Drugs : Drugs may cause

• predictable, dose-related, reversible marrow suppression, and
• unpredictable, dose-unrelated, idiosyncratic, usually irreversible damage.
  

Drugs that can seriously damage marrow usually do so in unpredictable and devastating fashion and in only in miniscule proportion of those exposed. Susceptibility is presumably genetic. This effect usually does not occur until after cessation of the drug - with chloramphenicol at least 6-10 weeks, and up to 12 months later.

Some drugs e.g. chloramphenicol, have both dose-related and idiosyncratic effect, rarely one following the other. Some (e.g. benzol) have a potential for causing leukemia, which usually does not occur until many years after exposure.

Table 2: Dose-related effects of chloramphenicol

	Timing
Reticulocytopenia, increase in serum Fe	2-5 days
Marrow : Erythroblast depletion, Vacuolation of precursor cells	3-7 days
Anemia	5-10 days
Thrombocytopenia (mild)	10-14 days
Neutropenia	10-21 days

Table 3 : Pediatric drugs and chemicals which may cause marrow aplasia

• Cytotoxics
  
  
  • Antibacterial
    
    • Chloramphenicol (more often oral than intravenous)
    • Sulphonamides
      
      
  • Antimalarial
    
    • Mepacrine
    • Quinacrine
    • Chloroquine
    • Trimethoprim
    • Pyrimethamine
      
      
• Antihistamine
  
  • Cimetidine
  • Ranitidine
  • Chlorpheniramine
    
    
• Anticonvulsants
  
  • Phenytoin
  • Other hydantoins
    
    
• Tranquillizers
  
  • Promazine
  • Chlorpromazine
  • Carbamazepine
    
    
• Anti-inflammatory
  
  • Indomethacin
  • Diclofenac
  • Gold
    
    
• Antipurines
  
  • Azathioprine
    
    
• Anti-diabetic
  
  • Chlorpropamide
  • Tolbutamide
    
    
• Antithyroid
  
  • Propylthioracil
  • Methimazole
    
    
• Other drugs
  
  • Allopurinol
  • Quinidine
  • Acetazolamide
  • Penicillamine
    
    
• Solvents
  
  • Benzol
  • White spirit (benzene, naphtha and other synonyms)
  • Carbon tetrachloride
  • Kerosene
  • Glue (sniffing)
  • Model aeroplane 'dope'
  • Hair dyes
    
    
• Insecticides
  
  • DDT
  • Lindane
  • Chlordane
  • Organophosphates