Continuation On Dosage Form

Inhalers

  • Definition:
    • Inhalers are either solutions, suspensions, or emulsions of drugs mixed with inert propellants, maintained under pressure in an aerosol dispenser.
    • Mechanism of Action: The aerosol releases a dose of medication in the form of droplets of 50 µm diameter or smaller through a spring-loaded valve that incorporates a metering device. The patient inhales the released drug through a mouthpiece.
    • Example: Ventolin Inhaler

Nebulizer (Atomizer)

  • Definition:
    • A nebulizer is a device that administers medication in the form of a liquid mist directly to the airways.
  • Common Uses:
    • Primarily used in treating asthma and other respiratory diseases.
    • Process: It pumps air or oxygen through the liquid medicine to convert it into vapor, which is inhaled by the patient.
  • Prescribing Preference:
    • Doctors usually prefer inhalers for patients due to:
    1. Lower cost
    2. Greater portability
    3. Reduced risk of side effects
    • Usage Limitation: Nebulizers are typically reserved for severe cases of respiratory disease or acute attacks.

Ophthalmic Dosage Forms

  1. Eye Drops:
    • Composition: Saline-containing drops used to deliver medication to the eye.
    • Contains: Depending on the condition, may include steroids, antihistamines, or topical anesthetics.
    • Non-medicated options are available as lubricating and tear-replacing solutions.
  2. Ophthalmic Ointment & Gel:
    • Sterile semi-solid preparations designed for application to the conjunctiva or eyelid margin.

Otic Dosage Forms

  • Ear Drops:
    • Definition: Solutions, suspensions, or emulsions of drugs instilled into the ear using a dropper.
    • Usage: Primarily to treat or prevent ear infections, notably of the outer ear and ear canal.

Nasal Dosage Forms

  • Nasal Drops and Sprays:
    • Definition: Drugs in solution administered into the nose via a dropper or squeeze bottle.
    • Effect: Can provide a local effect, e.g., antihistamine or decongestant effects.

General Considerations in Dosage Form Design

  • Choices Influenced By:
    • A balance of scientific, therapeutic, patient, and economic factors.

Factors Influencing Dosage Form Choice

  1. Nature of the Drug (Physicochemical Properties):

    • Physical and Chemical Characteristics: They determine the suitable dosage form for the active pharmaceutical ingredient (API).
    • Key Properties: a. Solubility:
      • Poorly soluble drugs need suspensions, emulsions, or solubilized systems.
      • Highly soluble drugs can use solid dosage forms.
        b. Stability:
      • Drugs unstable in water → require dry powders for reconstitution.
      • Light or air-sensitive drugs → use coated tablets or ampoules.
        c. Taste/Odor:
      • Bitter drugs → use coated tablets or capsules to mask taste.
        d. pKa and Ionization:
      • Determines absorption and formulation pH.
      • pKa: The pH at which 50% of the drug is ionized and 50% is unionized.
      • Ionization Impact:
        • Unionized form: More lipid-soluble, better for membrane permeation (absorption).
        • Ionized form: More water-soluble, favorable for aqueous formulations (solutions, injections).

  2. Melting Point:

    • Importance: Crucial for dosage forms designed to melt at body temperature.
    • Application in Suppositories:
      • Bases like cocoa butter or specific polyethylene glycols used in suppositories should have melting points close to 37°C for proper drug release post insertion.
    • Lower melting point compounds usually exhibit higher solubility and absorption compared to high-melting compounds.

  3. Particle Size/Surface Area:

    • Particle Size Ranges and Dosage Form Associations:
      • Nanosize (
      • Associated with suspensions, topical creams, and targeted injections.
      • Micronized (1 - 10 μm):
      • Utilized in inhalers (dry powder inhalers or DPIs) and ophthalmic solutions.
      • Coarse/Granules (>100 µm):
      • Commonly found in tablets, capsules, and suspensions.
    • Key Implications:
      • Smaller size enhances solubility/absorption and allows for deeper tissue penetration.
      • Improves the ability of poorly soluble drugs to reach lower airways and enhances bioavailability.
      • Smaller particle sizes also provide better flowability in manufacturing and ease of suspension in liquids.

Biopharmaceutical Considerations

  • ADME: Refers to the processes of Absorption, Distribution, Metabolism, and Excretion of drugs.
  1. Desired Onset and Duration of Action:
    • Rapid effect: Favored dosages include injections and sublingual tablets.
    • Sustained effect: Consider extended-release tablets and transdermal patches.
  2. Site of Absorption:
    • GI tract: Typically connects to oral dosage forms.
    • Skin/mucosa: Corresponds with topical, transdermal, or buccal formulations.
  3. Bioavailability:
    • Poor oral bioavailability drugs often necessitate parenteral administration methods.
  4. First-pass Metabolism:
    • Substantial metabolism in the liver might require alternative routes such as parenteral, sublingual, or transdermal administration.

Route of Administration

  • Unique Requirements: Each route imposes specific considerations that affect the choice of dosage form.
  1. Parenteral Route:
    • Requires strict sterility, defined physical form, absorption rate specifications, intended site of action, and volume limitations.
  2. Oral Route:
    • Requires designs that enable drugs to withstand the harsh gastrointestinal (GI) environment.
    • Example: The acidic environment (pH 1.5-2.5) can degrade acid-sensitive drugs; therefore, enteric-coated tablets or capsules are utilized to protect drugs until they reach the more neutral pH of the intestines.