Pharmacodynamics and Pharmacokinetics

Question 1

P450 enzyme inducers

Answer 1

PC BRAS

Phenytoin
Carbamazepine
Barbiturates
Rifampicin
Alcohol (excess)
Sulphonylureas

Question 2

P450 Inhibitors

Answer 2

AO DEVICES

Allopurinol
Omeprazole
Disulfiram
Erythromycin
Valproate
Isoniazid
Ciprofloxacin
Ethanol (acute intoxixation)
sulphonamides

Question 3

Drugs to increase during surgery

Answer 3

Long Term Corticosteroids

Question 4

Drugs to stop before surgery

Answer 4

I LACK OP
Insulin
Lithium
Anticoagulants/platelets
COCP/HRT
K sparing diuretics
Oral hyppglycaemics
Perindopril (ACEi)

Question 5

When do you stop drugs before surgery.

Answer 5

COCP and HRT- 4 weeks prior
Lithium- day prior
K sparing and ACEi- day of
Anticoagulants- variable
Insulin- continue on long acting and then short acting is variable
Oral Hypoglycaemics- day before

Question 6

When do you prescribe IV fluids?

Answer 6

Replacement Fluids

Maintenance for NBM

Question 7

In fluid replacement which fluid should you prescribe?

Answer 7

” Give - 0.9% saline (crystalloid) unless the patient is
o Hypernatraemic or hypoglycaemic - give 5% dextrose
o Has ascites - human albumin solution (HAS) (Albumin maintains oncotic pressure. High sodium in saline worsens ascites)
o Shocked systolic <90 - give gelofusine (colloid) (It has a higher osmotic content so stays intravascular í BP maintained
o Haemorrhagic shock - blood transfusion or colloid

Question 8

What are the signs of fluid depletion?

Answer 8

reduced urine output (oliguric <30ml/h. anuric 0ml/h)= 500mL fluid depletion.

reduced urine output+tachycardia- 1L fluidd depletion

reduced UO+ tachycardia+shcok >2L fluid depletion.

Never prescribe more than 2L without reassessing patient.

Question 9

Fluid Replacement- how much and how fast?

Answer 9

Tachycardic or hypotensive- 500ml bolus ( 250ml if HF)

Oliguric 1L over 2-4hrs (need to assess for signs of retention).

Question 10

Maintenance fluid- which fluid and how much?

Answer 10

Adults need 3L/24hrs (8hourly) , elderly need 2L/24hrs (12 hrly)
adequate electrolytes- 1L + 2L 5% dextrose (1 salt 2 sweet)
Potassium- in dextrose or saline.
Normally 40mmol KCL/day so 20mmol KCL in 2 bags. Not be given at a greater rate of 10mmol/hr

Question 11

When do you prescribe IV fluids?

Answer 11

1) replacement fluids for loss

2) maintenacne for NBM

Question 12

What IV fluid do you give for replacement?

Answer 12

0.9% Saline (crystalloid) unless the patient is:
Hypernatraemic or hypoglycaemic- 5% dextrose
Has ascites- give HAS
Shocked systolic <90 give gelofusine (colloid)