Canadian Journal of Analytical Sciences and Spectroscopy Simultaneous measurement of theophylline and cellulose acetate phthalate in phosphate buffer by UV analysis Anna Angela Barba 1 , Serafina Chirico 2 , Annalisa Dalmoro 2 and Gaetano Lamberti 2 * Abstract The oral administration of pH-sensitive drugs requires protecting the drug molecules from the acidic pH in the stomach: the simplest way is to use polymers as coating, especially polymers which are insoluble at low pH (in the stomach) and soluble under neutral conditions (in the intestine). The Cellulose Acetate Phosphate, CAP, is one of these polymers, and it is one of the most used coating polymers. Studies related to the behavior of such pharmaceutical systems require fast and accurate methods to assay the released drug concentration in dissolution medium. However, both the drug and the coating polymer are present in the dissolution bulk with unknown concentration, and they can interfere each other in assaying. In this communication, a simple method to assay, by UV analysis, Theophylline (TP) and Cellulose Acetate Phosphate concentrations in a dissolution medium, phosphate buffer pH 7.0 (BP), is proposed and validated. Keywords: UV-visible spectroscopy, Theophylline, CAP Résumé L’administration orale de médicaments sensibles au pH requiert la protection de ces molécules des * Author to whom correspondence should be addressed: E-mail: glamberti@unisa.it (Gaetano Lamberti), Tel: +39089964077, Fax: +390089964057 1 Dipartimento di Scienze Farmaceutiche, 2 Dipartimento di Ingegneria Chimica e Alimentare, Università degli Studi di Salerno, Via Ponte don Melillo, I-84084 Fisciano (SA) – Italia Received: September 15, 2008 Accepted (in revised form): December 11, 2008 effets de l’acidité stomacale. La façon la plus simple est de se servir d’une protection par des polymères insolubles au pH acide de l’estomac mais soluble aux conditions neutres de l’intestin. Le phosphate acétate de cellulose, CAP, est l’un de ces polymères et il est l’un de ceux les plus utilisés comme agent protecteur. Les études qui rapportent le comportement de tels systèmes pharmaceutiques requièrent des méthodes rapides et exactes pour mesurer la concentration du médicament relâché dans le milieu de dissolution. Cependant, le médicament et le polymère de protection sont tous deux présents dans la solution brute en concentrations inconnues et ils peuvent interférer l’un sur l’autre dans la mesure finale. Nous proposons et validons ici une méthode simple par analyse UV, qui permet de mesurer les concentrations de théophylline (TP) et du phosphate acétate de cellulose dans le milieu de dissolution, un tampon phosphate à pH 7.0 (BP). Introduction In pharmacology, enteric coated products are de- signed to remain intact in the acidic juices of the stomach and then to release the drug at higher pH (above pH 5.5) of the small intestine. If the drug is unprotected, its ef- fectiveness will be reduced by stomach acids or enzymes activity [1]. The polymers commonly used to achieve enteric properties are anionic polymethacrylates (copolymer of methacrylic acid and either methylmethacrylate or ethyl acrylate (Eudragit®)), cellulose based polymers, e.g. cellulose acetate phthalate or CAP (Aquateric®) and polyvinyl derivatives, e.g. polyvinyl acetate phthalate