PFIZER-E

Clinical safety rating: caution

Comprehensive clinical and safety monograph for PFIZER-E (PFIZER-E).

How it works

PFIZER-E (ethinyl estradiol and norethindrone) is a combined oral contraceptive. Ethinyl estradiol is an estrogen that prevents ovulation by inhibiting gonadotropin release, while norethindrone is a progestin that alters cervical mucus and endometrial lining.

What the body does with it

Metabolism	Ethinyl estradiol is metabolized primarily by CYP3A4 and undergoes first-pass metabolism. Norethindrone is metabolized via reduction and sulfate conjugation.
Excretion	Renal: 70% unchanged; biliary/fecal: 30% (metabolites).
Half-life	Terminal elimination half-life: 3.5 hours (range 2.5–4.5 h). Short half-life necessitates frequent dosing; prolonged in renal impairment.
Protein binding	92–98% bound to albumin and alpha-1-acid glycoprotein.
Volume of Distribution	Vd: 0.3–0.4 L/kg. Low Vd indicates limited extravascular distribution.
Bioavailability	Oral: 85% (high first-pass metabolism accounts for 15% loss).
Onset of Action	Oral: 30–60 min; IV: immediate.
Duration of Action	Oral: 4–6 h; IV: 4–6 h. Duration may be extended in hepatic impairment.

Classification & Brands

Dosing & administration

500 mg intramuscularly once every 4 weeks.

Dosage form	TABLET
Renal impairment	No adjustment required for any degree of renal impairment.
Liver impairment	No adjustment required for Child-Pugh Class A or B; not studied in Child-Pugh Class C.
Pediatric use	Weight ≥20 kg: 500 mg intramuscularly once; not approved for weight <20 kg.
Geriatric use	No specific dose adjustment; use with caution due to age-related decline in physiological function.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for PFIZER-E (PFIZER-E).

Breastfeeding	Compatible with breastfeeding. Milk/plasma ratio is approximately 0.25. Infant dose is less than 1% of maternal weight-adjusted dose. No adverse effects observed in breastfed infants.
Teratogenic Risk	FDA Pregnancy Category B. No evidence of teratogenicity in animal studies. In humans, first trimester exposure is not associated with major congenital malformations. Second and third trimester use may cause transient fetal tachycardia and decrease fetal heart rate variability. High doses near term may produce neonatal bradycardia, hypotonia, and apnea.

Warnings & precautions

■ FDA Black Box Warning

Cigarette smoking increases the risk of serious cardiovascular events from oral contraceptive use. This risk increases with age and with the number of cigarettes smoked. Women over 35 years old who smoke should not use oral contraceptives.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Hypersensitivity to any component","Current or history of thrombophlebitis or thromboembolic disorders","Cerebrovascular or coronary artery disease","Known or suspected breast carcinoma","Active liver disease or benign/malignant liver tumors","Undiagnosed abnormal uterine bleeding","Known or suspected pregnancy","Heavy smoking (≥15 cigarettes/day) in women >35 years","Cholestatic jaundice of pregnancy or jaundice with prior pill use"]

Clinical Precautions

Precautions

["Thrombotic disorders (deep vein thrombosis, pulmonary embolism, stroke, myocardial infarction)","Hepatic tumors (benign and malignant)","Gallbladder disease","Hypertension","Carbohydrate and lipid metabolism effects","Ocular lesions (retinal thrombosis)","Depression","Hereditary angioedema exacerbation"]

Clinical Tips & Counseling

Drug interactions

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PFIZER-E

Clinical safety rating: caution

Comprehensive clinical and safety monograph for PFIZER-E (PFIZER-E).

How it works

What the body does with it

Metabolism	Ethinyl estradiol is metabolized primarily by CYP3A4 and undergoes first-pass metabolism. Norethindrone is metabolized via reduction and sulfate conjugation.
Excretion	Renal: 70% unchanged; biliary/fecal: 30% (metabolites).
Half-life	Terminal elimination half-life: 3.5 hours (range 2.5–4.5 h). Short half-life necessitates frequent dosing; prolonged in renal impairment.
Protein binding	92–98% bound to albumin and alpha-1-acid glycoprotein.
Volume of Distribution	Vd: 0.3–0.4 L/kg. Low Vd indicates limited extravascular distribution.
Bioavailability	Oral: 85% (high first-pass metabolism accounts for 15% loss).
Onset of Action	Oral: 30–60 min; IV: immediate.
Duration of Action	Oral: 4–6 h; IV: 4–6 h. Duration may be extended in hepatic impairment.

Classification & Brands

Dosing & administration

500 mg intramuscularly once every 4 weeks.

Dosage form	TABLET
Renal impairment	No adjustment required for any degree of renal impairment.
Liver impairment	No adjustment required for Child-Pugh Class A or B; not studied in Child-Pugh Class C.
Pediatric use	Weight ≥20 kg: 500 mg intramuscularly once; not approved for weight <20 kg.
Geriatric use	No specific dose adjustment; use with caution due to age-related decline in physiological function.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for PFIZER-E (PFIZER-E).

Breastfeeding	Compatible with breastfeeding. Milk/plasma ratio is approximately 0.25. Infant dose is less than 1% of maternal weight-adjusted dose. No adverse effects observed in breastfed infants.
Teratogenic Risk	FDA Pregnancy Category B. No evidence of teratogenicity in animal studies. In humans, first trimester exposure is not associated with major congenital malformations. Second and third trimester use may cause transient fetal tachycardia and decrease fetal heart rate variability. High doses near term may produce neonatal bradycardia, hypotonia, and apnea.