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Pharmaceutical Products & Drug Action (Routes of administration…
Pharmaceutical Products & Drug Action
Introduction
Medicinal chemistry :a link between organic chemistry, pharmacology, biochemistry, biology and medicine
Objective : to produce compounds called pharmaceutical drugs which have a variety of effects on the human body including curing diseases, or assisting in medical diagnostics
Therapeutic effect : the desirable outcome of a pharmaceutical drug on the body
Placebo effect : the actual therapeutic effect achieved by a placebo
Side effect : non-desirable outcomes associated with a pharmaceutical drug
Routes of administration
Orally
Rectally (in the form of suppositories)
Parentally (under the skin, subcutaneous injection)
Into muscle tissue (intramuscular injection)
Into bloodstream (intravenous injection, produces fastest therapeutic effect)
Inhalation
Transdermally (applied to skin in the form of ointments of patches)
Effectiveness and safety
expressed using its therapeutic index (TI)
Effective dose (ED50): the minimum dose of the drug required to produce the desired therapeutic effect in 50% of the subjects
Lethal dose (LD50): the minimum dose of the drug that causes death in 50% of the subjects
Toxic dose (TD50): the minimum dose of the drug required to cause toxicity in 50% of the subjects (TD50 used because unethical to kill humans to determine LD50)
The higher the TI,the safer the drug
Therapeutic window
the range of doses where the drug provides the desired therapeutic effect without causing unacceptable adverse effects in most patients
In contrast to TI, therapeutic window is not strictly defined and only serves as a general indication
In general, window opens before ED50 and closes before TD50
Effective and toxic dose of drug depend on its route of administration. In order to reach target organ, has to go through bloodstream, which is problematic if drug insoluble
Drug bioavailability
the fraction of administered dose that reaches target part of body
intravenous injection has 100% drug bioavailability while other methods of administration decrease in bioavailability
Bioavailability of pharmaceutical drugs depend on their solubility, polarity, and the presence of certain functional groups. More soluble with polar groups.
Drug action and new development of drugs
At the molecular level, pharmaceutical drugs interact with binding sites of enzymes or cellular In binding to enzymes, most drugs act as inhibitors
The type and efficiency of drug-receptor interactions depend on chemical structure of drug and the site of activity
Drug Discovery
First step is identification of a lead compound (or new chemical entity, NCE) which shows promising activity towards a specific biological target. The lead compound is then isolated and screened against bacteria or animals
Very slow, expensive and inefficient process
Drug Design
Relies on knowledge about drug-receptor interactions. If chemical composition and three dimensional structure of a particular biological target are known, a molecule with complementary structure can be designed using computer modelling techniques.
The designed molecule is then synthesized and tested. If any difference occurs, the computer model can easily be adjusted and tried again
Preclinical trials
After lead compound is identified, each compound is rated according to toxicity, chemical stability, solubility, preparation costs, and many other properties that may be desirable.
The drug must also cause no side effects to other molecules and have minimal environmental impact in production
Clinical trials
Set of steps after the success of preclinical trials which includes testing on humans
Post-clinical trials
For determining the long term effects and chronic toxicity of the drug, including carcinogenic properties, effect on immune system, fertility, and reproductive functions
Tolerance and addiction
Drug tolerance
reduce the body’s response to specific medications due to accelerated drug metabolism. This is typical for opiates and other narcotic drugs where users need progressively higher doses to obtain desired effects. Increased dosage leads to more side effects
Drug addiction
The compulsive desire of the user to take drugs regardless of the health problems it might cause
dangerous when combined with drug tolerance
