A multiple-dose safety and bioequivalence study of a narrow therapeutic index drug: a case for carbamazepine.

BACKGROUND AND OBJECTIVES: Carbamazepine is among those drugs that have been considered to have a narrow therapeutic plasma concentration range, that is, a narrow therapeutic index. Although the US Food and Drug Administration has approved new generic products based on standard single-dose bioequivalence studies, several state formularies, including the New Jersey Drug Utilization Review Council, have recently established additional criteria for acceptance of bioequivalence of narrow therapeutic index drugs, limiting the use of some approved generic drugs in specific states. To further validate the adequacy of single-dose studies for the determination of bioequivalence of narrow therapeutic index drugs, a multiple-dose study was conducted that more closely reflected therapeutic use. METHODS: A single-center, multiple-dose, randomized, open-label, 2-way crossover bioequivalence study was conducted in 32 fasting volunteers at steady state. Subjects received the test and reference products as a 200 mg carbamazepine tablet 3 times a day in a crossover fashion. Concentrations of carbamazepine and carbamazepine-10,11-epoxide in plasma were measured by a validated specific HPLC method. RESULTS: A total of 28 subjects completed the study. Pharmacokinetic parameters and measures of fluctuation for both products at steady state were similar, with 90% and 95% confidence intervals falling within 90% and 110%. CONCLUSION: The multiple-dose study provided reliable safety and bioequivalence data under rigorous statistical conditions and confirmed bioequivalence of test and reference products determined by a single-dose study.

Enhanced bioavailability of itraconazole in hydroxypropyl-beta-cyclodextrin solution versus capsules in healthy volunteers.

The bioavailabilities and bioequivalences of single 200-mg doses of itraconazole solution and two capsule formulations were evaluated in a crossover study of 30 male volunteers. The two capsule formulations were bioequivalent. The bioavailabilities of the solutions itraconazole and hydroxyitraconazole were 30 to 33% and 35 to 37% greater, respectively, than those of either capsule. However, the maximum concentrations of the drug in plasma (Cmax), the times to Cmax, and the terminal half-lives were comparable for all three formulations. These data indicate that the bioavailabilities of itraconazole and hydroxyitraconazole are enhanced when administered as an oral solution instead of capsules.

Food interaction and steady-state pharmacokinetics of itraconazole oral solution in healthy volunteers.

STUDY OBJECTIVES: To evaluate the effect of food on the bioavailability of itraconazole (ITR) hydroxypropyl-beta-cyclodextrin (HP-beta-CD) solution under multiple-dose to steady-state conditions, and to determine the pharmacokinetics of ITR solution at steady state. DESIGN: Open-label, randomized, multiple-dose, crossover study SETTING: University-affiliated health center. PATIENTS: Thirty healthy men randomized to one of two treatment sequences (fasted-fed, fed-fasted). INTERVENTIONS: Subjects were either fasted or fed a standard breakfast before receiving ITR oral solution 200 mg once/day for 15 days. Crossover phases were separated by a 4-week washout period. MEASUREMENTS AND MAIN RESULTS: On day 1, blood samples were collected before the dose (time zero) and 0.5, 1, 2, 3, 4, 5, 6, 8, 12, and 24 hours after the dose. Trough samples were obtained before the dose on days 4, 7, 12, 13, and 14. On day 15, samples were obtained at the same times as day 1, and at 36, 48, 72, 96, 168, 240, and 360 hours. Samples were analyzed by high-performance liquid chromatography for ITR and its major metabolite hydroxyitraconazole (OH-ITR). Urine was collected on days 1 and 15 before and 0-8 and 8-24 hours after the dose; HP-beta-CD was measured by size-exclusion chromatography. Mean bioavailabilities of ITR and OH-ITR were 43% and 38% higher, respectively, when ITR solution was taken as a single dose under fasted conditions. With multiple dosing, steady state was achieved by day 14. At steady state, mean bioavailabilities were 29% and 17% higher, respectively, in the fasted state; terminal half-life was similar under fasted and fed conditions (mean 39.8 and 37.5 hrs for ITR, respectively; 27.3 and 26.2 hrs for OH-ITR, respectively). HP-beta-CD was eliminated almost exclusively in urine. CONCLUSION: The bioavailability of ITR and OH-ITR is enhanced when ITR oral solution is given in the fasted state; this was true for both single and multiple dosing to steady state.

Cisapride: a gastrointestinal prokinetic drug.

OBJECTIVE: To summarize the pharmacology, pharmacokinetics, efficacy, and safety of cisapride, and to evaluate its potential therapeutic role. DATA SOURCES: A computerized search of the MEDLINE database was used to identify English-language publications of cisapride data in humans. The MEDLINE search was supplemented by review article bibliographies. There was no attempt to limit the search to a specific gastrointestinal motility disorder. STUDY SELECTION: The MEDLINE search alone identified 165 citations. Because of the volume of available human cisapride data, the focus of the efficacy section is on complete published reports of controlled clinical studies. Abstracts and uncontrolled data are discussed only when other information is unavailable to address important aspects. DATA EXTRACTION: Information regarding study design, study population, results, and safety was recorded from each publication. The placebo response to gastrointestinal complaints in patients with motility disorders is high. Therefore, objective evidence of improvement was emphasized when documentation was available. DATA SYNTHESIS: Cisapride stimulates the motility of smooth muscle lining the esophagus, stomach, small intestine, and colon, and increases the tone of gut sphincters in vitro and in vivo. In controlled investigations, cisapride was superior to placebo in relieving symptoms associated with reflux esophagitis, nonulcer dyspepsia, and gastroparesis. Similar symptom and healing effects were observed with cisapride and histamine (H)2-antagonists in reflux esophagitis. Cisapride was either equal to or superior to metoclopramide in relieving reflux symptoms. However, metoclopramide was associated with significantly more central nervous system adverse effects. Cisapride was well tolerated, with adverse effects limited primarily to the gastrointestinal tract. CONCLUSIONS: Cisapride represents an attractive alternative to metoclopramide for the treatment of a variety of motility disorders. Because it addresses a primary underlying cause of reflux esophagitis, cisapride may also prove to be an effective alternative to acid suppressants in the management of this disorder.

Food interaction and steady-state pharmacokinetics of itraconazole capsules in healthy male volunteers.

The influence of food on itraconazole pharmacokinetics was evaluated for 27 healthy male volunteers in a single-dose (200 mg) crossover study with capsules containing itraconazole-coated sugar spheres. This study was followed by a study of the steady-state pharmacokinetics for the same subjects with 15 days of administration of itraconazole at 200 mg every 12 h. Concentrations of itraconazole and hydroxyitraconazole, the active main metabolite, were measured in plasma by high-performance liquid chromatography. The results of the food interaction segment showed that a meal significantly enhances the amount of itraconazole absorbed. The mean maximum concentration in plasma of unmetabolized itraconazole after fasting (140 ng/ml) was about 59% that after the standard meal (239 ng/ml). The rate of elimination was not affected (terminal half-life, approximately 21 h). The mean maximum concentration in plasma of hydroxyitraconazole after fasting was about 72% the postmeal concentration (287 and 397 ng/ml, respectively). The terminal half-life of hydroxyitraconazole was approximately 12 h. Steady-state concentrations of itraconazole and hydroxyitraconazole were reached after 14 or 15 days of daily dosing. The average steady-state concentrations were approximately 1,900 ng/ml for itraconazole and 3,200 ng/ml for hydroxyitraconazole. The shape of the elimination curve for itraconazole after the last dose was indicative of saturable elimination. This conclusion was confirmed by the sevenfold increase in the area under the curve from 0 to 12 h at steady state compared with the area under the curve from 0 h to infinity after a single dose. It was furthermore confirmed by the larger-than-expected number of half-lives required to achieve steady-state plasma drug levels.

Effect of food and gastric acidity on absorption of orally administered ketoconazole.

Effects of food and gastric acidity on the bioavailability of ketoconazole tablets were investigated in 12 volunteers using a six-treatment, randomized, Latin-square crossover design. All volunteers received all treatments, as follows: (A) ketoconazole 200 mg administered after a fast; (B) ketoconazole 200 mg with a standardized high-fat meal; (C) ketoconazole 200 mg with a standardized high-carbohydrate meal; (D) ketoconazole 200 mg after pretreatment with glutamic acid hydrochloride 680 mg as capsules; (E) ketoconazole 200 mg in a simulated achlorhydric state induced with cimetidine and sodium bicarbonate; and (F) ketoconazole 200 mg administered with glutamic acid hydrochloride in a simulated achlorhydric state. Ketoconazole concentrations were measured by high-performance liquid chromatography in plasma samples drawn immediately before and at various times over 24 hours after drug administration. Bioavailability variables, including natural logarithm transformation for area under the concentration-time curve (AUC), were subjected to analysis of variance followed by Duncan's Multiple Range testing. Treatments B and C significantly prolonged the times required to achieve the peak plasma ketoconazole concentration, and treatment C also significantly reduced the peak plasma ketoconazole concentration (Cmax) compared with treatment A. There was a trend toward increased AUC values with treatment B and decreased AUC values with treatment C. Treatment D produced a higher Cmax compared with treatment A, and treatment E produced large, significant reductions in Cmax and AUC values compared with treatment A. Treatment F significantly increased AUC values and Cmax compared with treatment E.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative dissolution performance of internationally available piroxicam products.

Piroxicam is a widely used nonsteroidal antiinflammatory drug available worldwide under various trade names by several manufacturers. Only one brand of piroxicam (Feldene) is currently marketed in the U.S., and the United States Pharmacopeial Convention established an official dissolution requirement for piroxicam in 1985. The purpose of this study was to evaluate and compare the dissolution performance of several internationally available piroxicam products using the United States Pharmacopeia (USP) dissolution test for piroxicam capsules. Of 25 brands of piroxicam capsules evaluated, 72 percent of the brands failed to meet the USP requirement, several by a wide margin. Although there is no specific USP dissolution test for tablets, the test for capsules was applied to five different brands of piroxicam tablets, and 80 percent of the tablet brands tested failed to meet the USP requirement. Although comparative bioavailability studies would be required to establish any definitive relationship between dissolution test performance and bioavailability, the failure of most of these products to meet the USP requirement for dissolution indicates formulation differences that could result in altered bioavailability. The substantial differences in dissolution performance observed among the piroxicam oral dosage forms tested have implications concerning the equivalency and standards of multisource products available on the international market, and should be taken into account by health care providers worldwide.

Bioavailability of three oral dosage forms of cisapride, a gastrointestinal stimulant agent.

Relative bioavailability of the investigational gastrointestinal stimulant agent cisapride after oral administration was determined in healthy men. Treatments administered were (A) two 5-mg tablets; (B) one 10-mg tablet; (C) 10 mL of a 1-mg/mL suspension; and (D) 10 mL of a 1-mg/mL aqueous reference solution. The study had a randomized four-way, crossover design; drug administration was followed by a standard breakfast. Plasma cisapride concentrations in blood samples drawn over 48 hours were measured by high-performance liquid chromatography. Individual and mean values for bioavailability parameters were subjected to analysis of variance followed by multiple comparison testing. Time to maximum concentration was shortest after administration of the solution. There was a significant difference in mean peak plasma concentrations between treatment A (48.8 +/- 12.8 ng/mL) and treatment D (41.6 +/- 10.6 ng/mL), with treatment A producing a 17.3% higher peak concentration. No significant differences between treatments were found for area under the plasma concentration-time curve. The overall mean elimination half-life was 7.01 hours. The results of the study indicate that the tablet and suspension dosage forms of cisapride are bioequivalent to the reference solution.

Pharmacokinetics and dose proportionality of domperidone in healthy volunteers.

Domperidone is a potent gastrokinetic agent and antinauseant currently undergoing clinical trials in the United States. The bioequivalence of 20 mg of domperidone given as free-base tablets and maleate salt tablets, and the bioavailability of base and maleate tablets relative to a solution, were studied in 21 fasting men using a crossover design. Plasma samples collected for up to 48 hours were analyzed for domperidone levels, using a sensitive and specific radioimmunoassay (RIA). The absorption of domperidone was very rapid, with mean peak plasma concentration (Cmax) values of 18.8, 15.0, and 20.7 ng/mL attained at 0.9, 1.2, and 0.6 hours after the administration of base tablet, maleate tablet, and solution, respectively. The mean elimination half-life (t1/2) ranged from 12.6 to 16.0 hours. The mean oral clearance (CL/F) after the solution dose was 4,735 +/- 2,017 mL/min and the mean apparent volume of distribution (Vd/F) was 6,272 +/- 5,100 L, indicating an extensive distribution of domperidone in the body. The area under the plasma concentration-time curve (AUC) data demonstrated bioequivalence of base and maleate tablets. The relative bioavailability for base tablet and maleate tablet was 107 +/- 50% and 116 +/- 47%, respectively, of that of the solution. Dose proportionality of domperidone was also studied in 12 subjects at solution doses of 10, 20, and 40 mg. Linear correlations between the dose and Cmax and AUC values were observed. Mean CL/F remained relatively constant after doses of 10, 20, and 40 mg (5,255 +/- 3,159, 4,842 +/- 1,774, and 4,380 +/- 1,289 mL/min, respectively), indicating linear pharmacokinetics of domperidone over the dose range studied.

Safety evaluation of ritanserin--an investigational serotonin antagonist.

Ritanserin is an investigational serotonin-S2 receptor antagonist with activity in a variety of psychiatric disturbances characterized by dysthymia or anxiety. This investigation evaluates acute safety and tolerability of ritanserin in 12 healthy males. Ritanserin 10 mg, 20 mg, and placebo were administered as single doses in a randomized, double-blind, crossover fashion. Treatment effects on vital signs, laboratory tests, a mood evaluation test, electrocardiograms (ECGs), and reported adverse experiences were monitored. Plasma levels were determined at two hours postdose. Results indicated no clinically relevant effects on vital signs, laboratory tests, ECGs, or mood evaluations. Dose proportionality was demonstrated. The incidence of total adverse effects (primarily somnolence and fatigue) after single-dose administration was 25 percent for placebo, 75 percent for 10 mg, and 81.8 percent for 20 mg. There was a relationship between incidence of adverse effects and dose, but no general correlation between plasma levels and severity of adverse experiences. The results indicate that ritanserin is safe and tolerable following acute administration of 10 mg and 20 mg oral doses.

Pharmacokinetics and dose proportionality of ketoconazole in normal volunteers.

Ketoconazole is an orally effective, broad-spectrum, systemic antifungal agent. The pharmacokinetics and bioavailability of ketoconazole given as a 200-mg single dose in a tablet, suspension, or solution were studied in 24 fasting healthy males by using a crossover design. Levels of ketoconazole in plasma were determined for up to 48 h by a sensitive reverse-phase high-performance liquid chromatography method. The absorption of ketoconazole was rapid, with mean maximum concentrations of the drug in plasma of 4.2, 5.0, and 6.2 micrograms/ml attained at 1.7, 1.2, and 1.0 h, respectively, after administration of the tablet, suspension, and solution, respectively. The mean distribution and elimination half-life values were 1.5 to 1.7 and 7.5 to 7.9 h, respectively. The mean oral clearance of the solution dose was 209 (+/- 82.9 [standard deviation]) ml/min, and the mean apparent volume of distribution was 88.31 (+/- 68.72) liters. The relative bioavailabilities for the tablet and suspension were 81.2 (+/- 33.5) and 89.0 (+/- 23.1)%, respectively, of that of the solution. The data indicated the bioequivalence of the tablet to the suspension and of the suspension of the solution. Dose proportionality of ketoconazole was also studied in 12 volunteers after they received solution doses of 200, 400, and 800 mg. Linear correlations between the dose and the maximum concentration of the drug in plasma, the time to the maximum concentration, and the area under the concentration-time curve were observed. However, the increase in the area under the curve was more than proportional to the dose given. The levels in plasma seemed to decay at a lower rate after 400- and 800-mg doses. The mean oral clearance decreased from 244.9 to 123.6 and 80.0 ml/min, respectively, as the dose increased from 200 to 400 and 800 mg. The apparent dose-dependent kinetics may have been due to the presystemic elimination and capacity-limited hepatic metabolism which become saturated at higher doses.

Critical therapeutic categories: a contraindication to generic substitution?

All 50 states either permit or require a pharmacist to substitute a generic drug for a prescribed brand-name drug unless the physician specifically notes on the prescription form that substitution is not to be made. In certain critical therapeutic categories and for certain patient populations, each substitution poses the risks of treatment failure and of increased toxicity. The therapeutic categories include cardiovascular drugs, psychotropic agents, and anticonvulsants. Additional potential therapeutic categories include cardiovascular drugs, psychotropic agents, and anticonvulsants. Additional potential therapeutic categories include low-dose oral contraceptives, bronchodilating agents, oral diuretics, and oral anticoagulants. The populations at risk include debilitated or elderly patients with abnormal gastrointestinal, renal, or hepatic function. The FDA's approach to approval of generic drugs, based primarily on the demonstration of bioequivalence, is considered by many professionals as likely to result in excessive variability among treated patients. Depending on the particular rule defining bioequivalence, indiscriminate switching among generic versions of a brand-name drug potentially could result in 40% to 60% differences in rate or extent of absorption. For drugs that require careful titration to assure efficacy and lack of toxicity, such variability can have important consequences. The FDA is now reviewing its policies for approval of generic drugs. Until the matter is resolved, however, caution should be exercised when prescribing or dispensing drugs that can be substituted. Indiscriminate switching among generic products should be avoided, especially for drugs in the critical therapeutic categories and for drugs prescribed for elderly or debilitated patients.

Critical evaluation of thioridazine bioequivalence.

The phenothiazines have exhibited a history of problems associated with the bioequivalence of solid oral dosage forms. The more recent availability of chemically equivalent forms of thioridazine has raised new and interesting questions about the appropriateness of generic product interchange, even among brands that have been designated "therapeutically equivalent" by the Food and Drug Administration. The scrutiny that has accompanied the consideration of thioridazine products for inclusion into various state generic substitution formularies has offered an opportunity to examine issues involving bioequivalency in considerable detail. Specific bioequivalency concerns relate to: correct analysis of drug in biological fluids; the importance of evaluating active metabolites: single-dose vs. multiple-dose crossover studies; appropriate statistical power analysis; the "70/70" rule, and comparison of product variabilities. Examples of problems are cited to illustrate that significant questions still remain about the appropriate factors that should be used to establish bioequivalency.

In vivo-in vitro correlations for trisulfapyrimidine suspensions.

A UV method is described for measuring total sulfa drug concentration in dissolution samples. This in vitro measurement was found to correlate well with several in vivo parameters obtained after administration of commercial trisulfapyrimidine suspensions to humans. The UV method, which is rapid, simple, inexpensive and easily automated, is recommended for studying the dissolution of trisulfapyrimidine suspensions.