Prescribing and Treatment

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Patient Assessment

Patients will present with a myriad of health issues. The aim is to identify the primary and secondary health issues which will benefit from lifestyle adjustments versus prescribed medical cannabis. In addition to the medical assessment, it is important to understand the patient’s base knowledge and expectations.

It is important to assess:

The patient’s primary source of information and their level of health literacy.
The patient’s level of medical cannabis knowledge. Does this patient need to be referred to a cannabinoid nurse for patient education prior to prescribing?
The patient’s goals and expectations of medical cannabis, are they realistic?
Is there a support system around the patient? Are their family, partner or friends in agreement with their decision?
Do they have the financial ability to afford this unsubsidized medication long term?
Do they understand the driving restrictions and lifestyle adjustments if they require THC or THC:CBD blends?
Are they interested in participating in observational or clinical research studies? Assess their level of knowledge about the pros and cons of participating.

Medical Assessment

It is important to document in detail for medico legal protection for ‘unapproved’ medical cannabis products accessed via the Special Access Scheme or Authorised Provider pathways.

- Identification of the primary symptom for which the medical cannabis can be prescribed
- - Location
  - Onset/cause
  - Quality
  - Duration
  - Intensity
  - Aggravating or alleviating factors
  - Other symptoms

- Prior treatments – pharmacological and reason for discontinuationPrior treatments - non-pharmacological and reason for discontinuation
- Prior Treatments – non-pharmacological and reason for discontinuation

- Current treatments – pharmacological, dose, duration and effect

- Current treatments - non-pharmacological, description, frequency and effect

- Past medical History (contra indications for cannabinoid medication – Psychosis personal or familial, Schizophrenia, unstable heart disease)

- Substance use – substance, duration, quantity and frequency of use

- Prior use of medical cannabis (illicit or prescription) – mode of administration, amount/dose, duration and effect on mood, sleep, driving, cognitive function and quality of life.

- Social History

- Results of physical examination

- List of other treating general practitioners and specialists and if they are aware of the request for medical cannabis treatment for a particular symptom or condition.

- Note the patient expectations of outcomes from use of medical cannabis. List their functional goals and points discussed – Does the patient require referral to a Cannabis nurse for further information and education on the endocannabinoid system?

- If assessed as a suitable patient for cannabinoid-based medications, note why alternative or conventional medicines or therapies are not suitable

Prescribing Guidelines

CanGuide_Medicinal Cannabis for HCP

Practical Applications in Product Selection

Precautions

Contra Indications

Drug to drug interactions

Enzyme Inhibition or Induction

‘Enzyme Inhibition or Induction The cytochrome P450 (CYP) enzymes CYP2C9 and CYP3A4 play a significant role in the metabolism of THC26. Pharmacogenetic data also supports CYP2C9 being a significant contributor to THC metabolism27. CBD is primarily metabolised by CYP2C19 and also CYP3A426 . Other CYP enzymes including CYP1A1, CYP1A2, CYP2C9, CYP2D6 and CYP3A5 may also play a role in CBD metabolism28,29’

‘Induction or inhibition of these CYP enzymes may affect the pharmacokinetics of THC and CBD.’

‘It is possible that other drugs which are inhibitors or inducers of the enzymes CYP3A4, CYP2C9 and CYP2C19 may affect the pharmacokinetics of THC and CBD. Care should be taken when prescribing such medications, during dose modifications or when discontinuing these medications in patients taking cannabinoids. For further information on drugs which are CYP inhibitors and inducers please refer to resources such as the Australian Medicines Handbook .’ (https://www.racgp.org.au/racgp-membership/member-offers/australian-medicines-handbook)

‘…caution should be exercised when considering prescribing cannabis products with medications that undergo significant metabolism by CYP2C19, CYP2C9 and CYP1A2 or by UGT enzymes due to the possibility of altered disposition32. Narrow therapeutic index (NTI) drugs which are metabolised by these enzymes should be closely monitored.’

‘Patients should also be informed of the possibility of drug-drug interactions when cannabinoids are co-administered with other medications, particularly with NTI drugs.’

Brown and Winterstein reviewed CBD’s potential for adverse drug events and drug-drug interactions (https://www.mdpi.com/2077-0383/8/7/989) whilst considering the underlying indications for CBD, the medications used for those disorders in the context of ADE/DDI risk, and proposed general recommendations for co-prescribing (i.e., reduced dose) or avoiding certain combinations. The table below outlines DDI between CBD and enzyme substrates, inhibitors, or inducters.

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Brown J.D, Winterstein A.G (2019) Potential Adverse Drug Events and Drug–Drug Interactions with Medical and Consumer Cannabidiol (CBD) Use, J. Clin. Med. Vol. 8, Page 989

Monitoring

References

Case Studies

Zac

10 years
ADHD/Anxiety

Fiona

41 years
PTSD

Ella

23 years
Medication Resistant Epilepsy

Sandra

84 years
Neuropathic Pain

Tom

35 years
Insomnia