Prescribing in special populations Flashcards
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
