Phamacology

Question 1

How urine pH affects drug clearance

Answer 1

• For an acidic drug, if urine is made basic then clearance will increase.
• For a basic drug, if urine is made acidic then clearance will increase.

Question 2

Macrolide in Cystric Fibrosis

Answer 2

1) Anti-inflammatory
2) Reduce sputum viscoelasticity, airway adhesion of P. aeruginosa, and increase the killing of mucoid P. aeruginosa
3) Low dose azithromycin has been shown to improve macrophage function, reduce neutrophil counts in the bronchial lavage fluid and reduce pulmonary tissue

Question 3

Omeprazole is assocaited with which electolyte disturnace

Answer 3

Hypomagnasaemia

Question 4

The effect of Erythromycin on warfarin

Answer 4

• Bioavailability is unchanged but warfarin clearance is reduced.
• Erythromycin stimulates the liver enzymes to produce metabolites that bind to cytochrome P450, forming inactive complexes and, thereby, reducing the metabolism of warfarin which enhances its effect.

The oral bioavailability of warfarin is nearly 100%. Warfarin is highly bound (approximately 97%) to plasma protein, mainly albumin.

Question 5

Bioavailability in cirrhosis

Answer 5

• Increased bioavailability.
• Bioavailability = 1 – Hepatic Extraction Ratio.
• Hepatic extraction ratio (HER) is determined by Total clearance of drug by liver over Total liver blood flow.
• In patients with cirrhosis, there is reduced hepatic clearance or reduced 1st pass effect therefore a lower HER which then leads to increased bioavailability.

Question 6

Bioavailability

Answer 6

Bioavailability = 1 - HER
Bioavailability = AUC oral / AUC iv. =

Question 7

Allopurinol and azathioprine

Answer 7

Allopurinol interferes with the metabolism of azathioprine, increasing plasma levels of 6-mercaptopurine which may result in potentially fatal blood dyscrasias. Bone marrow suppression occurs with azathioprine-allopurinol interaction.

Question 8

Volume Distribution

Answer 8

VD = total amount of blood in the body/plasma concentration

Question 9

Bio-availability

Answer 9

= 1 - hepatic extraction ratio

- cirrhosis - reduced hepatic blood flow and increased bioavailability

Question 10

hepatic extraction ratio

Answer 10

= total clearance by the liver/total liver blood flow

- cirrhosis - reduced hepatic blood flow and increased bioavailability

Question 11

T 1/2

Answer 11

= Volume distribution/clearance