Macrocytic anaemia is caused by all EXCEPT:

Trimethoprim: Being an antifolate, there is theoretical teratogenic risk. Neonatal haemolysis and methaemoglobinaemia can occur if it is given near term. Pyrimethamine is relatively safe. The only side effects are occasional nausea and rashes. Folate deficiency is rare; megaloblastic anaemia and granulocytopenia may occur with higher doses, especially in those with marginal folate stores. This can be treated by folinic acid. Antibiotics are primarily recommended for treatment of mild, moderate, or severe PJP. Trimethoprim-sulfamethoxazole (TMP-SMX) has been shown to be as effective as intravenous pentamidine and more effective than other alternative treatment regimens. Pentamidine(adverse effects): More common: Burning pain, dryness, or sensation of lump in throat chest pain or congestion coughing difficulty in breathing difficulty in swallowing skin rash wheezing Rare Nausea and vomiting pain in upper abdomen, possibly radiating to the back pain in side of chest (severe) shoness of breath (sudden and severe) Rare - with daily treatment doses only Anxiety chills cold sweats cool, pale skin decreased urination headache increased hunger loss of appetite nausea and vomiting nervousness shakiness stomach pain unusual tiredness methotrexate: Methotrexate has cell cycle specific actionkills cells in S phase; primarily inhibits DNA synthesis, but also affects RNA and protein synthesis. It exes major toxicity on bone marrow-low doses given repeatedly cause megaloblastic anaemia, but high doses produce pancytopenia. Desquamation and bleeding may occur in g.i.t. REFERENCE:ESSENTIALS OF MEDICAL PHARMACOLOGY, www.drugs.com, www.medscape.com