Lecture notes from Imperial College London, Medical Biosciences BSc, 2nd year, pharmacology module.
Phar 3 on psychoactive drugs, depressants (alcohol, cannabis):
- Lipid solubility: Predict how the lipid solubility of alcohol and cannabis will influence drug distribution.
- Dosing: Calcula...
PD/PK theory: depressant drugs
- depressants: drugs that suppress/ slow the activity of nerves within the central nervous system
=> ex: alcohol, benzodiazepines
=> BUT narcotics & opioids, cannabinoids are also depressant
Alcohol vs Cannabis: Pharmacokinetics
- “alcohol” in chemistry is any organic compound w/ 1 or more hydroxyl group attached to a C
- “alcohol”, the drug of abuse, is ethanol (ethyl alcohol)
very small
- cannabis: active components of cannabis sativa plant (>400 compounds, >60 cannabidoids)
=> most potent cannabidoid: Δ9-tetetrahydrocannabidol (Δ9-THC)
I
-
- octanol(=oil):water (lipophilic/ hydrophilic) partition coefficient determines drug lipid solubility
=> ethanol: <0.1 (water soluble)
=> BUT small + uncharged polar m => diffuse across lipid membranes + through aqueous pores
=> Δ9-THC: >6000 (lipid soluble)
Dosing
- dose administered (absolute amount) is easy to determine
=> alcohol dose (g) = alcohol by volume (ABV)*0.78*volume per 100mL
=> unit system: alcohol dose = ABV*volume(mL)/1000 (1 unit = 8g of alcohol)
- ex: for 350mL of 5% beer
=> ABV = 5 => volume per 100mL = 3.5 => volume = 350
- 1 drink = 40mL of 40%, 150 mL of 12%, 350mL of 5%
- body metabolises 10mg/100mL every 40min => reduces BAC by 10 every 40min
=> quicker if heavy drinker (alcohol tolerance) // slower if defective alcohol metabolising enzyme
- in the UK, driving limit is 80mg/100mL:
- difficult to determine cannabis dose (cigarettes from 10mg to 150mg THC)
Absorption
- most common administration:
=> oral for alcohol (small intestine absorption) membrane 1-200nm thick + close to capillaries
=> inhaled for cannabis (alveoli absorption) => quick diffusion
- inhalation limits: 50% of drug dose gets deep enough into lungs (remaining swallowed, breathed
back out, decomposed by heat (pyrolysis))
=> of the 50%: small amount will access alveoli
- oral limits: if drug in stomach, can’t access small intestine microvilli
=> liquid in empty stomach tends to promote stomach emptying
=> directly into small intestine (absorbed quickly)
>
Distribution
- alcohol must first pass through the liver => potential significant metabolism
- capillary permeability: little impact because both can cross any capillary
- plasma protein binding: THCs highly bound (90%) // ethanol not (<10%)
=> cannabis slow to be eliminated (can’t diffuse out) => can take many days (->30)
- regional blood flow: same for both (high blood flow to brain and kidney)
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller lisaribau. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $10.30. You're not tied to anything after your purchase.
