Pharmacokinetic Drug Interactions
Midazolam is metabolized by CYP3A4. Inhibitors and inducers of CYP3A4 have the potential to respectively increase and decrease the plasma concentrations and, subsequently, the effects of midazolam thus requiring dose adjustments accordingly. Pharmacokinetic interactions with CYP3A4 inhibitors or inducers are more pronounced for oral as compared to oromucosal or parenteral midazolam as CYP3A4 enzymes are also present in the upper gastro-intestinal tract. Hence, a careful monitoring of the clinical effects and vital signs is recommended during the use of midazolam with a CYP3A4 inhibitor even after a single dose.
Rifampicin
7 days of 600 mg once daily decreased the plasma concentrations of intravenous midazolam by about 60%. The terminal half-life decreased by about 50-60%.
Herbs
St John's Wort decreased plasma concentrations of midazolam by about 20-40% associated with a decrease in terminal half-life of about 15-17%. Depending on the specific St John's Wort extract, the CYP3A4-inducing effect may vary.
The effect of CYP3A4 inhibitors may be larger in infants.
Anaesthetics and narcotic analgesics
Fentanyl may reduce midazolam clearance.
Antiepileptics
After repeated administration of carbamazepine or phenytoin, the plasma concentration of oral midazolam is reduced by a whopping 90% and the terminal half-life is reduced by 60%.
Calcium-channel blockers
Diltiazem and verapamil have been shown to reduce the clearance of midazolam and other benzodiazepines and may potentiate their actions. A single dose of diltiazem increased the plasma concentrations of intravenous midazolam by about 25% and the terminal half-life was prolonged by 43%.
H2-receptor antagonists and ulcer-healing medicinal products
Cimetidine, ranitidine and omeprazole have been shown to reduce the clearance of midazolam and other benzodiazepines and may potentiate their actions. Cimetidine has been shown to increase the diazepam and metabolite plasma concentration by 57%.
Substance P antagonists
Aprepitant causes a dose dependent increase in the plasma concentrations of oral Midazolam. The plasma concentration of oral Midazolam increased by 3.3-fold after 80mg/day dose of aprepitant on day 5 and the terminal half-life increased by approximately 2-fold.
Xanthines
Metabolism of midazolam and other benzodiazepines is accelerated by xanthines.
Dopaminergic medicinal products
Midazolam may cause inhibition of levodopa.
Muscle relaxants
Midazolam may cause potentiation of muscle relaxants, with increased CNS depressant effects, e.g., baclofen.
Nabilone
Co-administration with midazolam may cause enhanced sedation or respiratory and cardiovascular depression.
Food
Grapefruit juice and caffeine reduces the clearance of midazolam and potentiates its action.
Azole antifungals
Ketoconazole increased the plasma concentrations of intravenous midazolam by 5-fold while the terminal half-life increased by about 3-fold.
Voriconazole increased the exposure of intravenous midazolam by 3-fold whereas its elimination half-life increased by about 3-fold.
Fluconazole and itraconazole both increased the plasma concentrations of intravenous midazolam by 2 to 3-fold associated with an increase in terminal half-life by 2.4-fold for itraconazole and 1.5-fold for fluconazole.
Posaconazole increased the plasma concentrations of intravenous midazolam by about 2-fold.
When bolus doses of midazolam (given for short term sedation) were administered to patients receiving itraconazole or fluconazole the effect of midazolam was not enhanced to a clinically significant degree and dosage reduction is not required. High doses of midazolam may require dosage adjustments.
Macrolide antibiotics
Erythromycin resulted in an increase in the plasma concentrations of intravenous midazolam by about 1.6 to 2 -fold associated with an increase of the terminal half-life of midazolam by 1.5 to 1.8-fold.
Clarithromycin increased the plasma concentrations of intravenous midazolam by up to 2.5-fold associated with an increase in terminal half-life by 1.5 to 2-fold.
Anticholinergics
Propiverine reduce the hepatic and intestinal CYP3A4 activity by 0.89-fold and to 0.80-fold, respectively, and with the combined effect resulting in a 1.46-fold increase in AUC of oral midazolam.
Selective serotonin reuptake inhibitors
Fluvoxamine has been shown to possess CYP3A4 inhibitory properties, therefore increase the midazolam AUC and Cmax by approximately 60% and decrease clearance by 30%.
Nefazodone
Treatment with nefazodone increased the AUC0-∞ of midazolam by about four times and doubled the Cmax.
Glucocorticoids (GCs)
Use of GCs decreased the mean AUC of Midazolam (63.9%), whereas total clearance of midazolam was increased to a mean of 125.7%. Terminal t1/2 and AUC0-∞ of the metabolite 1'-OH midazolam significantly declined in the patients taking GCs.
HIV Protease inhibitors
Co-administration with protease inhibitors (e.g. Saquinavir and other HIV protease inhibitors) may cause a large increase in the concentration of midazolam. Upon co-administration with ritonavir-boosted lopinavir, the plasma concentrations of intravenous midazolam increased by 5.4-fold, associated with a similar increase in terminal half-life.
Reverse transcriptase inhibitors:
Efavirenz: the ratio of α-hydroxymidazolam (metabolite that is generated by CYP3A4) increases by a factor of five compared to midazolam, confirming the induction effect of efavirenz on CYP3A4.
Various medicinal products
Atorvastatin showed a 1.4-fold increase in plasma concentrations of intravenous midazolam compared to control group.
Pharmacodynamic Drug Interactions
The co-administration of midazolam with other sedative/hypnotic medicinal products and CNS depressants, including alcohol, is likely to result in enhanced sedation and respiratory depression.
Examples include opiate derivatives (used as analgesics, antitussives or substitutive treatments), antipsychotics, other benzodiazepines used as anxiolytics or hypnotics, barbiturates, propofol, ketamine, etomidate; sedative antidepressants, non-recent H1-antihistamines and centrally acting antihypertensive medicinal products.
Alcohol (including alcohol-containing medicinal products may markedly enhance the sedative effect of midazolam. Alcohol intake should be strongly avoided in case of midazolam administration (see section 4.4).
Midazolam decreases the minimum alveolar concentration (MAC) of inhalation anaesthetics.
Midazolam may cause potentiation of muscle relaxants, with increased CNS depressant effects, e.g., baclofen.
Co-administration with midazolam may cause enhanced sedation or respiratory and cardiovascular depression.
Opioids
The concomitant use of sedative medicines such as benzodiazepines or related drugs such as midazolam with opioids increases the risk of sedation, respiratory depression, coma and death because of additive CNS depressant effect. The dosage and duration of concomitant use should be limited (see section 4.4).