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Flashcards in Prescribing in special populations Deck (17):

6 steps of rational drug prescribing

- define the patient's problem
- set therapeutic pbjectives
- verify the suitability of the drug
- write a prescription
- give information, instructions and warnings
- monitor and stop the treatment


List of special risk groups

- elderly
- very young
- liver disease
- kidney disease
- pregnancy
- lactation
- obesity
- porphyria
- palliative care
- competitive sports


3 processes in the kidney

- glomerular filtration
- passive tubular reabsorption
- active tubular secretion


Total renal elimination

Filtration + secretion - reabsorption


2 main processes in drug metabolism

Phase 1 = introduce or expose a functional group

Phase 2 = adds a polar conjugate for excretion into bile or urine


Inducers of Cyt P450

- Rifampicin
- Nevirapine
- Phenytoin


Inhibitors of Cyt P450

- Macrolides
- Protease inhibitors


Describe the First Pass effect

Drug is metabolised or eliminated by the GIT/liver before getting to the circulation (need much higher oral doses)


Describe the enterhepatic circulation of drugs

- drug/metabolite secreted into bile
- drug/ metabolite reabsorbed
- results in prolongation of drug effect
- can use charcoal to absorb drug in overdose


How to measure impaired liver function

Child-Pugh score


Principles of prescribing in liver disease

- try choose a drug with no hepatic metabolism (or conjugated instead of cytp450)
- reduce dose of drugs that undergo extensive first pass elimination
- higher risk of drug-induced hepatotoxicity
- try and measure drug concentrations


Principles of prescribing in elderly

- water soluble drugs can cause toxicity
- lipid soluble drugs can have longer half-lives
- beware of drugs with high hepatic extraction (morphine)
- decline in GFR


ADME of pregnancy

A - rate may be affected
D - increased plasma volume
M - variable hepatic metabolism
E - increased renal elimination


FDA pregnancy categories

A - no increased risk
B - inadequate results on humans
C - animal studies have shown harm
D - harm to fetus, but weigh risk
X - contraindicated


Calculating BSA in children

(cm x kg)/3600


How to dose by BSA

(adult dose x BSA)/ 1.73m2


Problem meds for children

- anithistamines (paradoxical excitation)
- chloramphenicol (grey baby syndrome)
- phenothiaxine anti-emetics (extrapyramidal SE)
- asprin (Reyes)
- sulphonamides (risk of kernicterus)
- tetracyclines (tooth discoloration)