Journal of the New Zealand Medical Association, 24-April-2009, Vol 122 No 1293
Party pills and drug-drug interactions
Meghan Murphy, Ushtana Antia, Hsin-Yao Chang, Jae Young Han, Abir Ibrahim, Malcolm Tingle, Bruce Russell
Party pills are commonly used recreational drugs in New Zealand.1 Benzylpiperazine (BZP) and trifluoromethylphenylpiperazine (TFMPP) are amphetamine-like compounds and the active ingredients of the majority of party pills sold in New Zealand (Figure 1).
Figure 1. Chemical structure of BZP (top left), TFMPP (top right), MDMA (bottom left), and amphetamine (bottom right)
Together BZP and TFMPP have been reported to exert effects similar to methyldioxymethamphetamine2 (MDMA, Ecstasy) in rodents (Figure 1). Despite their availability and liberal use, the metabolism of BZP and TFMPP, and their ability to alter the metabolism of other drugs in the human body is not well understood.
CYP isoenzymes CYP2D6, CYP3A4, and CYP1A2 seem to play a role in the metabolism of TFMPP.3 It has been predicted that BZP would be metabolised in a similar manner due to the structural similarities between the two compounds. Therefore, both TFMPP and BZP might interact with substrates of CYP2D6, CYP3A4, and CYP1A2 in the clinical setting.
It is important to investigate the possibility of drug-drug interactions because severe adverse effects may arise secondary to increased levels of a co-administered drug. For example, increased levels of the anti-depressant fluoxetine (a CYP2D6 substrate) may be associated with the serotonin syndrome.4
The substrates used as probes for a particular CYP reaction were selected as they are selectively metabolised by a single CYP isoenzyme. While a drug-drug interaction involving a probe substrate (such as dextromethorphan for CYP2D6) is unlikely to be problematic in the clinical setting, the data obtained can be extrapolated to include other CYP2D6 substrates. This approach has been used previously5,6 to explore drug-drug interactions and allows for multiple CYP isoenzyme reactions to be studied and produces results applicable to several commonly used drugs.
The aim of this study is to determine the effects of BZP and TFMPP on the metabolism of commonly used drugs. However, it is important to consider that a drug-drug interaction may influence the pharmacokinetics not only of the substrate, but also that of BZP/TFMPP. Hence, it is important to take into account the potential adverse effects.7
BZP, TFMPP, dextromethorphan, caffeine, ethinyloestradiol, omeprazole, phenytoin, quinidine, troleandomycin (TAO), tetrahydrofuran (THF), perchloric acid, and sodium dihydrogen phosphate were obtained from Sigma-Aldrich, USA. Acetonitrile (ACN), sodium dihydrogen phosphate, and methanol were obtained from Scharlau Chemie, Spain. NADPH was sourced from Applichem, Denmark. Furafylline was purchased from Ultrafine Chemicals, UK. Proguanil was obtained from Astra Zeneca, UK and ammonium formate was obtained from Acros Organics, USA.
Human liver microsome preparation—With approval from the Northern X Regional Ethics Committee, six livers were collected from human donors at Auckland City Hospital (Table 1). Portions of the livers were rinsed in ice-cold phosphate buffer and blotted dry. Livers were then homogenised in 67 mM phosphate buffer containing 1.15% potassium chloride. The volume of the buffer used was three times the weight of the liver to provide a 25% homogenate. This homogenate was centrifuged at 10,000 g for 20 minutes and the supernatant removed and centrifuged at 105,000 g for a further hour. The pellet was gently rinsed with phosphate buffer and re-suspended in a small volume (2–5 mL) of phosphate buffer8 and aliquots were stored at –80°C until use. An aliquot of the suspension (~200 µL) was removed for protein determination.5
HPLC—The chosen HPLC system included an Agilent 1100 series binary pump, an Agilent series 1100 Multiple Wavelength detector (UV), an Agilent series 1100 Autosampler, and an Agilent Extend reverse-phase C18 column (150×4.6 mm, 5 μm).
Table 1. Summary of liver donor details used is the HLM (human liver microsome) preparation. Each liver sample was received after liver resection for colorectal cancer metastasis
Due to the paucity of information about drug interactions with BZP and TFMPP, this study aimed to screen a wide range of potential drug interactions in vitro. To confirm that specific isoenzymes are involved in a drug interaction, probe drugs (or substrates whose metabolism is carried out chiefly by one isoenzyme) were co-incubated with selective isoenzyme inhibitors and BZP or TFMPP. Furthermore, the drugs chosen are commonly used drugs relevant to the demographic of people consuming party pills. For example ethinyloestradiol is present in numerous combined oral contraceptives.
In the inhibition assays, the substrate, inhibitor (BZP or TFMPP), NADPH, buffer, and the protein (pooled liver microsomes) were co-incubated at 37°C for 20 minutes, after which the reaction was stopped. Excess NADPH was added to each inhibition assay to ensure that any reduction in metabolism was due to inhibition and not simply due to lack of an energy generating source.
The inhibitors (BZP or TFMPP) were dissolved in phosphate buffer which was pH adjusted to improve solubility. Organic solvents were avoided due to the potential for confounding inhibitory effects. The liver microsome concentrations used were based on methods found in the literature and optimised for the metabolism of each probe substrate.8–11
All microsomal incubations without inhibitors resulted in a limited amount of metabolism (10–20%) so that inhibitory effects of any additional compounds could be observed. The rate of disappearance of each substrate was measured at the end of the 20-minute incubation.
There are no published studies demonstrating plasma or liver concentrations of BZP and TFMPP. Therefore, a wide range of concentrations was used (2, 20, and 200 μM), with the highest concentration of inhibitor corresponding to the substrate concentration. Results of inhibition studies were confirmed using pooled human liver microsomes (n=6). Positive and negative controls were included in each set of the inhibition assays.
Incubation mixtures (n=6) contained pooled liver microsomes (20 μL; 2 mg/mL), NADPH (20 μL; 10 mM), the substrate (20 μL; 1 mM), the proposed inhibitor (20 μL; BZP, or TFMPP 0, 2, 20, or 200 μM, final concentration), which was made up to volume using phosphate buffer (to 100 μL; 67 mM, pH 7.4). The samples were then incubated at 37°C in a water bath for 20 minutes and the reactions were terminated by the addition of perchloric acid (5 μL) and vortex-mixing. The samples were stored at -20ºC for 1 hour, thawed, then centrifuged at 10,000 rpm for 5 minutes and the supernatant used for analysis. Enzyme selective positive and negative controls were included (Table 2).
Dextromethorphan (CYP2D6)—10 mM formate buffer (pH 4.5) and ACN were used as the mobile phase with a flow rate of 1 mL/min. A gradient of 90:10 v/v (formate buffer: ACN) to 20:80 v/v was used. Substrate detection was carried out at 231 nm (UV) and the injection volume was 20 μL.
Caffeine (CYP1A2)—Formate buffer (pH 4.0, 1% methanol, 1% ACN, 1.6% THF) and 100% ACN were used as the mobile phase with a flow rate of 1 mL/min. A gradient of 100:0 v/v (formate buffer: ACN) to 20:80 v/v was used. Detection of substrate was carried out at 224 nm (UV) and the injection volume was 10 μL.
Ethinyloestradiol (CYP3A4)—Milli-Q water and 100% ACN were used as the mobile phase with a flow rate of 1 mL/min. A gradient of 55:45 v/v (milli-Q water: ACN) to 20:80 v/v was used. Detection of substrate was carried out at 212 nm and the injection volume was 10 μL.
Omeprazole (CYP2C19)—Formate buffer (pH 4.0, 1% methanol, 1% ACN, 1.6% THF) and 100% ACN were used as the mobile phase with a flow rate of 1.100mL/min. A gradient of 90:10v/v (formate buffer: ACN) to 20:80v/v was used. Detection of the substrate was carried out at 224nm and the injection volume was 10μL.
Table 3. Calculated precision and accuracy for each substrate assay; data produced from six repeats
Statistical analysis—Single factor ANOVA was used to compare differences in the metabolism of the substrate between the various inhibitors and control (no inhibitor). P<0.05 was statistically significant.
Metabolism observed in the absence of an inhibitor (the control) was set at 100%, with metabolism in the assays calculated as a percentage of the control.
TFMPP significantly inhibited of the metabolism of dextromethorphan in a concentration-dependent manner (Figure 2). Significant inhibition (p<0.001) was only observed at the highest concentration (200 μM) of BZP used.
Figure 2. Effect of BZP and TFMPP on the metabolism of 200 µM dextromethorphan (a CYP2D6 substrate) in pooled human liver microsomes
Note: Furafylline was used as the negative control; quinidine as the positive control. Values shown are mean ± standard deviation, n=6.
Caffeine metabolism was only inhibited by the two highest concentrations of BZP and TFMPP (p<0.001) (Figure 3).
Figure 3. Effect of BZP and TFMPP on the metabolism of 200 µM caffeine (a CYP1A2 substrate)
Note: Quinidine was used as the negative control; furafylline as the positive control. Values shown are mean ± standard deviation, n=6.
Only the highest concentration of TFMPP significantly inhibited the metabolism of ethinyloestradiol (P<0.001) (Figure 4). Results with the higher concentrations of BZP were also significant but, only a minor reduction metabolism was observed. Neither BZP nor TFMPP inhibited the metabolism of omeprazole. (Figure 5).
Figure 4. Effect of BZP and TFMPP on the metabolism of 200 µM ethinyloestradiol (a CYP3A4 substrate)
Note: Quinidine was used as the negative control; TAO (troleandomycin) as the positive control. Values shown are mean ± standard deviation, n=6.
Note: Quinidine was used as the negative control; proguanil as the positive control. Values shown are mean ± standard deviation, n=6.
TFMPP has been reported to be predominantly metabolised by CYP2D6 and to a lesser degree by CYP1A2 and CYP3A4.3 Therefore, TFMPP could potentially affect the metabolism of other CYP2D6, CYP1A2, and CYP3A4 substrates.
The results obtained from the human microsomal incubation assays used in this study revealed potentially significant interactions between TFMPP and BZP with dextromethorphan (a known CYP2D6 substrate) and caffeine (a known CYP1A2 substrate). TFMPP also had an inhibitory effect on the metabolism of ethinyloestradiol (a known CYP3A4 substrate).
The results from this research consistently indicate that TFMPP is a more potent inhibitor than BZP of the metabolism of dextromethorphan, caffeine, and ethinyloestradiol. This is also in agreement with data from published literature, suggesting that BZP is excreted mostly unchanged in the urine, whereas the metabolism of TFMPP principally involves the CYP isoenzymes.3,12
The magnitude of the inhibitory effects of BZP and TFMPP must not be dismissed because CYP2D6, CYP1A2, and CYP3A4 are involved in the metabolism of a wide range of drugs. Consequently many of the drugs frequently co-ingested with party pills could be poorly metabolised and in turn lead to higher than expected concentrations and consequences of clinical significance.13
For example, because the metabolism of dextromethorphan was altered, similar interactions with other CYP2D6 substrates such as paroxetine (a selective serotonin re-uptake inhibitor), or imipramine (a tricyclic antidepressant) can be predicted.10,11 Higher than expected plasma concentrations of these drugs in the human body can have severe adverse effects. Inhibiting the metabolism of paroxetine can effectively produce an overdose leading to the serotonin syndrome—a potentially fatal condition characterised by hypomania, confusion, hallucinations, agitation, myoclonus, nausea, diarrhoea, tachycardia, and coma.16
Interestingly the only fatalities associated with BZP-use occurred with simultaneous consumption of MDMA (Ecstasy).17 The finding that BZP can inhibit CYP2D6 may account for toxicity due to increased MDMA levels because MDMA is also metabolised by CYP2D6.18
Consideration must also be given to the possibility of synergistic pharmacodynamic interactions secondary to pharmacokinetic interactions. For example, BZP also has serotonergic effects.2 Continuing with the example of elevated paroxetine levels secondary to CYP2D6 inhibition, the potential for adverse effects is greater again because both of compounds enhance serotonergic activity.
In view of the circumstances under which party pills are consumed, caffeine becomes a relevant substrate. Many alcoholic drinks served at bars and clubs are caffeinated. In addition, caffeine is an ingredient of many medicines, for example Panadol Extra®.19 Caffeine is a useful probe substrate for CYP1A2 and results of this study could also be used to predict interactions between BZP and TFMPP and other CYP1A2 substrates such as theophylline (a bronchodilator used in chronic obstructive pulmonary disease and asthma) and olanzapine (an atypical antipsychotic), which are metabolised by this isoenzyme to a significant degree.20
Caffeine overdose can lead to hypokalaemia and agitation; however, very high levels of caffeine would need to be achieved.21 Increased serum concentrations of olanzapine can cause tachycardia, severe central nervous system depression, and may be associated with the potentially fatal neuroleptic malignant syndrome.22
Using ethinyloestradiol as a probe substrate, BZP and TFMPP demonstrated inhibitory effects on CYP3A4. Increased serum concentrations of ethinyloestradiol itself can lead to serious adverse effects such as an increased risk of thromboembolism.23 Once again this result is applicable to other CYP3A4 substrates such as carbamazepine which even at therapeutic concentrations can cause adverse effects such as drowsiness and leucopaenia, or in the case of an elevated plasma concentration, agranulocytosis.24,22
Drug-drug interactions via CYP isoenzymes may partly explain some of the adverse effects reported following ingestion of BZP such as insomnia, tachycardia, agitation, and psychosis.1,7,26 These adverse effects may not be solely due to increased levels of BZP but might be due to inhibition of its metabolism by co-ingested drugs.
Interactions observed with CYP2D6, CYP1A2, and CYP3A4 in this study are in agreement with our previous work in which quinidine (a CYP2D6 inhibitor), furafylline (a CYP1A2 inhibitor), and TAO (a CYP3A4 inhibitor) also reduced the metabolism of BZP.27
Taking these two studies together, it is apparent that BZP and dextromethorphan inhibit the metabolism of each other and co-ingestion of BZP and dextromethorphan may result in a variety of adverse effects because of the increased plasma concentration of both drugs.
These results also demonstrate that TFMPP and BZP may have a pharmacokinetic interaction with each other. This finding is of a great importance because BZP and TFMPP are frequently taken together.
A significant limitation of this research is that the expected plasma concentrations of BZP and TFMPP were unknown before these experiments began because there were no published pharmacokinetic trials in humans using either drug. Furthermore, variables such as the Ki of BZP and TFMPP, and the degree of their protein binding, are unknown which makes it difficult to use incubation parameters that accurately reflect in vivo parameters.
It is feasible to obtain Cmax for most drugs from blood samples, however free drug concentrations in the liver can only be obtained by liver biopsies which are undesirable due to their invasive nature.
This study confirms the possibility of drug-drug interactions involving party pills and concomitant medications metabolised by CYP2D6, CYP1A2, and CYP3A4; the severity of these interactions warrants further research. Despite the best efforts of clinicians to screen for and prevent drug-drug interactions, these adverse events may still occur in patients using party pills.
Many people might not consider party pills as illicit substances and are unlikely to report their use if asked about illicit drugs during the recording of a medication history. Therefore it is recommended that recording a thorough drug history includes not only an assessment of alcohol intake, smoking habits, and illicit drug-use, but also specific questions targeting party pill-use.
Competing interests: None known.
Author information: Meghan Murphy, Pharmacist and Masters Student, School of Pharmacy; Ushtana Antia, PhD Student, School of Pharmacy; Hsin-Yao Chang, Pharmacy Student, School of Pharmacy; Abir Ibrahim, Pharmacy Student, School of Pharmacy; Jae Young Han, Pharmacy Student, School of Pharmacy; Malcolm Tingle, Senior Lecturer in Toxicology, Department of Pharmacology; Bruce Russell, Senior Lecturer in Pharmacotherapy, School of Pharmacy; University of Auckland
Correspondence: Bruce Russell, Senior Lecturer in Pharmacotherapy, School of Pharmacy, University of Auckland. Private Bag 92019, Auckland, New Zealand. Email: firstname.lastname@example.org
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