What does drug half-life mean?
The half life or ‘t1/2’ of a drug is the time taken for the blood concentration to fall by a half.
What is the therapeutic range?
Maximum safe concentration (MSC) / Minimum effective concentration (MEC) = therapeutic window (T)
What is the acccumulated dose at 18 hours?
0 hours = 100mg = 100mg accumulated dose
6h = 100 + 50 = 150mg
12h = 100 + 50 +25 = 175mg
18 hours = 100 + 50 + 25 + 12.5 = 188.
Why use oral administration?
convenient economical portable safe (usually) pain-free variety of dosage forms no sterilisation needed
BUT
Concordance required
absorption variable
What is bioavailability?
The proportion of the drug in a dosage form which reaches the systemic circulation.
What is first-pass metabolism?
The liver (or gut wall) extracts and metabolises some drugs so efficiently that the amount reaching the systemic circulation is considerably less than the amount absorbed.
Why use sublingual administration
Because the same drug, given sublingually, bypasses the gut wall and liver, avoiding first-pass effect and thus more drug reaches the circulation.
Advantages and disadvantages of sublingual?
ADV-
-bypasses first pass effect
-bypasses destruction by stomach acid
-drug stability maintained because the pH of saliva is relatively neutral
-may cause immediate pharmacological effects.
DISADV
- limited to certain types of drugs that can be taken in small doses
- may lose part of the drug if swallowed.
What is the sublingual route?
Sublingual administration involves placing a drug under your tongue to dissolve and absorb into your blood through the tissue there.
Why use the rectal route of administration?
- useful in the presence of nausea and vomiting
- may reduce first-pass metabolism to a limited extent
- mainly used for topical effects, e.g. treatment of haemorrhoids.
Advantages and disadvantages of rectal route?
ADV - partially bypasses first-pass effect - bypasses destruction by stomach acid - ideal if drug causes vomiting - ideal in patients who are vomiting or comatose. DISADV- - drugs may irritate the rectal mucosa - not a well-accepted route - not convenient
Advantages of intravenous route?
ADV
- 100% bioavailability (bypasses absorption)
- rapid effects
- useful in emergencies
- allows titration of dosage since able to adjust dose
- suitable for large volumes
- irritating substances an be given if well diluted
- ideal for high molecular weight proteins and peptide drugs
Disadvantages of intravenous route?
DISADV
- relatively expensive
- requires trained administrators
- increased risk of ADR
- requires slow infusions
- unsuitable for oily substances
- pain
To what degree are Intradermal (I.D) Subcutaneous (S.C) Intramuscular (I.M) administered?
I.D - 10 to 15 degree angle
S.C - 45 degree angle
I.M - 90 Degree angle
Advantages of subcutaneous injections?
ADV
- can be given by patient, e.g. insulin.
- absorption is usually complete
- absorption can be fast from aqueous solution
- suitable for some poorly soluble suspensions and slow-release implants.
Disadvantages of subcutaneous injections?
DISADV
- can be painful
- can be a problem finding suitable sites for repeat injection
- irritant drugs can cause local tissue damage
- maximum of -2ml injection
Advantages of IM injections
ADV
- Prompt absorption of aqueous solutions
- slow, sustained absorption from repository preparations
- suitable for moderate volumes
- suitable for oily vehicles and some irritating substances
- preferable to IV if patient must self-administer
Disadvantages of IM injections
DISADV
- often the most painful routes
- immediate cost
- trained administrators needed
- can cause IM haemorrhage (problematic in anticoagulated patients)
- can cause elevation of laboratory tests, especially creatine kinase.
Advantages of inhaled route
ADV
- ideal for gases
- effective for patients with respiratory problems
- doses can be titrated
- localised effect to target lungs: lower doses used compared to that with oral or parenteral administration
- fewer systemic side-effects
Disadvantages of inhaled route
DISADV
- most addictive route
- patient may have difficulty regulating dose
- some patients may have difficulty using inhalers.
Advantages of transdermal route
ADV -
- Bypasses first-pass effect
- convenient and painless
- ideal for drugs that are lipophilic and have poor oral bioavailability
- ideal for drugs that are quickly eliminated from the body
- irritating substances can be given if well diluted
Disadvantages of transdermal route
DISADV0
- some patients are allergic to patches which can cause irritation
- drug must be highly lipophilic
- may cause delayed delivery of a drug to the pharmacological site of action
- limited to drugs that can be taken in small daily doses.
Advantages of topical route
ADV
- suitable when local effect of drug is desired
- may be used for skin, eye, vaginal and intranasal products
- minimises systemic absorption
- easy for patient
Disadvantages of topical route
DISADV
- some systemic absorption can occur
- unsuitable for drugs when high molecular weight and poor lipid solubility
- may cause delayed delivery of a drug to the pharmacological site of action
- limited to drugs that can be taken in small daily doses.
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Drug naming and formulation20
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Administration25
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Absorption studymate16
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Distribution studymate12
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Administration exercise studymate11
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Elimination studymate9
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Site of action studymate10
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Adverse drug reactions studymate11
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Absorption12
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Distribution6
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Elimination (metabolism and excretion)15
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ADR18
