Systematic review: Helicobacter pylori infection and impaired drug absorption. 
Impaired acid secretion may affect drug absorption and may be consequent to corporal Helicobacter pylori-gastritis, which may affect the absorption of orally administered drugs.  To focus on the evidence of impaired drug absorption associated with H. pylori infection.  Data sources were the systematic search of MEDLINE/EMBASE/SCOPUS databases (1980-April 2008) for English articles using the keywords: drug malabsorption/absorption, stomach, Helicobacter pylori, gastritis, gastric acid, gastric pH, hypochlorhydria, gastric hypoacidity.  Study selection was made from 2099 retrieved articles, five studies were identified.  Data were extracted from selected papers, investigated drugs, study type, main features of subjects, study design, intervention type and results were extracted.  In all, five studies investigated impaired absorption of l-dopa, thyroxine and delavirdine in H. pylori infection.  Eradication treatment led to 21-54% increase in l-dopa in Parkinson's disease.  Thyroxine requirement was higher in hypochlorhydric goitre with H. pylori-gastritis and thyrotropin levels decreased by 94% after treatment.  In H. pylori- and HIV-positive hypochlorhydric subjects, delavirdine absorption increased by 57% with orange juice administration and by 150% after eradication.  A plausible mechanism of impaired drug absorption is decreased acid secretion in H. pylori-gastritis patients.  Helicobacter pylori infection and hypochlorhydria should be considered in prescribing drugs the absorption of which is potentially affected by intragastric pH.