Pharmacokinetics is a branch of pharmacology which studies what happens when foreign substances enter the human body. It looks at what happens to the substances when they are administered, up until the point at which they are excreted. In humans, the substances that are normally studied are hormones, toxins or other pharmaceutical agents such as paracetamol or aspirin.
The knowledge of Pharmacokinetics is used to come up with an effective plan on how to administer drugs to patients. Some of the main goals of pharmacokinetics are to enhance the efficiency and reduce the toxicity of drugs.
Pharmacokinetics comprises of 5 pathways, these are: Administration, adsorption, ...view middle of the document...
When the drug enters the body, it is metabolised and goes through chemical alterations. All oral drugs must cross membranes and this is determined by lipid solubility, area available for absorption and specific carriers for Phase 2 metabolism. To calculate distribution you can use the following equation: Volume of distribution = Amount of drug administered / Initial drug concentration.
When substances enter the body, the majority of small molecule drugs get broken down and metabolised by metabolic enzymes such as cytochrome P450 in the liver. When the substance gets broken down, they are converted into smaller, new compounds called daughter metabolites. These new compounds are normally more pharmacologically active than their original parent form. There are 2 phases that drugs go through when they are being metabolised. The first phase involves the oxidation and reduction of the drug to make it more water soluble. After this phase completes however, the metabolites are inactive. Phase 2 then couples the metabolites to other water soluble molecules which makes them pharmacologically active again. There are however, factors that can also compromise an oral drug’s effectiveness and this is called the ‘First Pass’ effect. The First Pass effect happens during drug metabolism whereby the concentration of the drug is drastically reduced before it gets to the target cells. This is mainly due to when the drug passes through the liver, as the liver also plays a role in metabolising drugs. There are methods of delivering drugs that bypass the ‘First Pass’ effect, and these include: Rectal application, volatile anaesthetics, nasal inhalations, injections and IV.
Eventually the drug needs to be removed from the body as a build-up of the foreign substances could affect normal metabolism. There are 3 main ways that drug excretion can occur. The first way is via the urine, this is possible due to ultrafiltration which is carried out by the nephron in the kidney’s. Biliary excretion is another form of drug excretion that initiates in the liver and ends up in the gut where it passes out the body in faeces. The final method of excretion is through...