Haemolytic anaemia penicillins

Penicillin is an unstable, reactive molecule which in the body can easily react with constituents of the cells and tissues such as proteins. The reaction with proteins will alter their structure. They may become sufficiently different to be recognized by the immune system, and the body then mounts an immune attack on these altered proteins (known as antigens). This process can take one of several forms. For example, if the penicillin reacts with the proteins on the outside of the red blood cell, these may be recognized by the immune system. The immune system then reacts by producing antibodies, specific proteins which will recognize and bind to the altered red cells. The next stage is when a type of white blood cell called a natural killer cell sees and binds to the antibody on the red cell and destroys the red cell. The result of this is haemolytic anaemia, in which the number of red blood cells is depleted, possibly to dangerous levels. 

Type II reactions antibody-dependent cytotoxic type. The drug or metabolite combines with a protein in the body so that the body no longer recognises the protein as self, treats it as a foreign protein and forms antibodies (IgG, IgM) that combine with the antigen and activate complement which damages cells, e.g. penicillin- or methyldopa-induced haemolytic anaemia. 

White JM, Brown DL, Hepner GW, Worlledge SM. Penicillin-induced haemolytic anaemia. BMJ 1968 3(609) 26-9. 

This makes the blood cells antigenic and results in the production of IgG antibodies against them. The antibodies so produced activate the complement system. Complement destroys the blood cells. This can lead to haemolytic anaemia if red blood cells are involved and can occur in response to penicillin. If white blood cells are the target of the reaction then the result is agranulocytosis this can occur for example with carbimazole (used to treat an overactive thyroid gland, see Chapter 6). Thrombocytopenia can be the result if the cells involved are platelets this can happen in response to heparin (used in thrombotic disorders, see Chapter 4). 

Cases of penicillin-induced haemolytic anaemia continue to be reported. One case confirms that this side effect — usually occurring during treatment with high doses of penicillin — may arise at doses customarily used for minor infections (9 ). Two recent cases were unusual in so far as only IgM appeared to be involved, whereas normally in... 

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