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Pharmacodynamics and Pharmcokinetics



• Pharmacology is the study of drugs

• Pharmacodynamics is the effect drugs have on the body

• Pharmacokinetics is the effect the body has on drugs

• Pharmacokinetics includes

- Absorption

- Distribution

- Metabolism

- Excretion



• Main factor = route of administration

• Physiological considerations in absorption are blood flow, total surface area, time of arrival of the drug and time of drug at absorption site

• Others include solubility, chemical stability and how fat soluble the drug is



• Drugs are distributed into major body fluids (plasma)

• Specific tissues may take up certain drugs

• Drug distribution is affected by the extent that the drug binds to plasma proteins

• Drug distribution is affected by barriers (plasma and BBB)



• This is a process of metabolising drugs in the body

• Occurs mainly in the liver - hepatic impairment

• Some drugs are activated by hepatic metabolism - pro-drugs

• Drug metabolism is split into two phases in the liver - oxidation and conjugation



• Includes renal and faecal elimination

• Main method via renal excretion is active glomerular filtration

• Drugs can also be eliminated by passive methods in the distal tubules

• Drugs can be removed from the body in bile and so removed in faeces


General and molecular aspects

• Drugs exert their effects at molecular targets (receptors)

• Drugs can also act by stopping or partially stopping important ions entering the cell (calcium channel blockers)

• Drugs can interfere with enzymes that are produced by the body

• Drugs can work on the transport of chemicals into and out of cells


Drug action

• Relies of route of administration, rate of absorption and manner of distribution

• Duration of effect involves how quickly it is removed from the body

• Some drugs when absorbed from the stomach enter the portal circulation and pass through the liver = first pass effect


Agonistic and antagonistic drug action

• Agonists activate receptors to produce a response

• Antagonists bind with receptors but do not activate them or cause a response , they can block the activation of receptors

• Partial agonists produce a response - less than an agonistic drug

• Inverse agonists reduce normal activity of the cell

• Competitive antagonists are drugs that prevent activation of the cell by their normal agent

• Non-competitive antagonists are drugs that may block the receptor but not in a permanent way



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