WinRho | Pharmacology Mentor

Generic Name

WinRho

Mechanism

WinRho is a human anti‑D immunoglobulin (RhIg) that works by
• Injecting IgG anti‑D antibodies into an Rh‑negative mother,
• Binding free fetal RhD+ red blood cells in her circulation,
• Marking them for clearance by the reticuloendothelial system before maternal immune cells recognize them, thereby preventing sensitization.

This passive immunization eliminates the risk of future hemolytic disease of the fetus and newborn (HDFN).

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Pharmacokinetics

Parameter	Details
Route	Intramuscular (IM) or intravenous (IV)
Absorption	IM: 80–90% bioavailability; IV: 100%
Distribution	Mainly confined to the intravascular compartment; low plasma protein binding (~0.1%)
Metabolism	Catabolized as any IgG → lysosomal degradation
Half‑life	~10–16 days (depends on dose, maternal weight)
Elimination	Primarily renal (catabolized peptides)

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Indications

Primary prophylaxis in Rh‑negative mothers after delivery of an RhD+ infant (28 weeks gestation, 48 h postpartum, 72 h postpartum).
Second‑trimester prophylaxis (28 weeks).
Intrapartum prophylaxis after a suspected fetomaternal hemorrhage (FMH).
Post‑abortion or ectopic pregnancy prophylaxis.
Blood transfusion of RhD+ units to Rh‑negative patients.

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Contraindications

Category	Detail
Contraindications	Known hypersensitivity to IgG, allergic reaction to any component, documented hemolytic disease from previous Rh treatment.
Warnings	• Rare anaphylaxis, severe urticaria. • Potential for non‑immune fetal tachycardia post‑injection.
Precautions	• Use only in RhD‑negative patients. • Ensure blood type compatibility (ABO, Rh).
Drug Interactions	None known that alter WinRho’s action; concurrent IVIG is permissible.

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Dosing

Situation	Standard Dose	Timing
Gestational prophylaxis (28 weeks)	150 IU/kg or 150 IU if < 10 kg	Performed IM in the gluteus or deltoid
Post‑delivery	150 IU/kg or 150 IU (if < 10 kg)	48 h (or 72 h) postpartum
FMH (intrapartum)	0.5 IU/kg per estimated mL of fetal blood lost	Within 30 min of FMH suspected
Transfusion	150 IU/kg if RhD+ units transfused	Within 24 h of transfusion
Ectopic/induced abortion	150 IU/kg or 150 IU	Performed immediately after procedure
Route	IM (preferred). IV acceptable if IM not feasible	Avoid injection into muscle with impaired perfusion

*Always weigh the mother to adjust dose in IU/kg.*

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Adverse Effects

Common (≤ 10 %)
Mild injection‑site reaction (pain, erythema, induration)
Low‑grade fever, chills
Moderate (≤ 5 %)
Nausea, headache, mild fatigue
Serious (≤ 1 %)
Anaphylaxis, severe urticaria, hypotension
Rare hemolytic reaction (if antibody titer high)

*Monitoring for allergic reaction for 15 min post‑injection is advised.*

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Monitoring

Parameter	Frequency	Rationale
Anti‑D antibody titer	At 2 weeks, 6 weeks postpartum, and at each pregnancy	Detects inadvertent sensitization
Hemoglobin and Hct	If FMH suspected or after transfusion	Monitor for hemolysis
Injection‑site assessment	Immediate, then daily for 2 days	Detect local adverse reactions
Allergic symptoms	Immediate observation (15‑30 min)	Early detection of anaphylaxis
Pregnancy outcomes (if applicable)	Follow‑up visits	Ensure no HDFN signs

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Clinical Pearls

Timing is critical: Administer within 48 h postpartum (or 72 h if maternal BMI > 30) to achieve highest efficacy.
Weight‑based dosing: Use IU/kg rather than fixed dose in high‑weight patients to avoid under‑prophylaxis.
Injection technique: Use a 25‑gauge needle into the deltoid or vastus lateralis; rotate sites if multiple doses required.
Storage: Keep at 2–8 °C; never freeze. It can be reconstituted with 5 mL of sterile water (if not pre‑filled).
Cross‑reactivity: Though rarely, patients with IgA deficiency may develop IgA anti‑D; monitor for reactions.
Monitoring anti‑D titer: A positive titer > 1:160 post‑administration warrants repeat assessment and possible second dose.
Educational tip for students: Remember, *RhIg does not treat hemolytic disease—prevent it.*

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