metformin hydrochloride

metformin hydrochloride

(met fore' min)

Fortamet, Glucophage, Glucophage XR, Glumetza, Metformin HCl ER, Riomet

Pregnancy Category B

Drug class

Antidiabetic

Therapeutic actions

Exact mechanism is not understood; possibly increases peripheral utilization of glucose, decreases hepatic glucose production and alters intestinal absorption of glucose.

Indications

·        Adjunct to diet to lower blood glucose with type 2 (non–insulin-dependent) diabetes mellitus in patients > 10 yr; ER in patients > 17 yr

·        As part of combination therapy with a sulfonylurea or insulin when either drug alone cannot control glucose levels in patients with type 2 diabetes mellitus

Contraindications and cautions

·        Contraindicated with allergy to metformin; CHF; diabetes complicated by fever, severe infections, severe trauma, major surgery, ketosis, acidosis, coma (use insulin); type 1 (insulin-dependent) diabetes, serious hepatic impairment, serious renal impairment, uremia, thyroid or endocrine impairment, glycosuria, hyperglycemia associated with primary renal disease; labor and delivery (if metformin is used during pregnancy, discontinue drug at least 1 mo before delivery); lactation (safety not established).

·        Use cautiously with the elderly.

Available forms

Tablets—500, 850, 1,000 mg; ER tablets—500, 750, 1,000 mg; oral solution–500 mg/5 mL

Dosages

ADULTS

500–850 mg/day PO in divided doses to a maximum of 2,550 mg/day. Dose should be adjusted based on response and blood glucose level. ER tablet: Initially, 500 mg/day PO with the evening meal; may be increased by 500 mg each wk to a maximum of 2,550 mg once daily.

PEDIATRIC PATIENTS 10–16 YR

500 mg/day PO in divided doses with meals; may be increased by 500 mg each wk to a maximum of 2,000 mg/day. ER tablet is not recommended.

GERIATRIC PATIENTS AND PATIENTS WITH RENAL IMPAIRMENT

Smaller doses may be necessary; monitor closely and adjust slowly.

Pharmacokinetics

Route	Peak	Duration
Oral	2–2.5 hr	10–16 hr

Metabolism: T_1/2: 6.2 and 17.6 hr

Distribution: Crosses placenta; enters breast milk

Excretion: Urine

Adverse effects

·        Endocrine: Hypoglycemia, lactic acidosis

·        GI: Anorexia, nausea, vomiting, epigastric discomfort, heartburn, diarrhea, flatulence

·        Hypersensitivity: Allergic skin reactions, eczema, pruritus, erythema, urticaria

Interactions

Drug-drug

·        Increased risk of hypoglycemia with cimetidine, furosemide, cationic drugs such as digoxin, amiloride, vancomycin

·        Increased risk of lactic acidosis with glucocorticoids or ethanol

·        Increased risk of acute renal failure and lactic acidosis with iodinated contrast material used in radiologic studies; stop metformin for 48 hr before and after such studies

Drug-alternative therapy

·        Increased risk of hypoglycemia if taken with juniper berries, ginseng, garlic, fenugreek, coriander, dandelion root, celery

Nursing considerations

Assessment

·        History: Allergy to metformin; diabetes complicated by fever, severe infections, severe trauma, major surgery, ketosis, acidosis, coma; type 1 diabetes, serious hepatic or renal impairment, uremia, thyroid or endocrine impairment, glycosuria, hyperglycemia associated with primary renal disease, CHF, pregnancy, lactation

·        Physical: Skin color, lesions; T, orientation, reflexes, peripheral sensation; R, adventitious sounds; liver evaluation, bowel sounds; urinalysis, BUN, serumcreatinine, LFTs, blood glucose, CBC

Interventions

·        Monitor urine or serum glucose levels frequently to determine effectiveness of drug and dosage.

·        WARNING: Arrange for transfer to insulin therapy during periods of high stress (infections, surgery, trauma).

·        WARNING: Use IV glucose if severe hypoglycemia occurs as a result of overdose.

Teaching points

·        Do not discontinue this medication without consulting your health care provider.

·        Monitor urine or blood for glucose and ketones as prescribed.

·        Swallow extended-release tablets whole; do not cut, crush, or chew.

·        Do not use this drug during pregnancy; if you become pregnant, consult with your health care provider for appropriate therapy.

·        Avoid using alcohol while taking this drug.

·        Report fever, sore throat, unusual bleeding or bruising, rash, dark urine, light-colored stools, hypo- or hyperglycemic reactions.

Adverse effects in Italic are most common; those in Bold are life-threatening.