High-frequency capsule

The bioavailability of a drug after administration to different regions in the GI tract can be determined either by remote control capsules or by intubation techniques. The two most frequently used remote control devices, the high frequency capsule and Intellisite, are shown in Figure 4.17a and b (Parr et al. 1999). The drug must be dissolved or suspended in a small... 

Figure 4,17a The high-frequency [HF] capsule. When the capsule has reached the intended region, it is exposed to an HF field. This induces an increased temperature in a heating wire, which leads to melting of a nylon thread and release of a steel needle. The needle perforates a latex balloon which contains the drug solution, and the drug is released.

There are many possible stimuli, both physical and chemical, which can trigger the release of the capsule content. The physical ones are, for example, high-frequency ultrasounds, " magnetic fields, microwaves, " or near-infrared radiation. " " The capsules may also respond by changing size indeed, some could both shrink and expand when heated. " However, some of these stimuli, such as low-frequency high-power ultrasounds, are not applieable under in vivo conditions. " ... 

Fig. 3.4a-c. Color flow ultrasonography of the intrarenal vasculature. Using the power mode, with a low-frequency probe (a), the vasculature must be harmonious, without any defect. With a high-frequency probe (b), the cortical interlobular vessels must be visualized until the capsule, c Spectral sampling of interlobar arteries show a low resistivity of the flow... 

Application of external stimuli such as high-frequency magnetic field, ultrasound, microwave, and UV irradiation has been suggested as strategies to remotely affect the stability of the capsule membrane. Carrying a component, which exhibits different behavior when exposed to the specific stimulus, is an essential prerequisite to control the release of cargo molecules. The external stimulus typically affects the integrity of the capsule membrane, which may lead to destmction of the entire capsule or (reversible) formation of defects that would ultimately result in release of... 

Alloys (2 g each) in the Fe rich comer were melted in sinter Al203-cracibles in a high frequency furnace in air and waterquenched. Starting materials were electrolyte Fe (99.5 mass%), graphite (99.94%), crystalline B (98.5%) and a master alloy of Fe with 4.72 mass% C. A part of each alloy was annealed at 800°C for 200 h in vacuum sealed quartz capsules. The carbon content was determined via gas-volumetry. 

The manufacturer of efavirenz notes that taking a 600-mg efavirenz tablet with a high-fat meal increased its AUC by 28%, when compared with fasting conditions, and increased its maximum concentration by 79%. After a similar meal, the AUC and maximum level of the capsule formulation was increased by 22% and 39%, respectively, and after a low-fat meal the increases were 17% and 51%, respectively. The manufacturer says that these increases might increase the frequency of adverse effects. They recoimnend that efavirenz is taken without food, preferably at bedtime. ... 

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