Background: Nonstandard product information leaflets (PIs) may lead to medication errors. We assessed the completeness, and compatibility of, essential information against reference sources in selected PIs of medicines used in Sri Lanka.

Methods: Hundred PIs each were used to assess completeness and compatibility of information, respectively. Availability of essential information was checked against drug regulations of the country. Clinical facts were matched against the British National Formulary and/or Australian Medicines Handbook for compatibility. PIs were categorized as "compatible" if all facts stated under each clinical information type were mentioned in at least one of the references; "partially compatible" if only some facts mentioned under each clinical information type were available in at least one of the references; and "totally incompatible" if none of the facts stated in each clinical information type were mentioned in both references.

Results: Of the 100 PIs, 28% did not include at least one of the essential information required by the regulations. Pharmacokinetic data, duration of treatment, overdose, and special dosage information were frequently missing. Nine types of clinical information in PIs matched with reference sources resulted in 900 cross-matches. Among the cross-matches, 80 (8.9%) partial compatibilities and 8 (0.9%) total incompatibilities were encountered. Nearly half (48%) of the PIs had at least one incompatibility.

Conclusion: Some PIs lacked important medicines information and were incompatible with known references. PIs need to be carefully prepared by medicine manufacturers and meticulously reviewed by regulatory authorities for accuracy and completeness.