Lecture notes

Pharmacology 3: psychoactive drugs, depressants

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Module
Pharmacology

Institution
Imperial College London (ICL)

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...

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Uploaded on September 25, 2023
Number of pages 5
Written in 2022/2023
Type Lecture notes
Professor(s) Chris john
Contains All classes

pharmacology
psychoactive
depressants
alcohol
cannabis
solubility
distribution
dosing
bioavailibility
dose
pharmacokinetics
absorption
metabolism
toxicity
brain
target

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Pharmacology module Imperial College London

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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

, = bioavailability
PEAK
LEVELS

- estimatation of blood alcohol levels:
=> calculations:
1) alcohol dose = 13.65g (1 drink)
2) dose administered = 13650/
55 = 250mg/kg
3) blood level = 50mg/100ml
(don’t need to know how)

- 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)

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