Biphasic release pattern

The absorption half-life of the immediate-release oral formulation is 0.4 h in healthy adults. In contrast the controlled-release form exhibits a biphasic absorption pattern with two apparent half-lives of 0.6 and 6.9 h.41 Peak plasma concentrations are achieved in approximately 1.6 h with the immediate release compared with 2 to 3 h with the controlled-release formulation. After a 10-mg oral dose of the immediate release formulation, peak plasma concentrations ranged from 13 to 46 ng/ml (mean = 30 ng/ml, n = 12).36 After the administration of 20 mg of the prolonged-release formulation the peak plasma concentration averaged 23 ng/ml in a group of 28 adults.41 The plasma half-life has been reported to be 4 to 6 h with a volume of distribution of 1.8 to 3.7 L/kg.42... 

In normal volunteers, OxyContin tablets exhibit a biphasic absorption pattern with two apparent absorption half-lives of 0.6 and 6.9 hours, which describes the initial release of oxycodone from the tablet followed by a prolonged release [1,2]. 

A biodegradable and biocompatible dextran hydrogel system has been developed of which the degradation time can be tailored between 2 days and 3 months. This chapter shows that hydrogels based on crosslinked dextrans have unique properties as protein releasing matrices. Both the release pattern (first-order, zero-order or biphasic) as well as the duration of the release can be controlled by an appropriate selection of the characteristics and the geometry of the hydrogel. 

Various factors that influence the release of drugs from particulate carriers are listed in Table 10. Drugs can be released by diffusion or by surface erosion, disintegration, hydration, or breakdown (by a chemical or an enzymatic reaction) of the particles. The release of drugs from microspheres follows a biphasic pattern that is, an initial fast release followed by a slower... 

Gilabert JA, Parekh AB 2000 Respiring mitochondria determine the pattern of activation and inactivation of the store-operated Ca2+ current Icrac- EMBO J 19 6401-6407 lino M 1990 Biphasic Ca2+ dependence of inositol 1,4,5-trisphosphate-induced Ca2+ release in smooth muscle cells of the guinea pig taenia caeci. J Gen Physiol 95 1103-1122 Iizuka K, Yoshii A, Dobashi K, Horie T, More M, Nakazawa T 1998 InsP3, but not novel Ca2+ releasers, contributes to agonist-initiated contraction in rabbit airway smooth muscle. J Physiol 511 915-933... 

The second point is that the S-shapes of many of the release curves in this study indicate a biphasic pattern of drug release. This was also observed by Wakiyama et al (7-91. who used scanning electron microscopy to demonstrate that the second rise in the release rate was due to disintegration of the polylactide microspheres. 

The location of cytochrome C2 in the periplasmic space of purple photosynthetic bacteria has been demonstrated directly by its prompt release following the preparation of sphaeroplasts, and by its accessibility to antibodies in these preparations [220]. Cytochromes c are oxidized in single turnover experiments with a biphasic kinetics (<1 2 and 200-400 /is) this pattern has been interpreted as due to the presence in chromatophores of both cyt. Cj and C2, which are oxidized in series [122]. 

Using fluorescent indicators with single-cell video imaging, the [Ca], responses of individual parietal cells are typically found to be biphasic, consisting of an initial peak elevation that rapidly declines to a sustained steady-state elevation. This pattern of [Ca]i response is seen in many cell types and is interpreted to result from an initial release of calcium from intracellular storage sites followed by a sustained influx of calcium from the extracellular fluid via a receptor-operated Ca channel. Similar mechanisms appear to be involved in the agonist-induced elevation of [Ca], of parietal cells. Accordingly,... 

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