In general
Colesevelam may affect the bioavailability of other medicinal products. Therefore, when a drug interaction cannot be excluded with a concomitant medicinal product for which minor variations in the therapeutic level would be clinically important, colesevelam should be administered at least four hours before or at least four hours after the concomitant medication to minimize the risk of reduced absorption of the concomitant medication. For concomitant medications, which require administration via divided doses, it should be noted that the required dose of colesevelam can be taken once a day.
When administering medicinal products for which alterations in blood levels could have a clinically significant effect on safety or efficacy, physicians should consider monitoring serum levels or effects.
Interaction studies have only been performed in adults.
In interaction studies in healthy volunteers, colesevelam had no effect on the bioavailability of digoxin, metoprolol, quinidine, valproic acid, and warfarin. Colesevelam decreased the Cmax and AUC of sustained-release verapamil by approximately 31% and 11%, respectively. Since there is a high degree of variability in the bioavailability of verapamil, the clinical significance of this finding is unclear.
Co-administration of colesevelam and olmesartan decreases the exposure of olmesartan. Olmesartan should be administered at least 4 hours prior to colesevelam.
There have been very rare reports of reduced phenytoin levels in patients who have received colesevelam administered with phenytoin.
Anticoagulant therapy
Anticoagulant therapy should be monitored closely in patients receiving warfarin or similar agents, since bile acid sequestrants, like colesevelam, have been shown to reduce absorption of vitamin K and therefore interfere with warfarin's anticoagulant effect. Specific clinical interaction studies with colesevelam and vitamin K have not been performed.
Levothyroxine
In an interaction study in healthy volunteers, colesevelam reduced the AUC and Cmax of levothyroxine when administered either concomitantly or after 1 hour. No interaction was observed when colesevelam was administered at least four hours after levothyroxine.
Oral contraceptive pill
In an interaction study in healthy volunteers, colesevelam reduced the Cmax of norethindrone as well as the AUC and Cmax of ethinylestradiol when administered simultaneously with the oral contraceptive pill. This interaction was also observed when colesevelam was administered one hour after the oral contraceptive pill. However no interaction was observed when colesevelam was administered four hours after the oral contraceptive pill.
Ciclosporin
In an interaction study in healthy volunteers, co-administration of colesevelam and ciclosporin significantly reduced the AUC0-inf and Cmax of ciclosporin by 34% by 44%, respectively. Therefore advice is given to closely monitor ciclosporin blood concentrations (see also section 4.4). In addition, based on theoretical grounds colesevelam should be administered at least 4 hours after ciclosporin in order to further minimise the risks related to the concomitant administration of ciclosporin and colesevelam. Furthermore, colesevelam should always be administered at the same times consistently since the timing of intake of colesevelam and ciclosporin could theoretically influence the degree of reduced bioavailability of ciclosporin.
Statins
When colesevelam was co-administered with statins in clinical studies, an expected add-on LDL-C lowering effect was observed, and no unexpected effects were observed. Colesevelam had no effect on the bioavailability of lovastatin in an interaction study.
Antidiabetic agents
Co-administration of colesevelam and metformin extended-release (ER) tablets increases the exposure of metformin. Patients receiving concomitant metformin ER and colesevelam should be monitored for clinical response as is usual for the use of anti-diabetes drugs.
Colesevelam binds to glimepiride and reduces glimepiride absorption from the gastrointestinal tract. No interaction was observed when glimepiride was taken at least 4 hours before colesevelam. Therefore glimepiride should be administered at least 4 hours prior to colesevelam.
Co-administration of colesevelam and glipizide decreases the exposure of glipizide. Glipizide should be administered at least 4 hours prior to colesevelam.
Co-administration of colesevelam and glyburide (also known as glibenclamide) caused a decrease in the AUC0-inf and Cmax of glyburide by 32% and 47%, respectively. No interaction was observed when colesevelam was administered four hours after glyburide.
Co-administration of colesevelam and repaglinide had no effect on the AUC and caused a 19% reduction in the Cmax of repaglinide, the clinical significance of which is unknown. No interaction was observed when colesevelam was administered one hour after repaglinide.
No interaction was observed when colesevelam and pioglitazone were administered simultaneously in healthy volunteers
Ursodeoxycholic acid
Colesevelam predominantly binds hydrophobic bile acids. In a clinical study, colesevelam did not affect the faecal excretion of endogenous (hydrophilic) ursodeoxycholic acid. However, formal interaction studies with ursodeoxycholic acid have not been performed. As noted in general, when a drug interaction cannot be excluded with a concomitant medicinal product, colesevelam should be administered at least four hours before or at least four hours after the concomitant medication to minimise the risk of reduced absorption of the concomitant medication. Monitoring of the clinical effects of treatment with ursodeoxycholic acid should be considered.
Other forms of interaction
Colesevelam did not induce any clinically significant reduction in the absorption of vitamins A, D, E or K during clinical studies of up to one year. However, caution should be exercised when treating patients with a susceptibility to vitamin K or fat-soluble vitamin deficiencies, such as patients with malabsorption. In these patients, monitoring vitamin A, D and E levels and assessing vitamin K status through the measurement of coagulation parameters is recommended and the vitamins should be supplemented if necessary.