W5.3_Routes of Administration

Question 1

How are drugs put into the body?

Answer 1

• ∵ Human body is designed to take in nutrition and stop bacterial infection
• ∴ Drugs require technical input to trick the body defences

Question 2

What are the pros and cons, and examples of oral drugs?

Answer 2

• Most common (60%), simple
• Convenient and safe (no infection risk, body designed to absorb from gut)
• Modified-release can tailor drug delivery by altering its releasing rate
• High surface area of intestinal villi + well-vascularised provide good blood supply -> excellent absorptive capacity
• Lag time to reach effective concentration at interest site (dissolution as rate determining step, absorption depends on contents of stomach/small intestine)
• Hostile environment (X deliver proteins due to enzymes in stomach, pH has significant effect on solubility of drug
• Variability (GI tract’s capacity for absorption changes with age/sex/ethnicity, disease state)
• First pass metabolism (hepatic portal vein delivers absorbed drug from guts to liver for metabolism -> some metabolite immediately produced and excreted, where metabolised drugs can’t be used extensively)
• Difficult to reverse therapy
• Irritation to GI system (to mucosa and cause significant problems, ex. acid induced gastric ulcer)

Question 3

What are the pros and cons, and examples of buccal and sublingual drugs?

Answer 3

• Used for prolonged release of pain medication/neuroleptica
• Sublingual are used in fast treatment of angina pectoris (with glyceryl trinitrate)
• Have problems with taste masking

Question 4

What are the pros and cons, and examples of nasal, occular, and aural drugs?

Answer 4

• Nasal mainly used to treat rhinitis
• Aural generally used for young children with otitis media
• Nasal and aural encompass liquid and semi-liquid applications, ocular can also be tablets
• Locally to treat ailments of nose/eyes/ears
• Ocular most demanding, has to be sterile and isotonic (same ion concentration as eye fluid)

Question 5

What are the pros and cons, and examples of respiratory drugs?

Answer 5

• Can be delivered in gaseous (g/g)/mist(l/g)/aerosol(s/g), where drug particle size is critical for adequate drug deposition (too big leads to reflex swallowing, too small leads to direct exhalation)
• Local/systemic with protein delivery possible
• Minimal side effects for locally
• Many different devices to deliver drugs (pressurised metered-dose inhaler (pMDI), dry powder inhaler (DPI), nebuliser)
• Very large surface area for systemic delivery
• Can deliver macromolecules
• Fast relief treatment for asthma
• Patient has to trained
• DPI not suitable for children/patients with inadequate lung capacity
• Difficult formulation with tight parameters
• Unwanted systemic effect possible due to swallowing

Question 6

What are the pros and cons, and examples of parenteral drugs?

Answer 6

• Subcutaneous (just under skin), intramuscular (muscle), intravenous (veins)
• Rapid onset without first pass effect
• Can deliver proteins/macromolecules
• Can apply to unconscious patients/with swallowing difficulties
• Many different injection sites
• Infection risk and pain
• Only liquid preparations
• Cannot administer when patient moves
• Irreversible

Question 7

What are the pros and cons, and examples of topical drugs?

Answer 7

• Used for local conditions/systemic
• Formulation: cream (more aqueous)/ointment (more oily)/gel (multi-component/colloidal)/patch (slow release of high potency drugs)
• Limited side effects
• Non-invasive
• Local treatment without systemic effect, used for additional treatment
• Poor absorption but hard to reverse
• Less accurate in dosage
• Ointments can leave oily feeling
• Can have a grade of systemic absorption
• Soft skin and callused skin have different absorption rate

Question 8

What are the pros and cons, and examples of rectal drugs?

Answer 8

• Used for rectal suppository/foams/enemas
• Well-vascularised region in rectum (alternative to oral route, erratic absorption, used for drugs inactivated in GI tract)
• Local/systemic effect (ex. constipation/inflammation/epilepsy)
• To avoid first pass metabolism

Question 9

How can the choice of route be determined for drugs?

Answer 9

• ∵ Choice of route determined by physical characteristics of drugs/release and absorption rate/hepatic metabolism/high concentration needed at particular site/therapeutic use
• ∴ No single route is ideal for all drugs