Nitrous oxide (N2O)

[SH4:p43-p46]

Quick summary

Properties

• Low MW
  * MW = 44
• Nonflammable
  * But will support combustion
• Gas at room temperature
• Low potency
  * MAC = 104%
• Low solubility
  * Blood:gas = 0.46

NB:

Critical temperature = 36.5C
* [MCQ] [???]

Clinical relevance

• Analgesic
• Minimal skeletal muscle relaxation
• Increased incidence of PONV
• Small increase in P50
• Inactivate vitamin B12
• Mild sympathomimetic effect
• MAC awake is higher than other inhalational anaesthetic agents (> 0.6 MAC)
• Safe in malignant hyperthermia

 

Usage

What is the drug used for?

Structure

Structure

 

 

How is nitrous oxide manufactured?

[PHW2:p107]

Nitrous oxide is manufactured by heating ammonium nitrate to 250C

NH4NO4 ===> N2O + 2 H2O

Contaminants include: NH3, N2, NO, NO2, and HNO3

 

 

What is the proper name of the drug's structure?

What does the drug's structure look like?

Structure-activity relationship

How does the drug's structure change its activity or characteristics?

Pharmacodynamics

Main actions

Mechanisms of action

What receptors does the drug act on?

Where are these receptors?

What are the effects of these actions?

Effects by systems

 

(CNS, CVS, Resp, GIT, others)

Side Effects/Toxicity

What are the side-effects of the drug?

What happens in overdose? What are the toxic side-effects?

 

 

Pharmacokinetics (PK)

Absorption

How is the drug absorbed? Route of administration?

What is the bioavailability with non-IV routes?

Distribution

Where does the drug first get distributed to (e.g. VRG, muscle, fat)?

Where do the drug accumulate mostly?

How fast does it redistribute?

Does it cross BBB or placenta?

(Includes the Vd and Protein-binding)

Metabolism

How is the drug metabolised? Where does the metabolism take place(Liver, kidney, other organs)

What are the metabolites? Are they active or toxic?

Elimination

How is the drug eliminated? How are the metabolites eliminated?

How much of the drug is eliminated unchanged?

Clearance

Action profile

T1/2 (in different phases, alpha, beta, etc)

Onset of action, duration of action, time to peak effect

Physicochemical properties

Acid or base? pKa?

Pharmaceutics

Presentation

What sizes are the ampules? What packages, concentration, sizes are available on the market?

Composition

What is in an ampule? Active and inactive components?

pH of the content?

Price

Clinical

Administration

route of administration, and the dosage for each different route.

 

Indications/contraindication/precautions

When should the drug be used?

When should the drug NOT be used?

When should the drug be used, but only with caution?

 

Interactions

What other things can the drug interact with?

 

Special consideration

What issues should be considered when the drug is used in special circumstances, e.g.:

• Pregnancy/lactation
• Elderly
• Paediatrics
• Renal disease
• Hepatic disease

 

 

Trivia

History

 

Others