Drug interaction between oral atorvastatin and verapamil in healthy subjects: effects of atorvastatin on the pharmacokinetics of verapamil and norverapamil

Cutaneous leukocytoclastic vasculitis associated with verapamil and atorvastatin: A case report

We report a case of biopsy-proven cutaneous leukocytoclastic vasculitis developing 10 days after starting verapamil and atorvastatin in a patient with long-standing Sjogren's syndrome. This highlights the need to monitor for this rare adverse effect.

Interaction and potential mechanisms between atorvastatin and voriconazole, agents used to treat dyslipidemia and fungal infections

Purpose: Voriconazole (VOR) is combined with atorvastatin (ATO) to treat fungal infections in patients with dyslipidemia in clinical practice. However, the pharmacokinetic interactions and potential mechanisms between them are unknown. Therefore, this study aimed to investigate the pharmacokinetic interactions and potential mechanisms between ATO and VOR. Patients and methods: We collected plasma samples from three patients using ATO and VOR. Rats were administered either VOR or normal saline for 6 days, followed by a single dose of 2 mg/kg ATO, and then plasma samples were collected at different time points. The incubation models of human liver microsomes or HepG2 cells were constructed in vitro. A high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) system was developed to determine the concentration of ATO, 2-hydroxy-ATO, 4-hydroxy-ATO, and VOR. Results: In patients, VOR significantly reduced the metabolism of ATO and slowed the formation of 2-hydroxy- and 4-hydroxy-ATO. In rats pretreated with orally administered VOR for 6 days or normal saline given a single dose of 2 mg/kg ATO administered orally on Day 6, the t1/2 of ATO was significantly prolonged from 3.61 to 6.43 h, and the area under the concentration-time curve (AUC0-24h) values of ATO increased from 53.86 to 176.84 h μg.L-1. However, the pharmacokinetic parameters of VOR (20 mg/kg) with or without pretreatment with ATO (2 mg/kg) only slightly changed. In vitro studies indicated that VOR inhibited the metabolism of ATO and testosterone, and the IC50 values were 45.94 and 49.81 μM. However, no significant change in transporter behaviors of ATO was observed when VOR or transporter inhibitors were co-administered. Conclusion: Our study demonstrated that VOR has significant interactions with ATO, probably due to VOR's inhibition of the CYP3A4-mediated metabolism of ATO. Based on the clinical cases and potential interactions, the basic data obtained in our study are expected to help adjust the dose of ATO and promote the design of rational dosage regimens for pharmacotherapy for fungal infections in patients with dyslipidemia.

Targeted delivery of atorvastatin via asialoglycoprotein receptor (ASGPR)

Targeted drug delivery platforms can increase the concentration of drugs in specific cell populations, reduce adverse effects, and hence improve the therapeutic effect of drugs. Herein, we designed two conjugates by installing the targeting ligand GalNAc (N-acetylgalactosamine) onto atorvastatin (AT). Compared to the parent drug, these two conjugates, termed G2-AT and G2-K-AT, showed increased hepatic cellular uptake. Moreover, both conjugates were able to release atorvastatin, and consequently showed dramatic inhibition of β-hydroxy-β-methylglutaryl-CoA (HMG-CoA) reductase and increased LDL receptors on cell surface.

Results of a Doravirine-Atorvastatin Drug-Drug Interaction Study

Doravirine is a novel, highly potent, nonnucleoside reverse transcriptase inhibitor that is administered once daily and that is in development for the treatment of HIV-1 infection. In vitro and clinical data suggest that doravirine is unlikely to cause significant drug-drug interactions via major drug-metabolizing enzymes or transporters. As a common HIV-1 infection comorbidity, hypercholesterolemia is often treated with statins, including the commonly prescribed atorvastatin. Atorvastatin is subject to drug-drug interactions with cytochrome P450 3A4 (CYP3A4) inhibitors. Increased exposure due to CYP3A4 inhibition may lead to serious adverse events (AEs), including rhabdomyolysis. Furthermore, atorvastatin is a substrate for breast cancer resistance protein (BCRP), of which doravirine may be a weak inhibitor; this may increase atorvastatin exposure. The potential of doravirine to affect atorvastatin pharmacokinetics was investigated in a two-period, fixed-sequence study in healthy individuals. In period 1, a single dose of atorvastatin at 20 mg was administered followed by a 72-h washout. In period 2, doravirine at 100 mg was administered once daily for 8 days, with a single dose of atorvastatin at 20 mg concomitantly being administered on day 5. Sixteen subjects were enrolled, and 14 completed the trial; 2 discontinued due to AEs unrelated to the treatment. The atorvastatin area under the curve from time zero to infinity was similar with and without doravirine (geometric mean ratio [GMR] for doravirine-atorvastatin/atorvastatin, 0.98; 90% confidence interval [CI], 0.90 to 1.06), while the maximum concentration decreased by 33% (GMR for doravirine-atorvastatin/atorvastatin, 0.67; 90% CI, 0.52 to 0.85). These changes were deemed not to be clinically meaningful. Both of the study drugs were generally well tolerated. Doravirine had no clinically relevant effect on atorvastatin pharmacokinetics in healthy subjects, providing support for the coadministration of doravirine and atorvastatin.

Effect of Statin Treatment on Plasma 4β-Hydroxycholesterol Concentrations

The endogenous oxysterol 4β-hydroxycholesterol may be used as a marker for the drug-metabolizing enzymes cytochrome P450 3A (CYP3A). The primary aim of this study was to investigate the effect of statin treatment on plasma 4β-hydroxycholesterol concentrations. Plasma samples from a previously performed clinical study where gallstone patients had been treated with placebo (n = 6), 20 mg fluvastatin (n = 9) or 80 mg atorvastatin (n = 9) daily for 4 weeks were analysed. Hepatic CYP3A mRNA levels had previously been shown to be unchanged in all three treatment groups. Plasma 4β-hydroxycholesterol did not change significantly (p = 0.92) in the placebo group, but treatment with low-dose fluvastatin or high-dose atorvastatin resulted in reductions in plasma concentration of 10.7% (p < 0.05) and 36.5% (p < 0.01), respectively. However, the 4β-hydroxycholesterol/cholesterol ratio did not change significantly for the patients receiving placebo or patients receiving low-dose fluvastatin. The ratio for patients receiving high-dose atorvastatin increased by 12% (p < 0.05). In conclusion, the total plasma cholesterol level is an important determinant for the plasma 4β-hydroxycholesterol level.

Optical Isomers of Atorvastatin, Rosuvastatin and Fluvastatin Enantiospecifically Activate Pregnane X Receptor PXR and Induce CYP2A6, CYP2B6 and CYP3A4 in Human Hepatocytes

Atorvastatin, fluvastatin and rosuvastatin are drugs used for treatment of hypercholesterolemia. They cause numerous drug-drug interactions by inhibiting and inducing drug-metabolizing cytochromes P450. These three statins exist in four optical forms, but they are currently used as enantiopure drugs, i.e., only one single enantiomer. There are numerous evidences that efficacy, adverse effects and toxicity of drugs may be enantiospecific. Therefore, we investigated the effects of optical isomers of atorvastatin, fluvastatin and rosuvastatin on the expression of drug-metabolizing P450s in primary human hepatocytes, using western blots and RT-PCR for measurement of proteins and mRNAs, respectively. The activity of P450 transcriptional regulators, including pregnane X receptor (PXR), aryl hydrocarbon receptor (AhR) and glucocorticoid receptor (GR), was assessed by gene reporter assays and EMSA. Transcriptional activity of AhR was not influenced by any statin tested. Basal transcriptional activity of GR was not affected by tested statins, but dexamethasone-inducible activity of GR was dose-dependently and enantioselectively inhibited by fluvastatin. Basal and ligand-inducible transcriptional activity of PXR was dose-dependently influenced by all tested statins, and the potency and efficacy between individual optical isomers varied depending on statin and optical isomer. The expression of CYP1A1 and CYP1A2 in human hepatocytes was not influenced by tested statins. All statins induced CYP2A6, CYP2B6 and CYP3A4, and the effects on CYP2C9 were rather modulatory. The effects varied between statins and enantiomers and induction potency decreased in order: atorvastatin (RR>RS = SR>SS) > fluvastatin (SR>RS = SS>RR) >> rosuvastatin (only RS active). The data presented here might be of toxicological and clinical importance.

The effect of atorvastatin treatment on serum oxysterol concentrations and cytochrome P450 3A4 activity

AIMS

Atorvastatin is known to both inhibit and induce the cytochrome P450 3A4 (CYP3A4) enzyme in vitro. Some clinical studies indicate that atorvastatin inhibits CYP3A4 but there are no well-controlled longer term studies that could evaluate the inducing effect of atorvastatin. We aimed to determine if atorvastatin induces or inhibits CYP3A4 activity as measured by the 4β-hydroxycholesterol to cholesterol ratio (4βHC : C).

METHODS

In this randomized, double-blind, placebo-controlled 6 month study we evaluated the effects of atorvastatin 20 mg day(-1) (n = 15) and placebo (n = 14) on oxysterol concentrations and determined if atorvastatin induces or inhibits CYP3A4 activity as assessed by the 4βHC : C index. The respective 25-hydroxycholesterol and 5α,6α-epoxycholesterol ratios were used as negative controls.

RESULTS

Treatment with atorvastatin decreased 4βHC and 5α,6α-epoxycholesterol concentrations by 40% and 23%, respectively. The mean 4βHC : C ratio decreased by 13% (0.214 ± 0.04 to 0.182 ± 0.04, P = 0.024, 95% confidence interval (CI) of the difference -0.0595, -0.00483) in the atorvastatin group while no significant change occurred in the placebo group. The difference in change of 4βHC : C between study arms was statistically significant (atorvastatin -0.032, placebo 0.0055, P = 0.020, 95% CI of the difference -0.069, -0.0067). The ratios of 25-hydroxycholesterol and 5α,6α-epoxycholesterol to cholesterol did not change.

CONCLUSIONS

The results establish atorvastatin as an inhibitor of CYP3A4 activity. Furthermore, 4βHC : C is a useful index of CYP3A4 activity, including the conditions with altered cholesterol concentrations.

Effect of steady-state atorvastatin on the pharmacokinetics of a single dose of colchicine in healthy adults under fasted conditions

BACKGROUND AND OBJECTIVE

Colchicine is commonly prescribed for gout. While minimally metabolized by the cytochrome P450 (CYP) 3A4 isoenzyme, colchicine is a substrate for P-glycoprotein (P-gp). Atorvastatin is metabolized primarily by CYP3A4 and is a P-gp inhibitor. Patients with gout often have dyslipidemia; therefore, the potential for co-administration of atorvastatin and colchicine exists. The objective of this study was to determine the effect of oral atorvastatin on the pharmacokinetics of a single, oral dose of colchicine.

METHODS

Twenty-four healthy adult subjects were enrolled in this single-center, open-label, non-randomized, one-sequence, two-period drug-drug interaction study. On day 1, subjects received a single oral dose of colchicine 0.6 mg. After a 14-day washout, subjects received atorvastatin 40 mg once daily for 14 days followed by a single dose of colchicine 0.6 mg co-administered with atorvastatin 40 mg on day 28. Main outcome measures were colchicine maximum plasma concentration (C max), area under the plasma concentration-time curve (AUC) from time zero to the last measurable concentration (AUC last), and AUC from time zero to infinity (AUC∞), which were compared with and without concurrent atorvastatin.

RESULTS

Colchicine AUC last, AUC∞, and C max increased by 27, 24, and 31 %, respectively, when co-administered with atorvastatin. Corresponding 90 % confidence intervals around the ratios were outside the established no-effect 80-125 % interval.

CONCLUSION

Increased colchicine exposure was observed after a single dose of colchicine was administered with steady-state atorvastatin. Additional studies with multiple dosing of both drugs are needed to further determine the clinical implications of these results.

Direct In Vivo Human Intestinal Permeability (Peff ) Determined with Different Clinical Perfusion and Intubation Methods

Regional in vivo human intestinal effective permeability (Peff ) is calculated by measuring the disappearance rate of substances during intestinal perfusion. Peff is the most relevant parameter in the prediction of rate and extent of drug absorption from all parts of the intestine. Today, human intestinal perfusions are not performed on a routine basis in drug development. Therefore, it would be beneficial to increase the accuracy of the in vitro and in silico tools used to evaluate the intestinal Peff of novel drugs. This review compiles historical Peff data from 273 individual measurements of 80 substances from 61 studies performed in all parts of the human intestinal tract. These substances include: drugs, monosaccharaides, amino acids, dipeptides, vitamins, steroids, bile acids, ions, fatty acids, and water. The review also discusses the determination and prediction of Peff using in vitro and in silico methods such as quantitative structure-activity relationship, Caco-2, Ussing chamber, animal intestinal perfusion, and physiologically based pharmacokinetic (PBPK) modeling. Finally, we briefly outline how to acquire accurate human intestinal Peff data by deconvolution of plasma concentration-time profiles following regional intestinal bolus dosing.

Assessment of CYP3A-mediated drug-drug interaction potential for victim drugs using an in vivo rat model

The present study aims to determine if an in vivo rat model of drug-drug interaction (DDI) could be useful to discriminate a sensitive (buspirone) from a 'non-sensitive' (verapamil) CYP3A substrate, using ketoconazole and ritonavir as perpetrator drugs. Prior to in vivo studies, ketoconazole and ritonavir were shown to inhibit midazolam hydroxylation with IC50 values of 350 ± 60 nm and 11 ± 3 nm, respectively, in rat liver microsomes (RLM). Buspirone and verapamil were also shown to be substrates of recombinant rat CYP3A1/3A2. In the rat model, the mean plasma AUC0-inf of buspirone (10 mg/kg, p.o.) was increased by 7.4-fold and 12.8-fold after co-administration with ketoconazole and ritonavir (20 mg/kg, p.o.), respectively. The mean plasma AUC0-inf of verapamil (10 mg/kg, p.o.) was increased by 3.0-fold and 4.8-fold after co-administration with ketoconazole and ritonavir (20 mg/kg, p.o.), respectively. Thus, the rat DDI model correctly identified buspirone as a sensitive CYP3A substrate (>5-fold AUC change) in contrast to verapamil. In addition, for both victim drugs, the extent of DDI when co-administered was greater with ritonavir compared with ketoconazole, in line with their in vitro CYP3A inhibition potency in RLM. In conclusion, our study extended the rat DDI model applicability to two additional victim/perpetrator pairs. In addition, we suggest that use of this model would increase our confidence in estimation of the DDI potential for victim drugs in early discovery.

Effect of ABCB1 polymorphisms and atorvastatin on sitagliptin pharmacokinetics in healthy volunteers

OBJECTIVES

The objectives of this study were to determine if ABCB1 polymorphisms are associated with interindividual variability in sitagliptin pharmacokinetics and if atorvastatin alters the pharmacokinetic disposition of sitagliptin in healthy volunteers.

METHODS

In this open-label, randomized, two-phase crossover study, healthy volunteers were prospectively stratified according to ABCB1 1236/2677/3435 diplotype (n = 9, CGC/CGC; n = 10, CGC/TTT; n = 10, TTT/TTT). In one phase, participants received a single 100 mg dose of sitagliptin; in the other phase, participants received 40 mg of atorvastatin for 5 days, with a single 100 mg dose of sitagliptin administered on day 5. A 24-h pharmacokinetic study followed each sitagliptin dose, and the study phases were separated by a 14-day washout period.

RESULTS

Sitagliptin pharmacokinetic parameters did not differ significantly between ABCB1 CGC/CGC, CGC/TTT, and TTT/TTT diplotype groups during the monotherapy phase. Atorvastatin administration did not significantly affect sitagliptin pharmacokinetics, with geometric mean ratios (90 % confidence intervals) for sitagliptin maximum plasma concentration, plasma concentration-time curve from zero to infinity, renal clearance, and fraction of sitagliptin excreted unchanged in the urine of 0.93 (0.86-1.01), 0.96 (0.91-1.01), 1.02 (0.93-1.12), and 0.98 (0.90-1.06), respectively.

CONCLUSIONS

ABCB1 CGC/CGC, CGC/TTT, and TTT/TTT diplotypes did not influence sitagliptin pharmacokinetics in healthy volunteers. Furthermore, atorvastatin had no effect on the pharmacokinetics of sitagliptin in the setting of ABCB1 CGC/CGC, CGC/TTT, and TTT/TTT diplotypes.

Cytochrome P450-mediated cardiovascular drug interactions

INTRODUCTION

There are numerous drug-drug interactions (DDIs) related to cardiovascular medications and many of these are mediated via the cytochrome P450 (CYP) system. Some of these may lead to serious adverse events and it is, therefore, essential that clinicians are aware of the important interactions that occur.

AREAS COVERED

An extensive literature search was performed to analyze the CYP-mediated cardiovascular DDIs that lead to a loss of efficacy or potential toxicity. Cardiovascular drugs may be victims or act as perpetrators of DDIs. The paper analyzes CYP-mediated drug interactions concerning anticoagulants, antiplatelet agents, antiarrhythmics, β-blockers, calcium antagonists, antihypertensive medications, lipid-lowering drugs and oral antidiabetic agents.

EXPERT OPINION

Cardiovascular DDIs involving the CYP system are numerous. Additionally, the spectrum of drugs prescribed is constantly changing, particularly with cardiovascular diseases and it is not necessarily the case that drugs that had shown safety earlier will always show safety. Clinicians are encouraged to develop their knowledge of CYP-mediated DDIs so that they can choose safe drug combination regimens, adjust drug dosages appropriately and conduct therapeutic drug monitoring for drugs with narrow therapeutic indices.

P-glycoprotein related drug interactions: clinical importance and a consideration of disease states

IMPORTANCE OF THE FIELD

P-glycoprotein (P-gp) is the most characterized drug transporter in terms of its clinical relevance for pharmacokinetic disposition and interaction with other medicines. Clinically significant P-gp related drug interactions appear restricted to digoxin. P-gp may act as a major barrier to current and effective drug treatment in a number of diseases including cancer, AIDS, Alzheimer's and epilepsy due to its expression in tumors, lymphocytes, cell membranes of brain capillaries and the choroid plexus.

AREAS COVERED IN THIS REVIEW

This review summarizes the current understanding of P-gp structure/function, clinical importance of P-gp related drug interactions and the modulatory role this transporter may contribute towards drug efficacy in disease states such as cancer, AIDS, Alzheimer's and epilepsy.

WHAT THE READER WILL GAIN

The reader will gain an understanding that the clinical relevance of P-gp in drug interactions is limited. In certain disease states, P-gp in barrier tissues can modulate changes in regional distribution.

TAKE HOME MESSAGE

P-gp inhibition in isolation will not result in clinically important alterations in systemic exposure; however, P-gp transport may be of significance in barrier tissues (tumors, lymphocytes, brain) resulting in attenuated efficacy.

HepaRG human hepatic cell line utility as a surrogate for primary human hepatocytes in drug metabolism assessment in vitro

INTRODUCTION

Primary human hepatocytes are considered as a highly predictive in vitro model for preclinical drug metabolism studies. Due to the limited availability of human liver tissue for cell isolation, there is a need of alternative cell sources for pharmaceutical research.

METHODS

In this study, the metabolic activity and long-term stability of the human hepatoma cell line HepaRG were investigated in comparison to primary human hepatocytes (pHH). Hepatocyte-specific parameters (albumin and urea synthesis, galactose and sorbitol elimination) and the activity of human-relevant cytochrome P450 (CYP) enzymes (CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4) were assayed in both groups over a period of 14 days subsequently to a two week culture period in differentiated state in case of the HepaRG cells, and compared with those of cryopreserved hepatocytes in suspension. In addition, the inducibility of CYP enzymes and the intrinsic clearances of eleven reference drugs were determined.

RESULTS

The results show overall stable metabolic activity of HepaRG cells over the monitored time period. Higher albumin production and galactose/sorbitol elimination rates were observed compared with pHH, while urea production was not detected. CYP enzyme-dependent drug metabolic capacities were shown to be stable over the cultivation time in HepaRG cells and were comparable or even higher (CYP2C9, CYP2D6, CYP3A4) than in pHH, whereas commercially available hepatocytes showed a different pattern The intrinsic clearance rates of reference drugs and enzyme induction of most CYP enzymes were similar in HepaRG cells and pHH. CYP1A2 activity was highly inducible in HepaRG by β-naphthoflavone.

DISCUSSION

In conclusion, the results from this study indicate that HepaRG cells could provide a suitable alternative to pHH in pharmaceutical research and development for metabolism studies such as CYP induction or sub-chronic to chronic hepatotoxicity studies.

Influence of ABCB1 gene polymorphisms on the pharmacokinetics of verapamil among healthy Chinese Han ethnic subjects

AIMS

To assess the association between polymorphisms of the ABCB1 gene and the pharmacokinetics of verapamil among healthy Chinese Han ethnic subjects.

METHODS

Based on polymorphisms of the ABCB1 gene at positions 2677 and 3435, 24 healthy male participants were divided into three groups: 2677GG/3435CC (n = 6), 2677GT/3435CT (n = 12) and 2677TT/3435TT (n = 6). Each subject had received a single oral dose of verapamil (80 mg) under fasting conditions. Multiple blood samples were collected over 24 h, and plasma concentrations of verapamil were determined by HPLC. Pharmacokinetic characteristics were compared between the different genotypic groups.

RESULTS

The pharmacokinetics parameters of verapamil differed significantly among the three genotypic groups. AUC(last) was significantly lower among individuals with the 2677TT/3435TT (159.5 +/- 79.0 ng ml(-1) h) and 2677GT/3435CT (189.3 +/- 73.1 ng ml(-1) h) genotypes than those with the 2677GG/3435CC genotype (303.1 +/- 83.7 ng ml(-1) h) (P= 0.004 and P= 0.008, respectively). However, the CL/F value was higher among subjects with the 2677TT/3435TT (523.0 +/- 173.7 l h(-1)) genotype than those with the 2677GT/3435CT (452.2 +/- 188.6 l h(-1)) or 2677GG/3435CC (265.4 +/- 72.8 l h(-1)) genotypes. A significant difference was also found between the latter two groups (P= 0.034). In addition, the C(max) tended to be higher among subjects with the 2677GG/3435CC genotype than those with the 2677GT/3435CT or 2677TT/3435TT genotypes (42.2 +/- 3.9 vs 32.2 +/- 16.2 vs 38.1 +/- 13.7 ng ml(-1)).

CONCLUSIONS

Our study showed for the first time that verapamil pharmacokinetics may be influenced by particular genetic polymorphisms of the ABCB1 gene among healthy Chinese Han ethnic subjects. An individualized dosage regimen design incorporating such information may improve the efficacy of the drug whilst reducing adverse reactions.

Pharmacokinetic interaction between oral lovastatin and verapamil in healthy subjects: role of P-glycoprotein inhibition by lovastatin

BACKGROUND

Lovastatin is an inhibitor of P-glycoprotein (P-gp) and is metabolized by the cytochrome P450 (CYP) 3A4 isoenzyme. Verapamil is a substrate of both P-gp and CYP3A4. It is therefore likely that lovastatin can alter the absorption and metabolism of verapamil.

METHODS

The pharmacokinetic parameters of verapamil and one of its metabolites, norverapamil, were compared in 14 healthy male Korean volunteers (age range 22-28 years) who had been administered verapamil (60 mg) orally in the presence or absence of oral lovastatin (20 mg). The design of the experiment was a standard 2 x 2 crossover model in random order.

RESULTS

The pharmacokinetic parameters of verapamil were significantly altered by the co-administration of lovastatin compared to the control. The area under the plasma concentration-time curve (AUC (0-infinity)) and the peak plasma concentration of verapamil were significantly increased by 62.8 and 32.1%, respectively. Consequently, the relative bioavailability of verapamil was also significantly increased (by 76.5%). The (AUC (0-infinity)) of norverapamil and the terminal half-life of verapamil did not significantly changed with lovastatin coadministration. The metabolite-parent ratio was significantly reduced (29.2%) in the presence of lovastatin.

CONCLUSION

Lovastatin increased the absorption of verapamil by inhibiting P-gp and inhibited the first-pass metabolism of verapamil by inhibiting CYP3A4 in the intestine and/or liver in humans.

Verapamil for cluster headache. Clinical pharmacology and possible mode of action

Verapamil is used mainly in cardiovascular diseases. High-dose verapamil (360-720 mg) is, however, currently the mainstay in the prophylactic treatment of cluster headache. The oral pharmacokinetics are variable. The pharmacodynamic effect of verapamil, the effect on blood pressure, also varies considerably among subjects. The dose of verapamil used for cluster headache is approximately double the dose used in cardiovascular disease, most likely because verapamil is a substrate for the efflux transporter P-glycoprotein in the blood-brain barrier. The access of verapamil to the central nervous system is therefore limited. The clinical use of verapamil in cluster headache is reviewed and several relevant drug interactions are mentioned. Finally, its possible mode of action in cluster headache is discussed. The effect of verapamil in cluster headache most likely takes place in the hypothalamus.Verapamil is an L-type calcium channel blocker but it is also a blocker of other calcium channels (T-, P-, and possibly N- and Q-type Ca(2+) channels) and the human ether-a-go-go-related gene potassium channel. With so many different actions of verapamil, it is impossible at the present time to single out a certain mode of action of the drug in cluster headache.

Drug-drug interaction studies in preclinical species: should metabolite(s) kinetics be studied?

Drug-drug interaction studies are important building blocks in drug development to understand the perceived risk of a purported interaction due to the differing clinical pharmacology attributes of the co-administered drugs. Two case studies are presented that justify the importance of evaluating the metabolite kinetics data along with the parent in a preclinical model. Atorvastatin and verapamil have interesting clinical pharmacology attributes in that both agents are substrates and/or inhibitors of the dual cytochrome P450 (CYP) 3A4 and P-glycoprotein (Pgp) efflux transporter interplay. As articulated by the two case studies, the presence of metabolite kinetic data (i.e., norverapamil) provided unequivocal evidence in order to tease out the actual pathway responsible for the interaction between atorvastatin and verapamil. Therefore, consideration for metabolite kinetics, wherever feasible, appears to be prudent in defining the interaction liability between the two agents in a preclinical model.