Effect of propranolol on the myocardial contractility of normotensive and spontaneously hypertensive rabbits: relationship of pharmacokinetics and pharmacodynamics

A new description of arterial function: the compliance-pressure loop

Hypertension and atherosclerosis are associated with reduced arterial compliance, which is the principal component that reflects the dynamic behavior of the arterial system. Hence, change in arterial compliance has been used as a compass of arterial wall properties, as well as an effective parameter for assessing therapeutic treatment efficacy. The arterial compliance-blood pressure loop concept is introduced here for assessment of arterial function. Aortic pressure and flow were measured in experimental dogs during normal and acute hypertension. The compliance-pressure loops were constructed from pulsatile blood pressure waveforms and the corresponding compliances. The features of the loop are that, for any given heart beat, arterial compliance is seen to be maximal in early systole to facilitate ventricular ejection, compliance decreasing during the remainder of systole owing to increased blood pressure and reduced aortic flow, compliance in diastole increasing as pressure declines. The arteries are stiffer with reduced compliance in hypertension. Thus, the compliance-pressure loop can provide an effective characterization of the dynamic behavior of the arterial system in terms of pressure-flow relation and blood vessel properties.

Revisiting the effect compartment through timing errors in drug administration

The variations in the pharmacological effects induced by timing errors in drug intake are compared for two drugs, one acting by way of an effect compartment and the other directly from the central compartment. A simulation was performed for two drugs having the same concentration-effect relationship at the receptor site, the same mean effect at equilibrium and identical concentrations in the central compartment. In this article. Patrice Nony, Michel Cucherat and Jean-Pierre Boissel discuss how, for the same variability of concentrations in the central compartment, the variations in mean effects are different. When there is a large variability in the interval separating two consecutive doses, the model that includes an effect compartment dampens the pharmacokinetic variability present in the central compartment. Such an approach may be useful for the prescription recommendations of drugs, especially those with narrow therapeutic indices.

Response surface method: a novel strategy to optimize iontophoretic transdermal delivery of thyrotropin-releasing hormone

PURPOSE

To maximize the iontophoretic transdermal delivery rate of thyrotropin-releasing hormone (TRH) facilitated by periodically monophase-pulsed current across excised skin.

METHODS

The pH of the buffer, the ionic strength in the solution, the frequency of the periodically monophase-pulsed current and the current on/off ratio were chosen as the key variables. A response surface method was applied to optimize the transdermal delivery rate of TRH under different operational conditions.

RESULTS

The optimum operating conditions were achieved via experimentation based on the response surface method by systematically adjusting the pH of the buffer, the ionic strength in the solution, the current amplitude, frequency and the active temporal ratio of the pulsed current. The rate of permeation of TRH crossing the skin during iontophoresis varied from two to ten-fold, depending on operating conditions.

CONCLUSIONS

Only a few steps, two in this work, were needed to reach the optimal. The response surface near the region of the maximal point was thoroughly described with a quadratic function. A maximal transdermal rate of permeation of TRH, 103.2 micrograms h-1 cm-2, was obtained when the donor solution was at pH = 7.0, ionic strength = 0.037, and with a periodically monophase-pulsed current iontophoresis with duty cycle = 75%. The effect of pulse frequency was not statistically significant.