Zoster immune globulin

History

In 1969, zoster immune globulin (ZIG), prepared from patients convalescing from herpes zoster, was shown to prevent clinical varicella in susceptible, normal children if administered within 72 hours after exposure.

Herpes zoster neck

Early IVIG post exposure

• Subsequent uncontrolled studies of immunocompromised patients who received ZIG after exposure to V-Z virus showed that they also tended to have lower- than-expected clinical attack rates and higher-than-expected rates of subclinical infection when ZIG was administered no later than 96 hours after exposure.
• Patients who became ill tended to have modified illnesses with a low complication rate.
• The efficacy of ZIG in immunocompromised persons was further demonstrated by a study comparing the use of low-titer versus high- titer lots; patients who received the high-titer ZIG had significantly lower risks of complications.

VZIG availability

ln 1978, VZIG became available. Both serologic and clinical evaluations have demonstrated that the product is equivalent to ZIG in preventing or modifying clinical illness in susceptible, immunocompromised patients exposed to varicella. VZIG has been licensed by FDA's Office of Biologics. VZIG is prepared from plasma found in routine screening of normal, volunteer blood donors to contain high antibody titers to V-Z.

VZIG preparation

• VZIG (Human) is a sterile, 10%-18% solution of the globulin fraction of human plasma, primarily immunoglobulin G (IgG) in 0.3M glycine as a stabilizer and 1:10,000 thimerosol as a preservative.
• It is prepared by Cohn cold ethanol precipitation.

Herpes Zoster

Supply constraints

• ZIG was in short supply because of the continuous need to find new donors convalescing from herpes zoster.
• Because of the method of routinely screening plasma from regular blood donors for high titers of V-Z antibody and using those units to prepare VZIG, supplies became substantially greater.

Indications

When deciding whether to administer VZIG, the clinician must determine whether the patient is likely to be susceptible, whether the exposure is likely to result in infection, and whether the patient is at greater risk of complications from varicella than the general population.

Cost benefit ratio

• Whereas risks of VZIG administration appear to be negligible, costs of administration can be substantial (approximately $75 per 125 units, or $375 for persons over 40 kg {88 lbs} of body weight, i.e., for the maximum recommended dose.
• In addition, it is not known whether modified infection will lead to lifelong immunity or whether modified infections will increase or decrease the risk of later developing zoster.

When to use VZIG?

The following recommendations are made taking these factors into account. In some instances, VZIG is routinely recommended; in others, administration should be evaluated on an individual basis.

Susceptibility

• Both normal and immunocompromised adults and children, who are believed to have had varicella based on a carefully obtained history by an experienced interviewer. can be considered immune.
• Reports of second attacks of clinical varicella are rare.
• Since subclinical primary infections appear rare (less than 5% of infections among normal children), children (under 15 years old) without histories of clinical varicella should be considered susceptible unless proven otherwise (see below).
• On the other hand, most normal adults with negative or unknown histories of varicella are probably immune, since attack rates of varicella in such adults after household or hospital exposure have ranged from only 5% to 15%.

Dosage

• VZIG is supplied in vials containing 125 units per vial (volume is approximately 1.25 cc).
• The recommended dose is 125 units per 10 kg (22 lbs) body weight, up to a maximum of 625 units (i.e., five vials).
• The minimum dose is 125 units.
• Fractional doses are not recommended.
• Some experts recommend 125 units per 10 kg of body weight without limiting the total dose to 625 units.

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Herpes zoster chest

Prophylaxis

• VZIG has not been evaluated as a prophylactic measure for prevention or attenuation of varicella in normal or immunocompromised adults. Therefore, data do not exist with which to calculate the appropriate dose in adults.
• However, it seems likely that 625 units should be sufficient to prevent or modify infection in normal adults.
• Higher doses may be needed in immunocompromised adults.

Route of administration

• VZIG should be administered intramuscularly as directed by the manufacturer.
• IVIG should not be administered IV

Supply

• VZIG is produced by the Massachusetts Public Health Biologic Laboratories.
• Outside Massachusetts, distribution is arranged by the American Red Cross Blood Services--Northeast Region, through other centers.
• VZIG is distributed within Massachusetts by the Massachusetts Public Health Biologic Laboratories.

Side effects

• The most frequent adverse event following VZIG is local discomfort at the injection site.
• Pain, redness, or swelling occurs at the injection site in about 1% of patients.
• Less frequent adverse reactions are gastrointestinal symptoms, malaise, headache, rash, and respiratory symptoms that occur in approximately 0.2% of recipients.
• Severe reactions, such as angioneurotic edema and anaphylactic shock, are rare (less than 0.1%).

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