This pharmacokinetic study evaluated escalating single doses of oral CBD oil in healthy cats. While there are multiple proposed methods of CBD administration (inhalation, gel capsule, oil/tincture, and topical), we chose to dose the cats in this study with CBD oil orally based on the previous pharmacokinetic work in dogs suggesting this may be one of the more reliable methods of CBD delivery (Bartner et al., 2018). Cats (n = 4 cats/group) received 2.5, 5, 10, 20, 40, and 80 mg/kg doses. The CBD plasma pharmacokinetics were measured over 24 h. In this study, we were able to successfully demonstrate the CBD exposure and safety of a single administration of oral doses up to 80 mg/kg of highly purified CBD oil to a small cohort of healthy cats.

Overall, there was a large amount of inter‐individual variability across all doses and parameters (Table 2). For instance, the AUC after administration of a 2.5 mg/kg dose ranged from 8.1–165.9 ng/ml × h. This is about a 20‐fold difference between these individual cats. We suspect that as a lipid‐soluble drug, the fat content of each individual may serve as a reservoir for its uptake (Routledge, 1985). Given the large differences in body condition that we see across this population of cats, this may significantly affect its interindividual pharmacokinetic properties. This highlights the necessity of future studies to continue to evaluate the pharmacokinetics in a larger cohort of cats as well as to evaluate CBD plasma levels in treatment studies.

Although there was a large inter‐individual variability, the mean Cmax and AUC_0‐24 increased proportional to the dose.

There was some variability in the mean T_1/2 between the 2.5 mg/kg dosing group and the rest of the groups with a longer T_1/2 (13.2 h) in the 2.5 mg/kg dosing group._. This variation may be related to the fact that this value was calculated from two cats and may not represent the true mean. Excluding the 2.5 mg/kg dose, the mean T_1/2 ranged from 6.7–9.6 h across all other dosing groups.

There were no statistically significant changes to any of the parameters in the CBC in this study. When evaluating serum biochemistry analysis, there was a trend towards decreasing BUN and creatinine at 24 h when compared to Time 0 (Table 3). This was consistent and statistically significant among all dosing groups with p values consistently below 0.05. Approximately 42% of the Time 0 creatinine values were ≥1.6 μg/dl, which is the normal cutoff for chronic kidney disease in cats by the International Renal Interest Society (International Renal Interest Society, 2019). We do not have an explanation for this or why these values consistently decreased at the 24‐h blood draw. There was only a single cat that developed hypotension under sedation while all other values were within the normal limits or hypertensive. So, it would seem that hypotension or hypertension while under sedation was unlikely to be the cause. The significance of decreasing creatinine and BUN values 24 h after dose administration is unknown. This must be evaluated in future studies to investigate the repeatability of this finding. In many cats, the creatine kinase showed increased activity 24 h after CBD administration. This was attributed to jugular catheter placement. There was no elevation in ALT or ALP post‐dose in any dosing groups as has been seen in chronic administration in humans, dogs, and in a single cat (Bartner et al., 2018; Deabold et al., 2019; Scheffer et al., 2021; Vaughn et al., 2021).

There has been one previous report describing single‐dose CBD pharmacokinetics and safety in cats (n = 6) (Deabold et al., 2019). In this previous report, hypersalivation was noted after dosing. A 1:1 mixture of CBD and CBDA was delivered in fish oil capsules at a 2 mg/kg dose, the equivalent of 1 mg/kg CBD. The Tmax was 2.0 h, AUC was 164 ± 29 ng/ml × h, and Cmax was 43 ng/ml ± 9. A larger dose (2.5 mg/kg) in our study yielded a median Tmax of 2.0 h. The mean Cmax and AUC_0‐24 were considerably lower (17.8 ng/ml and 83.5 ng/ml × h, respectively). However, the high end of the Cmax range in our study was 45.3 ng/ml which is comparable to the previous study. The discrepancies between these investigations could be due to differences in the delivery method (oil capsule versus liquid oil), a consequence of the differences in the make‐up of the CBD oil itself, the substantial interindividual variability observed with oral CBD administration, or the small sample sizes in the studies. A small human study suggested that THCA‐A and CBDA enhance the bioavailability of the non‐acidic forms of THC and CBD (Eichler et al., 2012). As the previous feline pharmacokinetic study used a combination of CBD and CBDA in their oil, this could account for difference in bioavailability. However, additional research is needed to understand the influence of CBDA on CBD bioavailability in cats.

Another study in felines evaluated escalating doses of a CBD predominant oil, in which the Cmax and Tmax of a 25 mg/kg dose was evaluated following nine previously escalating doses each 3 days apart (Kulpa et al., 2021). Cmax concentration was measured to be 236.0 ± 193.0 ng/ml at this 25 mg/kg dose with a mean Tmax of 3 h. This is comparable to the current study in which a mean Cmax of 321.0 (14.5–467.4) ng/ml was achieved in the 20 mg/kg dosing group with a median Tmax of 2.0 h. However, it is not clear that 3 days between dosing provides an adequate washout period. As such, the CBD plasma concentrations likely did not start at zero which makes a full comparison to the current study difficult. This investigation also evaluated a THC/CBD combination oil. Following escalating doses with pharmacokinetics performed after a 34 mg/kg THC and 10.6 mg/kg CBD, a CBD Cmax was achieved almost double that of CBD oil alone. This suggests that THC may enhance the absorption of CBD. As such, both of these previous studies may indicate that the combination of CBD with other phytocannabinoids may enhance absorption of CBD.

There were no observed adverse events in the course of this study. In addition, there were no statistically significant changes to each cat's behavior when analyzed with a numerical behavior assessment. However, behavioral changes included lip licking, head shaking, and hypersalivation immediately after administration of the oil in the treatment and placebo groups. Other adverse events including, emesis, diarrhea, somnolence, muscle tremors, mydriasis, pruritis, ataxia, and hypothermia have been reported previously in canine and feline patients but were not observed in this study (Bartner et al., 2018; Chicoine et al., 2020; Deabold et al., 2019; Fernández‐Trapero et al., 2020; Gamble et al., 2018; Vaughn et al., 2020, 2021). However, some of the aforementioned studies included THC in their formulations as well as chronic administration which may affect pharmacokinetics and physiological effects. It is interesting to note that previous studies showed no notable differences in adverse event frequency between doses of CBD oil and delivery oil alone (placebo) administered to dogs although a statistical analysis was not evaluated to compare the adverse event profile (Vaughn et al., 2020, 2021). This finding was not mirrored in a similar feline study and instead suggested a greater occurrence of hypersalivation and lethargy in the treatment group as compared with the MCT oil placebo group (Kulpa et al., 2021). This same study also found a statistically significant difference in adverse events between the administration of MCT oil alone and sunflower oil alone suggesting fewer adverse events with the administration of sunflower oil. Most of the adverse events with MCT oil were vomiting or diarrhea, while gastro‐intestinal adverse events with sunflower oil were minimal (n = 1) (Kulpa et al., 2021).

Whether there are sex‐dependent differences in CBD pharmacokinetics remains to be seen. We were unable to determine with certainty in this cohort of cats whether there are sex‐dependent differences in the pharmacokinetics of CBD due to the small number of participants. Future studies to evaluate for differences in pharmacokinetics in males vs. females and intact or castrated animals should be performed.

All cats were fasted in this study as we were unable to standardize meals for these free‐fed cats. Given previous research in dogs, humans, and pre‐clinical models showing that THC and CBD oils administered in fed or fasted states changes the bioavailability of THC (Birnbaum et al., 2019; Łebkowska‐Wieruszewska et al., 2019; Millar et al., 2018; Zgair et al., 2016), future studies could evaluate the pharmacokinetics of CBD in fasted and post‐prandial states in cats. Along the same lines, one might suspect that varying volumes of CBD oil in the fasted state may alter bioavailability of the CBD. However, in this study we were able to show dose proportionality across all doses for AUC_0‐24. This suggests that although the volumes of CBD oil administered varied with varying doses (Table 1), the bioavailability was constant so the volume of oil was not a confounder in this study.

Limitations of this study include the use of a non‐validated behavior scoring system, though it has been used in a previous study (Quimby et al., 2011). Although clear definitions exist for each score, multiple evaluators may have led to varying results. Additionally, the small sample size may not allow detection of subtle changes to behavior. A single cat in the 10 mg/kg dosing group required sedation for its 12 and 24‐h blood draws due to dislodgement of the jugular catheter. It is unlikely that this affected the pharmacokinetics of the CBD oil at these time points, but may have affected behavior scores. However, it is unlikely that these data points would have altered the statistical significance of the behavior scores in this study. In addition, given the initial sampling for CBD levels every 2 h, it is possible we may have missed the true Cmax and Tmax. This may affect the reported Cmax in this study as the true Cmax may have been larger. Every 2‐h sampling may also have led to AUC being underestimated, which would have led to overestimation of CL/F and Vd/F. More frequent sampling would have allowed for more accurate information regarding absorption. Additional sampling after 24 h may have allowed for better characterization of the terminal phase as well.

There were two cats in the 80 mg/kg group that had measurable CBD plasma levels at Time 0 (<70 ng/ml). These cats had had a four‐month washout from their previous dosing which was a 10 mg/kg dose. One explanation could be storage of CBD in fat tissues as is seen with THC in humans (Gunasekaran et al., 2009), but this may not necessarily explain why the prolonged washout period was not suitable for this group. However, all other cats had no measurable plasma CBD at Time 0. More data are needed with regard to interindividual variability relating to clearance and half‐life.

Overall, we have found that single doses of CBD oil up to 80 mg/kg were well tolerated in this cohort of cats. However, safety and pharmacokinetic studies evaluating chronic CBD dosing are needed. In addition, this pilot study now provides statistical variables to aid in designing larger controlled pharmacokinetic studies. The half‐life would indicate that once to twice daily dosing would be appropriate for future studies to assess the therapeutic potential of CBD in cats. However, CBD efficacy for use as a medication and required plasma concentrations for these effects have yet to be evaluated.