Several drugs may affect the levels of carnitine in the body. For example, adefovir dipivoxil (Hepsera®), which is given for hepatitis B, may reduce free carnitine levels. Cephalosporin antibiotics may reduce plasma carnitine levels. Anticonvulsants (phenobarbital, phenytoin, carbamazepine) may decrease serum carnitine in children. Cisplastin may increase urinary excretion of carnitine. Ifosfamide (Mitoxana®), a chemotherapy drug, may increase urinary loss of carnitine; however, use of carnitine plus ifosfamide may help reduce fatigue (side effect of ifosfamide treatment). Patients suffering from neuropathy (nerve damage) induced by nucleosides may have reduced levels of acetyl carnitine. Penicillin derivatives (pivaloyloxymethyl esterified, pivampicillin, and pivmecillinam) may decrease the serum carnitine concentration, elevate excretion of acyl-carnitine, and reduce muscle carnitine concentration in adults and children.
L-carnitine supplementation may reduce side effects associated with interleukin-2 (IL-2) or nortriptyline (Pamelor®, Aventyl®). It may also improve liver and muscular side effects associated with isotretinoin (Accutane®) in acne patients. Carnitine may reduce nerve damage symptoms associated with paclitaxel (Taxol®) use.
Carnitine may prevent arrhythmias (abnormal heart rhythms) provoked by adriamycin (Doxorubicin®), which is used in chemotherapy. L-carnitine may decrease the need for antiarrhythmics (medications used to treat abnormal rhythms in the heart). Carnitine plus propafenone may improve arrhythmia (heart rhythm) better than propafenone alone.
Several combinations have shown positive interactions. For example, sildenafil and propionyl-L-carnitine may be more effective than sildenafil alone. Although not well studied in humans, L-carnitine used concurrently with antiviral agents such as zidovudin (Retrovir®) or carnitine used with nortryptiline may also have a positive interaction that reduces side effects. L-carnitine plus acetyl-L-carnitine plus cinnoxicam has been found more effective in improving sperm parameters as compared with L-carnitine plus acetyl-L-carnitine alone.
Patients with diabetes should use caution because L-carnitine may decrease blood sugar. However, carnitine levels did not change in diabetics using insulin or sulfonylurea therapy. It is unclear whether L-carnitine would have similar effects when combined with other medications that lower blood sugar. Consult with a qualified healthcare professional, including a pharmacist, before combining therapies.
Although not well studied in humans, carnitine may increase valproic acid concentrations in the brain, which might increase the effects of valproic acid. Caution is advised.
L-carnitine may decrease the need for herbs or supplements with anticoagulant effects ("blood thinners"). L-carnitine may also decrease the need for herbs or supplements with diuretic effects. Dosing adjustments may be necessary.
Patients with diabetes should use caution because L-carnitine may decrease blood sugar. However, carnitine levels did not change in diabetics using insulin or sulfonylurea therapy. It is unclear whether L-carnitine would have similar effects when combined with other herbs and supplements that lower blood sugar. Consult with a qualified healthcare professional, including a pharmacist, before combining therapies.
Choline supplementation may reduce excretion, renal (kidney) clearance, and fractional clearance of non-esterified carnitine.