A Randomised Bioequivalence Study On Vigrex In Twelve

Research Article ISSN: 0974-6943

Varaprasad Bobbarala et al. / Journal of Pharmacy Research 2009, 2(11),1751-1753

Available online through www.jpronline.info A Randomised Bioequivalence Study on Vigrex in Twelve Healthy Human Subjects under Fasting Conditions

Somasekhar Penumajji 1, Varaprasad Bobbarala2*, Rajesh Kumar Chadaram2, K. Chandrasekhar Naidu 3 2

1 Vivimed labs Limited, 2nd, 4th Floor, Veeranag towers, Habsiguda, Hyderabad, A.P. For U Biosciences, A/4A, Park lane Residency, East point colony, Visakhapatnam-17, A. P, 3 Department of Botany, Andhra University, Visakhapatnam-530003, A.P. India.

Received on: 20-05-2009; Accepted on:15-07-2009 ABSTRACT VIGREX (Sildenafil Citrate 50mg tablets) is a drug used to treat erectile dysfunction and pulmonary arterial hypertension (PAH). The single dose randomized bioequivalence study was done to compare the pharmacokinetic parameters of VIGREX versus VIAGRA (Sildenafil Citrate 50mg tablets). After the test formulation of VIGREX is found to be bioequivalent with the formulation Reference of VIAGRA. Keywords: VIGREX, VIAGRA, Sildenafil citrate, Cmax and Tmax. INTRODUCTION Vigrex (Sildenafil) is chemically designated as 1-[4-ethoxy-3(6, 7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo [4, 3-d] pyrimidin5-yl) phenylsulfonyl]-4-methylpiperazine. VIGREX is a drug used to treat erectile dysfunction and pulmonary arterial hypertension (PAH)

Figure 1: Structure of Sildenafil It acts by inhibiting cGMP specific phosphodiesterase type 5, an enzyme that regulates blood flow in the penis. Since becoming available in 1998, sildenafil has been the prime treatment for erectile dysfunction. The mechanism of action of Sildenafil citrate involves the release of nitric oxide (NO) in the corpus cavernosum of the penis. NO binds to the receptors of the enzyme guanylate cyclase which results in increased levels of cyclic guanosine monophosphate (cGMP), leading to smooth muscle relaxation (vasodilation) of the intimal cushions of the helicine arteries, resulting in increased inflow of blood and *Corresponding author. Dr. Varaprasad Bobbarala Scientist In-Charge, For U Biosciences/IMMA Labs, A/4A, Park lane Residency, East point colony, Visakhapatnam, A.P-530017, India. Tel.: + 91-9949129539 E-mail: [email protected]

an erection [1]. Sildenafil is a potent and selective inhibitor of cGMP specific phosphodiesterase type 5 (PDE5) which is responsible for degradation of cGMP in the corpus cavernosum. The molecular structure of sildenafil is similar to that of cGMP and acts as a competitive binding agent of PDE5 in the corpus cavernosum, resulting in more cGMP and better erections [1]. Without sexual stimulation, and therefore lack of activation of the NO/cGMP system, sildenafil should not cause an erection. Sildenafil is metabolised by liver enzymes and excreted by both the liver and kidneys. If taken with a high-fat meal, absorption is reduced; the time taken to reach the maximum plasma concentration increases by around one hour, and the maximum concentration itself is decreased by nearly one-third [2]. The primary indication of sildenafil is treatment of erectile dysfunction (inability to sustain a satisfactory erection to complete intercourse). It use is now standard treatment for erectile dysfunction in all settings, including diabetes [3]. People on antidepressants may experience sexual dysfunction, either as a result of their illness or as a result of their treatment. A 2003 study showed that sildenafil improved sexual function in men in this situation [4] Following up to earlier reports from 1999 [5] the same researchers found that sildenafil was able to improve sexual function in female patients on antidepressants as well [6] As well as erectile dysfunction, sildenafil citrate is also effective in the rare disease pulmonary arterial hypertension (PAH). It relaxes the arterial wall, leading to decreased pulmonary arterial resistance and pressure. This in turn reduces the workload of the right ventricle of the heart and improves symptoms of right-sided heart failure. Because PDE-5 is primarily distributed within the arterial wall smooth muscle of the lungs and penis, sildenafil acts selectively in both these areas without inducing vasodilatation in other areas of the body. Pfizer submitted an additional registration for sildenafil to the FDA, and sildenafil was approved for this indication in June 2005. The preparation is named Revatio, to avoid confusion with Viagra,

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Varaprasad Bobbarala et al. / Journal of Pharmacy Research 2009, 2(11),1751-1753 and the 20 milligram tablets are white and round. Sildenafil joins bosentan and prostacyclin-based therapies for this condition [7]. Sildenafil has been shown to be useful for the prevention and treatment of High altitude pulmonary edema associated with altitude sickness such as that suffered by mountain climbers [8][9] While this effect has only recently been discovered, sildenafil is already becoming an accepted treatment for this condition, particularly in situations where the standard treatment of rapid descent has been delayed for some reason [10]. The objective of the single dose randomized bioequivalence study was to compare the pharmacokinetic parameters of VIGREX versus VIAGRA. MATERIALS AND METHODS The Drug controller General of India approved the study to do at Mamata Hospitals and Diagnostics Center for Vivimed Labs Limited. Twelve volunteers participated in a randomized, two treatment, two way, two period, single dose crossover study. To be included in this study, the subjects should be healthy Male volunteers, 21 to 35 years of age and within 15 percent of ideal body weight for their height and build. One week prior to enrolment, a complete physical exam and biochemical screening was performed and history of alcoholism or other drug abuse during the past year. Volunteers were asked to abstain from taking any drug for at least one-week prior and during the study, and to fast for at least 10 hours prior to the study. They were asked to read and sign an informed consent, prior to the study. The study was divided in to two periods where the two commercial trades Vigrex (sildenafil citrate 50mg) which is the test sample and a reference sample Viagra (sildenafil citrate 50mg) were orally taken in a randomized, double-blind, crossover order on each Sunday with a washout period of 28 days. At 8:00 AM, a blood sample was taken and each subject received a single oral dose of either brand with 240 ml of water. Volunteers were remained fasting 2 hours after the administration of the tablet. This was followed by a light breakfast, standardized lunch and dinner 2, 6 and 12 hours after drug administration, respectively. All subjects abstained from smoking and exercise during the day of the study. Blood samples (5ml) were obtained form the cubital and forearm veins through an indwelling heparinized plastic tube, put into coded plain tubes 0.00 (predose), 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 2.00 2.50, 3.00, 4.00, 6.00, 9.00 12.00 and 24.00 post dosing. After the 24 hours sampling the volunteers were released. The withdrawn blood (5 ml) was placed in labelled tubes each according to the volunteers’ Identification Number, time, and drug code. Thereafter, these tubes were sent to the lab, and the plasma was separated by centrifugation (within 30 minutes) at a rate of 5000 rpm for 10 minutes. Plasma separated was stored at -70°C until the assay. The stability of these samples at –70° C is three years. All samples were analyzed in duplicates. The plasma samples were analysed by reverse phase HPLC for the content of Sildenafil Citrate, the pharmacokinetic parameters were computed and subjected to statistical analysis. Sildenafil citrate is extracted by taking 1.0mL of Plasma (containing Sildenafil) or standard or blank in a vial. In blank add 100ul of water. Then vortex the samples to ensure complete mixing of contents. To each vial add about 3.0mL of 2% isoamyl alcohol in hexane and shake for 10minutes

by using extractor. Centrifuge for 15 minutes at 3500rpm. Transfer the organic layer into another vial containing 0.3mL of 0.01N HCl and shake for 10 minutes by using vortex mixer then centrifuge for 10minutes at 3500 rpm. Inject 50µl of acidic layer into chromatograph. The chromatographic pattern has the mobile phase 0.5M KH2PO4 buffer: 0.0114M Diethyl ammonium chloride buffer: Acetonitrile (15:60:25) with C18 column with a UV detection at 230nm. For data analysis the chromatograms were acquired using computer based software supplied by VP series, Japan. The concentration of the unknown is calculated from the regression equation using plasma calibration standard with the reciprocate of the drug concentration as weighing factor (1/concentration). Y=mx+c where, x=peak area ratio with internal standard peak, y=concentration, m=slope of the calibration curve and c=x-axis intercept value. Bioavailability is defined as rate and extent to which the drug reaches from the site of application G.I tract to the site of measurement in the body (plasma). Cmax and Tmax determine the rate at which the drug is absorbed and was directly computed from the mean plasma concentration curve. AUC0-t: Area under the plasma concentration time curve from time 0 to t was obtained by the trapexoidal rule. K el is the elimination rate constant determined by linear regression of the last three sampling points, T1/2 is determined by the formula T 1/2 = 0.693/ Kel. The pharmacokinetic parameters were compared using paired test and analysis of variance. The following analysis was conducted on least square means (LSM) of test and reference products using Win Nonlin Enterprise software version 3.2. Analysis of variance was performed (a=0.05) on the untransformed pharmacokinetic parameters AUC0-t, AUC0-a, Cmax and Tmax . Additionally, log-transformed data was used for analysis of AUC0-t, AUC0-a, and Cmax . The analysis of variance model included sequences; subjects nested within sequence, period and drug formulation as factors. The significance of the sequence effect was tested using the subjects nested within the sequence as the error term. Two-one sided t-test for Bioequivalence, with 90%confidence intervals for difference between drug formulations were calculated for AUC0-t, AUC0-a, and Cmax using both untransformed and log transformed data. Power of ANOVA was calculated to detect as large or greater than 20% of the reference mean. Ratio analysis was reported for untransformed and log transformed AUC0-t, AUC0-a, and Cmax . The geometric mean value was reported for log-transformed data. RESULTS AND DISCUSSION The test formulation showed a Tmax of 0.9797±0.167 as compared to 1.0±0.151 of reference formulation. Thus the test and reference formulations have nearly same mean value. The least square mean ratios for C max , AUC0-t and AUC0-a, are 104.58, 98.97 and 98.83 for untransformed data and 100.60, 100.23 and 100.01 for log-transformed data respectively indicating a comparable bioequivalence of test formulation to the reference formulation. Their 90% confidence intervals are 90.435-119.27, 89.309-115.677 and 87.093-114.69 respectively for untransformed data and 91.244-118.352, 90.411-114.878 and 88.796115.688 respectively for log-transformed data. The 90% confidence intervals are within the bioequivalence acceptance range of 80-120% for the untransformed and 80-125% for the log-transformed data (as per DCGI draft guidelines).

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Varaprasad Bobbarala et al. / Journal of Pharmacy Research 2009, 2(11),1751-1753

Figure 2: Bioequivalence of Sildenafil Citrate The test formulation of VIGREX (Sildenafil citrate 50mg tablets), is bioequivalent with the reference formulation Reference VIAGRA (Sildenafil citrate 50mg tablets). REFERENCES 1.

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Source of support: Nil, Conflict of interest: None Declared

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