INTRODUCTION TO PHARMACEUTICAL CHEMISTRY
Pharmaceutical chemistry is related with drug design and synthesis of biologically active molecules.
The aim of pharmaceutical chemistry is to gain new chemical molecules that could help the discovery of new pharmaceuticals or optimize already known drug structures, of chemical drugs.
SCOPE:- There are following scope
1. Drug Design
2. Drug Synthesis
3. Analysis
4. Optimization
5. Quality control
1.Drug Desigsn:- Design of a molecule that will bind tightly to its target. Although design techniques for prediction of binding affinity are reasonable succesful, there are many other properties, such as bioavailbility, metabolic half-life and side effect.
2. Drug Synthesis:- A chemical synthesis involves one or more compounds(reagents, reactant) that will experience a transformation when subjected to certain conditions.
(A). Inorganic synthesis- Inorganic synthesis and organometallic synthesis are applied to the preparation of compounds with significant non -organic content Eg- Anti cancer drug Cisplastin from potassium tetrachloroplatinate.
(B). Organic Synthesis- These synthesis is special type of chemical synthesis dealing with the synthesis of organic compounds.
3. Analysis- It is the process determination of physical properties or chemical composition of sample of matter and identifying, seprating and quantifying the components of a to understand its nature and composition.
4. Optimization:- It is the primary focus of the devision of Pharmacotherapy and Experimental Therapeutics (DPET) is the optimization of drug therapy through the discovery and evaluation of key factors that influence how therapeutic agents work in patients.
5.Quality control:- Employees frequently begin testing using samples collected from the production line, finished products and raw material.
Testing during various production phases can help identify the cause of a production problem and th necessary corrective actions to prevent it from happening again.
Key Components of Quality Control
⦁ Inspection
⦁ Testing
⦁ Statistical Process Control (SPC)
⦁ Documentation and Records
⦁ Corrective Action
⦁ Training and Education
⦁ Continuous Improvement
Source and types of errors:-
Errors- It is refers to the difference in the standard values and the true value(accepted true result).
Sources of errors-
⦁ Sometimes even standard weights have error.
⦁ Fluctuation of scale reading.
⦁ Dust particle in air may adhere to the balance.
⦁ Air could react with the substance being weighed.
⦁ Moisture from wet items evaporates while weighing.
⦁ Hot or cold items affected in weight.
⦁ Improper measurement quantity of chemical.
⦁ Wrong procedure are applied.
⦁ Vibration disturbances as produced by passing heavy vehicle which also affect weighing.
⦁ Delay in calibration and wrong in calculation.
⦁ Contaminated chemicals are used.
Types of error-
It can be broadly categorized into two categories.
1. Determinate errors (Systematic errors)
2. Indeterminate errors( Random errors)
1.Determinate errors (Systematic errors)- Determinate errors are those errors that are known and controllable errors these are known and avoidable.
Types of systematic errors-
i. Personal errors- These errors are completely due to the analyst's human error and have nothing to do with the prescribed procedure or methodology.
ii. Instrumenatl errors- Instruments need calibration and are not accurate. Eg- pH meter, single pan electric balance, UV spectrophotometer, potentiometer.
iii. Reagent errors- These errors are the results of the reagent itself, such as impurities inherent to th reagent. - Platinum volatilization due to high temprature. OR Unwanted foreign substances introduced by reagents when they react with porcelain and glass apparatus.
iv. Proportional errors- No matter how many samples are taken, the absolute error value remains constant regardless of that change.
v. Errors due to methodology- These errors consist of a poor sample selection and incomplete reaction.
2. Indeterminate errors (Random errors)- Indetermined errors are represents random fluctuation in measuring devices that are not controllable. Eg- Students open and close lab doors cause changes in pressure reading.
Sailent features of indeterminate errors-
i. Repeat measurement Same variable several times and yielding correction to apply between replicates of the same variable is simply a coincidence.
ii. Sample handled improperly.
iii. Presence of bubbles in burettes.
iv. Temprature variation.
v. Noise as well as drift from an electronic circuit.
vi. Vibrations caused to building by heavy vehicular-traffic.
Accuracy- These are measures of observational error. Accuracy is refers to how close a given set of (observation or reading) measurement is the true or accepted value.
Precision- These are also measures of observational error. Precision of measurements system is the degree to which repeated measurements give the same result.
A measurement system can be accurate but not precise ,precise but not accurate ,neither or both.
Precision measurements can be of two types:
(1). Repeatability(Test- Retest reliability)- The variation which arises in successive of the same variable taken under the same conditions ( Eg- Same observer, location, instrument and procedure) in a short period of time.
(2). Reproducibility - The variation which arises by extent to which a tool is capable of producing the same result when use repeatedly in the same process for measurement.
Significant Figures-
The significant figures of a given number are those important digits, which convey the meaning according to its accuracy. Eg- 7.898 has four significant digits. These substantial figures provide precision to the numbers. They are also termed as significant digits.
Rules for significant figures-
I. All non-zero digits are significant. Eg- 78982592 contains eight significant digits.
II. Zero between two non-zero digits are significant. Eg- 3021 has four significant figures.
III. Leading zeroes are not significant. Eg- 0.12,0.0089 has only two significant figures.
IV. Trailing zeros to the right of the decimal are significant. Eg- 25.00 there are four significant figures.
V. Trailing zeros in a whole number with the decimal shown are significant. Eg-248. indicates that the trailing zero is significant there are three significant figures.
VI. Trailing zeros in whole number with no decimal shown are not significant. Eg- 248 indicates that the zero is not significant, there are only two significant figures in this value.
VII. Exact numbers have an infinite number of significant figures. Eg- 1 Meter= 1.00 meters = 1.0000 meters = 1.000000000000000000000 meters ,etc.
Impurities in Pharmaceuticals-
The origin of impurities in drug is form various sources and phases of the synthetic process and prepration of pharmaceutical dosage forms. There are several possibilities of synthesizing a drug ,it is possible that the same product of different sources may give rise to different impurities.
Sources of impurities-
According to the ICH(International Council of Harmonization) impurities are as follows:
1. Raw materials used in the manufacture-Chemicals may be carried through the manufacturing process and contaminate the final product.
2. Reagents used in the manufacturing process- If reagents usd in the manufacturing process are not completely removed by washing, these may find entry into the final product.
3. Method /Process used during manufacturing- Drugs and chemicals are manufacture from different methods .The type and amount of impurity present vary in the drugs/chemicals.
4. Inadequate storage condition- Reactions with the content material or the occurence of changes in the physical form of the drug due to temprature.
5. Decomposition of the product during storage- Substances may decompose in storage due to light, air, oxygen leading to the final product being contaminate.
6. Accidental substitution with spurious or useless material- Many pharmaceutical chemicals are adultrated with cheaper substances.
7. Chemical process used in manufacturing
8. Atmospheric contamination during the manufacturing process
9. Intermediate products in the manufacturing process
10. Defects during manufacturing.
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