16.4
Systèmes d’administration de médicaments à libération modifiée: Biodisponibilité
Les formes galéniques à libération modifiée (LM) sont conçues pour prolonger la libération du médicament dans le temps, ce qui permet de maintenir des…
Les formes posologiques à libération modifiée ou IRM sont conçues pour prolonger la libération du médicament et maintenir des niveaux plasmatiques stables, minimisant les fluctuations par rapport aux formulations à libération conventionnelle et améliorant les résultats thérapeutiques.
Leur biodisponibilité est généralement inférieure à 100 % en raison d’une libération incomplète du médicament, d’une phase d’absorption prolongée et d’un métabolisme de premier passage dans les médicaments administrés par voie orale.
Il est donc crucial d’étudier la biodisponibilité in vivo des formulations d’IRM. Ces études mesurent la fraction de médicament absorbée, le potentiel de déversement de dose, ainsi que les effets des aliments et des rythmes circadiens sur l’absorption du médicament. Les études à dose unique évaluent l’absorption, tandis que les études à doses multiples évaluent les niveaux thérapeutiques soutenus, les rapports de concentration en régime permanent et les fluctuations en pourcentage.
Les formulations à libération immédiate, et dans certains cas les solutions orales ou les suspensions, servent de référence pour la comparaison lors de l’évaluation des produits IRM.
De plus, les tests de bioéquivalence in vitro simulent des conditions in vivo afin d’évaluer les profils de libération de médicaments. Cela utilise des milieux de dissolution biopertinents, en tenant compte des variations du pH gastro-intestinal, des états nourris versus à jeun, ainsi que de la présence de sécrétions digestives.
View the full transcript and gain access to JoVE Core videos
Q1: Why is bioavailability typically below 100% for modified-release formulations?
Modified-release formulations have bioavailability below 100% due to incomplete drug release, prolonged absorption phases, and first-pass metabolism in orally administered drugs. Additionally, limitations in drug permeability across the gastrointestinal epithelium restrict the fraction of drug reaching systemic circulation, reducing overall bioavailability compared to conventional formulations.
Q2: What is dose dumping and why is it evaluated in single-dose bioavailability studies?
Dose dumping refers to the unintended rapid release of drug that could lead to toxicity. Single-dose studies evaluate absorption profiles and detect dose dumping risk by measuring maximum plasma concentration (Cmax), time to reach Cmax (tmax), and area under the concentration-time curve (AUC), which reflects total drug exposure.
Q3: How do multiple-dose studies differ from single-dose studies in assessing modified-release formulations?
Multiple-dose studies assess the formulation's ability to maintain sustained therapeutic levels over extended periods, determining steady-state plasma concentrations where drug administration rate equals elimination rate. They evaluate steady-state concentration ratios and percentage fluctuation to minimize peaks and troughs, reducing side effects and enhancing therapeutic efficacy.
Q4: What factors does in vitro bioequivalence testing simulate to predict modified-release drug performance?
In vitro bioequivalence tests simulate gastrointestinal conditions using biorelevant dissolution media that account for pH variations, fed versus fasted states, and the presence of bile or pancreatic secretions. These assessments predict in vivo performance and ensure formulations meet regulatory bioequivalence criteria before advancing to clinical testing.
Q5: What reference standards are used when comparing modified-release formulations?
Modified-release formulations are compared to reference standards such as oral solutions, suspensions, or existing modified-release products with well-established pharmacokinetics. Immediate-release formulations serve as primary reference standards for evaluating modified-release products. These comparisons ensure consistent bioavailability and therapeutic performance across formulations.
Q6: How do food and circadian rhythms affect modified-release drug bioavailability?
In vivo bioavailability studies measure the effects of food and circadian rhythms on drug absorption in modified-release formulations. These factors influence gastrointestinal pH, transit time, and digestive secretion levels, which can alter drug release profiles and absorption rates, affecting therapeutic outcomes and plasma concentration fluctuations.
Q7: Why are both in vivo and in vitro assessments necessary for optimizing modified-release formulations?
Integrating in vivo bioavailability studies with in vitro bioequivalence assessments enables researchers to optimize modified-release formulations for consistent drug release and improved therapeutic outcomes. In vitro tests predict in vivo performance, while in vivo studies confirm actual bioavailability, minimizing variability in patient response and ensuring regulatory compliance.