Controlled release metoprolol formulations. A review of their pharmacodynamic and pharmacokinetic properties, and therapeutic use in hypertension and ischaemic heart disease.

Conventional formulations of metoprolol have become well established in cardiovascular medicine and are particularly useful in the management of hypertension and ischaemic heart disease. Recently developed controlled release metoprolol delivery systems (metoprolol CR/ZOK and metoprolol OROS) were designed to overcome the drug delivery problems of matrix-based sustained release forms by releasing the drug at a relatively constant rate over a 24-hour period, and thus producing sustained and consistent metoprolol plasma concentrations and beta 1-blockade while retaining the convenience of once daily administration. Clinically and statistically significant reductions in blood pressure have been observed with metoprolol CR/ZOK and metoprolol OROS 24 hours after administration in mildly or moderately hypertensive patients. Studies in patients with mild to moderate hypertension have demonstrated that a similar or higher percentage of patients achieved a goal response with metoprolol CR/ZOK compared with matrix-based sustained release formulations of metoprolol, or conventional atenolol or bisoprolol, while metoprolol OROS achieved an equal or greater response rate compared with conventional or matrix-based sustained release metoprolol preparations. In patients with stable effort angina pectoris, once daily administration of metoprolol CR/ZOK provided at least equal antianginal efficacy as conventional metoprolol in divided doses, while metoprolol OROS reduced the mean number of anginal attacks by the same margin as atenolol. Controlled release metoprolol formulations have been well tolerated in clinical trials. Metoprolol CR/ZOK was associated with a similar or lesser degree of adverse effects related to the central nervous system compared with atenolol or long acting propranolol. Metoprolol CR/ZOK also demonstrated less pronounced beta 2-mediated bronchoconstrictor effects than atenolol in asthmatics, and less general fatigue and leg fatigue in healthy subjects. Metoprolol OROS produced less pronounced bronchoconstrictor effects than atenolol, matrix-based sustained release metoprolol or long acting propranolol in patients with asthma or obstructive airways disease, and healthy volunteers. These results are presumably due to the beta 1-selectivity of metoprolol in addition to the relatively low plasma concentrations maintained by metoprolol CR/ZOK and metoprolol OROS, and the avoidance of high peak plasma concentrations with these agents. Despite the relative safety of the controlled release forms of metoprolol, the use of all beta-adrenoceptor antagonists should be avoided in patients with a history of bronchospasm. Thus, controlled release metoprolol formulations offer the potential to maximise the confirmed benefits of this agent in the management of hypertension and angina, by maintaining clinically effective plasma concentrations within a narrow therapeutic range over a 24-hour dose interval.     

Single- and multiple-dose pharmacokinetics of an oral once-a-day osmotic controlled-release OROS (methylphenidate HCl) formulation

Methylphenidate is used for the treatment of attention deficit hyperactivity disorder (ADHD). OROS (methylphenidate HCl) is an osmotic controlled-release delivery system designed for once-daily oral dosing. The pharmacokinetics of OROS (methylphenidate HCl) 18 mg qd, sustained-release (SR) methylphenidate 20 mg qd, and the immediate-release (IR) formulation given as three 5 mg doses every 4 hours (tid) were compared in adults. In addition, the single- and multiple-dose pharmacokinetics of the OROS formulation were studied. Following OROS (methylphenidate HCl), there was a gradual increase in the mean methylphenidate plasma concentrations with peak concentrations noted at 6 to 8 hours. With the SR formulation, peak plasma concentrations were noted at approximately 4 hours. Following the IR regimen, methylphenidate plasma concentrations fluctuated in tandem with oral dosing; peak concentrations were noted at 6.5 hours. The terminal half-life of methylphenidate was similar for the three formulations. The dose-normalized methylphenidate Cmax for OROS (methylphenidate HCl) was significantly lower than for IR and SR methylphenidate. The bioavailability of methylphenidate and PPA from OROS (methylphenidate HCl) relative to the IR and SR formulations was complete. Mean methylphenidate AUC and terminal half-life were similar after single (32.9 ng.h/mL and 3.9 hours) and multiple doses (35.2 ng.h/mL and 3.9 hours) of OROS (methylphenidate HCl).     

Bioequivalence, pharmacokinetic and pharmacodynamic response to combined extended release formulations of felodipine and metoprolol in healthy volunteers

Objective: The primary aim of this study was to investigate whether bioequivalence is achieved for a new fixed combination of extended-release (ER) felodipine and controlled-release (CR/ZOK) metoprolol␣compared with the free combination of felodipine ER metoprolol CR/ZOK. The second aim was to study whether there was an interaction in pharmacokinetics and pharmacodynamics between felodipine and metoprolol when administered as ER formulation. Methods: Two four-way cross-over studies were performed in 36 young subjects and 24 elderly subjects with frequent measurement of drug plasma concentrations, blood pressures and heart rate. The pharmacokinetic analysis included enantioselective analysis in six subjects. Results: Bioequivalence between the fixed combination and the free combination was observed for the two drugs (mean difference 27%) except for a minor deviation regarding C_max of metoprolol in the elderly. No significant interaction was shown except for a small increase (6%) of metoprolol AUC in the younger subjects. Mean plasma S-/R-enantiomer ratios were almost identical for the different treatments. Blood pressure and heart rate was significantly reduced for the fixed combination compared with felodipine ER in the younger and the elderly subjects. No significant difference regarding pharmacodynamics was detected between the fixed combination and the corresponding free combination. Conclusion: The fixed combination consistently provides fairly constant and effective felodipine and metoprolol concentrations after once-daily administration of one tablet. It is clinically interchangeable with the free combination of metoprolol CR/ZOK tablets and felodipine ER tablets. Finally, felodipine and metoprolol do not interact on a pharmacokinetic level when administered as the fixed combination. Received: 29 October 1996 / Accepted in revised form: 21 March 1997     

Effect of food on early drug exposure from extended-release stimulants: results from the Concerta,Adderall XR Food Evaluation (CAFE) Study

Stimulant therapy is the mainstay of treatment for children, adolescents and adults with attention-deficit/hyperactivity disorder (ADHD). Once-daily, extended-release oral formulations offer long acting control of symptoms by modifying drug delivery and absorption. In particular, consistency in early drug exposure is important for symptom control during school or work hours. Because these once-daily formulations are usually taken in the morning, the timing of the doses with breakfast is important. This study compared the effect of a high-fat breakfast on early drug exposure from a morning dose of two extended-release stimulant formulations: the osmotic-controlled OROS tablet of methylphenidate HCI (CONCERTA) and the capsule containing extended-release beads of mixed amphetamine salts (ADDERALL XR). The study had a single-dose, open-label, randomised, four-treatment, crossover design in which healthy subjects received either 36 mg CONCERTA or 20 mg ADDERALL XR in the morning after an overnight fast or a high-fat breakfast. Serial blood samples were collected over 28h to determine plasma concentrations of methylphenidate and amphetamine. The food effect on early drug exposure and the pharmacokinetic profiles up to 8 h after dosing of the two extended-release stimulants were directly compared using partial area (AUC(p4h), AUC(p6h) and AUC(p8h)) fed/fasted ratios. Amphetamine concentrations were markedly lower when the subjects had eaten breakfast, resulting in lower early drug exposures (p < 0.0001). By contrast, methylphenidate concentrations over the same 8 h were unaffected by breakfast, providing consistent levels of early drug exposure. Therefore, as a child's or adult's eating pattern varies, methylphenidate exposure over the first 8 h would be expected to have less day-to-day variation compared with amphetamine exposure. The osmotic-controlled OROS tablet provides a reliable and consistent delivery of methylphenidate HCI, independent of food, for patients with ADHD.     

Pharmacokinetics of an oral once-a-day controlled-release oxybutynin formulation compared with immediate-release oxybutynin

Oxybutynin is used for the treatment of urge urinary incontinence. In this randomized, open-label, two-way crossover, multiple-dose study, the pharmacokinetics of a once-daily, controlled-release formulation, OROS oxybutynin chloride, was compared with that of immediate-release (IR) oxybutynin (Ditropan). Thirteen healthy female volunteers received three 5 mg OROS oxybutynin chloride tablets once daily for 4 days or IR oxybutynin 5 mg administered every 8 hours for 4 days. On day 1, with OROS oxybutynin chloride, mean plasma concentrations rose slowly over approximately 6 hours following dosing (mean Cmax 4.2 ng/mL) and remained fairly constant over the 24-hour dosing interval, whereas with IR oxybutynin, mean plasma concentrations rose rapidly within the first hour after dosing (mean Cmax 12.0 ng/mL), then declined. The mean oxybutynin degree of fluctuation was much lower for OROS oxybutynin chloride (78%) than for IR oxybutynin (371%). For both formulations, the plasma concentration-time profiles for the metabolite N-desethyloxybutynin paralleled those of oxybutynin but at higher concentrations. Steady-state oxybutynin concentrations were achieved by day 3 for both formulations. Mean area under the concentration-time curve (AUC) values for both oxybutynin and its metabolite were similar between day 1 and day 4 for each treatment, suggesting time-invariant pharmacokinetics. With OROS oxybutynin chloride, mean relative bioavailability was higher (153%) for oxybutynin and lower (69%) for N-desethyloxybutynin compared with IR oxybutynin. This increased bioavailability may be due to reduced first-pass metabolism; within 3 to 5 hours after dosing, OROS systems are thought to reach the colon, where cytochrome P450-mediated oxidation (oxybutynin's primary metabolic pathway) may be less extensive than in the small intestine. Fewer subjects reported any adverse event with OROS oxybutynin chloride than with IR oxybutynin (including dry mouth, oxybutynin's most frequently reported anticholinergic adverse effect).     

Clinical spectrum of the osmotic-controlled release oral delivery system (OROS), an advanced oral delivery form

ABSTRACT

Background: The osmotic-controlled release oral delivery system, OROS, is an advanced drug delivery technology that uses osmotic pressure as the driving force to deliver pharmacotherapy, usually once-daily, in several therapeutic areas.

Objective: The purpose of this review is to discuss the evolution of OROS technology and examine the many therapeutic areas where OROS products are being used.

Methods: A search of Medline and EMBASE were performed using the keywords ‘OROS’ and ‘osmotic delivery’ for the period January 1990 to June 2005. Data were also obtained from the manufacturers’ websites and associated publications.

Results: OROS technology has evolved over the last 30 years, resulting in four systems: the elementary osmotic pump; the two-layer osmotic push–pull tablet; the advanced longitudinally compressed tablet multilayer formulation; and, the L-OROS system. OROS technology is employed for drug delivery in many therapeutic areas including: cardiovascular medicine, endocrinology, urology, and central nervous system (CNS) therapeutics. Two calcium channel blockers utilizing OROS technology for the treatment of hypertension are nifedipine and verapamil. Glipizide extended-release is used for the treatment of type 2 diabetes. Doxazosin is used for the treatment of benign prostatic hyperplasia, and oxybutynin for overactive bladder. Most recent developments are with drugs that affect the CNS, including the use of methylphenidate for treatment of attention deficit hyperactivity disorder, paliperidone extended-release and OROS hydromorphone, which are under clinical development for schizophrenia and chronic pain, respectively.

Conclusions: Drug delivery using the various OROS products can result in an improved safety profile, stable drug concentrations, uniform drug effects, and reduced dosing frequency. OROS technology has also enabled the use of an effective starting dose, without the need for dose titration, which allows the achievement of symptom control much earlier than that observed with immediate-release preparations. Such attributes can enhance patient compliance and convenience, thereby ensuring efficacy and improving patient outcomes.     

Pharmacokinetics and pharmacodynamics of a novel nizatidine controlled-release formulation in healthy subjects

The pharmacokinetics and intragastric pH effects of a novel nizatidine controlled-release (CR) formulation were compared to a currently marketed immediate-release (IR) nizatidine formulation (Axid). The bimodal pulsatile release characteristics of nizatidine CR decreased its Cmax by approximately 42% compared to nizatidine IR while maintaining 90% relative bioavailability; tmax was approximately 1.6 times longer with the CR formulation. These characteristics enabled controlled-release nizatidine to sustain effective plasma drug concentrations for a greater duration than immediate-release nizatidine over the dosing intervals. In multiple doses, the 24-hour AUC ratio for all comparisons of nizatidine CR 150 mg bid, nizatidine CR 300 mg daily, and nizatidine IR 150 mg bid was between 97% and 99%. Mean pH AUC values for nizatidine CR 150 mg bid and nizatidine IR 150 mg bid were similar overall during the 0- to 14-hour and 14- to 24-hour dosing intervals. For the 14- to 24-hour dosing interval, nizatidine CR 150 mg maintained gastric pH over 3.0 and 4.0 for 42% and 27% of the time compared to 39% and 23% for nizatidine IR, respectively. Nizatidine CR 300 mg, compared to the 150-mg CR and IR regimens, had a greater effect on increasing evening intragastric pH, thus providing support for the potential utility of nizatidine CR 300 mg dosed at night in alleviating nocturnal symptoms of gastroesophageal reflux disease.     

The effect of food on the relative bioavailability of rapidly dissolving immediate-release solid oral products containing highly soluble drugs

The purpose of this study is to test the hypothesis that rapidly dissolving immediate-release (IR) solid oral products containing a highly soluble and highly permeable drug [biopharmaceutical classification system (BCS) class I] are bioequivalent under fed conditions. Metoprolol and propranolol (BCS class I) as well as hydrochlorothiazide (BCS class III) were selected as model drugs. The relative bioavailability of two FDA approved (Orange Book AB rating) solid oral dosage forms of metoprolol and propranolol/hydrochlorothiazide (combination tablets) was evaluated in human volunteers under fed conditions using a two-way crossover design. Equal numbers of male and female volunteers were recruited, and racial and/or ethnic minorities were not excluded. The plasma concentrations of metoprolol, propranolol, and hydrochlorothiazide were determined using validated high-performance liquid chromatography (HPLC) methods. Eighteen subjects completed the metoprolol study while 17 subjects completed the propranolol/hydrochlorothiazide combination tablet study. In the metoprolol study, the 90% confidence intervals of Cmax and AUC(inf) were 98-118% and 92-115%, respectively. For propranolol, the 90% confidence intervals of Cmax and AUC(inf) were 91-121% and 89-117%, and for hydrochlorothiazide, the 90% confidence intervals for Cmax and AUC(inf) were 96-107% and 97-106%, respectively. These study results appear to support the hypothesis that rapidly dissolving IR solid oral products containing a BCS class I drug are likely to be bioequivalent under fed conditions. In addition, BCS class III drugs may have the potential to be bioequivalent under fed conditions.     

Pharmacokinetic evaluation of conventional and controlled-release product of naproxen

The bioavailability and pharmacokinetics of a new controlled-release tablet (CRT) of naproxen (750 mg tablet) have been determined, relative to an equivalent dose of conventional product (CT), by a cross-over study in twenty healthy volunteers. The two dosage forms were bioequivalent in terms of total AUC; however, the Cmax of the controlled-release product was lower, and the Tmax longer than that of the conventional product. The mean residence time and the absorption and elimination half-lives of the CRT were also substantially longer than those of the CT. The pharmacokinetic features offered by the novel formulation suggest that it may be suitable for once-daily dosing.     

Bioavailability evaluation of a controlled-release dextromethorphan liquid

A randomized, two-way, steady-state crossover study was performed in 24 healthy male volunteers to evaluate the bioavailability of a controlled-release (CR) dextromethorphan (DM) suspension. Only slow and intermediate DM metabolizers were allowed to participate in the study; determination of metabolizer status was performed before study enrollment. Each volunteer was administered 30 mg of an immediate-release (IR) DM solution qid or 60 mg DM as a CR suspension bid for two weeks, for a total daily dose of 120 mg. After a two-week washout period, the subjects were administered the alternate treatment. Blood samples were collected over a 12-hour dosing period on the last day of each treatment and analyzed for DM and its active metabolite, dextrorphan (DP). In addition, urine was collected over the 12-hour steady-state dosing interval and measured for DM and two metabolites. Pharmacokinetic determinations were made from plasma DM and DP data, and total urinary excretion was determined. All comparisons made between the two formulations indicated that the CR DM suspension was bioequivalent to the IR DM solution at steady state, while producing a prolonged release of the drug over time.     

Pharmacokinetic and pharmacodynamic characterization of OROS® and immediate-release amitriptyline

AIMS: To characterize the pharmacokinetics of amitriptyline and its metabolite nortriptyline following OROS and IR treatments, and to correlate them with anticholinergic side-effects. METHODS: The pharmacokinetics and safety of amitriptyline following administration of an osmotic controlled release tablet (OROS and an immediate release (IR) tablet were evaluated in 14 healthy subjects. In this randomized, open label, three-way crossover feasibility study, the subjects received a single 75 mg OROS tablet, three 25 mg IR tablets administered every 8 h, or 3x25 mg IR tablets administered at nighttime. In each treatment arm serial blood samples were collected for a period of 84 h after dosing. The plasma samples were analysed by gas chromatography for amitriptyline and its metabolite nortriptyline. Anticholinergic effects such as saliva output, visual acuity, and subject-rated drowsiness and dry mouth were measured on a continuous scale during each treatment period. RESULTS: Following dosing with OROS (amitriptyline hydrochloride), the mean maximal plasma amitriptyline concentration Cmax (15.3 ng ml-1 ) was lower and the mean tmax (25.7 h) was longer than that associated with the equivalent IR dose administered at nighttime (26.8 ng ml-1 and 6.3 h, respectively). The bioavailability of amitriptyline following OROS dosing was 95% relative to IR every 8 h dosing, and 89% relative to IR nighttime dosing. The metabolite-to-drug ratios after the three treatment periods were similar, suggesting no change in metabolism between treatments. The relationships between plasma amitriptyline concentration and anticholinergic effects (e.g. reduced saliva weight, dry mouth, and drowsiness) were similar with all three treatments. Of the anticholinergic effects, only decreased saliva weight and dry mouth correlated well with plasma amitriptyline concentrations; drowsiness did not. There was no apparent correlation between anticholinergic effects and the plasma nortriptyline concentration. CONCLUSIONS: The bioavailability of OROS (amitriptyline hydrochloride) was similar to that of the IR treatments and the pharmacokinetics of amitriptyline after OROS dosing may decrease the incidence of anticholinergic effects compared with that seen with nighttime dosing of the IR formulation. Therefore, this controlled-release formulation of amitriptyline may be appropriate for single daily administration.     

Comparative bioavailability and steady state fluctuations of Tegretol commercial and carbamazepine OROS tablets in adult and pediatric epileptic patients.

The comparative bioavailability and steady state fluctuations resulting from the administration of Tegretol 200 mg commercial tablets and carbamazepine OROS controlled delivery tablets were investigated in 22 adult and 12 pediatric epileptic patients. Tegretol commercial tablets were dosed according to previously established clinical regimens of 400 to 2000 mg daily doses divided into four equal or unequal intervals. Carbamazepine OROS was dosed every 12 h at the same corresponding daily dose. Comparisons of the pharmacokinetic parameters AUC, Cmax, Cmin, and tmax at steady state for the two dosage forms demonstrated definitively the bioequivalence of carbamazepine OROS with Tegretol commercial tablet over a 24-h treatment interval.     

Mini-tablets: a contemporary system for oral drug delivery in targeted patient groups

Introduction: Mini-tablets represent a new trend in solid dosage form design, with the main goal of overcoming some therapeutic obstacles such as impaired swallowing and polypharmacy therapy, and also offering some therapeutic benefits such as dose flexibility and combined release patterns. Mini-tablets are a promising patient-friendly drug delivery system.

Areas covered: Mini-tablets are tablets with a diameter ≤ 3 mm produced on conventional tablet presses equipped with multiple tooling. Mini-tablet production is similar to the production of standard tablets but requires excellent powder flow due to the small dies, exact control of process parameters and special caution during tablet press assembly in order to avoid tool damage. Mini-tablets (coated or uncoated and single- or multiple-unit systems) are mainly developed as patient-friendly systems for pediatric and geriatric patients and also for personalized medicine because they offer improved swallowing and flexible dosing, combining various release kinetics, doses and active compounds in only one system. Mini-tablets may also be successfully used as multiple-unit modified release systems (extended release, delayed-colon release, pulsatile and bi-modal release and gastroretentive systems) providing improved drug bioavailability compared with single-unit systems.

Expert opinion: Mini-tablets used as single- or multiple-unit oral dosage forms have enormous potential as a patient-friendly drug delivery system for targeted populations, providing improved swallowing, flexible dosing and a combination of different release patterns and/or different active compounds (decreasing dosing frequency and/or polypharmacy therapy problems). In terms of complete expression of the benefits of mini-tablets over other oral dosage forms on the market, further investigation in formulation possibilities and development of suitable dosing devices is of essential importance.     

Relative bioavailability of a controlled-release albuterol formulation for twice-daily use

A two-way-crossover bioavailability study was completed with 15 healthy male volunteers to evaluate the relative bioavailability of an orally administered controlled-release (CR) formulation of albuterol as compared to the immediate-release (IR) formulation of albuterol. The CR formulation of albuterol used in this study was based mechanistically on the elementary osmotic pump. Each subject received one 8 mg CR tablet every 12 h for 8 consecutive days and one 4 mg IR tablet every 6 h for 8 consecutive days, with 7 days separating each phase. During day 8 of dosing, hourly blood samples (0-12 h) were collected after the morning dose and three additional samples were obtained 16, 20 and 24 h following this dose. Plasma concentrations were measured using a gas chromatography-mass spectrometry procedure. No statistically significant differences were observed in mean steady-state values for Cmax, Cmin, AUC(0-12 h) and peak-to-trough fluctuations (PTF) in comparing the two dosage formulations. Mean steady state Tmax values were 2.6 and 6.0 h for the TR and CR formulations, respectively. It was concluded that twice daily administration of the controlled-release formulation of albuterol provides an alternative to four times daily administration of conventional (immediate-release) albuterol tablets.     

Effects of controlled-release on the pharmacokinetics and absorption characteristics of a compound undergoing intestinal efflux in humans.

OBJECTIVE: The number of active pharmaceutical ingredients (API) undergoing inhibitable and saturable intestinal efflux is considerable. As a consequence, absorption and bioavailability may depend on the intestinal concentration profile of the drug and may vary as a function of dose and release rate of the drug from the dosage form. The impact of controlled versus immediate-release on the absorption of P-glycoprotein substrates is currently unknown. Thus, the main focus of the present study was a comparison of the pharmacokinetics of the P-gp model substrate talinolol following administration of immediate-release (IR) and controlled-release (CR) tablets to healthy human volunteers with a particular focus on the absorption characteristics of the active pharmaceutical ingredients. METHODS: Talinolol immediate-release (Cordanum), 100mg), one controlled-release (100mg) and two controlled-release tablets (200mg) were administered as single doses to fasting healthy volunteers in a crossover design with a 1 week washout period between treatments. Sufficient blood and urine samples were drawn and analysed using a specific HPLC method with UV detection to describe the resulting plasma and urinary excretion versus time profiles. RESULTS: The bioavailability of talinolol in term of AUC(0-->infinity) for IR talinolol was approximately twice as high as compared to the administration of the same dose in a controlled-release dosage form. After administration of talinolol IR tablets, the drug was rapidly absorbed and reached maximum concentrations C(max) of 204.5 ng/ml+/-121.8 (means+/-S.D.) 2h after dosing. The terminal half-life of the drug averaged 19.8h following IR administration in comparison to 32 h under CR dosing conditions. Following administration of the IR dosage form, significant secondary peaks were observed in one healthy subject. Secondary peaks were not clearly apparent in the CR plasma profiles. CONCLUSION: The present study demonstrates a considerable loss of bioavailability of drugs that are substrates of intestinal secretory transporters upon their administration in controlled-release dosage forms.     

Bioequivalence of a novel minitablet formulation of levetiracetam

To investigate whether rapidly dissolving levetiracetam minitablets are bioequivalent to a single tablet of the same strength. 2 bioequivalence studies were carried out investigating the 1?000?mg and 1?500?mg strength of such novel medicinal products relative to single-unit film-coated originator tablets for reference. In each study, 16 young healthy subjects (8 males, 8 females) were investigated according to a 2,2,2-cross-over design with 1 week between periods for washout purposes. Each time, the plasma pharmacokinetics were profiled for 36?h after dosing.There were no relevant differences between the formulations with regard to tmax, apparent terminal half-life and the mean residence time. For the 1?000?mg strength, the estimated ratios of the true treatment means for test to reference were 1.008 (90% CI: 0.897-1.133), 1.010 (90% CI: 0.964-1.057), and 1.012 (90% CI: 0.965-1.062) for Cmax, AUC(0-tz), and AUC(0-∞), respectively; for the 1?500?mg strength, the respective ratio estimates were 0.960 (90% CI: 0.892-1.034), 1.005 (90% CI: 0.971-1.040), and 1.006 (90% CI: 0.970-1.042).Rapidly dissolving levetiracetam minitablets are bioequivalent with the originator single-unit reference tablets. Such alternative medicinal products make it easier and more convenient to individualise treatment of patients with epilepsy eligible to treatment with levetiracetam, particularly at higher doses when single-unit tablets, by being very large are difficult to swallow.     

Bioequivalence assessment of Lovrak (Julphar, UAE) compared with Zovirax (Glaxo Wellcome, UK)--Two brands of Acyclovir--in healthy human volunteers

Two studies were performed to assess the relative bioavailability of Lovrak (Julphar, UAE) compared with Zovirax (Glaxo Wellcome, UK) at the International Pharmaceutical Research Center (IPRC), Amman, Jordan. One study involved acyclovir tablets and the other acyclovir suspension. Each study enrolled 24 volunteers and in both studies, after an overnight fasting, the two brands of acyclovir were administered as a single dose on 2 treatment days separated by 1 week washout period. After dosing, serial blood samples were collected for a period of 16 h. Plasma harvested from blood, was analysed for acyclovir by an HPLC method with UV detection. Various pharmacokinetic parameters including AUC0-t, AUC0-infinity, Cmax, Tmax, T1/2 and Kelm were determined from plasma concentrations for both formulations and found to be in good agreement with the reported values. AUC0-t, AUC(0-proportional to), and Cmax were tested for bioequivalence after log-transformation of data. No significant difference was found based on ANOVA; 90% confidence intervals for the test/reference ratio of these parameters were found within the bioequivalence acceptance range 80%-125%. Based on these statistical inferences it was concluded that a Lovrak tablet is bioequivalent to a Zovirax tablet and that Lovrak suspension is bioequivalent to Zovirax suspension.     

Bioequivalence of Methylphenidate Immediate-Release Tablets Using a Replicated Study Design to Characterize Intrasubject Variability

Purpose. To determine the relative bioavailability of two marketed,immediate-release methylphenidate tablets. The study used a replicatedstudy design to characterize intrasubject variability, and determinebioequivalence using both average and individual bioequivalencecriteria. Methods. A replicated crossover design was employed using 20subjects. Each subject received a single 20 mg dose of the reference tableton two occasions and two doses of the test tablet on two occasions.Blood samples were obtained for 10 hr after dosing, and plasma wasassayed for methylphenidate by GC/MS. Results. The test product was more rapidly dissolved in vitro and morerapidly absorbed in vivo than the reference product. The mean Cmaxand AUC(0 – ) differed by 11% and 9%, respectively. Using anaverage bioequivalence criterion, the 90% confidence limits for theLn-transformed Cmax and AUC(0 – ), comparing the two replicatesof the test to the reference product, fell within the acceptable range of80–125%. Using an individual bioequivalence criterion the test productfailed to demonstrate equivalence in Cmax to the reference product. Conclusions. The test and reference tablets were bioequivalent usingan average bioequivalence criterion. The intrasubject variability of thegeneric product was greater and the subject-by-formulation interactionvariance was borderline high. For these reasons, the test tablets werenot individually bioequivalent to the reference tablets.     

Influence of food on the bioavailability of metoprolol from an OROS system; a study in healthy volunteers

The influence of food intake on the bioavailability of metoprolol from an OROS system has been investigated. No significant difference was found between OROS administration to fasting subjects or after breakfast in any of the kinetic parameters (AUC, Cmax, tmax, C24 and lag time). Therefore, metoprolol OROS can be administered with breakfast.     

Morning versus evening dosing of ibuprofen using conventional and time-controlled release formulations.

Many functions of the human body vary considerably during a day. These variations can lead to changes in drug plasma concentrations. In the study on healthy volunteers described here it was determined whether ibuprofen plasma levels following single oral doses of immediate-release and press-coated time-controlled release tablet formulations depend on time of drug administration (08:00 or 22:00 h). The difference between morning and evening dosing of the immediate-release formulation was minimal. The results with the press-coated formulation were unexpected having regard to results of previous studies on non-steroidal anti-inflammatory analgesics. Time to peak concentration was 6 h after morning administration, 4 h after evening administration. Both the rate and extent of bioavailability of ibuprofen were lower when dosing took place at 08:00 h than when dosing took place at 22:00 h. The influence of food on the pharmacokinetic profile of an evening dose of the press-coated formulation was also studied. When tablets were administered with a meal the ratio C(max)/AUC and t(max) and AUC values indicated that bioavailability was reduced. The main conclusion was that the chronopharmacokinetic behaviour of the press-coated ibuprofen tablet is related to the formulation, not the drug substance as such.