Introduction to Pharmaceutical Chemistry - Chapter 1

Pharmaceutical Chemistry Study Notes

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Introduction to Pharmaceutical Chemistry

• Topics & Page Numbers:
  • Pharmaceutical chemistry (Page 3)
  • Objective (Page 4)
  • Scope (Page 4)
  • Source and Types of Errors (Page 4)
  • Accuracy (Page 4)
  • Precision (Page 4)
  • Significance (Page 5)
  • Impurities in pharmaceuticals (Page 5)
  • Limit Tests (Chlorides, Sulphates, Iron, Heavy Metals, Arsenic) (Page 6)

Pharmaceutical Chemistry - Chapter 1

• Pharmaceutical Chemistry: The chemistry of drug design and synthesis of biologically active molecules. It includes drug discovery, metabolism, absorption, and delivery methods.

• Careers: Pharmaceutical companies, biotechnology companies, drug development & research facilities.

• Objective: To ensure the fitness for purpose of medicinal products by analyzing and evaluating them according to quality control standards.

• Objectives:

  • Enhances knowledge base for synthesis, isolation, and purification.
  • Enhances skill in handling chemicals & glassware.
  • Provides proper skills & qualities for job responsibilities.
  • Trains students about effects of chemicals.

• Skills Required: Good writing/verbal skills, organic chemistry skills, ability to purify drugs/intermediates, spectroscopic techniques, teamwork/interpersonal skills, good communication skills.

Errors in Pharmaceutical Chemistry

• Error: Difference between a calculated/estimated and actual theoretical value.

• Classification of Errors:

  • Systematic/Determinate: Constant or slightly changing errors.
    • Instrumental: Errors from faulty instruments or reagents.
    • Operational/Personal: Errors during experimental procedures.
    • Methodological: Serious errors often difficult to correct. Examples include errors due to co-precipitation of impurities.
  • Non-Systematic/Indeterminate (Random): Unpredictable errors.
    • Source: Bubbles in burettes, improper sample handling.
  • Gross: Avoidable mistakes (e.g., calculation errors, wrong sample sizes, mixing up reagents, transcription errors)

Accuracy and Precision

• Accuracy: Difference between calculated and actual values.

• Precision: Reproducibility/Repeatability of measurements.

• Repeatability: Variation in results in short-term experiments for the same conditions and repeated measurements, with the same instruments and personnel.

• Reproducibility: Variation from applying the same tests over different time periods or using varying instruments and personnel.

• Significant Figures: Digits indicating precision in a measurement.

  • Rules: Non-zero digits are significant; zeroes between non-zero digits are significant; leading zeros are not significant; trailing zeros after a decimal point are significant.

Impurities in Pharmaceuticals

• Impurities: Organic materials other than the main drug substance.

  • Occur during manufacturing processes.
  • Can affect the product's quality and safety.
  • Can arise from raw materials, reagents, and processes.

• Raw Materials: Impurities in raw materials (e.g., calcium sulfate, magnesium chloride in rocksalt, sodium chloride) may transfer to the final product.

• Manufacturing: Impurities from reagents or processes can contaminate the final product. (e.g. mixing of mercuric chloride with dilute ammonia.)

• Environmental Contaminants: Aspects like humidity, exposure to adverse temperatures, and environmental gases (e.g., hydrogen sulfide, smoke).

Limit Tests (Specific Examples)

• Limit tests are quantitative tests to control small impurities in substances.

• Arsenic Test (Page 7): The limit test for arsenic involves converting arsenic into arsine (AsH3), which reacts with mercuric chloride paper to produce a stain.

• Chloride Test (Page 8): The limit test for chloride involves reacting soluble chloride with silver nitrate to produce insoluble silver chloride leading to turbid solution.

• Sulphate Test (Page 9): The limit test for sulfate involves reacting sulfate with barium chloride to form insoluble barium sulfate.

• Iron Test (Page 9): The limit test for iron involves reacting iron with thioglycollic acid to produce a purple-coloured solution.

• Heavy Metals Test (Page 10): The limit test for heavy metals involves using a reaction with hydrogen sulfide (H₂S) to precipitate the heavy metal as a sulphide in the presence of acid.