Dosage calculations

Question 1

Importancy in prescribing micrograms

Answer 1

Write out the full word in the case of ‘micrograms’

Question 2

Expressing infusion dosages

Answer 2

May be expressed per body weight or a standard adult dose.

Aminophylline is used at 500 micrograms per kg per hour (and then adjusted accorded to monitoring)

• E.g. a 65kg man would need:
  
  • 500 micrograms x 65 x 1 = 32.5 mg per hour infusion

Question 3

Percentage solutions

Answer 3

This means grams per 100 ml of solution

• 100% = 100 g per 100 ml or 10 g per 10 ml or 1g per ml
• 10% = 10 g per 100 ml or 1 g per 10 ml or 100 mg per ml
• 1% = 1 g per 100 ml or 100 mg per 10 ml or 10 mg per ml
• 0.1% = 100 mg per 100 ml or 10 mg per 10 ml or 1 mg per ml

E.G. 1% Means 10 mg/mL

Question 4

Lidocaine dosing example

Answer 4

• Lidocaine: an anti-arrhythmic and local anaesthetic
• Supplied as 1 or 2 % solutions
• 1 % is 10 mg/ml
  
  • A 2 ml ampoule contains 20 mg
  • A 10 ml syringe contains 100 mg
• 2 % is 20 mg/ml
  
  • A 2 ml ampoule contains 40 mg
  • A 5 ml ampoule contains 100 mg

Question 5

Ratio dosing

Answer 5

Adrenaline is supplied as a ratio:

• 1:1,000 = 1 mg/ml
• 1:10,000 = 100 micrograms/ml
• 1:200,000 = 5 micrograms/ml

Question 6

Adrenaline dosing example

Answer 6

• The standard adult dose for anaphylaxis is 500 micrograms i.m.
• So, with 1ml vial of 1:1,000 adrenaline the volume given would be 0.5 ml.
• Reason: 1:1000 = 1 mg/ml and need to give 500 micrograms

Question 7

Drugs prescribed as units

Answer 7

A unit is measure of biological activity.

• INSULIN
• Heparin (injectable anticoagulant)
  
  • (The quantity of required to keep 1 ml of cat’s blood fluid for 24 hr at 0°C)
• Streptokinase (thrombolytic)
• Vasopressin (ADH/vasoconstrictor)