Geneva cocktail for cytochrome p450 and P-glycoprotein activity assessment using dried blood spots.

The suitability of the capillary dried blood spot (DBS) sampling method was assessed for simultaneous phenotyping of cytochrome P450 (CYP) enzymes and P-glycoprotein (P-gp) using a cocktail approach. Ten volunteers received an oral cocktail capsule containing low doses of the probes bupropion (CYP2B6), flurbiprofen (CYP2C9), omeprazole (CYP2C19), dextromethorphan (CYP2D6), midazolam (CYP3A), and fexofenadine (P-gp) with coffee/Coke (CYP1A2) on four occasions. They received the cocktail alone (session 1), and with the CYP inhibitors fluvoxamine and voriconazole (session 2) and quinidine (session 3). In session 4, subjects received the cocktail after a 7-day pretreatment with the inducer rifampicin. The concentrations of probes/metabolites were determined in DBS and plasma using a single liquid chromatography-tandem mass spectrometry method. The pharmacokinetic profiles of the drugs were comparable in DBS and plasma. Important modulation of CYP and P-gp activities was observed in the presence of inhibitors and the inducer. Minimally invasive one- and three-point (at 2, 3, and 6 h) DBS-sampling methods were found to reliably reflect CYP and P-gp activities at each session.

Identification and weighting of the most critical "real-life" drug-drug interactions with acenocoumarol in a tertiary care hospital.

PURPOSE: The objective of this study was to identify the most clinically relevant drug-drug interactions (DDIs) at risk of affecting acenocoumarol safety in our tertiary care university hospital, a 2,000 bed institution. METHODS: We identified DDIs occurring with acenocoumarol by combining two different sources of information: a 1-year retrospective analysis of acenocoumarol prescriptions and comedications from our Computerized Physician Order Entry (CPOE) system (n = 2,439 hospitalizations) and a retrospective study of clinical pharmacology consultations involving acenocoumarol over the past 14 years (1994-2007) (n = 407). We classified these DDIs using an original risk-analysis method. A criticality index was calculated for each associated drug by multiplying three scores based on mechanism of interaction, involvement in a supratherapeutic international normalized ratio (INR) (≥ 6) and involvement in a severe bleeding. RESULTS: One hundred and twenty-six DDIs were identified and weighted. Twenty-eight drugs had a criticality index ≥ 20 and were therefore considered at high risk for interacting with acenocoumarol by increasing its effect: 75% of these drugs involved a pharmacokinetic mechanism and 14 % a pharmacodynamic mechanism. An unknown mechanism of interaction was involved in 11 % of drugs. CONCLUSION: Twenty-eight specific drugs were identified as being at high risk for interacting with acenocoumarol in our hospital using an original risk-analysis method. Most analyzed drugs interact with acenocoumarol via a pharmacokinetic mechanism. Actions such as the implementation of alerts in our CPOE system should be specifically developed for these drugs.

[Comparison of four drug interaction screening programs]. / Quel programme informatique de détection des interactions médicamenteuses néfastes?

Adverse drug events (ADE) are a major public health issue, with drug-drug interactions (DDI) being one of well-recognized causes of ADE that could be preventable by the use of DDI screening software. We compared the ability of four programs to detect clinically important DDI. We tested 62 drug pairs with and 12 drug pairs without clinically important DDI. Lexi-Interact and Epocrates were the most sensitive (95%) compared to the Compendium and Theriaque (80 and 73%, respectively). The Compendium and Theriaque also showed the lowest negative predictive value. All programs showed high specificity and positive predictive value. The qualitative assessment showed the best performances for Compendium and Lexi-Interact. The last one seems to be the best screening program, but the Compendium is in French and is freely available.

The paraoxonase-1 pathway is not a major bioactivation pathway of clopidogrel in vitro.

BACKGROUND AND PURPOSE: Clopidogrel is a prodrug bioactivated by cytochrome P450s (CYPs). More recently, paraoxonase-1 (PON1) has been proposed as a major contributor to clopidogrel metabolism. The purpose of this study was to assess the relative contribution of CYPs and PON1 to clopidogrel metabolism in vitro. EXPERIMENTAL APPROACH: Clopidogrel metabolism was studied in human serum, recombinant PON1 enzyme (rePON1), pooled human liver microsomes (HLMs), HLMs with the CYP2C19*1/*1 genotype and HLMs with the CYP2C19*2/*2 genotype. Inhibition studies were also performed using specific CYP inhibitors and antibodies. Clopidogrel and its metabolites were measured using LC/MS/MS method. KEY RESULTS: PON1 activity was highest in the human serum and there was no difference in PON1 activity between any of the HLM groups. The production of clopidogrel's active metabolite (clopidogrel-AM) from 2-oxo-clopidogrel in pooled HLMs was approximately 500 times that in serum. When 2-oxo-clopidogrel was incubated with rePON1, clopidogrel-AM was not detected. Clopidogrel-AM production from 2-oxo-clopidogrel was lower in CYP2C19*2/*2 HLMs compared with CYP2C19*1/*1 HLMs, while PON1 activity in HLMs with both genotypes was similar. Moreover, incubation with inhibitors of CYP3A, CYP2B6 and CYP2C19 significantly reduced clopidogrel bioactivation while a PON1 inhibitor, EDTA, had only a weak inhibitory effect. CONCLUSION AND IMPLICATIONS: This in vitro study shows that the contribution of PON1 to clopidogrel metabolism is limited at clinically relevant concentrations. Moreover, CYP2C19, CYP2B6 and CYP3A play important roles in the bioactivation of clopidogrel.

Oral flurbiprofen metabolic ratio assessment using a single-point dried blood spot.

We investigated whether a single blood measurement using the minimally invasive technique of a finger prick to draw a blood sample of 5 µl (to yield a dried blood spot (DBS)) is suitable for the assessment of flurbiprofen (FLB) metabolic ratio (MR). Ten healthy volunteers who had been genotyped for CYP2C9 were recruited as subjects. They received FLB alone in session 1 and FLB with fluconazole in session 2. In session 3, the subjects were pretreated for 4 days with rifampicin and received FLB with the last dose of rifampicin on day 5. Plasma and DBS samples were obtained between 0 and 8 h after FLB administration, and urine was collected during the 8 h after administration. The pharmacokinetic profiles of the drugs were comparable in DBS and plasma. FLB's apparent clearance values decreased by 35% in plasma and DBS during session 2 and increased by 75% in plasma and by 30% in DBS during session 3. Good correlations were observed between MRs calculated from urine, plasma, and DBS samples.

Impact of genetic polymorphisms and drug-drug interactions on clopidogrel and prasugrel response variability.

Thienopyridine antiaggregating platelet agents (clopidogrel and prasugrel) act as irreversible P2Y12 receptor inhibitors. They are used with aspirin to prevent thrombotic complications after an acute coronary syndrome or percutaneous coronary intervention. A large interindividual variability in response to clopidogrel and to a lesser extent to prasugrel is observed and may be related to their metabolism. Clopidogrel and prasugrel are indeed prodrugs converted into their respective active metabolites by several cytochromes P450 (CYPs). Besides clopidogrel inactivation (85%) by esterases to the carboxylic acid, clopidogrel is metabolized by CYPs to 2-oxo-clopidogrel (15%) and further metabolized to an unstable but potent platelet-aggregating inhibitor. Prasugrel is more potent than clopidogrel with a better bioavailability and lower pharmacodynamic variability. Prasugrel is completely converted by esterases to an intermediate oxo-metabolite (R-95913) further bioactivated by CYPs. Numerous clinical studies have shown the influence of CYP2C19 polymorphism on clopidogrel antiplatelet activity. Moreover, unwanted drug-drug pharmacokinetic interactions influencing CYP2C19 activity and clopidogrel bioactivation such as with proton pump inhibitors remain a matter of intense controversy. Several studies have also demonstrated that CYP3A4/5 and CYP1A2 are important in clopidogrel bioactivation and should also be considered as potential targets for unwanted drug-drug interactions. Prasugrel bioactivation is mainly related to CYP3A4 and 2B6 activity and therefore the question of the effect of drug-drug interaction on its activity is open. The purpose of this review is to critically examine the current literature evaluating the influence of genetic and environmental factors such as unwanted drug-drug interaction affecting clopidogrel and prasugrel antiplatelet activity.

The effects of CYP2D6 and CYP3A activities on the pharmacokinetics of immediate release oxycodone.

BACKGROUND AND PURPOSE: There is high interindividual variability in the activity of drug-metabolizing enzymes catalysing the oxidation of oxycodone [cytochrome P450 (CYP) 2D6 and 3A], due to genetic polymorphisms and/or drug-drug interactions. The effects of CYP2D6 and/or CYP3A activity modulation on the pharmacokinetics of oxycodone remains poorly explored. EXPERIMENTAL APPROACH: A randomized crossover double-blind placebo-controlled study was performed with 10 healthy volunteers genotyped for CYP2D6 [six extensive (EM), two deficient (PM/IM) and two ultrarapid metabolizers (UM)]. The volunteers randomly received on five different occasions: oxycodone 0.2 mg x kg(-1) and placebo; oxycodone and quinidine (CYP2D6 inhibitor); oxycodone and ketoconazole (CYP3A inhibitor); oxycodone and quinidine+ketoconazole; placebo. Blood samples for plasma concentrations of oxycodone and metabolites (oxymorphone, noroxycodone and noroxymorphone) were collected for 24 h after dosing. Phenotyping for CYP2D6 (with dextromethorphan) and CYP3A (with midazolam) were assessed at each session. KEY RESULTS: CYP2D6 activity was correlated with oxymorphone and noroxymorphone AUCs and C(max) (-0.71 < Spearman correlation coefficient rhos < -0.92). Oxymorphone C(max) was 62% and 75% lower in PM than EM and UM. Noroxymorphone C(max) reduction was even more pronounced (90%). In UM, oxymorphone and noroxymorphone concentrations increased whereas noroxycodone exposure was halved. Blocking CYP2D6 (with quinidine) reduced oxymorphone and noroxymorphone C(max) by 40% and 80%, and increased noroxycodone AUC(infinity) by 70%. Blocking CYP3A4 (with ketoconazole) tripled oxymorphone AUC(infinity) and reduced noroxycodone and noroxymorphone AUCs by 80%. Shunting to CYP2D6 pathway was observed after CYP3A4 inhibition. CONCLUSIONS AND IMPLICATIONS: Drug-drug interactions via CYP2D6 and CYP3A affected oxycodone pharmacokinetics and its magnitude depended on CYP2D6 genotype.

Genetic polymorphisms and drug interactions modulating CYP2D6 and CYP3A activities have a major effect on oxycodone analgesic efficacy and safety.

BACKGROUND AND PURPOSE: The major drug-metabolizing enzymes for the oxidation of oxycodone are CYP2D6 and CYP3A. A high interindividual variability in the activity of these enzymes because of genetic polymorphisms and/or drug-drug interactions is well established. The possible role of an active metabolite in the pharmacodynamics of oxycodone has been questioned and the importance of CYP3A-mediated effects on the pharmacokinetics and pharmacodynamics of oxycodone has been poorly explored. EXPERIMENTAL APPROACH: We conducted a randomized crossover (five arms) double-blind placebo-controlled study in 10 healthy volunteers genotyped for CYP2D6. Oral oxycodone (0.2 mg x kg(-1)) was given alone or after inhibition of CYP2D6 (with quinidine) and/or of CYP3A (with ketoconazole). Experimental pain (cold pressor test, electrical stimulation, thermode), pupil size, psychomotor effects and toxicity were assessed. KEY RESULTS: CYP2D6 activity was correlated with oxycodone experimental pain assessment. CYP2D6 ultra-rapid metabolizers experienced increased pharmacodynamic effects, whereas cold pressor test and pupil size were unchanged in CYP2D6 poor metabolizers, relative to extensive metabolizers. CYP2D6 blockade reduced subjective pain threshold (SPT) for oxycodone by 30% and the response was similar to placebo. CYP3A4 blockade had a major effect on all pharmacodynamic assessments and SPT increased by 15%. Oxymorphone C(max) was correlated with SPT assessment (rho(S)= 0.7) and the only independent positive predictor of SPT. Side-effects were observed after CYP3A4 blockade and/or in CYP2D6 ultra-rapid metabolizers. CONCLUSIONS AND IMPLICATIONS: The modulation of CYP2D6 and CYP3A activities had clear effects on oxycodone pharmacodynamics and these effects were dependent on CYP2D6 genetic polymorphism.

The AmpliChip CYP450 test: cytochrome P450 2D6 genotype assessment and phenotype prediction.

Polymorphisms of the cytochrome P450 2D6 (CYP2D6) gene affecting enzyme activity are involved in interindividual variability in drug efficiency/toxicity. Four phenotypic groups are found in the general population: ultra rapid (UM), extensive (EM), intermediate (IM) and poor (PM) metabolizers. The AmpliChip CYP450 test is the first genotyping array allowing simultaneous analysis of 33 CYP2D6 alleles. The main aim of this study was to evaluate the performance of this test in CYP2D6 phenotype prediction. We first verified the AmpliChip CYP450 test genotyping accuracy for five CYP2D6 alleles routinely analysed in our laboratory (alleles 3,4,5,6, x N; n=100). Results confirmed those obtained by real-time PCR. Major improvements using the array are the detection of CYP2D6 intermediate alleles and identification of the duplicated alleles. CYP2D6 phenotype was determined by assessing urinary elimination of dextromethorphan and its metabolite dextrorphan and compared to the array prediction (n=165). Although a low sensitivity of UM prediction by genotyping was observed, phenotype prediction was optimal for PM and satisfying for EM and IM.

Lack of interaction of the NMDA receptor antagonists dextromethorphan and dextrorphan with P-glycoprotein.

The anti-N-methyl-D-aspartate (NMDA) effect of dextromethorphan (DEM) seems to be mainly related to the unchanged drug rather than to its more potent metabolite dextrorphan (DOR). The aim of our study was to assess the involvement of P-glycoprotein (P-gp) and pH conditions in the transmembranal transport of these two NMDA antagonists, using a human in vitro Caco-2 cell monolayer model. Transmission electron microscopy, transepithelial electrical resistance, [(3)H]-mannitol permeability, Western blot analysis and the bidirectional transport of the positive controls, rhodamine and digoxine were used to confirm model's integrity and validity. The bidirectional transport of DEM and DOR (1 to 100microM) across the monolayers was investigated in the presence and absence of the P-gp inhibitor cyclosporine A (10microM) at two pH conditions (pH 6.8/7.7-pH 7.4/7.4) and assessed with the specific and more potent P-gp inhibitor GF120918 (4microM). Analytical quantification was achieved using high performance liquid chromatography. At a pH gradient, DEM and DOR were subject to a significant active efflux transport (Papp(B-A) > 2-3x Papp(A-B); p<0.01). However, neither the influx nor the efflux was affected by P-gp inhibitors. At physiological pH, we observed no more efflux of the drugs and no influence of the inhibitors. In conclusion, dextromethorphan and dextrorphan are not P-gp substrates. However, pH-mediated efflux mechanisms seem to be involved in limiting DEM gastrointestinal absorption. The preferential anti-NMDA central effect of DEM appears to be P-gp independent.

Development and validation of a chemical hydrolysis method for dextromethorphan and dextrophan determination in urine samples: application to the assessment of CYP2D6 activity in fibromyalgia patients.

Dextromethorphan (DEM) is a widely used probe drug for human cytochrome P450 2D6 isozyme activity assessment by measuring the ratio between DEM and its N-demethylated metabolite dextrorphan (DOR). DOR is excreted in urine mainly conjugated to glucuronic acid. Prior to quantification, DOR must be deconjugated to avoid variability caused by the polymorphic glucuronosyltransferase enzyme. A chemical hydrolysis method was optimized using a chemometric approach. Three factors (acid concentration, hydrolysis time and temperature) were selected and simultaneously varied to study their effect on conjugated DOR hydrolysis. Hydrolysis conditions that maximize DOR release without significant degradation of both DEM and DOR were chosen and results were compared to those obtained by enzymatic method using beta-glucuronidase. An HPLC method with fluorescence detection was developed for the simultaneous quantitation of DEM, DOR and levallorphan, used as an internal standard. Separation was performed on a phenyl analytical column (150 mmx4.6 mm i.d., 5 microm) with a mobile phase consisting of 18% acetonitrile and 50 mM phosphoric acid (pH 3). The overall analytical procedure was validated and showed good performances in terms of selectivity, linearity, sensitivity, precision and accuracy. Finally, this assay was used to determine DEM/DOR molar ratios in fibromyalgia patients for the purpose of determining phenotype status for the CYP2D6.

[Behavioural and psychological symptoms of dementia (BPSD): pharmacological management]. / Prise en charge médicamenteuse des symptômes comportementaux et psychologiques liés à la démence.

BPSD affect all demented patients during their illness. They are part of the process of the disease and can be correlated to neurotransmitter dysfunctions as well as to the coping difficulties due to the patient's cognitive decline. The major consequences of BPSD are a decreased quality of life of both patient and caregivers and an increased need of professional care. Physicians should exclude precipitating factors such as intercurrent somatic, psychiatric or drug-related problems first and then proceed with behavioural or environment therapy. Introduction of a pharmacological treatment should be the last resort. This systematic review discusses the causes and consequences of BPSD and focuses on the evidence-based pharmacological approach. Only three drugs can be recommended at the present time: risperidone, olanzapine and donepezil.

[A link between sodium sensitivity and pharmacogenomics of antihypertensive drugs]. / Entre sel et gènes ou pharmaco- génomique des antihypertenseurs.

Pharmacogenomics studies the links between polymorphisms (genetic variants) and the variability of the response to some treatments in a given individual. Pharmacogenomics thus allows to explore polymorphisms that could potentially explain heterogeneous efficacy of diuretics, ACE inhibitors or angiotensin receptor blockers, beta-blockers and calcium channel blockers among populations of varied ethnical origin. There have been many studies on the relation between the efficacy of these treatments and the specific polymorphisms involved in the regulation of blood pressure. So far, no unique mutation is by itself predictive of the therapeutic response to these drugs; more elaborated polygenetic models are required so that pharmacogenomics can one day offer an individualized prescription for a complicated disease such as high blood pressure.

Systemic allergic reaction and diffuse bone pain after exposure to a preparation of betamethasone.

Allergic reactions to corticosteroids are unexpected as they seem to contradict their pharmacodynamic action. Nevertheless, they are not infrequent, with an estimated incidence of up to 4% for cutaneous reactions. Systemic reactions are rarely reported, but their incidence might be underestimated. We report here an unusual allergic reaction to betamethasone presenting with diffuse bone pain, erythema, and bronchoconstriction, which was confirmed by a positive rechallenge in a double-blind procedure. This is the first case report of a systemic reaction to betamethasone confirmed by a positive rechallenge. An impurity in betamethasone diproprionate cannot be excluded. As this substance is frequently used in rheumatologic soft-tissue injections, it is important to recognize this potentially life-threatening side effect.

Development and validation of a new reversed-phase ion pairing liquid chromatographic method with fluorescence detection for penciclovir analysis in plasma and aqueous humor.

A simple, sensitive and reliable HPLC ion-pairing method with fluorescence detection, was developed for penciclovir determination in plasma and aqueous humor, with a Zorbax SB-aq C18 (100 mmx2.1 mm) column. Plasma samples were treated by solid-phase extraction with Oasis MCX (30 mg) cartridges. Ganciclovir, an antiviral drug structurally related to penciclovir, was used as internal standard (I.S.). Aqueous humor samples were directly injected into the chromatographic system. Separation was performed by a gradient elution with a mobile phase consisting of a mixture of acetonitrile and phosphate buffer 50mM containing 5mM of sodium octanesulfonate, pH 2.0, at a flow rate of 0.3 ml/min. The method was validated and showed good performances in terms of linearity, sensitivity, precision and trueness. Quantification limit was obtained at 0.05 microg/ml for aqueous humor and at 0.1 microg/ml for plasma. Finally, the proposed analytical method was used to measure penciclovir in clinical samples for a pharmacokinetic study, after oral administration of famciclovir.

[Treating hypertension: a challenge for the general practitioner]. / Le traitement de l'hypertension artérielle: un défi pour le praticien.

Hypertension is associated with a greater risk of developing a stroke or a coronary heart disease, but remains, for the meanwhile, undertreated in a vast majority of patients. Non pharmacological interventions can reduce blood pressure and should be recommended to every patient suffering from hypertension. Nevertheless, a drug therapy must often be introduced. The threshold at which a treatment should be started depends mostly on the cardiovascular risk of each patient and the benefit of antihypertensive drug therapy depends primarily on the reduction of the blood pressure itself.

[The selection of a drug in a defined therapeutic class: the case of the HMG-CoA reductase inhibitors]. / Sélection d'un medicament dans une classe thérapeutique donnée: l'exemple des "inhibiteurs de l'HMG-CoA reductase"

The HMG-CoA reductase inhibitors have similar therapeutic targets and indications. However, their potential pharmacokinetic drug-drug interaction profile may play a significant role in their safety profile in polymedicated and polymorbid patients and can serve as a selection criterion. If their utility is clearly demonstrated in selected conditions, their safety profile remains of concern. Beside dose-related hepatic and muscular injury, other rare and important adverse drug reactions have been reported after prolonged administration such as polyneuropathy, fibrotic interstitial pulmonary disease and lupus-like syndrome. Teratogenicity has also been associated with statin therapy.

Clinical pharmacology and rationale of analgesic combinations.

BACKGROUND AND OBJECTIVE: Oral fixed drug combination analgesics have potential advantages over monotherapy, but these can only be attained through careful design. RESULTS: The main reasons for developing combination analgesics are to gain efficacy and to reduce toxicity. Analgesic combinations interact pharmacokinetically, or pharmacodynamically, or both, in positive or negative terms. The t(max) value for both enantiomers of tramadol occur two hours following administration, and that for the active, (+)-M1 metabolite occurs after three hours. Thus, pairing tramadol with acetaminophen, a rapid-onset analgesic, represents a pharmacokinetically rational combination. Analgesic combinations should satisfy two important pharmacodynamic criteria: the components of the combination should display additive or synergistic analgesia; and this interaction should allow lower doses of each substance to be used in combination, resulting in an improved safety profile. Clinical studies of the pharmacodynamic between oral tramadol and acetaminophen in third molar extraction and cold pressor models have provided evidence that this combination provides better efficacy than either individual component of the combination. CONCLUSIONS: In summary, combination analgesics can play a valuable role in pain management. However, dubious combinations (directed against the same targets or with unwanted interactions) and 'old fashioned' fixed-dose multiple analgesic agent combinations should be avoided. Fixed-dose combination analgesics are of value only when they have been developed according to rational pharmacokinetic and pharmacodynamic criteria, and when claims for their benefits have been supported by evidence-based data and well-designed clinical studies.

Neurophysiologic evidence for a central sensitization in patients with fibromyalgia.

OBJECTIVE: To determine whether abnormalities of peripheral and central nociceptive sensory input processing exist outside areas of spontaneous pain in patients with fibromyalgia (FM) as compared with controls, by using quantitative sensory testing (QST) and a neurophysiologic paradigm independent from subjective reports. METHODS: A total of 164 outpatients with FM who were attending a self-management program were invited to participate in the study. Data for 85 patients were available and were compared with those for 40 non-FM controls matched for age and sex. QST was performed using thermal, mechanical, and electrical stimuli at locations of nonspontaneous pain. Pain assessment was 2-fold and included use of subjective scales and the spinal nociceptive flexion reflex (NFR), a specific physiologic correlate for the objective evaluation of central nociceptive pathways. Questionnaires regarding quality of life and the impact of FM were available. RESULTS: Participants were mainly middle-aged women, with a mean disease duration of 8 years. Between-group differences were significant for neurophysiologic, clinical, and quality of life measures. In patients with FM, peripheral QST showed significantly altered cold and heat pain thresholds, and tolerance to cold pain was radically reduced. The median NFR threshold in patients with FM (22.7 mA [range 17.5-31.7]) was significantly decreased compared with that in controls (33 mA [range 28.1-41]). A cutoff value of <27.6 mA for NFR provided sensitivity of 73% and specificity of 80% for detecting central allodynia in the setting of FM. CONCLUSION: Our results strongly, although indirectly, point to a state of central hyperexcitability of the nociceptive system in patients with FM. The NFR can be used to assess central allodynia in FM. It may also help discriminate patients who may benefit from use of centrally acting analgesics.

Quantitative drug interactions prediction system (Q-DIPS): a dynamic computer-based method to assist in the choice of clinically relevant in vivo studies.

Metabolic drug interactions are a major source of clinical problems, but their investigation during drug development is often incomplete and poorly specific. In vitro studies give very accurate data on the interactions of drugs with selective cytochrome P450 (CYP) isozymes, but their interpretation in the clinical context is difficult. On the other hand, the design of in vivo studies is sometimes poor (choice of prototype substrate, doses, schedule of administration, number of volunteers), with the risk of minimising the real potential for interaction. To link in vitro and in vivo studies, several authors have suggested using extrapolation techniques, based on the comparison of in vitro inhibition data with the active in vivo concentrations of the inhibitor. However, the lack of knowledge of one or several important parameters (role of metabolites, intrahepatocyte accumulation) often limits the possibility for safe and accurate predictions. In consequence, these methods are useful to complement in vitro studies and help design clinically relevant in vivo studies, but they will not totally replace in vivo investigation in the future. We have developed a computerised application, the quantitative drug interactions prediction system (Q-DIPS), to make both qualitative deductions and quantitative predictions on the basis of a database containing updated information on CYP substrates, inhibitors and inducers, as well as pharmacokinetic parameters. We also propose a global approach to drug interactions problems--'good interactions practice--to help design rational drug interaction investigations, sequentially associating in vitro studies, in vitrolin vivo extrapolation and finally well-designed in vivo clinical studies.