Essential Pharmaceutical Principles and Dosage Forms

Posted on Jul 7, 2026 in Pharmacy

Prescriptions: Definition, Parts, and Handling

Definition: A prescription is a written, electronic, or verbal order given by a registered medical practitioner to a pharmacist for preparing and dispensing medicines to a patient with proper directions for use.

Parts of a Prescription

  • Date: Date on which the prescription is written.
  • Patient’s details: Name, age, sex, and address.
  • Superscription (Rx): Symbol “Rx” indicating a prescription.
  • Inscription: Name, strength, and quantity of the medicine.
  • Subscription: Instructions to the pharmacist for preparation and dispensing.
  • Signa (Sig.): Directions to the patient regarding dose, route, frequency, and duration.
  • Refill instructions: Indicates whether the medicine can be dispensed again.
  • Prescriber’s details: Doctor’s name, qualification, registration number, signature, address, and contact details.

Handling a Prescription

  1. Receive the prescription politely.
  2. Check the date, patient’s details, and doctor’s signature.
  3. Read and interpret the prescription carefully.
  4. Check for errors, incompatibilities, allergies, and drug interactions.
  5. Calculate the required quantity of medicine.
  6. Prepare or select the medicine correctly.
  7. Label the medicine properly with directions for use.
  8. Recheck the prescription and dispensed medicine.
  9. Explain the dosage, precautions, and storage to the patient.
  10. Record the prescription if required and hand over the medicine.

Posology: Definition and Factors

Definition: Posology is the branch of pharmacology that deals with the study and determination of the proper dose of drugs for patients.

Factors Affecting Posology

  • Age: Children and elderly patients usually require lower doses.
  • Body Weight: Dose is often calculated based on weight.
  • Body Surface Area (BSA): Used for accurate calculation, especially in children and anticancer therapy.
  • Sex: Females may require different doses due to physiological differences.
  • Pathological Condition: Liver, kidney, or heart diseases may require dose adjustment.
  • Route of Administration: Dose varies by oral, intravenous, or intramuscular routes.
  • Time of Administration: Some drugs are more effective at specific times (e.g., before/after food).
  • Tolerance: Repeated use may reduce effect, requiring a higher dose.
  • Idiosyncrasy: An unusual or abnormal response due to individual variation.
  • Allergy (Hypersensitivity): Allergic patients must avoid specific drugs.
  • Drug Interactions: One drug may increase or decrease the effect of another.
  • Psychological Factors: Mental condition, anxiety, or placebo effect may influence response.

Indian Pharmacopoeia (IP)

Introduction: The Indian Pharmacopoeia (IP) is the official book of drug standards in India, ensuring the identity, purity, strength, quality, storage, labeling, and testing of drugs.

Objectives

  • Establish official standards for drugs.
  • Ensure quality, safety, purity, and efficacy.
  • Provide standard methods for identification and testing.
  • Promote uniformity in manufacturing and quality control.
  • Protect public health.

Classification of Dosage Forms

A dosage form is the physical form in which a drug is prepared and administered.

Main Categories

  1. Solid: Tablets, Capsules, Powders, Granules, Lozenges.
  2. Semi-solid: Ointments, Creams, Gels, Pastes, Suppositories.
  3. Liquid: Syrups, Elixirs, Suspensions, Emulsions, Solutions, Drops.
  4. Gaseous: Medical Oxygen, Nitrous Oxide, Carbon Dioxide.
  5. Parenteral: Injections, Infusions.
  6. Inhalational: MDIs, DPIs, Nebulizer Solutions.
  7. Topical: Lotions, Liniments, Paints, Sprays, Transdermal Patches.

Powders: Classification and Types

Definition: Powders are solid dosage forms consisting of finely divided drugs with or without excipients.

Types

  • Simple Powder: Contains only one medicinal ingredient.
  • Compound Powder: Contains two or more medicinal ingredients mixed uniformly.
  • Dusting Powder: Finely divided powders for external skin application.
  • Effervescent Powder: Contains citric acid, tartaric acid, and sodium bicarbonate; releases CO2 in water.

Solubility Enhancement Techniques

Methods to increase the solubility and dissolution rate of poorly soluble drugs to improve bioavailability:

  • Particle size reduction
  • Salt formation
  • pH adjustment
  • Use of co-solvents
  • Use of surfactants
  • Complexation
  • Solid dispersion
  • Hydrotropy

Syrups and Elixirs

Syrups: Concentrated, viscous, aqueous preparations containing sugar (sucrose). Ideal for children due to pleasant taste.

Elixirs: Clear, sweetened hydroalcoholic liquid preparations. Suitable for drugs poorly soluble in water.

Emulsions: Preparation and Stability

Definition: A biphasic liquid dosage form where one immiscible liquid is dispersed in another using an emulsifying agent.

Methods of Preparation

  • Dry Gum Method (Continental): Mix oil and gum, add water, triturate.
  • Wet Gum Method (English): Prepare mucilage, add oil slowly.
  • Bottle Method (Forbes): Shake gum and oil in a bottle, add water.

Stability Problems

Creaming, Cracking, Phase Inversion, Flocculation, Coalescence, and Microbial contamination.

Suspensions: Flocculated vs. Deflocculated

Definition: A biphasic liquid dosage form with insoluble solid particles dispersed in a liquid vehicle.

  • Flocculated: Particles form loose aggregates (flocs); sediment is easily redispersed; no hard cake.
  • Deflocculated: Particles remain separate; sediment is compact and difficult to redisperse; forms hard cake.

Suppositories: Preparation and Evaluation

Definition: Solid dosage forms for insertion into the rectum, vagina, or urethra.

Methods

  • Hand Rolling
  • Compression Moulding
  • Fusion (Moulding) Method

Evaluation

Appearance, Weight variation, Content uniformity, Melting range, Liquefaction time, Disintegration test, Hardness, and Stability.

Pharmaceutical Incompatibility

Undesirable reactions when ingredients are mixed, making the preparation unsuitable.

  • Physical: Insolubility, immiscibility, precipitation.
  • Chemical: Oxidation, reduction, hydrolysis, double decomposition.
  • Therapeutic: Wrong dose, drug interactions, contraindications.

Dermal Penetration

The process by which a drug passes through the skin. Factors include drug properties, skin condition, thickness, age, blood flow, and the use of penetration enhancers.

Semi-solid Dosage Forms

Includes Ointments, Creams, Gels, and Pastes. Evaluation includes pH, viscosity, spreadability, extrudability, and drug content uniformity.

Transdermal Drug Delivery System (TDDS)

Delivers drugs through the skin into systemic circulation at a controlled rate. Advantages: Avoids first-pass metabolism, sustained release, improved patient compliance. Disadvantages: Skin irritation, limited to potent drugs, higher cost.