Blood drugs actions

Fhtients with kidney disease may exhibit drug toxicity and a longer duration of drug action. The dosage of drugp may be reduced to prevent the accumulation of toxic levels in the blood or further injury to the kidney. 

A drug administered by the intravenous (IV) route is given directly into die blood by a needle inserted into a vein. Drug action occurs almost immediately. 

The amphetamines, such as amphetamine, dextroamphetamine (Dexedrine), and metliainphetainine (Desoxyn), are sympatiiomimetic (ie, adrenergic) dru that stimulate the CNS (see Chap. 22). Their drug action results in an elevation of blood pressure, wakefulness, and an increase or decrease in pulse rate The ability of these drugs to act as anorexiants and suppress the appetite is thought to be due to their action on the appetite center in the hypothalamus. 

These detailed cell models can be used to study the development in time of processes like myocardial ischaemia (a reduction in coronary blood flow that causes under-supply of oxygen to the cardiac muscle), or effects of genetic mutations on cellular electrophysiology. They allow to predict the outcome of changes in the cell s environment, and may even be used to assess drug actions. 

The onset of drug action with intravenous injection is quick, and this method is especially useful for emergency cases. However, intravenous injection is potentially the most dangerous. Once a drug is injected, there is no means to stop it from circulating throughout the body. The complete circulation of blood in the body takes about a minute, and hence an adverse reaction can occur almost instantaneously. 

That blood drug measurements can sometimes provide valuable additional information is, however, not seriously in doubt. For some drugs the intensity of the pharmacological action and severity of side-effects correlates much better with the plasma steady-state concentration than with... 

Advantages of the intramuscular and subcutaneous routes include an increased reliability and precision in the drug blood level Anally achieved and reasonably rapid absorption and onset of drug action. There are, however, serious disadvantages as well. Pain, tenderness, local tissue necrosis (primarily with highly alkaline injections), microbial contamination, and nerve damage may be associated with these forms of parenteral administration. 

The reduced risk of CHD achieved with the statins may also be due to drug actions independent of lowering blood cholesterol. Many important molecules besides cholesterol are generated by intermediates in the complex cholesterol synthesis pathway. These include the isoprenes geranylgeranyl and farnesyl, which are covalently attached to some proteins (isoprenylation) and target them to membranes where they function. The re-... 

An often-misunderstood principle is that concentration in the blood rises until the rate of absorption equals the rate at which drug is being removed from the body (the so-called peak). This peak does not occur when absorption is complete but rather when the rate of absorption equals the rate of elimination. The time to peak is therefore determined by both absorption and elimination rates in the individual patient. Patients with faster elimination will have earlier peaks than will patients with slower elimination, even when the rate of drug absorption is the same (Fig. 4.2). The extent of absorption is usually expressed as the fraction absorbed or bioavailability. This is an important determinant of drug action. While rate and extent of absorption are related, they are different. In general, the onset and magnitude of effects are related to the rate of absorption, while the average steady state concentrations are related to the extent of absorption. 

The drug is injected as a bolus or infused slowly directly into a vein to produce rapid action. It is also useful for certain irritant and hypertonic solutions, as they are rapidly diluted by the blood. Drugs in an oily vehicle or those which precipitate blood constituents or haemolyze erythrocytes should not be given by this route. 

A claim that enzyme mechanisms and receptor structures, or even cell biology suffice as a basis to understand drug action in the human body (how do you measure blood pressure on a cell culture ). In fact, we are going to spend some time with physiological phenomena such as cell exitation and synaptic transmission that are targeted by many practically important drugs. 

Jackson, C.M., Suttie, J.W. (1977). Recent developments in understanding the mechanism of vitamin K and vitamin K-antagonist drug action and the consequences of vitamin K action in blood coagulation. Prog. Haematol. 10 333-59. 

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