Comparative bioavailability studies of citric acid and malonic acid based aspirin effervescent tablets.

PURPOSE: The present investigation is aimed at comparing the pharmacokinetic profile (Bioavailability) of aspirin in tablet formulations, which were prepared by using different effervescent excipients such as citric acid and malonic acid.
MATERIALS AND METHODS: The relative bioavailability and pharmacokinetics of citric acid based aspirin effervescent tablet (Product A) and malonic acid based aspirin effervescent tablet (Product B) formulations were evaluated for an in-vitro dissolution study and in-vivo bioavailability study, in 10 normal healthy rabbits. The study utilized a randomized, crossover design with a one-week washout period between doses. Blood samples were collected at 0, 1, 2, 4, 6, 8, 12 and 24 hours following a 100 mg/kg dose. Plasma samples were assayed by High Performance Liquid Chromatography. T(max), C(max), AUC(0-24), AUC(0- ∞,) MRT, K(a,) and relative bioavailability were estimated using the traditional pharmacokinetic methods and were compared by using the paired t-test. RESULT: In the present study, Products A and B showed their T(max), C(max), AUC(0-24), AUC(0- ∞,) MRT, and K(a) values as 2.5 h, 2589 ± 54.79 ng/ml, 9623 ± 112.87 ng.h/ml, 9586 ± 126.22 ng.h/ml, 3.6 ± 0.10 h, and 0.3698 ± 0.003 h (-1) for Product A and 3.0 h, 2054 ± 55.79 ng/ml, 9637 ± 132.87 ng.h/ml, 9870 ± 129.22 ng.h/ml, 4.76 ± 0.10 h, and 0.3812 ± 0.002 h (-1) for Product B, respectively.
CONCLUSION: The results of the paired t-test of pharmacokinetics data showed that there was no significant difference between Products A and B. From both the in vitro dissolution studies and in vivo bioavailability studies it was concluded that products A and B had similar bioavailability.

RCT Entities:   Population Interventions Outcomes

Effervescent tablets are uncoated tablets that generally contain acid substances and carbonates or bicarbonates, and react rapidly in the presence of water by releasing carbon dioxide. They are intended to be dissolved or dispersed in water before use. It generally contains, in addition to active ingredients, a mixture of acids / acid salts (citric acid, tartaric acid, malonic acid or any other suitable acid or acid anhydride), and carbonate and hydrogen carbonates (sodium, potassium or any other suitable alkali metal carbonate or hydrogen carbonate), which release CO2 when mixed with water. The advantage of the effervescent tablets as a dosage form is that it provides a means of extemporaneously preparing a solution containing an accurate drug dose.[1]

Aspirin[2] is a new generation non-steroidal anti-inflammatory agent, which is widely used as an analgesic. As its major adverse drug reactions are peptic ulcer and gastrointestinal bleeding,[34] and its biological half-life is equal to 30 minutes,[5] effervescent tablets could be preferred over the conventional tablets of aspirin because conventional tablets have many side effects. Therefore, aspirin is considered for effervescent drug release. The aim of the present study is to prepare and compare the bioavailability of citric acid based effervescent tablet with the malonic-acid based effervescent tablet.

Materials and Methods

Aspirin, the internal standard was generously donated by Ranbaxy Pvt. Ltd. All other chemical and solvents were of analytical grade and were supplied by Ranbaxy, Fine Chemicals (New Delhi, India). The formulation that was based on citric acid was coded as Product A and the formulation based on malonic acid was coded as Product B.

Preparation of citric acid and malonic acid based aspirin effervescent tablets 450 mg:

All the raw materials were weighed accurately with the help of an electronic balance (CITIZEN SCALE (I) PVT.LTD. Mumbai, Maharashtra, India) and then compressed directly in the tablet punching machine. The tablets were prepared by the direct compression method.

Characterization of the effervescent tablets

The prepared effervescent tablets were characterized for weight variation, friability test, hardness test, disintegration test, effervescence time, and in vitro release studies. The weight variation test was conducted on 20 tablets. The friability was checked using the friabilator. The hardness of the tablets was measured using the Monsanto as well as the Pfizer hardness tester. The disintegration test was performed in the disintegrating apparatus.

In vitro release and ageing studies[6]

In vitro drug release profiles for Products A and B were carried out using an USP XXI dissolution apparatus type II. Dissolution studies were carried out on the formulation containing citric acid as an effervescent excipient and compared with malonic acid as an effervescent excipient, in 900 ml dissolution medium (pH 7.2 phosphate buffer). The dissolution media was maintained at 37° ± 0.5° and stirred at 50 rpm. Drug releases from the formulations were determined by withdrawing 5 ml of sample using a guarded pipette. Samples were taken at 0, 5, 10, 15, 20, 25, and 30 minutes and replaced by fresh medium. Release studieswere carried out in triplicate. The drug release from Products A and B was calculated using the standard drug release equations, and then compared with each other.

The effect of aging on drug release studies were carried out on Products A and B, which were stored in a dessicator at 25° and 11% relative humidity, for a period of eight weeks. Each product (100 mg) was taken out on the first, second, fourth, and eighth week and subjected to in vitro drug release studies. The release studies were carried out in triplicate.

In vivo studies[7]

Approval to carry out pharmacokinetic studies was obtained from the Institutional Animal Ethics Committee of Noida, Institute of Engineering and Technology, Greater Noida. Ten healthy adult rabbits were included in this study. The age of the rabbits was in the range of five to six years and their body weight ranged between 1.8-2.0 kg. Based on medical history, examination, and laboratory investigation, none of the subjects had any medical abnormality. Provisions were made to record all the observed signs and symptoms occurring during the study period.

Study design[8]

The study was conducted as an open, randomized complete crossover design, wherein a single 100 mg dose of each product (A and B) was administered to fasted, healthy adult rabbits on two different occasions, separated by a washout period of one week between dosing interval.

Blood sampling[9]

All the animals were reported to the pre-clinical trial laboratory from the animal house at 7.00 a.m., after overnight fasting of 10 hours. Then an 18 gauge cannula was inserted in ear vein and retained there with a heparinized saline lock for ensuing 24 hour blood sampling. Test medication Products A and B were administered to the subjects with 100 ml of water. Light food was provided after one hour followed by two standard meals two and eight hours following administration of the drug. Blood samples of 2 ml each were collected at zero hour (pre-dose) and 0, 1, 2, 4, 6,812 and 24 hours post dose intervals. The samples were centrifuged at 1500 rpm for 10 minutes; the plasma was separated and stored at -20° prior to analysis. Plasma concentrations of the drug from all the formulations were quantified by a modified HPLC method.

Statistical data analysis[10]

The pharmacokinetic parameters were calculated using the WinNonlin and Kinetica 4.4 software. The drug plasma concentration and pharmacokinetic parameters were subjected to paired t-test and analysis of variance at 95% confidence limit.

Results and Discussion

From the release studies, it was observed that drug release from Products A and B at intestinal pH was found to be 94.80 and 99.41%, respectively. The cumulative percent drug release after aging from Products A and B was within the range (94%), and no significant change in the in vitro drug release was noticed after eight weeks of aging. The mean plasma concentration time profiles and comparative mean pharmacokinetic parameters of aspirin, following the administration of the two Products (A and B), are shown in Figure 1 and Table 1.

Figure 1

Plasma concentration for product A and product B

Table 1

Mean pharmacokinetic parameters (± SD, n = 6) of product A and product B

After oral administration, the highest mean C max value was observed for Product A (2586 ± 54.79 ng/ml) compared to Product B (2054 ± 55.79 ng/ml. However, the difference in the C max values recorded for both products was statistically insignificant. Comparison of the mean concentration time curve of Product A with that of Product B, indicated that Product B was associated with a significantly lower peak plasma concentration than that of Product A. The time taken to reach peak plasma concentration Tmax was 2.5 and 3 hours for Products A and B, respectively. The Tmax of Aspirin was a little higher in case of Product B, but no statistical significant difference was found between the two products. The mean Ka for Products A and B were found to be 0.3698 ± 0.003 h-1 and 0.3812 ± 0.002 h-1, respectively, and the difference between the two products was insignificant.

However, a small difference between both products is related to C max, T max, and reduced fluctuations (peak to trough ratios) of the plasma concentrations. All these effects may probably be due to the dissolution rate limited drug release and hence absorption. From the present study it can be observed that reduced fluctuations combined with elevated mean plasma concentration in both the products, offers the advantage of protecting patients against morning stiffness.

Mean residence time (MRT) of Products A and B was found to be 3.6 ± 0.10 h and 4.76 ± 0.10 h, respectively. The difference in mean values of MRT in both the formulations was statistically insignificant.

The mean AUC0-24 values for Products A and B were 9623 ± 112.87 ng h/ml and 9637 ± 129.22 ng h/ml. The results of the statistical analysis indicated that Product B exhibited a smaller and non-significant reduction in the AUC values. It was observed that the slow release of IM from Products A and B could be responsible for the decreased AUC values when compared to the reported conventional dosage forms. The observed mean AUC o-oo values for Products A and B were 9870 ± 129.22 ng h/ml and 8617 ± 46.88 ng h/ml, which did not show any significant statistical difference between the products. The individual and mean AUC 0-24 ratios (B/A), reflected the relative extent of absorption of Product B to that of Product A, which is presented in Table 2. The average values of the individual and mean AUC 0-24 ratios at 95% confidence limit were within acceptable limits for bioequivalent products.

Table 2

Relative bioavailability (AUC ratio) of product A and product B

On the basis of the FDA recommendation, the two Products A and B can be considered bioequivalent. No untoward effects were observed by any of the subjects after the administration of either product. Thus, the two formulations can be considered similar, because all the subjects tolerated them very well. The present study concludes that Products A and B have the same bioavailability.