Vaporization

Cannabinoid Administration

            Cannabinoid Molecules             

Cannabinoid medications are available to patients in several formats. Cannabinoid medications in pill form are designed for oral administration with absorption via the gastrointestinal tract. Cannabinoid spray medication is buccal, meaning it is absorbed through the cheek inside the mouth, however, some is also swallowed and absorbed in gastrointestinal tract. Cannabinoids in their dried herbal format are generally inhaled, thus absorbed via the pulmonary alveoli.

Intravenous administration is currently not available for cannabinoids due to the characteristics of cannabinoid molecules. Cannabinoids are hydrophobic, meaning they do not mix well with water, thus are difficult to produce as an injectate. Other methods of cannabinoid administration, such as topical applications - absorbed through the skin are under development but not commercially available.

 

 

Pharmacokinetics:

Pharmacokinetic Profiles


 

 

 

The orally administered synthetic cannabinoid nabilone has an onset of action of approximately 1 – 1.5 hours, with a duration of action of 8 – 12 hours (1). Similarly, orally administered dronabinol (THC) has an onset of action of approximately 0.5 – 1 hour, peak effect of 2 – 4 hours, psychoactive effects lasting up to 6 hours and effects on appetite for 24 hours or longer (2). When ingested orally, herbal cannabis pharmacokinetic profiles are similar to the oral cannabinoid medications described above, with peak plasma concentrations after approximately 1 – 2 hours and a effect duration of 6 hours (3).

Spray administration leads to a maximum plasma concentration of approximately 2 – 4 hours. This may include an earlier peak effect from buccal absorption and a later one due to slower absorption through the gastrointestinal tract (4).

Inhaling cannabinoids as smoke or vapor have a rapid onset of action and maximum effects occurring within 15 minutes (3, Zuurman 2009, Ware 2010). Effects reach a plateau which can last for several hours. Approximately 2 hours after inhaling cannabis smoke, plasma concentrations decline to about half of the peak level (3).

These pharmacokinetic properties result in different pharmacodynamic effects. Rapid onset and short duration of effect may only be achieved through inhaled delivery, and may therefore be more desirable in management of acute symptoms such as nausea, appetite stimulation sleep initiation, seizures or spontaneous neuropathic pain episodes. Oral administration may be more desirable for persistent symptoms such as chronic pain, sleep maintenance, or spasticity.

 
  1. Cesamet Product Monograph
  2. Marinol Product Monograph
  3. Health Canada – Information for health care professionals – Medical marihuana
  4. Sativex Product Monograph

 

Inhalation

Vaporization or volatization is the conversion of a solid or liquid substance into a gas. (1)
 
Combustion or burning is a chemical reaction between a substance and the oxygen in the surrounding air. Organic compound combustion involves a diverse range of molecules and radicals producing smoke containing carbon monoxide, hydrogen and other by-products while releasing heat and light as a flame. (2)
 

Abrams, 2007, Figure 1.

Inhalation of cannabinoids is most commonly associated with smoking dried herbal cannabis. The well established carcinogenic effects of tobacco smoke raise legitimate concerns for patients, health care professionals and policy makers when considering smoking as a route of administration for cannabinoids. Research suggests that cannabis smoke is not associated classic tobacco-related respiratory and colon cancers (Hashibe 2005, Tashkin 2002, Melamede 2005), but may be associated with prostate cancers (Hashibe 2005). There have been conflicting results regarding cannabis smoke and the development of chronic obstructive pulmonary disease (Tashkin 2010) which is a major concern with tobacco smoke.

Despite being apparently less harmful to the respiratory system than tobacco smoke, inhalation of cannabis smoke may potentially lead to the development of respiratory symptoms (Hall 2005, 2009, Tashkin et al 2002, Tetrault 2007) including reduced lung function, chronic bronchitis, cough, and increased production of sputum and wheezing (Hall and Solowij, 1998).

Vaporization should be considered as an alternative delivery system for the inhalation of cannabinoids. Vaporization is advantageous because it involves heating herbal cannabis to a degree at which cannabinoid vapors are effectively produced without the harmful byproducts of combustion (Gieringer et al 2004, Fischedick 2010).

Research comparing vaporization and smoking of herbal cannabis has been conducted, and several of the recent studies are outlined below.

Van Dam and Earleywine (2010) found that “the vaporizer might improve pulmonary function in cannabis users who experience respiratory symptoms”. For patients currently smoking cannabis, their findings suggest administering herbal cannabis by vaporization may be a potential harm reduction strategy for respiratory symptoms caused by smoking.

Pomahacova et al (2009) found that the ratio of cannabinoids to potentially harmful by-products are significantly higher in the vapor (when heated to 200 and 230 degrees C) compared to cannabis smoke. The exact properties of by-products were not identified but were speculated to be non-toxic at the lower vaporizer temperatures and more toxic at the high combustion temperature.

Bloor et al (2008) demonstrated lower levels of hydrogen cyanide and methanol in cannabis vapor in comparison to cannabis smoke. Vaporization of seized street cannabis in this study yielded higher levels of ammonia, which they propose may be due to the enclosed heating system and containment, otherwise thought to be lost as ‘side stream’ in smoking.

Abrams et al (2007) found that the THC levels produced by vaporizing herbal cannabis were comparable to that of smoking (see figure), and that vaporizing “does not result in exposure to combustion gasses” including carbon monoxide, and furthermore vaporization was preferred by most subjects compared to smoking.

Earleywine and Barnwell (2007) found that the respiratory symptoms associated with smoked cannabis may decrease with the use of a vaporizer. Results of their survey indicate that “vaporizer users are only 40% as likely to report respiratory symptoms as [cannabis] users who do not vaporize, even when age, sex, cigarette use and amount of cannabis consumed are controlled”.

Inhalation may be suitable for patients who lack ability to swallow, for example in ALS.

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