1\. Initial Therapy - Laboratory studies should be done to ascertain that the lipid levels are consistently abnormal. Before instituting gemfibrozil therapy, every attempt should be made to control serum lipids with appropriate diet, exercise, weight loss in obese patients, and control of any medical problems such as diabetes mellitus and hypothyroidism that are contributing to the lipid abnormalities.

2\. Continued Therapy - Periodic determination of serum lipids should be obtained, and the drug withdrawn if lipid response is inadequate after three months of therapy.

3\. Drug Interactions

(A) HMG-CoA Reductase Inhibitors: The concomitant administration of gemfibrozil with simvastatin is contraindicated (see CONTRAINDICATIONS and WARNINGS). Avoid concomitant use of gemfibrozil with rosuvastatin. If concomitant use cannot be avoided, initiate rosuvastatin at 5 mg once daily. The dose of rosuvastatin should not exceed 10 mg once daily. The risk of myopathy and rhabdomyolysis is increased with combined gemfibrozil and HMG-CoA reductase inhibitor therapy. Myopathy or rhabdomyolysis with or without acute renal failure have been reported as early as three weeks after initiation of combined therapy or after several months (see WARNINGS). There is no assurance that periodic monitoring of creatine kinase will prevent the occurrence of severe myopathy and kidney damage.

(B) Anticoagulants: CAUTION SHOULD BE EXERCISED WHEN WARFARIN IS GIVEN IN CONJUNCTION WITH GEMFIBROZIL. THE DOSAGE OF WARFARIN SHOULD BE REDUCED TO MAINTAIN THE PROTHROMBIN TIME AT THE DESIRED LEVEL TO PREVENT BLEEDING COMPLICATIONS. FREQUENT PROTHROMBIN DETERMINATIONS ARE ADVISABLE UNTIL IT HAS BEEN DEFINITELY DETERMINED THAT THE PROTHROMBIN LEVEL HAS STABILIZED.

(C) CYP2C8 Substrates: Gemfibrozil is a strong inhibitor of CYP2C8 and may increase exposure of drugs mainly metabolized by CYP2C8 (e.g., dabrafenib, enzalutamide, loperamide, montelukast, paclitaxel, pioglitazone, rosiglitazone). Therefore, dosing reduction of drugs that are mainly metabolized by CYP2C8 enzyme may be required when gemfibrozil is used concomitantly (see WARNINGS).

Repaglinide: In healthy volunteers, co-administration with gemfibrozil (600 mg twice daily for 3 days) resulted in an 8.1-fold (range 5.5- to 15.0- fold) higher repaglinide AUC and a 28.6-fold (range 18.5- to 80.1-fold) higher repaglinide plasma concentration 7 hours after the dose. In the same study, gemfibrozil (600 mg twice daily for 3 days) + itraconazole (200 mg in the morning and 100 mg in the evening at Day 1, then 100 mg twice daily at Day 2–3) resulted in a 19.4- (range 12.9- to 24.7-fold) higher repaglinide AUC and a 70.4-fold (range 42.9- to 119.2-fold) higher repaglinide plasma concentration 7 hours after the dose. In addition, gemfibrozil alone or gemfibrozil + itraconazole prolonged the hypoglycemic effects of repaglinide. Co-administration of gemfibrozil and repaglinide increases the risk of severe hypoglycemia and is contraindicated (see CONTRAINDICATIONS).

Dasabuvir: Co-administration of gemfibrozil with dasabuvir increased dasabuvir AUC and Cmax (ratios: 11.3 and 2.01, respectively) due to CYP2C8 inhibition. Increased dasabuvir exposure may increase the risk of QT prolongation, therefore, co-administration of gemfibrozil with dasabuvir is contraindicated (see CONTRAINDICATIONS).

Selexipag: Co-administration of gemfibrozil with selexipag doubled exposure to selexipag and increased exposure to the active metabolite by approximately 11-fold. Concomitant administration of gemfibrozil with selexipag is contraindicated (see CONTRAINDICATIONS).

Enzalutamide: In healthy volunteers given a single 160 mg dose of enzalutamide after gemfibrozil 600 mg twice daily, the AUC of enzalutamide plus active metabolite (N-desmethyl enzalutamide) was increased by 2.2 fold and corresponding Cmax was decreased by 16%. Increased enzalutamide exposure may increase the risk of seizures. If co-administration is considered necessary, the dose of enzalutamide should be reduced (see WARNINGS).

(D) OATP1B1 substrates: Gemfibrozil is an inhibitor of OATP1B1 transporter and may increase exposure of drugs that are substrates of OATP1B1 (e.g., atrasentan, atorvastatin, bosentan, ezetimibe, fluvastatin, glyburide, SN-38 [active metabolite of irinotecan], rosuvastatin, pitavastatin, pravastatin, rifampin, valsartan, olmesartan). Therefore, dosing reductions of drugs that are substrates of OATP1B1 may be required when gemfibrozil is used concomitantly (see WARNINGS). Combination therapy of gemfibrozil with simvastatin or with repaglinide, which are OATP1B1 substrates, is contraindicated (see CONTRAINDICATIONS).

(E) In vitro studies of CYP enzymes, UGTA enzymes and OATP1B1 transporter: In vitro studies have shown that gemfibrozil is an inhibitor of CYP1A2, CYP2C8, CYP2C9, CYP2C19, OATP1B1, and UDP-glucuronosyltransferase (UGT) 1A1 and 1A3 (see WARNINGS).

(F) Bile Acid-Binding Resins: Gemfibrozil AUC was reduced by 30% when gemfibrozil was given (600 mg) simultaneously with resin-granule drugs such as colestipol (5 g). Administration of the drugs two hours or more apart is recommended because gemfibrozil exposure was not significantly affected when it was administered two hours apart from colestipol.

(G) Colchicine: Myopathy, including rhabdomyolysis, has been reported with chronic administration of colchicine at therapeutic doses. Concomitant use of gemfibrozil may potentiate the development of myopathy. Patients with renal dysfunction and elderly patients are at increased risk. Caution should be exercised when prescribing gemfibrozil with colchicine, especially in elderly patients or patients with renal dysfunction.

4\. Carcinogenesis, Mutagenesis, Impairment of Fertility - Long-term studies have been conducted in rats at 0.2 and 1.3 times the human exposure (based on AUC). The incidence of benign liver nodules and liver carcinomas was significantly increased in high dose male rats. The incidence of liver carcinomas increased also in low dose males, but this increase was not statistically significant (p=0.1). Male rats had a dose-related and statistically significant increase of benign Leydig cell tumors. The higher dose female rats had a significant increase in the combined incidence of benign and malignant liver neoplasms.

Long-term studies have been conducted in mice at 0.1 and 0.7 times the human exposure (based on AUC). There were no statistically significant differences from controls in the incidence of liver tumors, but the doses tested were lower than those shown to be carcinogenic with other fibrates.

Electron microscopy studies have demonstrated a florid hepatic peroxisome proliferation following gemfibrozil administration to the male rat. An adequate study to test for peroxisome proliferation has not been done in humans but changes in peroxisome morphology have been observed. Peroxisome proliferation has been shown to occur in humans with either of two other drugs of the fibrate class when liver biopsies were compared before and after treatment in the same individual.

Administration of approximately 2 times the human dose (based on surface area) to male rats for 10 weeks resulted in a dose-related decrease of fertility. Subsequent studies demonstrated that this effect was reversed after a drug-free period of about eight weeks, and it was not transmitted to the offspring.

5\. Pregnancy - Gemfibrozil has been shown to produce adverse effects in rats and rabbits at doses between 0.5 and 3 times the human dose (based on surface area). There are no adequate and well-controlled studies in pregnant women. Gemfibrozil should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Administration of gemfibrozil to female rats at 2 times the human dose (based on surface area) before and throughout gestation caused a dose-related decrease in conception rate, an increase in stillborns, and a slight reduction in pup weight during lactation. There were also dose-related increased skeletal variations. Anophthalmia occurred, but rarely.

Administration of 0.6 and 2 times the human dose (based on surface area) of gemfibrozil to female rats from gestation day 15 through weaning caused dose-related decreases in birth weight and suppressions of pup growth during lactation.

Administration of 1 and 3 times the human dose (based on surface area) of gemfibrozil to female rabbits during organogenesis caused a dose-related decrease in litter size and, at the high dose, an increased incidence of parietal bone variations.

6\. Nursing Mothers - It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk and because of the potential for tumorigenicity shown for gemfibrozil in animal studies, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

7\. Hematologic Changes - Mild hemoglobin, hematocrit, and white blood cell decreases have been observed in occasional patients following initiation of gemfibrozil therapy. However, these levels stabilize during long-term administration. Rarely, severe anemia, leukopenia, thrombocytopenia, and bone marrow hypoplasia have been reported. Therefore, periodic blood counts are recommended during the first 12 months of gemfibrozil administration.

8\. Liver Function - Abnormal liver function tests have been observed occasionally during gemfibrozil administration, including elevations of AST, ALT, LDH, bilirubin, and alkaline phosphatase. These are usually reversible when gemfibrozil is discontinued. Therefore, periodic liver function studies are recommended and gemfibrozil therapy should be terminated if abnormalities persist.

9\. Kidney Function - There have been reports of worsening renal insufficiency upon the addition of gemfibrozil therapy in individuals with baseline plasma creatinine >2.0 mg/dL. In such patients, the use of alternative therapy should be considered against the risks and benefits of a lower dose of gemfibrozil.

10\. Pediatric Use - Safety and efficacy in pediatric patients have not been established.