PSI Pharmaceutical Sciences 3

Question 1

Which cytochrome P450 enzyme is responsible for the metabolism of the largest number of drugs?

Accepted Answer

CYP3A4

Answer

CYP3A4 is the most abundant hepatic CYP enzyme and metabolises approximately 50% of all drugs. It is subject to many important drug interactions.

Question 2

Renal clearance of a drug is increased when the drug is:

Accepted Answer

Ionised at urinary pH

Answer

Ionised drugs cannot readily be reabsorbed through tubular epithelium, so they remain in urine and are excreted. Manipulating urinary pH to increase ionisation is used in poisoning management.

Question 3

Which dosage form is designed to release drug in the small intestine rather than the stomach?

Accepted Answer

Enteric-coated tablet

Answer

Enteric coatings (e.g., HPMC phthalate) resist acidic gastric pH but dissolve at the higher pH of the small intestine, protecting acid-labile drugs or preventing gastric irritation.

Question 4

Steady-state plasma concentration is reached after approximately how many half-lives of continuous dosing?

Accepted Answer

5 half-lives

Answer

With repeated dosing, drug accumulates until input equals output. Steady state is effectively reached after 4–5 half-lives, when ~97% of the final plateau concentration is achieved.

Question 5

Which type of isomerism involves non-superimposable mirror image molecules?

Accepted Answer

Enantiomerism

Answer

Enantiomers are mirror images that cannot be superimposed. They have identical physical properties but can differ in pharmacological activity, toxicity and metabolism.

PSI Pharmacy Practice Test

PSI Pharmacy Practice Test

PSI Pharmaceutical Sciences 3