PHARMACOKINETICS MADE EASY PDF
Pharmacokinetics Made Easy (2nd edn). By Donald J Birkett, Sydney, McGraw- Hill Australia,. pp. $A (paperback). ISBN he relationship bet een pharmacodynamics and pharmacokinetics. 2. . don't easily cross cell membranes they can leak out of capillaries and get into the. Nov 2, Download. Ebook: pocket guide pharmacokinetics made easy in PDF Format. also available for mobile reader. Mon, 12 Nov
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Pharmacokinetics made easy 9: Non-linear pharmacokinetics
The Km for alcohol is about 0. This amount of alcohol is contained in mL light beer, mL standard beer, 88 mL wine or 27 mL spirit.
Higher rates of ingestion will result in further accumulation. Clearance by glomerular filtration is a passive process which is not saturable, but secretion involves saturable drug binding to a carrier. Even when secretion is saturated, filtration continues to increase linearly with plasma drug concentration.
The extent to which saturation of renal secretion results in non-linear pharmacokinetics depends on the relative importance of secretion and filtration in the drug's elimination. Because of the baseline of filtration clearance, saturation of renal secretion does not usually cause clinically important problems. Saturation of first pass metabolism causing an increase in bioavailability After oral administration, the drug-metabolising enzymes in the liver are exposed to relatively high drug concentrations in the portal blood.
For drugs with high hepatic extraction ratios, e.
Steady state drug concentration then increases more than proportionately with dose equation 3. Other drugs with saturable first pass metabolism are tropisetron and paroxetine. The total concentration of albumin in plasma is about 0.
Usually drug concentrations are well below those of the binding proteins and unbound protein Pu approximates to total protein PT. Then, fu depends only on the affinity constant and the total concentration of protein binding sites, and remains constant with changes in drug concentration.
In a few cases e. This occurs more commonly for drugs such as disopyramide which bind to a1 acid glycoprotein because of the lower concentration of binding protein.
What are the practical consequences of saturable protein binding? From equation 3, it can be seen that as fu increases, total drug concentration at steady state decreases.
However, fu does not affect the steady state concentration of the unbound drug. A drug which binds to a receptor and produces a maximum response is called a full agonist; a drug which binds and produces less than a maximal response is called a partial agonist. Drugs which bind but do not activate second messenger systems are called antagonists.
Antagonists can only produce effects by blocking the access of the natural transmitter agonist to the receptor. Thus, beta blockers produce relatively little change in heart rate when given to subjects at rest as there is low sympathetic tone and little noradrenaline the natural agonist to be antagonised at the beta receptor. The effects of beta blockers are therefore measured after stimulating the sympathetic system usually by exercise e. Partial agonists produce an effect if no agonist is present, but act as antagonists in the presence of a full agonist.
Pharmacokinetics made easy 10 Pharmacodynamics - the concentration-effect relationship
Pindolol, a beta blocker which is a partial agonist, produces less decrease in heart rate than pure antagonists such as propranolol. Selectivity in drug action is related to the structural specificity of drug binding to receptors. Propranolol binds equally well to beta1 and beta2 adrenoceptors, whereas atenolol and metoprolol bind selectively to and block are antagonists at beta 1 adrenoceptors.
Salbutamol is a selective beta2 adrenoceptor agonist and, in this case, additional selectivity is achieved by inhaling the drug directly to its site of action in the lungs.
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How does drug effect vary with drug concentration? The interaction of a drug with a receptor involves it binding to the receptor in the same structurally specific way that a substrate binds to the active site of an enzyme. The same equation and similar parameters are therefore used to describe the concentration effect relationship Fig. The affinity of the drug for the receptor is described by the EC50 , the concentration of the drug required to give half maximal response.
The different actions of a drug, such as therapeutic and adverse effects, are often due to the drug binding to different receptors with different EC50 values. Ideally, adverse effects should occur at higher drug concentrations than therapeutic effects.
As drug concentration increases, the response rises to a maximum, at which point the receptor is saturated. This type of concentration-response curve is produced by measuring a continuous parameter, such as blood pressure or exercise-induced heart rate, at various drug concentrations.The pKa is the negative log of the ionization constant, particular for each acidic or basic drug.
Isolated mucosal cells Isolated mucosal cell suspensions have been used to study enzyme activity, drug transport, and cellular metabolism. The best part?
Drug absorption through transcellular and paracellular pathways 9. Intestinal ring preparation can be used to measure the rate of uptake and accumulation of a drug from the intestines. Phagocytosis is involved in the acquisition of nutrients for some cells.
Here, the protein binding plays an important role [ 4 , 5 ].
Various models from low-throughput in situ rat model to high-throughput in silico models are used. Learn more.
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