An Investigation into the Influence of Experimental Conditions on In Vitro Drug Release from Immediate-Release Tablets of Levothyroxine Sodium and Its Relation to Oral Bioavailability

The aim of this study was to investigate the influence of experimental conditions on levothyroxine sodium release from two immediate-release tablet formulations which narrowly passed the standard requirements for bioequivalence studies. The in vivo study was conducted as randomised, single-dose, two-way cross-over pharmacokinetic study in 24 healthy subjects. The in vitro study was performed using various dissolution media, and obtained dissolution profiles were compared using the similarity factor value. Drug solubility in different media was also determined. The in vivo results showed narrowly passing bioequivalence. Considering that levothyroxine sodium is classified as Class III drug according to the Biopharmaceutics Classification System, drug bioavailability will be less sensitive to the variation in its dissolution characteristics and it can be assumed that the differences observed in vitro in some of investigated media probably do not have significant influence on the absorption process, as long as rapid and complete dissolution exists. The study results indicate that the current regulatory criteria for the value of similarity factor in comparative dissolution testing, as well as request for very rapid dissolution (more than 85% of drug dissolved in 15 min), are very restricted for immediate-release dosage forms containing highly soluble drug substance and need further investigation. The obtained results also add to the existing debate on the appropriateness of the current bioequivalence standards for levothyroxine sodium products

In vitro/in silico ispitivanje lekovite supstance i tableta telmisartana

Telmisartan acts as antagonist of angiotensin II type-1 (AT1) receptor and is indicated in the treatment of essential hypertension. In order to rationalize the pharmacokinetic characteristics, pharmacological activity, as well as the optimal method of administration of this drug, knowledge of its physico-chemical properties is needed. The assessment of the drug physico-chemical parameters on the basis of its chemical structure at different pH values, which are characteristic for physiological conditions, enables the prediction of its behaviour in the body before the drug is synthesized. Such assessment of its physico-chemical parameters during the preformulation phase is important for the development of a safe, efficient and stable dosage form. Based on the calculated pKa values, this paper is focused on the prediction of distribution of the ionized and nonionized drug species in the pH gradient of 1 to 8 and the calculation of physico-chemical parameters such as telmisartan lipophilicity (log P) and intrinsic solubility (log S0). On the basis of the calculated physicochemical parameters, the pH-dependent solubility and lipophilicity curves of this medicinal substance have been constructed. The assessment of intrinsic dissolution rate and dissolution rate of telmisartan from tablets was used to investigate the influence of medium pH values applied on the model substance behavior. The results obtained from predicting the physico-chemical properties and from experimental evaluation of the model substance intrinsic dissolution rate and telmisartan dissolution rate from tablets, indicate the importance of physico-chemical characterization of the active substance during the preformulation investigation for predicting the drug behaviour in the body (absorption, bioavailability, tissue penetration, elimination). .Telmisartan deluje kao antagonista angiotenzinskog II tipa-1 (AT1) receptora i indikovan je u terapiji esencijalne hipertenzije. Da bi se razjasnile farmakokinetičke osobine, farmakološka aktivnost, kao i optimalni način primene ove lekovite supstance, potrebno je poznavanje njenih fizičko-hemijskih osobina. Određivanje fizičko-hemijskih parametara lekovite supstance na osnovu hemijske strukture pri različitim pH vrednostima koje su karakteristične za fiziološke uslove omogućava predviđanje njenog ponašanja u organizmu pre nego što se lekovita supstanca sintetiše. Određivanje fizičko-hemijskih parametara u toku preformulacionih ispitivanja značajno je za razvijanje bezbednog, efikasnog i stabilnog farmaceutskog oblika. U ovom radu je, na osnovu izračunatih pKa vrednosti, izvršeno predviđanje raspodele jonizovanih i nejonizivanog oblika lekovite supstance u pH gradijentu od 1 do 8 i izračunavanje fizičko-hemijskih parametara telmisartana kao što su lipofilnost (log P) i osnovna rastvorljivost (log S0). Na osnovu izračunatih fizičko-hemijskih parametara konstruisane su krive pH-zavisne rastvorljivosti i lipofilnosti ove lekovite supstance. Određivanjem osnovnih brzina rastvaranja i brzina rastvaranja telmisartana iz tableta ispitan je uticaj pH vrednosti primenjenog medijuma na ponašanje model supstance. Rezultati dobijeni predviđanjem fizičko-hemijskih osobina, kao i eksperimentalnim određivanjem osnovne brzine rastvaranja model supstance i brzine rastvaranja telmisartana iz tableta ukazuju na značaj fizičko-hemijske karakterizacije aktivne supstance tokom preformulacionih ispitivanja za predviđanje njenog ponašanja u organizmu (resorpcije, biološke raspoloživosti, penetracije u tkiva, eliminacije)

Predviđanje resorpcije i farmakokinetičkog profila karbamazepina iz tableta sa kontrolisanim oslobađanjem kod ljudi korišćenjem modela kunića

Controlled-release (CR) pharmaceutical formulations offer several advantages over the conventional, immediate release dosage forms of the same drug, including reduced dosing frequency, decreased incidence and/or intensity of adverse effects, greater selectivity of pharmacological activity, reduced drug plasma fluctuation, and better compliance. After a drug product has been registered, and is already on market, minor changes in formulation might be needed. At the same time, the product has to remain effective and safe for patients that could be confirmed via plasma drug concentrations and pharmacokinetic characteristics. It is challenging to predict human absorption and pharmacokinetic characteristics of a drug based on the in vitro dissolution test and the animal pharmacokinetic data. Therefore, the objective of this study was to establish correlation of the pharmacokinetic parameters of carbamazepine (CBZ) CR tablet formulation between the rabbit and the human model, and to establish in vitro in vivo correlation (IVIVC) based on the predicted fractions of absorbed CBZ. Although differences in mean plasma concentration profiles were notified, the data concerning the predicted fraction of drug absorbed were almost superimposable. Accordingly, it can be concluded that rabbits may be representative as an in vivo model for predicting the pharmacokinetics of the CR formulation of CBZ in humans.Farmaceutske formulacije sa kontrolisanim oslobađanjem imaju nekoliko prednosti u odnosu na konvencionalne dozirane oblike sa trenutnim oslobađanjem iste lekovite supstance. To se pre svega ogleda u redukovanoj učestalosti doziranja, smanjenoj pojavi i/ili intenzitetu neželjenih efekata, većoj farmakološkoj selektivnosti, redukovanoj fluktuaciji lekovite supstance u plazmi i boljoj podnošljivosti. Kada se posle završene registracije preparat nađe na tržištu, može se javiti potreba za manjim izmenama u formulaciji. U isto vreme on treba da ostane efikasan i bezbedan za pacijente, što može biti potvrđeno na osnovu koncentracije lekovite supstance u plazmi i farmakokinetičkih podataka. Poseban izazov predstavlja predviđanje resorpcije i farmakokinetičkih osobina lekovite supstance kod ljudi na osnovu određivanja in vitro brzine rastvaranja i farmakokinetičkih podataka dobijenih ispitivanjem na životinjskom modelu. Zbog toga je cilj ovog ispitivanja bio da se uspostavi korelacija farmakokinetičkih parametara između modela kunića i humanog modela za formulacije tableta sa kontrolisanim oslobađanjem karbamazepina (KBZ) kao i in vitro in vivo korelacija zasnovana na predviđenoj frakciji resorbovanog leka. I pored uočenih razlika u srednjim profilima plazma koncentracija, rezultati koji se odnose na predviđenu frakciju resorbovane lekovite supstance bili su gotovo identični. Na osnovu toga se može zaključiti da se kunić može koristiti kao reprezentativan in vivo model za predviđanje farmakokinetičkih karakteristika formulacije sa kontrolisanim oslobađanjem KBZ kod ljudi

Uporedno ispitivanje brzine rastvaranja metformin-hidrohlorida iz tableta različitih proizvođača

With the introduction of Biopharmaceutics Classification System (BCS) and 'biowaiver' concept, there is an increased interest in the extension of biowaiver criteria to highly soluble/low permeable drugs (i.e. BCS class 3 drugs). In order to justify the exemption from in vivo studies, a discriminating in vitro dissolution method should be established. The aim of this study was to evaluate the effects of the type of apparatus, agitation intensity and pH value on metformin hydrochloride release from commercially available immediate release tablets. The tablets were also assayed for their disintegration time. The results obtained revealed that the drug release rate was considerably influenced by the agitation intensity. The fastest dissolution rates were observed in the basket apparatus while the slowest drug release from all the investigated products was obtained in the mini paddle apparatus. Significant differences were observed between the dissolution profiles of the investigated products nevertheless of the experimental conditions applied. The results obtained showed that there is a connection between tablet disintegration times and dissolution rates. The results obtained indicate that current similarity factor criteria might be too conservative, as well as the recommended request for very rapid dissolution in the biowaiver application for highly soluble drugs and merits further consideration.Prihvatanje Biofarmaceutskog sistema klasifikacije (BSK) i 'biowaiver' koncepta od strane regulatornih agencija, doveo je do povećanog interesa za mogućnost njihove primene u slučaju visoko rastvorljivih/nisko permeabilnih lekova (koji pripadaju BSK grupi 3). Da bi se opravdao zahtev za izostavljanje in vivo ispitivanja, potrebno je razviti diskriminatoran metod za in vitro ispitivanje brzine rastvaranja. Cilj ovog rada bio je da se ispita uticaj vrste aparature, intenziteta mešanja i pH vrednosti medijuma na brzinu rastvaranja metformin-hidrohlorida iz tableta različitih proizvođača. Takođe je ispitana i raspadljivost tableta. Rezultati ispitivanja su pokazali da intenzitet mešanja u znatnoj meri utiče na brzinu rastvaranja metformin-hidrohlorida iz tableta. Najbrže rastvaranje postignuto je u aparaturi sa korpicom, pri 100 rpm, dok je rastvaranje metformin-hidrohlorida bilo najsporije u aparaturi tipa mini lopatice, pri 50 rpm. Uočene su značajne razlike između ispitivanih preparata bez obzira na primenjene eksperimentalne uslove. Rezultati ispitivanja brzine rastvaranja bili su u korelaciji sa raspadljivošću tableta. Dobijeni rezultati ukazuju da je postojeći kriterijum prihvatljivosti za vrednost faktora sličnosti pri uporednom ispitivanju brzine rastvaranja, kao i zahtev za 'veoma brzo rastvaranje' s ciljem izostavljanja in vivo ispitivanja u slučaju visoko rastvorljivih lekovitih supstanci veoma strog i zaslužuje da bude dodatno razmotren

Biopharmaceutical characterization of carbamazepine immediate release tablets - In vitro-in vivo comparison

A growing concern for the biopharmaceutical characterization of pharmaceutical products increased the interest in the evaluation and identification of physicochemical properties of drugs and dosage forms that govern its biological performance. In vitro and in vivo characteristics of two carbamazepine (CAS 298-46-4) immediate release tablets were investigated and compared in order to establish level A in vitro-in vivo correlation. An in vivo study was conducted as a controlled, two-way, complete cross-over, single dose, pharmacokinetic trial in 18 subjects. The in vitro study was performed using various dissolution media in order to evaluate their potential influence on drug release and distinguish the set of experimental conditions relevant to the in vivo behavior of the investigated drug products. Beside significant differences among in vitro release profiles, the in vivo data indicated bioequivalence of the two formulations. Although a high level of correlation between in vivo and in vitro data was observed in some media, there was no single in vitro-in vivo correlation model applicable products. The obtained results add to the existing debate on the rationale for the use of surfactants in drug release media and their in vivo relevance, emphasizing the importance of in vitro dissolution testing in addition to in vivo bioequivalence testing

An in vitro - in silico - in vivo approach in biopharmaceutical drug characterization: metformin hydrochloride IR tablets

The integrated in vitro - in silico - in vivo approach has emerged into a biopharmaceutical toolkit that could accelerate drug development and improve drug product clinical performance in patients. In the present study, the influence of physiologically based media and dynamic dissolution testing on drug release from two metformin hydrochloride immediate release products with proven bioequivalence was tested. Metformin-specific physiologically based pharmacokinetic (PBPK) model was developed based on a range of literature or in silico predicted data using gastrointestinal simulation technology implemented in the Simcyp (R) software package. Various approaches were employed in order to estimate the human effective permeability which was used as input for metformin plasma profile simulation. Influence of the rate and extent of metformin dissolution on drug absorption was evaluated. Both convolution and deconvolution approaches were used in order to establish a correlation between the in vitro and in vivo data. The results obtained indicate that physiologically based dissolution media and glass bead dissolution device exhibit certain advantages over the compendial dissolution apparatus and simple buffers which tended to be over-discriminative. Gastrointestinal simulation technology implemented in the Simcyp (R) Simulator was successfully used in developing drug-specific PBPK model for metformin. Simulations indicate that in vitro dissolution kinetics has no significant effect on metformin absorption, if more than 65% of drug is released in 1 hour. Level A in vitro-in vivo correlation was obtained using both convolution and deconvolution approaches

Justification of metformin hydrochloride biowaiver criteria based on bioequivalence study

The Biopharmaceutics Classification System (BCS) represents the framework for predicting the intestinal drug absorption based on its solubility and intestinal permeability. Recent research has lead to the use of in vitro tests to waive additional in vivo bioequivalence studies for some pharmaceutical products (i.e. biowaiver). The current regulations permit waivers for BCS Class I (highly soluble/highly permeable) drug substances, which represent up to 25% of the drugs. Efforts in both the science and regulatory bodies are being made to extend biowaivers to certain Class II and III products, which would represent more than 50% of all drugs coming to the market. The aim of this study was to investigate the influence of experimental conditions on metformin hydrochloride (CAS 1115-70-4) release from two immediate-release tablet formulations with proven bioequivalence and justify the biowaiver request for dissolution profile similarity in three pH media. The results obtained indicate that differences in drug dissolution observed in vitro were not reflected in vivo. Such data support the existing idea that BCS Class III drugs are eligible biowaiver candidates, even if a very rapid dissolution criterion is not fulfilled

Justification of Biowaiver for Carbamazepine, a Low Soluble High Permeable Compound, in Solid Dosage Forms Based on IVIVC and Gastrointestinal Simulation

The aim of the present study was to use gastrointestinal simulation technology and in vitro-in vivo correlation (IVIVC) as tools to investigate a possible extension of biowaiver criteria to BCS class II drugs using carbamazepine (CBZ) as a candidate compound. Gastrointestinal simulation based on the advanced compartmental absorption and transit model implemented in GastroPlus was used. Actual in vitro and in vivo data generated in CBZ bioequivalence studies were used for correlation purposes. The simulated plasma profile, based on the CBZ physicochemical and pharmacokinetic properties, was almost identical with that observed in vivo. Parameter sensitivity analysis (PSA) indicated that the percent of drug absorbed is relatively insensitive to the variation of the input parameters. Additionally, plasma concentration-time profiles were simulated based on dissolution profiles observed under the different experimental conditions. Regardless of the differences observed in vitro, the predicted pharmacokinetic profiles were similar in the extent of drug exposure (AUC) while there were certain differences in parameters defining the drug absorption rate (C-max, t(max)). High level A IVIVC was established for the pooled data set (r = 0.9624), indicating that 1% SLS may be considered as the universal biorelevant dissolution medium for both the IR and CR CBZ tablets. The proposed methodology involving gastrointestinal simulation technology and IVIVC suggests that there is a rationale for considering CBZ biowaiver extension and introduction of the wider dissolution specifications for CBZ immediate release tablets