BP102T Unit 2 – Prescription & Posology
Unit 2 covers the scientific rationale for formulating Active Pharmaceutical Ingredients (APIs) into finished dosage forms, physical classification (solid, liquid, semisolid, sterile, gaseous), routes of drug administration, and complete prescription anatomy, Latin terminology, dispensing errors, and calculations.
📋 Prescribed Syllabus Topics
📖 Detailed Lecture Notes & Solved Examples
11. Need for Dosage Forms & Systematic Classification
Dedicated Webpage➔An Active Pharmaceutical Ingredient (API) cannot usually be administered in its pure bulk chemical form because pure drugs may be chemically unstable (e.g., degraded by gastric acid), unpalatable, irritating to gastrointestinal mucosa, or require minute microgram doses that cannot be accurately measured on domestic spoons (e.g., Digoxin 0.25 mg). A dosage form is a physical transformation of pure drug substance combined with non-medicinal adjuvants (excipients) to ensure accurate dosing, chemical stability, optimal bioavailability, and patient compliance.Pure raw drug (API) ko seedhe nahi diya ja sakta kyunki wo kadvii ho sakti hai, pet me acid se nasht ho sakti hai (jaise Omeprazole), ya uski dose itni kam hoti hai (Digoxin 0.25 mg) ki use bina excipient ke tola nahi ja sakta. API me binder, diluent, flavor milakar use Tablet, Syrup ya Injection banaya jata hai jise Dosage Form kehte hain.
▶Rationale for Selected Pharmaceutical Dosage Forms
Specific chemical challenges and their dosage form solutions.
| Physical State | Dosage Form Examples | Key Excipients Used | Primary Clinical Advantage |
|---|---|---|---|
| Solid | Tablets, Hard & Soft Gelatin Capsules | Lactose (diluent), Starch (disintegrant), Mg Stearate | Accurate unit dosing, excellent chemical stability, portable |
| Liquid (Monophasic) | Syrups, Elixirs, Drops | Sucrose, Sorbitol, Ethanol, Flavoring agents | Easy swallowing for pediatrics/geriatrics, rapid absorption |
| Liquid (Biphasic) | Suspensions, Emulsions | Tragacanth, Methylcellulose, Polysorbate 80 (Tween) | Delivers insoluble or unpalatable lipophilic drugs |
| Semisolid | Ointments, Creams, Pastes | White soft paraffin, Wool fat, Cetomacrogol | Localized dermatological delivery, protective barrier |
| Sterile Formulations | IV Injections, Eye Drops | Water for Injections (WFI), Benzalkonium chloride | Instant systemic bio-availability, bypasses GI tract |
- •Dosage Form = API (Drug) + Excipients (Binders, Diluents, Disintegrants, Preservatives, Flavors).
- •Solid Dosage Forms: Tablets, Capsules, Powders, Granules, Lozenges, Suppositories.
- •Liquid Dosage Forms: Monophasic (Solutions, Syrups, Elixirs) and Biphasic (Emulsions, Suspensions).
- •Semisolid Dosage Forms: Ointments, Creams, Pastes, Gels, Jellies.
- •Sterile / Parenteral Dosage Forms: Injections, Transfusion fluids, Ophthalmic drops.
22. Routes of Drug Administration: Comparative Biopharmaceutics
Dedicated Webpage➔The route of administration is the path by which a drug formulation is brought into contact with the body. The selection of an administration route depends on the physicochemical properties of the drug (solubility, molecular weight, ionization), therapeutic urgency (routine vs emergency), site of intended action (local vs systemic), and patient physiological status (conscious, vomiting, pediatric).Dawa shareer me kis raste se di jaye ye bimari ki urgency par depend karta hai. Emergency me IV injection dete hain (100% Bioavailability aur instant asar). Sublingual route (jeebh ke neeche) se liver ka First-Pass Metabolism bypass ho jata hai. Oral route sabse safe aur aasan hota hai.
▶Comparison of Bioavailability and Onset across Routes
Differences in pharmacokinetic profile between Intravenous, Oral, Sublingual, and Transdermal routes.
| Route | Onset of Action | Bioavailability ($F$) | Advantages | Disadvantages |
|---|---|---|---|---|
| Oral | 30 - 60 minutes | Variable (5% - 90%) | Safest, convenient, self-administered, non-invasive | Slow onset, destroyed by gastric acid, first-pass effect |
| Intravenous (IV) | Immediate (seconds) | Strictly 100% | Immediate effect in emergencies, precise blood levels | Invasive, pain, risk of embolism, irreversible if overdosed |
| Sublingual | 1 - 3 minutes | High (bypasses liver) | Rapid absorption, avoids first-pass metabolism | Limited to small-dose, lipid-soluble non-irritant drugs |
| Transdermal | Slow (hours to days) | Moderate to High | Continuous steady blood levels, improved compliance | Only for potent lipophilic drugs, risk of skin irritation |
- •Enteral Routes: Oral, Sublingual, Buccal, Rectal (involves gastrointestinal tract).
- •Parenteral Routes: Intravenous (IV), Intramuscular (IM), Subcutaneous (SC), Intradermal (ID) (bypasses GI tract).
- •First-Pass Hepatic Metabolism: Pre-systemic clearance of orally absorbed drugs by hepatic enzymes before reaching systemic circulation.
- •Bioavailability ($F$): 100% for IV injections; variable for oral dosage forms.
33. Prescription Anatomy, Latin Abbreviations & Dispensing Precautions
Dedicated Webpage➔A prescription is a legally binding written or electronic order from a registered medical practitioner (physician, dentist, veterinarian) to a registered pharmacist authorizing the dispensing of a specific medication. A complete prescription consists of 8 standardized structural components: (1) Prescriber's details, (2) Date, (3) Patient demographics, (4) Superscription ($\text{R}_x$), (5) Inscription (names and quantities of ingredients), (6) Subscription (instructions to the pharmacist), (7) Signatura (instructions to the patient), and (8) Prescriber's signature and registration number.Prescription doctor ka ek legal order hota hai jo pharmacist ko dawai dene ke liye likha jata hai. Isme 8 parts hote hain: Rx (Superscription - Take Thou), Inscription (dawa ka naam aur dose), Subscription (pharmacist ke liye directions), aur Signatura/Sig (marij ke liye nirdesh jaise b.i.d. = din me 2 baar, p.c. = khane ke baad).
▶Common Latin Abbreviations Used in Prescriptions
Standard medical Latin shorthand used in dispensing practice.
- •Superscription: Symbol $\text{R}_x$ (derived from the Latin 'Recipe' and historically associated with the Eye of Horus or Jupiter sign for healing).
- •Inscription: The core body containing API name, dose, strength, and formulation type.
- •Subscription: Direction to the dispensing pharmacist regarding formulation method or quantity of tablets to pack.
- •Signatura (Sig.): Clear, translated instructions for the patient regarding dose, frequency, route, and timing with food.
- Memorize and correctly translate common Latin terms (b.i.d., t.i.d., p.c., a.c., stat., h.s., p.r.n.) in 2-mark questions.
- In a 10-mark question on Prescriptions, draw a complete sample prescription format labeling all 8 structural parts.