18- Drug concentration vs time profiles after an oral or extravascular dose

Question 1

What extravascular routes of drug administration

Answer 1

subcutaneous injection (e.g. insulin)
intramuscular injection (e.g. some antibiotics)
rectal (e.g. analgesics, anti-nausea)
buccal (mucoadhesive tablets and films, absorbed through the oral mucosa)
Transdermal (absorbed through the skin)

Question 2

What are topical routes of administration

Answer 2

Eye, ear, nasal drops and solutions
Inhalation
Rectal (e.g. laxative enema, hydrocortisone for ulcerative colitis)
Dermal (into the skin)
Vaginal
Topical creams and ointments

Question 3

What are routes of injection

Answer 3

Epidural into the epidural space (anaesthesia)
Intracerebral directly into the brain
Intraventricular directly into the ventricles of the brain
Intra-arterial into an artery (rare, may be accidental)
Intra-articular into the joint space (osteoarthritis)
Intracardiac directly into the heart
Intraocular into the eye
Intraosseous directly into bone
Intraperitoneal into the peritoneal cavity
Intrathecal into the spinal canal (anaesthesia, chemotherapy)

Question 4

What factors influence systemic effects

Answer 4

Bioavailability – fraction of dose absorbed systemically

Rate of absorption – how quickly the drug is absorbed
first order: constant proportion per time, units /h
zero order: constant amount per time, units mg/h
a mixture of first order and zero order
more complex absorption profiles – especially with new modified release formulations

Question 5

When do plasma concentrations increase with time

Answer 5

When the absorption rate is greater than the elimination rate

Question 6

After how many half lives does absorption stop

Answer 6

5 absorption§ half-lives (97% absorbed)

Question 7

What factors determine the concentration-time profile after a single oral dose

Answer 7

Dose
Bioavailability
Salt /molar correction
Input rate (ka)
Elimination rate (k = CL/V)
Time after administration

Question 8

What determines the time to maximum concentration after an oral dose

Answer 8

Depends on absorption rate (formulation)
Depends on elimination rate (patient characteristics)

Question 9

What formulations does zero order absorption apply

Answer 9

Iv and Transdermal patches - things that have a constant supply of drug

Question 10

What happens to concentration when input stops in zero order absorbtion

Answer 10

The concentration declines expinentially