Drug variability

Question 1

Both the desired and unwanted reposes to any given drug may vary between individuals. This could be because of 2 main reasons…

Answer 1

Absolute difference in dose administered- e.g. different formulation, patient non-compliance or an error in prescription or dispensing- or relative underdose/overdose.

Question 2

Name 5 reasons for relative overdose/underdose

Answer 2

Chemical exposure, food intake, fluid intake, age, nutritional status and disease.

E.g. cardiac failure leas to reduced splanchnic blood flow, intestinal mucosal oedema and reduced hepatic clearance.

Question 3

How would a newborn metabolise a drug differently to an adult?

Answer 3

1) Lower capacity for drug metabolism 2) renal tubules and lower renal mass 3) more body water 4) immature BBB.

Question 4

How would an elderly person metabolise a drug differently from an adult?

Answer 4

DRUG ABSORPTION: decreased absorptive surface are of SI and increased rate of gastric emptying. DRUG DISTRIBUTION: more body fat, lower body water (affects Vd and plasma level in oppsoite directions), also have reduced plasma albumin. DRUG METABOLISM: lower hepatic and splanchnic blood supply, lower hepatic mass and hepatic enzyme activity decreases. DRUG EXCRETION: lower renal mass, reduced renal perfusion too as well as reduced GFR and reduced tubular excretion. DIFFERENT ORGAN SESNIRTITY.

Question 5

Name 7 CYP450 inhibitors

Answer 5

Cimetidine (H2 re antagonist), Erythromycin, Ciprofloxacon, Flueoxetine (SSRIs), Ritonavir (HIV drugs) , Grapefruit juice, Ketoconzaole ( anti flungal).

Question 6

Name 5 CYP450 inducers

Answer 6

Phenytoin, phenobarbitone, hypericin of St Johns Wort, Rifampicin and Carbamazepine.