Voriconazole greatly increases the exposure to oral buprenorphine.

PURPOSE: Buprenorphine has low oral bioavailability. Regardless of sublingual administration, a notable part of buprenorphine is exposed to extensive first-pass metabolism by the cytochrome P450 (CYP) 3A4. As drug interaction studies with buprenorphine are limited, we wanted to investigate the effect of voriconazole, a strong CYP3A4 inhibitor, on the pharmacokinetics and pharmacodynamics of oral buprenorphine. METHODS: Twelve healthy volunteers were given either placebo or voriconazole (orally, 400 mg twice on day 1 and 200 mg twice on days 2-5) for 5 days in a randomized, cross-over study. On day 5, they ingested 0.2 mg (3.6 mg during placebo phase) oral buprenorphine. We measured plasma and urine concentrations of buprenorphine and norbuprenorphine and monitored their pharmacological effects. Pharmacokinetic parameters were normalized for a buprenorphine dose of 1.0 mg. RESULTS: Voriconazole greatly increased the mean area under the plasma concentration-time curve (AUC0-18) of buprenorphine (4.3-fold, P < 0.001), its peak concentration (Cmax) (3.9-fold), half-life (P < 0.05), and excretion into urine (Ae; P < 0.001). Voriconazole also markedly enhanced the Cmax (P < 0.001), AUC0-18 (P < 0.001), and Ae (P < 0.05) of unconjugated norbuprenorphine but decreased its renal clearance (P < 0.001). Mild dizziness and nausea occurred during both study phases. CONCLUSIONS: Voriconazole greatly increases exposure to oral buprenorphine, mainly by inhibiting intestinal and liver CYP3A4. Effect on some transporters may explain elevated norbuprenorphine concentrations. Although oral buprenorphine is not commonly used, this interaction may become relevant in patients receiving sublingual buprenorphine together with voriconazole or other CYP3A4 or transporter inhibitors.

Voriconazole more likely than posaconazole increases plasma exposure to sublingual buprenorphine causing a risk of a clinically important interaction.

PURPOSE: This study aimed to determine possible effects of voriconazole and posaconazole on the pharmacokinetics and pharmacological effects of sublingual buprenorphine. METHODS: We used a randomized, placebo-controlled crossover study design with 12 healthy male volunteers. Subjects were given a dose of 0.4 mg (0.6 mg during placebo phase) sublingual buprenorphine after a 5-day oral pretreatment with either (i) placebo, (ii) voriconazole 400 mg twice daily on the first day and 200 mg twice daily thereafter or (iii) posaconazole 400 mg twice daily. Plasma and urine concentrations of buprenorphine and its primary active metabolite norbuprenorphine were monitored over 18 h and pharmacological effects were measured. RESULTS: Compared to placebo, voriconazole increased the mean area under the plasma concentration-time curve (AUC0-∞) of buprenorphine 1.80-fold (90 % confidence interval 1.45-2.24; P < 0.001), its peak concentration (Cmax) 1.37-fold (P < 0.013) and half-life (t ½ ) 1.37-fold (P < 0.001). Posaconazole increased the AUC00-∞ of buprenorphine 1.25-fold (P < 0.001). Most of the plasma norbuprenorphine concentrations were below the limit of quantification (0.05 ng/ml). Voriconazole, unlike posaconazole, increased the urinary excretion of norbuprenorphine 1.58-fold (90 % confidence interval 1.18-2.12; P < 0.001) but there was no quantifiable parent buprenorphine in urine. Plasma buprenorphine concentrations correlated with the pharmacological effects, but the effects did not differ significantly between the phases. CONCLUSIONS: Voriconazole, and to a minor extent posaconazole, increase plasma exposure to sublingual buprenorphine, probably via inhibition of cytochrome P450 3 A and/or P-glycoprotein. Care should be exercised in the combined use of buprenorphine with triazole antimycotics, particularly with voriconazole, because their interaction can be of clinical importance.

Effects of terbinafine and itraconazole on the pharmacokinetics of orally administered tramadol.

BACKGROUND: Tramadol is widely used for acute, chronic, and neuropathic pain. Its primary active metabolite is O-desmethyltramadol (M1), which is mainly accountable for the µ-opioid receptor-related analgesic effect. Tramadol is metabolized to M1 mainly by cytochrome P450 (CYP)2D6 enzyme and to other metabolites by CYP3A4 and CYP2B6. We investigated the possible interaction of tramadol with the antifungal agents terbinafine (CYP2D6 inhibitor) and itraconazole (CYP3A4 inhibitor). METHODS: We used a randomized placebo-controlled crossover study design with 12 healthy subjects, of which 8 were extensive and 4 were ultrarapid CYP2D6 metabolizers. On the pretreatment day 4 with terbinafine (250 mg once daily), itraconazole (200 mg once daily) or placebo, subjects were given tramadol 50 mg orally. Plasma concentrations of tramadol and M1 were determined over 48 h and some pharmacodynamic effects over 12 h. Pharmacokinetic variables were calculated using standard non-compartmental methods. RESULTS: Terbinafine increased the area under plasma concentration-time curve (AUC0-∞) of tramadol by 115 % and decreased the AUC0-∞ of M1 by 64 % (P < 0.001). Terbinafine increased the peak concentration (C max) of tramadol by 53 % (P < 0.001) and decreased the C max of M1 by 79 % (P < 0.001). After terbinafine pretreatment the elimination half-life of tramadol and M1 were increased by 48 and 50 %, respectively (P < 0.001). Terbinafine reduced subjective drug effect of tramadol (P < 0.001). Itraconazole had minor effects on tramadol pharmacokinetics. CONCLUSIONS: Terbinafine may reduce the opioid effect of tramadol and increase the risk of its monoaminergic adverse effects. Itraconazole has no meaningful interaction with tramadol in subjects who have functional CYP2D6 enzyme.

Ticlopidine inhibits both O-demethylation and renal clearance of tramadol, increasing the exposure to it, but itraconazole has no marked effect on the ticlopidine-tramadol interaction.

PURPOSE: We assessed possible drug interactions of tramadol given concomitantly with the potent CYP2B6 inhibitor ticlopidine, alone or together with the potent CYP3A4 and P-glycoprotein inhibitor itraconazole. METHODS: In a randomized, placebo-controlled cross-over study, 12 healthy subjects ingested 50 mg of tramadol after 4 days of pretreatment with either placebo, ticlopidine (250 mg twice daily) or ticlopidine plus itraconazole (200 mg once daily). Plasma and urine concentrations of tramadol and its active metabolite O-desmethyltramadol (M1) were monitored over 48 h and 24 h, respectively. RESULTS: Ticlopidine increased the mean area under the plasma concentration-time curve (AUC0-∞) of tramadol by 2.0-fold (90 % confidence interval (CI) 1.6-2.4; p < 0.001) and Cmax by 1.4-fold (p < 0.001), and reduced its oral and renal clearance (p < 0.01). Ticlopidine reduced the AUC0-3 of M1 (p < 0.001) and the ratio of the AUC0-∞ of M1 to that of tramadol, but did not influence the AUC0-∞ of M1. Tramadol or M1 pharmacokinetics did not differ between the ticlopidine alone and ticlopidine plus itraconazole phases. CONCLUSIONS: Ticlopidine increased exposure to tramadol, reduced its renal clearance and inhibited the formation of M1, most likely via inhibition of CYP2B6 and/or CYP2D6. The addition of itraconazole to ticlopidine did not modify the outcome of the drug interaction. Concomitant clinical use of ticlopidine and tramadol may enhance the risk of serotonergic effects, especially when higher doses of tramadol are used.

Rifampicin markedly decreases the exposure to oral and intravenous tramadol.

PURPOSE: Tramadol is mainly metabolized by the cytochrome P450 (CYP) 2D6, CYP2B6 and CYP3A4 enzymes. The aim of this study was to evaluate the effect of enzyme induction with rifampicin on the pharmacokinetics and pharmacodynamics of oral and intravenous tramadol. METHODS: This was a randomized placebo-controlled crossover study design with 12 healthy subjects. After pretreatment for 5 days with rifampicin (600 mg once daily) or placebo, subjects were given tramadol either 50 mg intravenously or 100 mg orally. Plasma concentrations of tramadol and its active main metabolite O-desmethyltramadol (M1) were determined over 48 h. Analgesic and behavioral effects and whole blood 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were measured. RESULTS: Rifampicin reduced the mean area under the time-concentration curve (AUC0-∞) of intravenously administered tramadol by 43 % and that of M1 by 58 % (P < 0.001); it reduced the AUC0-∞ of oral tramadol by 59 % and that of M1 by 54 % (P < 0.001). Rifampicin increased the clearance of intravenous tramadol by 67 % (P < 0.001). Bioavailability of oral tramadol was reduced by rifampicin from 66 to 49 % (P = 0.002). The pharmacological effects of tramadol or whole blood serotonin concentrations were not influenced by pretreatment with rifampicin. CONCLUSIONS: Rifampicin markedly decreased the exposure to tramadol and M1 after both oral and intravenous administration. Therefore, rifampicin and other potent enzyme inducers may have a clinically important interaction with tramadol regardless of the route of its administration.

S-ketamine concentrations are greatly increased by grapefruit juice.

PURPOSE: We examined the effect of grapefruit juice on the pharmacokinetics and pharmacodynamics of oral S-ketamine. METHODS: A randomized crossover open-label study design with two phases at an interval of 4 weeks was conducted in 12 healthy volunteers. Grapefruit juice or water was ingested 200 ml t.i.d. for 5 days. An oral dose of 0.2 mg/kg of S-ketamine was ingested on day 5 with 150 ml grapefruit juice or water. Plasma concentrations of ketamine and norketamine were determined for 24 h, and pharmacodynamic variables were recorded for 12 h. Noncompartmental methods were used to calculate pharmacokinetic parameters. RESULTS: Grapefruit juice increased the geometric mean value of the area under the plasma ketamine concentration-time curve(AUC0-∞) by 3.0-fold (range 2.4- to 3.6-fold; P<0.001), the peak plasma concentration (Cmax) by 2.1-fold (range 1.8- to 2.6-fold; P<0.001), and the elimination half-life by 24% (P<0.05) as compared to the water phase. The ratio of main metabolite norketamine to ketamine (AUCm/AUCp) was decreased by 57% (P<0.001) during the grapefruit phase.Self-rated relaxation was decreased (P<0.05) and the performance in the digit symbol substitution test was increased (P<0.05) after grapefruit juice, but other behavioral or analgesic effects were not affected. CONCLUSIONS: Grapefruit juice significantly increased the plasma concentrations of oral ketamine in healthy volunteers.Dose reductions of ketamine should be considered when using oral ketamine concomitantly with grapefruit juice.

Inhibition of cytochrome P450 3A by clarithromycin uniformly affects the pharmacokinetics and pharmacodynamics of oxycodone in young and elderly volunteers.

The aim of this study was to investigate the effect of the cytochrome P450 3A4 inhibitor clarithromycin on the pharmacokinetics and pharmacodynamics of oral oxycodone in young and elderly subjects. Ten young and 10 elderly healthy subjects participated in this placebo-controlled, randomized, 2-phase crossover study. Subjects took clarithromycin 500 mg or placebo twice daily for 5 days. On day 4, subjects ingested an oral dose of 10 mg oxycodone. Plasma concentrations of oxycodone and its oxidative metabolites were measured for 48 hours, and pharmacological response for 12 hours. Clarithromycin decreased the apparent clearance of oxycodone by 53% in young and 48% in elderly subjects (P < 0.001) and prolonged its elimination half-life. The mean area under the plasma concentration-time curve (AUC0-∞) of oxycodone was increased by 2.0-fold (range, 1.3-fold to 2.7-fold) (P < 0.001) in young and 2.3-fold (range, 1.1-fold to 3.8-fold) (P < 0.001) in elderly subjects. The formation of noroxycodone was decreased by 74% in young and 71% in elderly subjects (P < 0.001). The ratio of AUC0-∞ of oxycodone during the clarithromycin phase compared with the one with placebo did not differ between the age groups. Clarithromycin did not alter the pharmacological response to oxycodone. Clarithromycin increased the exposure to oral oxycodone, but the magnitude of this effect was not age related. Although the pharmacological response to oxycodone was not significantly influenced by clarithromycin, dose reductions may be necessary in the most sensitive patients to avoid adverse effects when oxycodone is used concomitantly with clarithromycin.

Effect of inhibition of cytochrome P450 enzymes 2D6 and 3A4 on the pharmacokinetics of intravenous oxycodone: a randomized, three-phase, crossover, placebo-controlled study.

BACKGROUND AND OBJECTIVE: Oxycodone is a µ-opioid receptor agonist that is mainly metabolized by hepatic cytochrome P450 (CYP) enzymes. Because CYP enzymes can be inhibited by other drugs, the pharmacokinetics of oxycodone are prone to drug interactions. The aim of this study was to determine whether inhibition of CYP2D6 alone by paroxetine or inhibition of both CYP2D6 and CYP3A4 by a combination of paroxetine and itraconazole alters the pharmacokinetics of and pharmacological response to intravenous oxycodone. METHODS: We used a randomized, three-phase, crossover, placebo-controlled study design in 12 healthy subjects. The subjects were given 0.1 mg/kg of intravenous oxycodone after pre-treatments with placebo, paroxetine or a combination of paroxetine and itraconazole for 4 days. Plasma concentrations of oxycodone and its oxidative metabolites were measured over 48 hours, and pharmacokinetic and pharmacodynamic parameters subsequently evaluated. RESULTS: The effect of paroxetine on the plasma concentrations of oxycodone was negligible. The combination of paroxetine and itraconazole prolonged the mean elimination half-life of oxycodone from 3.8 to 6.6 hours (p < 0.001), and increased the exposure to oxycodone 2-fold (p < 0.001). However, these changes were not reflected in pharmacological response. CONCLUSION: The results of this study indicate that there are no clinically relevant drug interactions with intravenous oxycodone and inhibitors of CYP2D6. If both oxidative metabolic pathways via CYP3A4 and 2D6 are inhibited the exposure to intravenous oxycodone increases substantially.

Exposure to oral oxycodone is increased by concomitant inhibition of CYP2D6 and 3A4 pathways, but not by inhibition of CYP2D6 alone.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: Oxycodone is an opioid analgesic that is metabolized mainly in the liver by cytochrome P450 (CYP) 2D6 and 3A4 enzymes. So far, the effects of CYP2D6 or CYP3A4 inhibitors on the pharmacokinetics of oxycodone in humans have not been systematically studied. WHAT THIS STUDY ADDS: Drug interactions arising from CYP2D6 inhibition most likely have minor clinical importance for oral oxycodone. When both of CYP2D6 and CYP3A4 pathways are inhibited, the exposure to oral oxycodone is increased substantially. AIM: The aim of this study was to find out whether the inhibition of cytochrome P450 2D6 (CYP2D6) with paroxetine or concomitant inhibition of CYP2D6 and CYP3A4 with paroxetine and itraconazole, altered the pharmacokinetics and pharmacological response of orally administered oxycodone. METHODS: A randomized placebo-controlled cross-over study design with three phases was used. Eleven healthy subjects ingested 10 mg of oral immediate release oxycodone on the fourth day of pre-treatment with either placebo, paroxetine (20 mg once daily) or paroxetine (20 mg once daily) and itraconazole (200 mg once daily) for 5 days. The plasma concentrations of oxycodone and its oxidative metabolites were measured for 48 h, and pharmacological (analgesic and behavioural) effects were evaluated. RESULTS: Paroxetine alone reduced the area under concentration-time curve (AUC(0,0-48 h)) of the CYP2D6 dependent metabolite oxymorphone by 44% (P < 0.05), but had no significant effects on the plasma concentrations of oxycodone or its pharmacological effects when compared with the placebo phase. When both oxidative pathways of the metabolism of oxycodone were inhibited with paroxetine and itraconazole, the mean AUC(0,infinity) of oxycodone increased by 2.9-fold (P < 0.001), and its C(max) by 1.8-fold (P < 0.001). Visual analogue scores for subjective drug effects, drowsiness and deterioration of performance were slightly increased (P < 0.05) after paroxetine + itraconazole pre-treatment when compared with placebo. CONCLUSIONS: Drug interactions arising from CYP2D6 inhibition most likely have minor clinical importance for oral oxycodone if the function of the CYP3A4 pathway is normal. When both CYP2D6 and CYP3A4 pathways are inhibited, the exposure to oral oxycodone is increased substantially.

Oxycodone concentrations are greatly increased by the concomitant use of ritonavir or lopinavir/ritonavir.

PURPOSE: this study aimed to investigate the effect of antivirals ritonavir and lopinavir/ritonavir on the pharmacokinetics and pharmacodynamics of oral oxycodone, a widely used opioid receptor agonist used in the treatment of moderate to severe pain. METHODS: a randomized crossover study design with three phases at intervals of 4 weeks was conducted in 12 healthy volunteers. Ritonavir 300 mg, lopinavir/ritonavir 400/100 mg, or placebo b.i.d. for 4 days was given to the subjects. On day 3, 10 mg oxycodone hydrochloride was administered orally. Plasma concentrations of oxycodone, noroxycodone, oxymorphone, and noroxymorphone were determined for 48 h. Pharmacokinetic parameters were calculated with standard noncompartmental methods. Behavioral effects and experimental cold pain analgesia were assessed for 12 h. ANOVA for repeated measures was used for statistical analysis. RESULTS: ritonavir and lopinavir/ritonavir increased the area under the plasma concentration-time curve of oral oxycodone by 3.0-fold (range 1.9- to 4.3-fold; P <0.001) and 2.6-fold (range 1.9- to 3.3-fold; P <0.001). The mean (± SD) elimination half-life increased after ritonavir and lopinavir/ritonavir from 3.6 ± 0.6 to 5.6 ± 0.9 h (P <0.001) and 5.7 ± 0.9 h (P <0.001), respectively. Both ritonavir (P <0.001) and lopinavir/ritonavir (P <0.05) increased the self-reported drug effect of oxycodone. CONCLUSIONS: ritonavir and lopinavir/ritonavir greatly increase the plasma concentrations of oral oxycodone in healthy volunteers and enhance its effect. When oxycodone is used clinically in patients during ritonavir and lopinavir/ritonavir treatment, reductions in oxycodone dose may be needed to avoid opioid-related adverse effects.

Effects of itraconazole on the pharmacokinetics and pharmacodynamics of intravenously and orally administered oxycodone.

BACKGROUND: The aim of this study was to investigate the effects of the cytochrome P450 3A4 (CYP34A) inhibitor itraconazole on the pharmacokinetics and pharmacodynamics of orally and intravenously administered oxycodone. METHODS: Twelve healthy subjects were administered 200 mg itraconazole or placebo orally for 5 days in a four-session paired cross-over study. On day 4, oxycodone was administered intravenously (0.1 mg/kg) in the first part of the study and orally (10 mg) in the second part. Plasma concentrations of oxycodone and its oxidative metabolites were measured for 48 h, and pharmacodynamic effects were evaluated. RESULTS: Itraconazole decreased plasma clearance (Cl) and increased the area under the plasma concentration-time curve (AUC0-infinity) of intravenous oxycodone by 32 and 51%, respectively (P<0.001) and increased the AUC(0-infinity) of orally administrated oxycodone by 144% (P<0.001). Most of the pharmacokinetic changes in oral oxycodone were seen in the elimination phase, with modest effects by itraconazole on its peak concentration, which was increased by 45% (P=0.009). The AUC(0-48) of noroxycodone was decreased by 49% (P<0.001) and that of oxymorphone was increased by 359% (P<0.001) after the administration of oral oxycodone. The pharmacologic effects of oxycodone were enhanced by itraconazole only modestly. CONCLUSIONS: Itraconazole increased the exposure to oxycodone by inhibiting its CYP3A4-mediated N-demethylation. The clinical use of itraconazole in patients receiving multiple doses of oxycodone for pain relief may increase the risk of opioid-associated adverse effects.

Rifampin greatly reduces the plasma concentrations of intravenous and oral oxycodone.

BACKGROUND: Oxycodone is a mu-opioid receptor agonist that is metabolized mainly in the liver by cytochrome P450 3A and 2D6 enzymes. Rifampin is a strong inducer of several drug-metabolizing enzymes. The authors studied the interaction of rifampin with oxycodone. Their hypothesis was that rifampin enhances the CYP3A-mediated metabolism of oxycodone and attenuates its pharmacologic effect. METHODS: The protocol was a four-session, paired crossover. Twelve volunteers were given 600 mg oral rifampin or placebo once daily for 7 days. Oxycodone was given on day 6. In the first part of the study, 0.1 mg/kg oxycodone hydrochloride was given intravenously. In the second part of the study, 15 mg oxycodone hydrochloride was given orally. Concentrations of oxycodone and its metabolites noroxycodone, oxymorphone, and noroxymorphone were determined for 48 h. Psychomotor effects were characterized for 12 h by several visual analog scales. Analgesic effects were characterized by measuring the heat pain threshold and cold pain sensitivity. RESULTS: Rifampin decreased the area under the oxycodone concentration-time curve of intravenous and oral oxycodone by 53% and 86%, respectively (P < 0.001). Oral bioavailability of oxycodone was decreased from 69% to 21% (P < 0.001). Rifampin greatly increased the plasma metabolite-to-parent drug ratios for noroxycodone and noroxymorphone (P < 0.001). Pharmacologic effects of oral oxycodone were attenuated. CONCLUSIONS: Induction of cytochrome P450 3A by rifampin reduced the area under the oxycodone concentration-time curve of intravenous and oral oxycodone. The pharmacologic effects of oxycodone were modestly attenuated. To maintain adequate analgesia, dose adjustment of oxycodone may be necessary, when used concomitantly with rifampin.

Voriconazole drastically increases exposure to oral oxycodone.

OBJECTIVE: We investigated the effect of voriconazole on the pharmacokinetics and pharmacodynamics of oxycodone. METHODS: Twelve healthy subjects ingested either voriconazole or placebo for 4 days in a randomized, cross-over study. On day 3, they ingested 10 mg oxycodone. Timed plasma samples were collected for the measurement of oxycodone, noroxycodone, oxymorphone, noroxymorphone and voriconazole up to 48 h, and pharmacodynamic effects were recorded. RESULTS: When voriconazole was taken at the same time as oxycodone, the mean area under the plasma concentration-time curve (AUC(0-infinity)) of oxycodone increased 3.6-fold (range 2.7- to 5.6-fold), peak plasma concentration 1.7-fold and elimination half-life 2.0-fold (p < 0.001) when compared to placebo. The AUC(0-infinity) ratio of noroxycodone to oxycodone was decreased by 92% (p < 0.001), and that of oxymorphone increased by 108% (p < 0.01). Pharmacodynamic effects of oxycodone were modestly increased by voriconazole. CONCLUSIONS: Voriconazole inhibits the CYP3A-mediated N-demethylation of oxycodone, drastically increasing exposure to oral oxycodone. Clinically, lower doses of oxycodone may be needed during voriconazole treatment to avoid opioid-related adverse effects especially after repeated dosing.

Oxycodone: new 'old' drug.

PURPOSE OF REVIEW: Since the introduction of oral immediate release and controlled-release oxycodone preparations to the market in the 1990s, the clinical use and scientific interest in oxycodone has increased greatly. RECENT FINDINGS: Recent studies have shown that the pharmacokinetics of oxycodone are dependent on age of the patient and therefore individual titration of the dose is necessary, especially in the elderly. Oxycodone has good oral bioavailability and it produces more predictable plasma concentrations than morphine, which has a poor and more variable bioavailability. Oxycodone has clinically significant drug interactions with drugs affecting cytochrome P450 3A enzymes. Clinical studies have demonstrated that oxycodone is a useful opioid analgesic in acute postoperative pain, cancer pain, visceral pain and chronic nonmalignant pain. SUMMARY: The availability of oxycodone preparations has increased its clinical use exponentially during the last decade. Further clinical studies are still needed to fully understand its clinical pharmacology. Oxycodone is still a new 'old' drug whose pharmacology and clinical potential is not yet fully understood.

Ketamine: A Review of Clinical Pharmacokinetics and Pharmacodynamics in Anesthesia and Pain Therapy.

Ketamine is a phencyclidine derivative, which functions primarily as an antagonist of the N-methyl-D-aspartate receptor. It has no affinity for gamma-aminobutyric acid receptors in the central nervous system. Ketamine shows a chiral structure consisting of two optical isomers. It undergoes oxidative metabolism, mainly to norketamine by cytochrome P450 (CYP) 3A and CYP2B6 enzymes. The use of S-ketamine is increasing worldwide, since the S(+)-enantiomer has been postulated to be a four times more potent anesthetic and analgesic than the R(-)-enantiomer and approximately two times more effective than the racemic mixture of ketamine. Because of extensive first-pass metabolism, oral bioavailability is poor and ketamine is vulnerable to pharmacokinetic drug interactions. Sublingual and nasal formulations of ketamine are being developed, and especially nasal administration produces rapid maximum plasma ketamine concentrations with relatively high bioavailability. Ketamine produces hemodynamically stable anesthesia via central sympathetic stimulation without affecting respiratory function. Animal studies have shown that ketamine has neuroprotective properties, and there is no evidence of elevated intracranial pressure after ketamine dosing in humans. Low-dose perioperative ketamine may reduce opioid consumption and chronic postsurgical pain after specific surgical procedures. However, long-term analgesic effects of ketamine in chronic pain patients have not been demonstrated. Besides analgesic properties, ketamine has rapid-acting antidepressant effects, which may be useful in treating therapy-resistant depressive patients. Well-known psychotomimetic and cognitive adverse effects restrict the clinical usefulness of ketamine, even though fewer psychomimetic adverse effects have been reported with S-ketamine in comparison with the racemate. Safety issues in long-term use are yet to be resolved.

Rifampicin decreases exposure to sublingual buprenorphine in healthy subjects.

Buprenorphine is mainly metabolized by the cytochrome P450 (CYP) 3A4 enzyme. The aim of this study was to evaluate the role of first-pass metabolism in the interaction of rifampicin and analgesic doses of buprenorphine. A four-session paired cross-over study design was used. Twelve subjects ingested either 600 mg oral rifampicin or placebo once daily in a randomized order for 7 days. In the first part of the study, subjects were given 0.6-mg (placebo phase) or 0.8-mg (rifampicin phase) buprenorphine sublingually on day 7. In the second part of the study, subjects received 0.4-mg buprenorphine intravenously. Plasma concentrations of buprenorphine and urine concentrations of buprenorphine and its primary metabolite norbuprenorphine were measured over 18 h. Adverse effects were recorded. Rifampicin decreased the mean area under the dose-corrected plasma concentration-time curve (AUC 0-18) of sublingual buprenorphine by 25% (geometric mean ratio (GMR): 0.75; 90% confidence interval (CI) of GMR: 0.60, 0.93) and tended to decrease the bioavailability of sublingual buprenorphine, from 22% to 16% (P = 0.31). Plasma concentrations of intravenously administered buprenorphine were not influenced by rifampicin. The amount of norbuprenorphine excreted in the urine was decreased by 65% (P < 0.001) and 52% (P < 0.001) after sublingual and intravenous administration, respectively, by rifampicin. Adverse effects were frequent. Rifampicin decreases the exposure to sublingual but not intravenous buprenorphine. This can be mainly explained by an enhancement of CYP3A-mediated first-pass metabolism, which sublingual buprenorphine only partially bypasses. Concomitant use of rifampicin and low-dose sublingual buprenorphine may compromise the analgesic effect of buprenorphine.

The association between physicians' attitudes to psychosocial aspects of low back pain and reported clinical behaviour: A complex issue.

Background and aim Physicians' attitudes predict clinical decision making and treatment choices, but the association between attitudes and behaviour is complex. Treatment guidelines for non-specific low back pain (LBP) include recommendations of early assessment of psychosocial risk factors forchronic pain, patient education and reassurance. Implication of these principles is demanding, and many patients are not referred for appropriate treatments due to a lack of systematic screening of psychosocial risk factors for chronic pain. Even though health care providers recognise the need for psychosocial assessment in LBP, psychosocial issues are seldom raised in acute settings. The aim of this study is to evaluate how physicians' attitudes towards assessing psychological issues of LBP patients are associated with their treatment practice, and to assess if their clinical actions follow current treatment guidelines. Methods The study was amixed methods study of primary care physicians (n = 55) in Finland. Physicians' attitudes were measured with a psychological subscale of attitudes to back pain scales for musculoskeletal practitioners (ABS-mp). Treatment practice of LBP was evaluated by as king physicians to describe a typical LBP treatment process and by asking them to solve a LBP patient case. Members of the research team individually evaluated the degree to which psychosocial issues were taken into account in the treatment process and in the patient case answer. Qualitative and quantitative data were combined to examine the role of attitudes in the treatment of LBP. Results The attitudes of physicians were generally psychologically oriented. Physicians who addressed to psychosocial issues in their treatment practice were more psychologically oriented in their attitudes than physicians who did not consider psychosocial issues. Only 20% of physicians mentioned psychosocial issues as being a part of the LBP patient's typical treatment process, while 87% of physicians paid attention to psychosocial issues in the LBP patient case. On the level of the treatment process, radiological investigations were over-represented and pain assessment, patient information and reassurance infrequently performed when compared to LBP guidelines. Conclusions Although primary care physicians were generally psychosocially oriented in their attitudes on LBP, psychological issues were inconsistently brought up in their reported clinical behaviour. Physicians recognised the need to assess psychosocial factors. Those who were psychologically oriented in their attitudes were more inclined to take psychosocial issues into account. However on a process level, evaluation and treatment of LBP featured biomechanical principles. LBP guidelines were only partially followed. Implications Clinical behaviour of physicians in the treatment of LBP is complex and only partly explained by attitudes.

St John's wort greatly decreases the plasma concentrations of oral S-ketamine.

Ketamine is an intravenous anaesthetic and analgesic agent but it can also be used orally as an adjuvant in the treatment of chronic pain. This study investigated the effect of the herbal antidepressant St John's wort, an inducer of cytochrome P450 3A4 (CYP3A4), on the pharmacokinetics and pharmacodynamics of oral S-ketamine. In a randomized cross-over study with two phases, 12 healthy subjects were pretreated with oral St John's wort or placebo for 14 days. On day 14, they were given an oral dose of 0.3 mg/kg of S-ketamine. Plasma concentrations of ketamine and norketamine were measured for 24 h and pharmacodynamic variables for 12 h. St John's wort decreased the mean area under the plasma concentration-time curve (AUC(0-∞)) of ketamine by 58% (P < 0.001) and decreased the peak plasma concentration (C(max)) of ketamine by 66% (P < 0.001) when compared with placebo. Mean C(max) of norketamine (the major metabolite of ketamine) was decreased by 23% (P = 0.002) and mean AUC(0-∞) of norketamine by 18% (P < 0.001) by St John's wort. There was a statistically significant linear correlation between the self-reported drug effect and C(max) of ketamine (r = 0.55; P < 0.01). St John's wort greatly decreased the exposure to oral S-ketamine in healthy volunteers. Although this decrease was not associated with significant changes in the analgesic or behavioural effects of ketamine in the present study, usual doses of S-ketamine may become ineffective if used concomitantly with St John's wort.