Bioequivalence study of paracetamol tablets: in vitro-in vivo correlation

In-vitro and in-vivo performance of locally manufactured glimepiride tablet generics compared to the innovator (Amaryl®) tablets

Both physicians and patients in Egypt often express concern as to the clinical efficacy of locally manufactured glimepiride tablet generics whenever adequate control of blood sugar is not achieved with these products. The present study addresses this issue. The pharmaceutical quality of four glimepiride 3 mg tablet generics purchased in Egypt from local pharmacies was assessed relative to the innovator product (Amaryl^®), 3 mg tablets. Uniformity of Content, dissolution rate, disintegration time and hardness were determined. Products were subjected to a 6-month stability study under stress condition (40 °c/75%RH). The same brands were evaluated in vivo in a clinical study conducted in the Main Alexandria University Hospital involving 100 patients (20 patients per brand including innovator). Patients recruited were newly diagnosed type II diabetics. Glimepiride tablets were used as a monotherapy. Fasting blood glucose (FBG) and glycosylated hemoglobin (HbA1C) were measured over a period of 3 months. The results indicated differences (p ≤ .05) in the in vitro and in vivo performance of the tested products; innovator and tested generics substitution was not evident. The stability study indicated that the tablets were prone to deterioration in their physical characteristics, particularly dissolution profiles, upon storage of blisters in a hot humid climate. In vitro/in vivo correlations were investigated seeking to identify an in vitro test to serve as a performance indicator for glimepiride tablets in the post-marketing period. The similarity factor (f₂) of the dissolution data proved to be a good indicator of in vivo performance of the tablets.

Bioequivalence Evaluation of Two Oral Formulations of Acetaminophen in Healthy Subjects: Results From a Randomized, Single-Blind, Crossover Study

Despite widespread availability of acetaminophen in Mexico, data on its pharmacokinetic properties in Mexican populations are limited. This single‐center, single‐blind, randomized, 2‐period, 2‐treatment, crossover, single‐dose‐per‐period, 2‐sequence study evaluated the bioequivalence of a test acetaminophen product available in Mexico compared with a reference 500‐mg acetaminophen product in 28 healthy adults under fasting conditions. Blood samples were collected predose and at specified intervals across a 16‐hour period following administration and were analyzed for acetaminophen using a validated reverse‐phase high‐performance liquid chromatography method. Drug products were considered to be bioequivalent if confidence intervals of natural log‐transformed C_max, AUC_0‐t, and AUC_0‐∞ data were within the range of 80% to 125%. Results were inconclusive for C_max due to high levels of intrasubject variability with this parameter. However, criteria for bioequivalence were met for AUC_0‐t and AUC_0‐∞. All measured acetaminophen concentrations in this study were within a safe therapeutic range, and no adverse events were reported. The level of C_max intrasubject variability observed in this study does not have any apparent clinical implications that could affect either safety or efficacy.

“Insight” into Drug Quality: Comparison of Simvastatin Tablets from the US and Canada Obtained via the Internet

Background:

Recently, there has been much debate in the US concerning drug importation from Canadian Internet pharmacies. The Food and Drug Administration and US drug manufacturers assert that drugs obtained from international markets via the Internet present a health risk to consumers from substandard products. The public's perception is that drugs from Canada are as safe as those from the US.

Objective:

To determine whether simvastatin tablets obtained via the Internet from Canadian generic manufacturers are comparable in blend uniformity, a major attribute of tablet quality, with the US innovator product.

Methods:

Generic simvastatin tablets from 4 Canadian Internet pharmacy Web sites and the US innovator product were obtained for pharmaceutical analysis, Tablet samples were analyzed using near-infrared spectroscopic imaging techniques, which are designed to detect formulation defects of drug products during the manufacturing process. Digital images were created, revealing the tablets’ internal structures.

Results:

The blend uniformity of the active pharmaceutical ingredient in the tablet samples from Canada was determined and compared with that of the US innovator product. Results indicated that there is little significant difference in blend uniformity among US innovator and Canadian generic tablets.

Conclusions:

Results of this study suggest comparable quality assurance manufacturing standards for the US innovator product and the Canadian generic drug products tested. These findings have clinical, legal, and economic implications that should be addressed by policy makers to safeguard consumers who choose to purchase Canadian-manufactured drugs via the Internet.

Biowaiver monographs for immediate release solid oral dosage forms: Acetaminophen (paracetamol)

Literature data are reviewed on the properties of acetaminophen (paracetamol) related to the biopharmaceutics classification system (BCS). According to the current BCS criteria, acetaminophen is BCS Class III compound. Differences in composition seldom, if ever, have an effect on the extent of absorption. However, some studies show differences in rate of absorption between brands and formulations. In particular, sodium bicarbonate, present in some drug products, was reported to give an increase in the rate of absorption, probably caused by an effect on gastric emptying. In view of Marketing Authorizations (MAs) given in a number of countries to acetaminophen drug products with rapid onset of action, it is concluded that differences in rate of absorption were considered therapeutically not relevant by the Health Authorities. Moreover, in view of its therapeutic use, its wide therapeutic index and its uncomplicated pharmacokinetic properties, in vitro dissolution data collected according to the relevant Guidances can be safely used for declaring bioequivalence (BE) of two acetaminophen formulations. Therefore, accepting a biowaiver for immediate release (IR) acetaminophen solid oral drug products is considered scientifically justified, if the test product contains only those excipients reported in this paper in their usual amounts and the test product is rapidly dissolving, as well as the test product fulfils the criterion of similarity of dissolution profiles to the reference product.

Biopharmaceutical characterization of sustained release matrix tablets based on novel carbomer polymers: formulation and in vivo investigation

With the increased interest in modified release dosage forms and drug delivery systems, there is an increasing concern for biopharmaceutical characterization of the formulation in the early stages of drug product development. The main objectives of biopharmaceutical characterization are the in vitro and in vivo evaluation of the selected formulations in order to identify the factors influencing drug release; define the in vitro test methodology that would be predictive of drug products in vivo behavior and develop quantitative in vitro - in vivo correlation. The purpose of this study was to assess the potential of novel carbomer polymers, Carbopol 971P and Carbopol 71G, as a sustained release agents in matrix tablets containing high dosage drug substance. Although chemically identical, the two polymers exhibited substantially different drug release properties in vitro. Hypothetical in vivo drug release profiles were calculated by numerical deconvolution from cumulative urinary excretion data observed in vivo. The obtained results indicated that sound and reliable in vivo drug release profiles could be obtained from urinary excretion data and also, emphasized the need for in vitro testing under a range of experimental conditions in order to develop the biorelevant drug release methodology.

Development of the second-order derivative UV spectrophotometric method for direct determination of paracetamol in urine intended for biopharmaceutical characterisation of drug products

Paracetamol is a widely used nonsalicylate analgesic and antipyretic drug. The existing methods for the determination of paracetamol in biological fluids are mainly HPLC techniques, although there are some reported methods based on spectrophotometric determinations. However, all these methods involve some extraction or derivatisation procedures. In the present study the UV spectra of investigated samples were recorded over the wavelength range 220-400 nm (lambda step 0.21 nm; scan speed 60 nm/min) and second-order derivative spectra were calculated. Second-order derivative spectra of different blank urine samples displayed the presence of a zero-crossing point at 245-247 nm defined as lambdazc. The zero-order absorption spectra of paracetamol in water displays maximum absorbance at 243 nm, while in second derivative spectra, a minimum peak at 246 nm was observed. Therefore, the application of zero-crossing technique to the second-derivative UV absorption spectrum should be useful for the determination of paracetamol using 2Dlambdazc. The proposed method enables determination of total paracetamol in urine directly and simply by reading the 2Dlambdazc of the diluted samples. The obtained results were in good accordance with published data on cumulative urinary excretion after per oral administration of paracetamol obtained applying different spectrophotometric methods of determination. It could be useful for biopharmaceutical characterisation of drug products (monitoring of the levels of paracetamol in urine in bioavailability testing, for the evaluation of in vitro-in vivo correlation and screening of different formulations during drug product development).

Determination of bioequivalence of lomefloxacin tablets using urinary excretion data

The present study describes development of a sensitive and simple HPTLC method for estimation of lomefloxacin (LMF) in human urine. The drug was extracted using chloroform after adjusting the pH of urine to 7.0. Chloroform extract was spotted on silica gel 60 F(254) TLC plate and was developed in a mixture of n-butanol-methanol-ethyl acetate-6 M ammonia (4:2:3:2, v/v/v/v) as the mobile phase and scanned at 290 nm. The peak for LMF resolved at R(F) of 0.40+/-0.02. The method was validated in terms of linearity (50-600 microgram/ml), precision, specificity and accuracy. The limit of detection and limit of quantification for LMF in urine were found to be 20 and 50 microgram/ml, respectively. The average recovery of LMF from urine was 91.93%. The proposed method was applied to generate urinary excretion data for LMF after administration of two market LMF tablet formulations (400 mg, Formulation R and Formulation T) to six healthy human volunteers in a two-treatment, open, crossover design. Various pharmacokinetic parameters like peak excretion rate ((dAU/dt)(max)), time for peak excretion rate (t(max)), AUC(0-48), AUC(0- infinity ), cumulative amount and % cumulative amount of LMF excreted, elimination half-life (t(1/2)), terminal elimination rate constant (k(el)) and overall elimination rate constant (K), were calculated for both the formulations. The average cumulative amounts of LMF excreted in urine after administration of Formulation R and Formulation T were found to be 321.60 mg (80.40% of dose) and 296.51 mg (74.13% of dose), respectively. The urinary excretion profiles of LMF upto 48 h for both the formulations were found to be similar. Statistical comparison (90% confidence intervals of ratio) of various pharmacokinetic parameters of Formulation T with that of Formulation R revealed that Formulation T is bioequivalent with Formulation R.

A new rapidly absorbed paracetamol tablet containing sodium bicarbonate. II. Dissolution studies and in vitro/in vivo correlation

The objective of this study was to compare the in vitro dissolution profile of a new rapidly absorbed paracetamol tablet containing sodium bicarbonate (PS) with that of a conventional paracetamol tablet (P), and to relate these by deconvolution and mapping to in vivo release. The dissolution methods used include the standard procedure described in the USP monograph for paracetamol tablets, employing buffer at pH 5.8 or 0.05 M HCl at stirrer speeds between 10 and 50 rpm. The mapping process was developed and implemented in Microsoft Excel worksheets that iteratively calculated the optimal values of scale and shape factors which linked in vivo time to in vitro time. The in vitro-in vivo correlation (IVIVC) was carried out simultaneously for both formulations to produce common mapping factors. The USP method, using buffer at pH 5.8, demonstrated no difference between the two products. However, using an acidic medium the rate of dissolution of P but not of PS decreased with decreasing stirrer speed. A significant correlation (r = 0.773; p < .00001) was established between in vivo release and in vitro dissolution using the profiles obtained with 0.05 M HCl and a stirrer speed of 30 rpm. The scale factor for optimal simultaneous IVIVC in the fasting state was 2.54 and the shape factor was 0.16; corresponding values for mapping in the fed state were 3.37 and 0.13 (implying a larger in vitro-in vivo time difference but reduced shape difference in the fed state). The current IVIVC explains, in part, the observed in vivo variability of the two products. The approach to mapping may also be extended to different batches of these products, to predict the impact of any changes of in vitro dissolution on in vivo release and plasma drug concentration-time profiles.

Impaired bioavailability of rifampicin in presence of isoniazid from fixed dose combination (FDC) formulation

The present study describes comparative bioavailability of rifampicin (RIF) after administration of a single component RIF (450 mg) capsule and rifampicin-isoniazid (RIF-INH) (450+300 mg) fixed dose combination (FDC) capsule formulations. Six healthy male volunteers participated in a single dose, two treatment, two period, cross-over study. A sensitive, specific and accurate HPTLC method was developed, validated and employed for estimation of RIF and its major active metabolite, 25-Desacetylrifampicin (25-DAR) levels, in urine. Using the urinary excretion data various pharmacokinetic parameters: AUC(0-24), AUC(0-infinity), cumulative amount excreted in 24 h, peak excretion rate, etc. for both RIF and 25-DAR were calculated and compared statistically (ANOVA, 90% confidence interval for ratio). Significant decrease in the bioavailability ( approximately 32% as RIF and approximately 28% as 25-DAR) of RIF from FDC capsules was observed. The present bioavailability study confirms our serious doubts about the stability of RIF in presence of INH in acidic environment of stomach, which probably is the main factor responsible for the reduced bioavailability of RIF from RIF-INH combination formulations. This study underlines the fact that there is an urgent need to reconsider the formulation of the FDC product in order to minimize or avoid the decomposition of RIF in gastrointestinal tract.