Too many patients in England and Wales hospitals are not getting the medicines they need, according to UK safety watchdog the National Patient Safety Agency (NPSA).
The watchdog said it had evidence of thousands of cases of patients getting their drugs late or not at all, including 27 resulting in deaths.
Antibiotics, along with anti-coagulants used to prevent blood clotting, are the drugs most likely to cause patients harm if they are forgotten, the NPSA said.
The most common reason given was that the drug was unavailable on the ward. In other cases, however, no reason was given, prompting fears that nurses were forgetting to hand out drugs.
The NPSA received reports, from September 2006 to June 2009, of 27 deaths, 68 cases of severe harm, including permanent disability, as well as another 21,000 less serious cases where drugs were not given or were given too late.
The NPSA has now ordered all hospitals, including mental health units and community centres, to review their practices and carry out regular audits to monitor the issue.
The watchdog has also called for hospitals to draw up a list of critical medicines that must always be given on time as well as for a system that will prevent staff from forgetting.