Dosage forms

Pharmacy (B.Pharm) · Pharmaceutics · free study notes for exams, placements and interviews

In short

A dosage form is the physical form in which a drug substance is presented to the patient together with excipients — tablet, capsule, syrup, injection, ointment, suppository, inhaler, patch — so that an accurate dose reaches the right site by a chosen route. Dosage-form design converts a bulk chemical into a safe, stable, palatable, legally labelled medicine; the drug alone is rarely administrable. In Indian universities this is the opening and highest-weightage unit of Pharmaceutics I (AICTE/PCI B.Pharm curriculum), and it is examined in GPAT, NIPER-JEE and drug-inspector/pharmacist recruitment papers. In industry it is the common language of formulation development, production, packing and QA at Cipla, Sun, Dr. Reddy's, Lupin, Zydus, Torrent, Mankind and the CDMOs, and of regulatory work under the Drugs and Cosmetics Act, 1940 and Rules, 1945.

Explained

Definitions and the basic vocabulary

Drug substance / API: the pharmacologically active molecule. Drug product / formulation: the finished dosage form, API plus excipients, in its container.
Excipient: any ingredient other than the API — diluent, binder, disintegrant, lubricant, glidant, solvent, preservative, buffer, antioxidant, surfactant, suspending/emulsifying agent, sweetener, flavour, colour, base, propellant.
Dose: quantity taken at one time; dosage regimen: dose plus frequency and duration; unit dose (one tablet, one ampoule) versus multi-dose/bulk (100 mL syrup bottle, multi-dose vial).
Pharmaceutical equivalents: same API, same salt, same strength, same dosage form. Pharmaceutical alternatives: different salt/ester or different form. Bioequivalents: equivalent rate and extent of absorption.
Potency expressions: mg, mg/mL, % w/w, % w/v, % v/v, ratio strength (1:1000), IU for biologicals; strengths are stated as the base or as the salt — both must be read carefully.

Classification of dosage forms

By physical state
- Solid: powders, granules, tablets, capsules, pills, lozenges, pastilles, suppositories, pessaries, implants, dry powder inhalers.
- Liquid: solutions, syrups, elixirs, linctuses, drops, suspensions, emulsions, lotions, liniments, enemas, injections, mouthwashes, gargles.
- Semisolid: ointments, creams, gels, pastes, poultices, jellies.
- Gaseous/pressurised: inhalational anaesthetics, medical oxygen, metered-dose inhalers, aerosols, sprays.
By route of administration: oral, sublingual/buccal, rectal, vaginal, parenteral, topical/transdermal, ophthalmic, otic, nasal, pulmonary.
By phase system: monophasic (true solution) and biphasic (suspension = solid-in-liquid; emulsion = liquid-in-liquid).
By release pattern: immediate (conventional), modified — delayed/enteric, extended/sustained, controlled, pulsatile, targeted.
By origin/status: official (monograph in IP/BP/USP), non-official, proprietary brand, generic, fixed-dose combination (FDC), extemporaneous (compounded in pharmacy against prescription).
By sterility requirement: sterile (parenteral, ophthalmic, large wound/irrigation preparations) and non-sterile, with microbial limits.

Routes of administration — what each route forces on the formulation

Oral: cheapest, safest, self-administered; limited by gastric acid and enzymes, first-pass metabolism, food effects and slow onset; unsuitable in vomiting or unconscious patients. Needs palatability and a disintegration/dissolution step.
Sublingual/buccal: rapid, bypasses first pass (glyceryl trinitrate); small dose only, taste critical.
Rectal: usable in vomiting, unconscious patients and infants; partial first-pass bypass; absorption erratic, poor patient acceptance.
Parenteral: 100% bioavailability by IV, immediate action, usable when oral fails; must be sterile, pyrogen-free, particle-free and near isotonic/iso-pH; invasive, costly, needs trained staff, not retrievable.
Topical/transdermal: local action with low systemic exposure, or steady systemic input; stratum corneum limits flux to potent, low-dose, lipophilic drugs.
Ophthalmic/otic/nasal: sterility (eye), tonicity and pH comfort, small volume (one eye drop ≈ 50 µL against a tear capacity of ~30 µL, so most drains away).
Pulmonary: direct delivery to the lung with small doses; needs 1–5 µm aerodynamic particle size and correct inhaler technique.

Preformulation — the data that decides the dosage form

Organoleptic and bulk properties: colour, odour, taste; particle size and shape, bulk and tapped density, Carr's index/Hausner ratio, angle of repose (flow), crystallinity and polymorphism, hygroscopicity.
Solubility and pKa: aqueous solubility across pH, intrinsic solubility, salt selection, partition coefficient (log P) for membrane permeability; solubility and permeability together give the BCS class that guides the choice of form.
Stability: hydrolysis, oxidation, photolysis, racemisation; forced-degradation studies; drug–excipient compatibility by DSC/FTIR/HPLC.
Melting point, loss on drying, moisture sorption decide drying, granulation and packaging.
Decision logic: poor flow and low dose → granulate or go to a liquid/capsule; acid-labile → enteric or parenteral; bitter → coat, encapsulate or form an insoluble salt; low solubility → salt, co-solvent, micronisation, solid dispersion; unstable in water → dry powder for reconstitution.

Excipients, containers and labelling standards

Functional roles: diluents (lactose, MCC, dibasic calcium phosphate), binders (PVP, starch paste, HPMC), disintegrants and superdisintegrants (starch, croscarmellose, sodium starch glycolate), lubricants/glidants (magnesium stearate, talc, colloidal silica), vehicles (purified water, glycerin, propylene glycol, alcohol, fixed oils), preservatives (methyl/propyl paraben, benzalkonium chloride, benzyl alcohol), antioxidants (sodium metabisulphite, BHA/BHT), buffers (citrate, phosphate), chelators (EDTA), viscosity builders (sodium CMC, carbomer, xanthan), bases (white soft paraffin, emulsifying ointment, theobroma oil, PEGs).
An excipient is never inert: lactose in lactose intolerance, aspartame in phenylketonuria, benzyl alcohol in neonates, tartrazine and sulphites as sensitisers, sorbitol as a laxative — so excipients are disclosed and controlled by pharmacopoeial monographs.
Containers: well-closed, tight, light-resistant, single-dose, multi-dose, pressurised. Glass types per pharmacopoeia — Type I borosilicate (most resistant, for parenterals and sensitive products), Type II treated soda-lime, Type III soda-lime (non-parenteral), Type NP general purpose. Plastics (LDPE/HDPE/PP/PET), blisters (PVC/PVdC–aluminium), strips, Alu-Alu for moisture-sensitive products; rubber and elastomeric closures tested for extractables, fragmentation and self-sealing.
Indian legal framework: Drugs and Cosmetics Act, 1940 and Rules, 1945; Indian Pharmacopoeia 2026 (10th edition, in effect from 1 July 2026, IPC Ghaziabad) with its amendment lists is the statutory standard, with BP/USP recognised for non-IP drugs. Revised Schedule M prescribes GMP and premises requirements, with a Pharmaceutical Quality System, product quality review and computerised-system controls added by the 2023 revision; implementation for smaller manufacturers was phased by CDSCO notification, so confirm the current deadline before quoting it. Manufacturing licences on Form 25/28 (non-specified/specified drugs) are issued by State Licensing Authorities; new drugs and FDCs are approved centrally by CDSCO/DCGI under the New Drugs and Clinical Trials Rules, 2019.
Schedules to remember: H and H1 (prescription-only; H1 drugs need a separate register for three years and a box warning), X (narcotic/psychotropic-type controls), G (caution: to be taken under medical supervision), P (shelf life/expiry), K (classes of drugs exempted from certain provisions, including household remedies), F/F1 (vaccines, blood products), J (diseases for which no cure may be claimed).
Labelling essentials: proper and generic name, strength, net content, batch no., manufacturing and expiry dates, manufacturing licence no., manufacturer's name and address, "Schedule H/H1 — warning", storage conditions, Rx symbol, and for most formulations the retail price; ceiling prices for scheduled formulations are fixed by the NPPA under the Drugs (Prices Control) Order, 2013. Since the 22 September 2025 GST revision the slabs are 5%/18%/40%; most medicines fall in the lowest slab with several life-saving drugs exempt — rates change by notification, so verify the current rate.

Stability, storage and shelf life

Storage terminology (IP): cold 2–8 °C; cool 8–25 °C; room temperature; "store below 30 °C"; "protect from light and moisture"; "do not freeze" for vaccines and biologicals (cold chain 2–8 °C).
Shelf life/expiry: the period over which the product remains within specification, typically not less than 90% of the labelled content with degradants under limit; most degradation follows first-order or pseudo-zero-order kinetics.
Stability studies: long-term, intermediate and accelerated (40 °C ± 2 °C / 75% RH ± 5% RH for six months) per ICH Q1A as adopted in India; India falls largely in Climatic Zone IVb, so long-term testing is commonly at 30 °C ± 2 °C / 75% RH ± 5% RH.
Reconstituted and opened products get a separate, much shorter in-use shelf life, stated on the label.

Key points

Dosage form - the API plus excipients in a container, designed to deliver an accurate dose by a defined route.
Excipient - non-active ingredient with a defined function; never assume it is pharmacologically or allergenically silent.
Biphasic forms - suspensions and emulsions; thermodynamically unstable, so they carry the direction "shake well before use".
Monophasic forms - solutions; dose-uniform by nature, bulkier and more prone to hydrolysis.
First-pass metabolism - the reason sublingual, rectal, transdermal and parenteral routes exist for some drugs.
BCS class - solubility plus permeability; Class I/III may qualify for a biowaiver, Class II/IV usually need enabling formulation.
Polymorphism - different crystal forms of the same API differ in solubility and stability; the chosen form must be controlled.
Preformulation - solubility, pKa, log P, flow, polymorph, stability and compatibility data that dictate the dosage form.
Unit dose versus multi-dose - multi-dose aqueous containers need an antimicrobial preservative; single-dose parenterals do not.
Sterile forms - parenterals and ophthalmics must be sterile, pyrogen-free and particle-free; also near isotonic and comfortable in pH.
Glass Type I - borosilicate, highest hydrolytic resistance, default for parenterals and alkali-sensitive products.
Official versus proprietary - a monograph in IP 2026 makes the standard legally enforceable; a brand name does not.
FDC - fixed-dose combination; needs separate central approval and rational therapeutic justification.
Schedule H1 - prescription drugs (certain antibiotics, anti-TB, habit-forming agents) with a mandatory separate register and boxed warning.
Revised Schedule M - GMP for premises, plant and quality system; adds a formal Pharmaceutical Quality System and product quality review.
Shelf life - normally the time to 90% of labelled potency; Indian long-term stability usually 30 °C/75% RH (Zone IVb).
Alligation and dilution - standard tools for making a required strength from available stocks.
Paediatric dosing - body-surface-area scaling is more reliable than Young's or Clark's rules.

Formulas and examples

% w/w = (g solute / g product) × 100; % w/v = (g solute / mL product) × 100; % v/v = (mL solute / mL product) × 100
Ratio strength 1 : n (w/v) = (1/n) × 100 % w/v; ppm = mg solute per litre of water-like solution = % w/v × 10,000
Dilution: C₁V₁ = C₂V₂ (C = strength in same units, V = volume in same units)
Alligation (two stocks): parts of stronger : parts of weaker = (desired − weaker) : (stronger − desired)
Young's rule (1–12 yr): child dose = adult dose × age(yr) / [age(yr) + 12]
Clark's rule: child dose = adult dose × weight(lb) / 150 (≈ weight(kg)/68)
BSA method: child dose = adult dose × BSA(m²) / 1.73; Mosteller BSA = √[height(cm) × weight(kg) / 3600]
Tonicity: NaCl to add (g) = 0.009 × V(mL) − Σ[E_i × weight of drug_i (g)]; E = NaCl equivalent of 1 g drug
Displacement value (suppositories): base required = (n × mould capacity) − (n × drug per unit / DV)
Shelf life (first order): t₉₀ = 0.105 / k; t₁/₂ = 0.693 / k (k = rate constant, per month or per year)

1. Alligation — 500 mL of 20% w/v from 70% and 10% stocks. Parts of 70% = 20 − 10 = 10; parts of 10% = 70 − 20 = 50; total 60 parts. 70% stock = (10/60) × 500 = 83.3 mL; 10% stock = (50/60) × 500 = 416.7 mL. Check: 83.3 × 0.70 = 58.3 g, 416.7 × 0.10 = 41.7 g → 100 g in 500 mL = 20% w/v. ✓

2. Dilution and ratio strength. Prepare 250 mL of 5% w/v dextrose solution from a 25% w/v stock. V₁ = C₂V₂ / C₁ = (5 × 250)/25 = 50 mL of stock, made up to 250 mL with purified water. The same 5% w/v = 50 mg/mL = ratio strength 1 : 20 (w/v) = 50,000 ppm. A 0.02% w/v benzalkonium chloride preservative = 0.2 mg/mL = 1 : 5000 = 200 ppm.

3. Paediatric dose by three methods. Adult dose 500 mg; child 6 years, 18 kg, BSA 0.75 m².

Young's rule: 500 × 6/(6 + 12) = 166.7 mg
Clark's rule: 18 kg ≈ 39.7 lb → 500 × 39.7/150 = 132 mg
BSA: 500 × 0.75/1.73 = 216.8 mg

The three differ by over 60%; BSA (or an mg/kg dose from the product label) is preferred, and the practical dose is rounded to a measurable volume of syrup.

4. Isotonic eye drops. 30 mL of 1% w/v ephedrine hydrochloride drops; E = 0.30. Drug present = 0.3 g; NaCl equivalent contributed = 0.3 × 0.30 = 0.09 g. NaCl needed for isotonicity = 0.009 × 30 = 0.27 g. NaCl to add = 0.27 − 0.09 = 0.18 g (0.6% w/v).

5. Suppositories by displacement value. Make 12 suppositories of 1 g mould, each with 200 mg zinc oxide (DV = 4.7); calculate for 14 to allow for wastage. Drug = 14 × 0.2 = 2.8 g; base displaced = 2.8/4.7 = 0.596 g. Base required = (14 × 1) − 0.596 = 13.40 g of theobroma oil, with 2.8 g zinc oxide.

6. Shelf life. A solution degrades by first order with k = 0.0035 per month. t₉₀ = 0.105/0.0035 = 30 months; t½ = 0.693/0.0035 ≈ 198 months. The labelled expiry is set from t₉₀, not t½.

Feature	Solid (tablet/capsule)	Liquid (solution/suspension)	Semisolid (ointment/cream)	Parenteral
Dose accuracy	Highest (unit dose)	Depends on measuring device	Approximate (per application)	High
Chemical stability	Best	Lowest (hydrolysis)	Intermediate	Needs strict control
Onset of action	Slower (disintegration + dissolution)	Faster	Local, slow	Fastest (IV)
Patient groups	Adults, school children	Paediatric, geriatric, dysphagia	Skin and mucosa	Emergency, unconscious
Sterility	Not required	Only for eye/injectable	Only for eye/wounds	Mandatory
Cost per dose	Lowest	Moderate (bulk, freight)	Moderate	Highest

Where it is used

Formulation development (F&D) and R&D roles at Sun, Cipla, Dr. Reddy's, Lupin, Zydus, Alkem, Mankind, Torrent and CDMOs — selecting the form, excipients and pack for a new generic or FDC.
Production and packing in Schedule M-compliant plants in Baddi, Sikkim, Ahmedabad, Hyderabad, Goa and Pithampur — granulation, compression, filling, sterile fill-finish and blister/strip packing lines.
QA/QC and regulatory affairs — monograph testing against IP 2026, stability chambers at 30 °C/75% RH, dossier filing with CDSCO and with the US FDA/EU for exports.
Hospital and community pharmacy — dispensing, extemporaneous compounding, reconstituting dry syrups and injections, cold-chain handling of vaccines under Ayushman Bharat and the Universal Immunisation Programme.
Public-sector and policy roles — drug inspectors and government analysts under the Drugs and Cosmetics Act, NPPA price monitoring, Jan Aushadhi generic forms, and quality-control work in state drug testing laboratories.
Veterinary, nutraceutical and Ayush manufacture — the same dosage-form science under separate schedules and standards.

Interview questions

Q: Why can a drug not simply be given as the pure chemical? A: Doses are often a few milligrams, which cannot be measured or handled accurately; the dosage form adds bulk, protects the drug, masks taste, controls release and delivers a reproducible dose.
Q: Which is the most common dosage form and why? A: Oral tablets — they are stable, dose-accurate, cheap to make and pack, easy to transport and self-administered.
Q: Differentiate pharmaceutical equivalence and bioequivalence. A: Pharmaceutical equivalents have the same API, salt, strength and form; bioequivalents additionally give statistically comparable rate and extent of absorption.
Q: Why do suspensions and emulsions carry "shake well before use"? A: They are biphasic and thermodynamically unstable, so the dispersed phase settles or creams; redispersion restores dose uniformity.
Q: What is the significance of pKa and log P in preformulation? A: pKa predicts ionisation and hence solubility at a given pH and the feasibility of salt formation; log P indicates lipophilicity and membrane permeability.
Q: Why must a multi-dose aqueous preparation contain a preservative but a single-dose ampoule need not? A: Repeated withdrawal risks microbial entry during use; a single-dose container is sterilised, used once and discarded.
Q: What are Type I, II and III glass? A: Type I is borosilicate with the highest hydrolytic resistance (parenterals); Type II is surface-treated soda-lime; Type III is untreated soda-lime for non-parenteral use.
Q: What does Schedule M cover, and what did its revision change? A: GMP for premises, plant and equipment; the revision added a formal Pharmaceutical Quality System, product quality review, stability and computerised-system requirements, implemented in a phased manner by CDSCO.
Q: Which Schedule mandates a separate register for dispensing, and why? A: Schedule H1 — to track antibiotics, anti-TB and habit-forming drugs for three years and curb misuse and resistance.
Q: What climatic zone is India for stability testing and what does that mean? A: Mostly Zone IVb (hot and very humid), so long-term studies are commonly run at 30 °C ± 2 °C and 75% RH ± 5% RH.
Q: If a drug is destroyed by gastric acid, what are the options? A: Enteric coating, a parenteral or sublingual form, a prodrug, or co-administration with an acid suppressant.
Q: Why is a 50 µL eye drop considered inefficient? A: The normal tear film holds only about 30 µL, so most of the drop overflows or drains through the nasolacrimal duct, giving low ocular bioavailability and some systemic absorption.

Common mistakes

Confusing % w/v with % w/w, or treating ratio strength 1:1000 as 1% instead of 0.1% w/v.
Mixing units in dilution and alligation problems (mL with g, mg with g) and not checking the answer back against the total solute.
Applying Young's or Clark's rule to neonates or to drugs dosed by body surface area, and quoting the result to a precision the measuring device cannot deliver.
Calling excipients "inert" in a viva — several are allergenic, laxative or contraindicated in specific patients.
Forgetting the displaced base in suppository calculations, or omitting the drug's contribution when computing sodium chloride for isotonicity.
Confusing the pharmacopoeial storage terms (cold, cool, room temperature) and treating t½ as the shelf life instead of t₉₀.
Naming withdrawn or superseded standards and schedules — IP 2026 (10th edition) replaced IP 2022 as the current statutory compendium, and the Schedule M timelines were notified in phases.