Double peak phenomenon

RL Oberle, GL Amidon. The influence of variable gastric emptying and intestinal transit rates on the plasma level curve of cimetidine An explanation for the double peak phenomenon. J Pharmacok Biopharm 15 529-544, 1987. 

Some drugs, such as ranitidine, cimetidine, and dipyridamole, after oral administration produce a blood concentration curve consisting of two peaks. This double-peak phenomenon is generally observed after the administration of a single dose to fasted patients. The rationale for the double-peak phenomenon has been attributed to variability in stomach emptying, variable intestinal motility, presence of food, enterohepatic recycling, or failure of a tablet... 

M l s-1), and then decrease. The decrease is caused by separation of the single peak into two individual peaks. The double peak phenomenon, which has been previously ascribed to the depletion of the reactant at low concentrations of M, has also been found to occur experimentally (5b). This phenomenon can be visualized by considering the effect of k in two ways. The first and most... 

The description and quantification of between-subject variability become very important in a population of patients. For example, the double-peak phenomenon observed on median PK profiles of sustained-release diclofenac is due to large differences in individual values (39). 

There are several explanations for the double-peak phenomenon after oral administration. There may be two distinct sites of absorption (42), gastric emptying hmited absorption (43), or a variable gastric emptying rate (44-50), or it may be due to formulation characteristics (39). However, the concept of parallel first-order absorption is not limited to two absorption processes (51-55). 

Y. PlusqueUec, G. Campiston, S. Staveris, J. Barre, L. Jung, J. P. TiUement, and G. Houin, A double-peak phenomenon in the pharmacokinetics of veraUpride after oral administration a donble-site model for drug absorption. J Pharmacokinet Biopharm 15 225-239 (1987). 

Y. Wang, A. Roy, L. Sun, and C. E. Lau, A double-peak phenomenon in the pharmacokinetics of alprazolam after oral administration. Drug Metab Dispos 27 855-859 (1999). P. Veng Pedersen, Pharmacokinetic analysis by linear system approach I cimetidine bioavailability and second peak phenomenon. J Pharm Sci 70 32-38 (1981). 

In these pro-EDC maps, the kink phenomenon [6] is visualized as the crossover from the low energy quasi-particle branch to the high-energy incoherent branch. This crossover region is the region of low intensity (indicated by white dashed line, and blue and red arrows), where the two dispersions mix and give rise to a double peak structure, commonly referred to as a peak-dip-hump structure, of EDC s [6,12-14], In this terminology,... 

Another source of confusion had its origin in the twin carbonyl stretching band found in the IR spectrum of furfuraldehyde. The double peak was assumed to arise from the two species, oxygen-cis and oxygen-trans, even though the results were difficult to fit to those revealed by other physical probes. The same phenomenon occurs in the thiophene series where it was eventually traced to Fermi resonance between the carbonyl and the C(5)—H vibrations.360 That Fermi resonance is also responsible in the furan series has been demonstrated by showing that there is only one carbonyl band in furfuraldehyde when position 5 is deuterated.361... 

In other cases, there is experimental evidence in the excitation spectra for aggregate formation such as dimers (double peak) which are not visible in the absorption spectra of the solutions with low dye concentrations. This has been confirmed by absorption measurements of adsorbed dye layers (crystal violet on ZnO electrodes [23]. Even polymers can be formed by adsorbed dye molecules, as found, for example, with pseu-doisocyanine on ZnO [24]. One example is given in Fig. 10.10. This is a well-known phenomenon for cyanine dyes [25] where polymer bands have been found at high dye concentrations. 

Fig. 7.17B). This indicates that the source of the double overshoot phenomenon is simpler than previously thought. Figure 7.19 shows the concentrations of the various isotopic species of DAP during the double overshoot simulation shown in Fig. 7.17B. The peaks of the two overshoots are indicated in Fig. 7.19, demonstrating... 

The sequence of events as the system passes through film resonance is illustrated schematically in Fig. 4 [25], in which the total (observed) impedance (full line) is the combination of the crystal (dotted hne), and film (dashed hne) components. As film thickness increases (moving from frame 1 to frame 5), the film component moves rapidly downwards in frequency. As it passes through the crystal component, the prediction is that the total resonance will - transiently - split into two peaks (frame 3). As the resonance condition is passed (frame 5), the response returns to a more normal appearance. More detailed theoretical exploration of this phenomenon [25] shows that both the absolute and relative values of the shear modulus components have significant influence over the resonator response. In particular, the double-peak nature of the response shown in Fig. 4 is only predicted for low loss films (i.e. films for which the loss tangent, G"jG < 1). 

The existence of this double-resonance-peak phenomenon is particularly notable in the Terathane 2000 series with most of the types of chain extender investigated. In the low-temperature region a peak is always present and one is also seen to exist at higher temperatures, usually greater than 160 C exceptionally the Dianol 22 TPU possesses a resonance tan 6 that commences at 120" C. 

Further, there are distinct double peaks in the dynamic mechanical spectra ascribed to the glass transition of each component. Since the peak temperature of the E curve is located at those of the individual pure components, mutual dissolution does not take place in the blends. Blending PBS, however, accelerates the crystallization of PLA, which is directly detected by DSC and optical microscope measurements at the cooling process. This is a significantly interesting phenomenon because molten PBS droplets act as crystallization nuclei for PLA. Furthermore, the PLA crystallites generated during the quench operation are responsible for the enhancement of the cold-crystallization behavior for the blends. 

At temperatures above 180 °C, an additional melt peak forms besides the original double peaks recognizable in DSC [776], [777], Figure 5.206. This phenomenon is credited to Brill transitions. The usual crystal shape of polyamides is triclinic the result of Brill transition is a pseudo-hexagonal shape induced by post-crystallization at temperatures above 180 °C [778]. 

A minimum in the spectrum occurs at v = 367 cm implying the associated weighting function is maximum near z = 30 km, where the temperature (and hence the Planck intensity) has a minimum. Thus the weighting function and Planck intensity tend to counteract each other, and their product results in the broad, double-peaked contribution function shown in Fig. 4.2.6. In this case the concept of an effective emission level has little meaning, since there exists a broad altitude range over which individual levels contribute about equally to the outgoing intensity. This phenomenon is characteristic of temperature minima... 

The above-mentioned relative ineffeetiveness of THA during the onset phase of seopolamine also oeeurred when physostigmine was given before peak effeets. We first reported this early laek of effeet of physostigmine in 1967, demonstrating its ability to reverse seopolamine delirium under double-blind eontrolled eonditions (Fig. 69). We have, however, yet to hear an explanation of this phenomenon (whieh also oeeurs with BZ and other belladonnoids). 

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