Immunoglobulin replacement and antimicrobial prophylaxis — formative SAQs

SAQ 1 (10)

A six-year-old boy with X-linked agammaglobulinaemia has been on intravenous immunoglobulin since infancy, given every four weeks in a hospital two hours from his home. He has had three proven pneumonias in the past year despite a trough IgG that sits in the lower half of the normal range. His family finds the travel and the missed school increasingly difficult. [3] [2]

a) What are the four structured questions you must ask before simply raising the dose, and why is the trough alone an incomplete target? (3 marks) [2]

b) Discuss the relative pharmacokinetic and practical advantages of switching this child to home subcutaneous immunoglobulin, and the evidence that supports it. (3 marks) [5] [8]

c) Outline a plan to dose this child's regimen to his clinical outcome rather than to a trough number alone, including the role of antimicrobial prophylaxis. (2 marks) [2] [6]

d) Describe the lung surveillance and the family capacity assessment that belong in the revised plan. (2 marks) [3] [8]

SAQ 2 (10)

A nine-year-old girl with documented recurrent sinopulmonary infection has normal total IgG, IgA and IgM but a proven failure of pneumococcal polysaccharide vaccine response, consistent with specific antibody deficiency. Her parents have read that low antibodies are treated with immunoglobulin and are asking why she cannot have it. [6] [2]

a) Why is a trial of prophylactic antibiotics the rational first move in this child, and why is giving immunoglobulin first a mechanistic mistake? (4 marks) [6]

b) Outline the antimicrobial prophylaxis options and the triggers that would prompt escalation to immunoglobulin replacement. (3 marks) [6] [1]

c) Explain to the parents, in plain language, the difference between a quantitative and a functional antibody defect and why it changes the treatment. (2 marks) [2] [1]

d) State two conditions in which immunoglobulin replacement is clearly indicated, and two in which it is not. (1 mark) [3] [1]