous absorption avoids the first-pass effect to which orally and rectally administered molecules are submitted, although these molecules can be metabolized in the skin, but to a much lesser degree that by hepatic metabolism. Transdermal devices present many advantage compared to forms administered by other routes: improved patient compliance, easy self-administration, prolonged plasma plateau levels. However, it depends on the skin type and, in the case of allergic reactions, other classical forms designed for the cutaneous route, such as ointments or gels. There are two types of transdermal device: so-called matricial forms, which are semi-solid or solid preparations in which the active ingredient(s) can be dispersed or dissolved; reservoir systems, in which one of the walls is a membrane, placed directly on the skin. In the case of the nitroglycerin, plasma curves are essentially identical regardless of the type of device used. The active ingredients currently available on the market in the form of transdermal devices are scopolamine, nitroglycerin, 17-beta-oestradiol, nicotine, and, for the future, forms containing fentanyl, timolol, ephedrine ... are currently being developed.

[Problems raised by the reformulation of inhalations after the removing of propulsors "chlorofluorocarbons" (CFC)]. / Problèmes posés par la reformulation des inhalations après la suppression des propulseurs "les chlorofluorocarbones (CFC)".

The application of the Montreal convention which not only plans to remove CFCs from pressurized preparations but to stop also the production, will affect companies. However, for pharmaceutical use, antiasthmatic drugs are considered as essential and at the moment the use of CFCs is allowed. But if the production stops, a reformulation will be necessary. Three solutions are conceivable: The first one is to replace CFC 11, 12 and 114 with the old well known propellants as butane, isobutane, propane but they are not very compatible with pulmonary use. The second one is the use of new official substitutes as 134a (tetrafluorethane) or R227 (heptafluoropropane). The former is immediately available and can be used because its take of toxicity has been demonstrate by an international consortium, IPACT as well as the absence of action on ozone but a light "greenhouse effect" is expected. However, the simple substitution of CFCs for those two propellants is not easy due to their physical-chemical properties which are different from the old CFCs. This reformulation is so delicate that pharmaceutical companies have chosen a third solution: precompression pumps or clever devices which can deliver directly the pure drug in powder form. The other preparations to be used for dermatological or cosmetological uses have been reformulated since a long time with original and special presentation (bags in can or volatile solvents).