Following a medication regimen means taking the right medication dose at the right time, in the right way and frequency. Irrespective of disease or health condition, medication adherence is important because it contributes to improved health outcomes in patients. Poor adherence could worsen a person’s disease or condition, leading to diminished quality of life, hospitalisation or even death.
In the event that a patient, prescribing health practitioner or pharmacist doesn’t know the right dose for a medication, what then? This question is an important unresolved issue confronting the medical cannabis industry. What is the safest dose of medical cannabis to administer that minimises side effects?
Currently, there are no precise dosing or established dosing schedules for medical cannabis products in Australia.1 Table 1 shows common medical cannabis products distinguished according to the route of administration.
|Route of administration||Medical Cannabis Product|
|Oral||Liquid: oil, tincture and beverage;|
Solid: Tablet; capsule; edible/normal food with cannabis powder or oil
|Topical||Cream; balm; ointment; transdermal patch|
|Inhalation||Dried flower; resin; vapouriser|
Table 1: Route of administration of common medical cannabis products
The route of administration is an important aspect of pharmaceutical dosing. It affects how rapidly and efficiently the active ingredient in the medication is metabolised and consequently on its concentration in the body.
Inhalation of medical cannabis
Inhalation through the pulmonary route is a rapid and efficient method of administering medical cannabis. Following inhalation through smoking, plasma concentrations of tetrahydrocannabinol (Δ9-THC) peak between 2-4 minutes. In people with chronic pain, this rapid increase in Δ9-THC concentration leads to analgesia in roughly 5-10 minutes. However, the bioavailability of Δ9-THC through inhalation varies greatly – between 2-56% – due to user differences in the depth of inhalation, puff duration, or breath-holding time. These differences degrade the available Δ9-THC dose.2,3 Given the rapid onset of action, inhaled medical cannabis is most suited for symptoms or conditions where rapid relief is needed.
Medical cannabis vapourisation is a technology that may circumvent the limitations of smoked cannabis. As in smoked medical cannabis, vapourised cannabis leads to rapid absorption and high blood concentrations of cannabinoids. However, vapourised cannabis is heated at a lower temperature than smoked cannabis, resulting in less cannabis lost to side-stream ‘smoke’ or combustion. The effects of vapourised cannabis are perceived by users within 90 seconds, peaking between 15-30 minutes, and bottoming out after 2-4 hours.1 However, no vapourisers are currently approved in Australia by the Therapeutic Goods Administration (TGA).1 While a variety of vaporising technologies are on the market, precise and reliable dosing using vapourisers is a problem.1,4 The limitations of administering medical cannabis through inhalation may convince GPs and specialists that inhaled cannabis products should not be prescribed. This means that dosing remains an unanswered question for patients and clinicians alike.
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- Guidance for the use of medicinal cannabis in Australia: Overview. 2017. Available at: https://www.tga.gov.au/publication/guidance-use-medicinal-cannabis-australia-overview
- Grotenhermen F. Pharmacokinetics and pharmacodynamics of cannabinoids. Clinical Pharmacokinetics 2003;42(4):327-60.
- Huestis MA. Chemistry & Biodiversity 2007;4(8):1770-1804.
- Eisenberg E et al. J Pain Pall Care Pharmacothera 2014;28(3):216-225.
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