part 1 Flashcards
(42 cards)
drug administration methods: speed of onset
I/V: 30-60 seconds (FASTEST)
Inhalation: 2-3 mins
Sublingual: 3-5 mins
I/M: 10-20 mins
S/C (subcutaneous): 15-30 mins
Rectal: 5-30 mins
Oral 30-90 mins (SLOWEST)
Duration of action
- Dependant upon whether effects are local or systemic (ADME)
- Half-life of drug, 1st pass effect - enzymatic susceptibility
- Type of formulation administered (e.g. uncoated tab v CR tab)
Patient factors
- Is patient conscious?
- Fear (or phobia) of a particular route
- Age of patient?
- Any surgery?
e.g. Age, disease
oral drug requirements
Oral Drug MUST be in solution before it can be absorbed and exert its biological effect
Enteric coating
- To prevent disintegration in stomach at low pH
- In drugs that irritate the mucosal lining
- In drugs that break down under acidic conditions
Delays release of drug until it reaches s. intestine
Delays onset of action thus therapeutic response
Protects drug from degradation: - improves oral bioavailability compared to conventional uncoated
tablets.
Protects mucosal lining of stomach from effects of drug (aspirin) – ulceration
E.C. Formulations
Granules contained within a rapidly dissolving hard gelatin capsule or rapidly disintegrating tablet.
Enable to pass through pyloric sphincter even when closed
ELIMINATES
E.C granules/ pellets exhibit a gradual but continual release of drug from stomach to duodenum
Avoids complete dose release of drug as seen with E.C tablets
Bioavailability
Aqueous solution > aqueous suspensions > hard gelatin capsules > uncoated tablet > coated tablet
Tablets go through high compression force -> slower in dispersing the drug particles from the tablet after administration (excipients and drugs are compressed together)
Buccal & Sublingual
buccal: a medicine given between the gums and the inner lining of the mouth cheek
sublingual: under the tongue
Very rapid effect
100 % bioavailability – No 1st pass effect
Capsules
Soft gelatin- drug is dispersed or dissolved in non-toxic, non aqueous vehicle
Drug released is dependent on dissolution of flexible shell -> vehicle disperses, drug is dissolved in GI
fluids -> releasing drug -> rapid absorption (depending on the solubility of drug, solution: faster,
suspension: slower)
Factors affecting bioavailability:
- Solubility of drug in vesicle
- P.S of drug
- Nature of vesicle (hydrophilic or lipophilic)
Digestible/non-digestible oil
Digestible oil (lipophilic drug): can be absorbed via fat absorption process
Non digestible oil/less lipophilic drug: bioavailabilty depends on drug partitioning out of oil
phase
Hard gelatin- Provided shell dissolves rapidly in GI fluid, drug is released rapidly and efficiently
Bioavailability dependent upon rapid dissolution of gelatin shell AND Rate of penetration of GI fluids
into encapsulated mass
Dissolution of HGC
table …
Excipients
To aid in preparation (Binders- Bind the tablet ingredients together)
Patient acceptability (mask taste eg. Sweeteners)
Aid functioning of dosage form as a delivery system (Disintegrants -> so drugs can disintegrate in the
body)
oral administration summary
Aqueous solution: solution of drugs in GI fluids -> absorption from GIT to blood -> first pass into
the liver -> systemic circulation
Aqueous suspension: suspension of fine particles of drug in GI fluids -> dissolution -> solution of
drug in GI fluids -> absorption from GIT to blood -> first pass into the liver -> systemic circulation
Hard gelatin capsule and uncoated tablet: disintegration -> granules -> deaggregation -> suspension of fine particles of drug in GI fluids -> dissolution -> solution of drug in GI fluids -> absorption from GIT to blood -> first pass into the liver -> systemic circulation
Eye – drops, suspn, gels, oint
LOCAL EFFECT ONLY
Dosage forms must be: STERILE (free of foreign particles, free of pathogens)
be Isotonic and pH neutral
ALL formulation is lost in 10-20 min (Improve duration of action using gels or ointments)
Parenteral products
Intradermal (diagnostic tests)
Subcutaneous S/C (e.g. insulin)
Intramuscular I/M (e.g. vaccines)
Intravenous I/V (e.g. infusions, drugs, EMERGENCIES)
Intra-arterial I/A (EMERGENCY)
FYI: parenteral = administered or occurring elsewhere in the body than the mouth and alimentary canal.
Why use the parenteral route?
- To ENSURE adequate delivery
- To TARGET delivery e.g. to organ or malignancy
- Oral route unavailable…unconscious, elderly
- Low or NO oral bioavailability
- For Unstable drug (pH) in the stomach
- To give a LOCAL effect (anaesthesia)
- To give a rapid effect
- To give sustained effect
- To assure compliance – administered by trained personnel
- In EMERGENCIES!!!
Potential issues with the parenteral route
DISADVANTAGES: - Dosage forms MUST be sterile
- Costs - drug prep & administration
- Effects (adverse) are almost immediate – no way back!
Formulation of Parenteral Products
Factors to consider:
Factors to consider:
1) Route
2) Volume of injection
3) Vehicle
4) Osmotic pressure (isotonic: 0.9% w/v NaCl)
5) Use of preservative
6) pH – transfer across biol. membranes
7) Stability of components
Role of vehicle
- must mix with the circulating blood (miscible)
- must NOT precipitate from solution
Properties of vehicle
- pharmacologically inert (must not interfere with drugs effect)
- non-toxic (non-sensitizing, non-irritating)
- maintain solubility of drug
- chemically and physically stable (inert)
- unaffected by pH changes
- must be an aqueous solution (e.g. water for injection)
Hypotonic and Hypertonic solutions
Injection of Hypertonic solution results in rapid EFFLUX (goes out) of H2O
- Cell shrinks and becomes crenate
- REVERSIBLE
- When osmotic pressure returns to normal - cell swells
Injection of Hypotonic solution results in rapid INFLUX of H2O
- Cell (r.b.c) swells and bursts
- IRREVERSIBLE
- Severity dependent on no. of cells affected
Rectal route – suppository / gel
Useful where drug is inactivated by GI fluids (drug is ineffective when taken orally due to incompatibility with GI fluids) or by 1st pass effect
Useful if patient is: sedated, vomiting, can’t swallow or not safe to swallow
systemic effect: e.g. paracetamol supp., hydrocortisone supp.
local effect: e.g. laxative effect
Skin
Topical/Local effects - Creams, ointments, pastes
Systemic effects - Transdermal patches
Nasal – sprays, drops, inhalations
Sprays generally used for systemic effects (steroid nasal spray)
Drops generally for local effects (decongestants)
Must use preservatives
