Main characteristics of prevalence surveys and equivalence studies of antidiabetic medicines included in the reviewBecause of the limited number of samples tested for quality in the studies included in this review, the numbers should not be interpreted as representative of the prevalence of specific SF antidiabetics (please refer to the discussion section of the current paper for more details)
| Study | Country | Active pharmaceutical ingredient | Total no of samples collected | Failed samples n (%) |
| Prevalence surveys | ||||
| Blume et al85 | Argentina, Australia, Austria, Belgium, Canada, Chile, Commonwealth of Independent States, Denmark, Egypt, Finland, France, Germany, Greece, Hungary, Indonesia, Italy, Japan, Luxembourg, Netherlands, Pakistan, Portugal, Spain, Sweden, Switzerland, Thailand, Turkey, UK, USA | Glibenclamide | 187 | 8 (4.3) |
| Westenberger et al40 | Unstated | Metformin | 4 | 0 (0.0) |
| Central Drugs Standard Control Organisation86 | India | Metformin, gliclazide, glimepiride | 45 | 0 (0.0) |
| Ebenezer87 | Nigeria | Metformin | 179 | 7 (3.9) |
| Islam39 | Cambodia | Metformin, glibenclamide | 112 | 21 (18.8)* |
| Equivalence studies | ||||
| Attorrese and Massi-Benedetti70 | Unstated | Glimepiride | 23 | 12 (52.2) |
| Hamdan and Jaber88 | Jordan | Metformin | 5 | 1 (20.0) |
| Chandrasekaran et al89 | Malaysia | Metformin | 5 | 0 (0.0) |
| Afifi and Ahmadeen90 | Saudi Arabia | Metformin | 6 | 0 (0.0) |
| Chatur et al91 | Unstated | Voglibose | 5 | 1 (20.0) |
| Olusola et al92 | Nigeria | Metformin | 8 | 1 (12.5) |
| Oyetunde et al93 | Nigeria | Metformin | 5 | 2 (40.0) |
| El-Sabawi et al94 | Jordan | Glibenclamide | 6 | 3 (50.0) |
| Labu et al95 | Bangladesh | Metformin | 7 | 0 (0.0) |
| Ajala et al96 | Nigeria | Metformin | 8 | 3 (37.5) |
| Betari and Haidar97 | Unstated | Sitagliptin | 5 | 2 (40.0) |
| Elango and Shanmuganathan98 | India | Metformin | 15 | 3 (20.0) |
| Elhamili et al99 | Libya | Glibenclamide | 3 | 0 (0.0) |
| Abdulhameed et al100 | Iraq | Metformin | 5 | 0 (0.0) |
| Gupta et al101 | Trinidad and Tobago | Metformin | 4 | 0 (0.0) |
| Sachan et al102 | India | Metformin | 4 | 0 (0.0) |
| Sakr et al103 | Saudi Arabia | Glibenclamide | 8 | 0 (0.0) |
| Alam et al104 | Saudi Arabia | Glibenclamide | 5 | 0 (0.0) |
| Eraga et al105 | Nigeria | Metformin | 10 | 8 (80.0)† |
| Aivalli et al106 | India | Metformin, glibenclamide | 10 | 0 (0.0) |
*In Islam 2017,39 only the number of medicine failing each quality test was mentioned. Since one medicine may fail more than one test, the failure rate was recorded as the highest possible number of samples failing one of the tests.
†In Eraga 2017,105 uniformity of content was assessed using two methods that is, UV spectrophotometry and reverse-phase high-performance liquid chromatography. There are several discrepancies in the results of these two tests. Therefore, if samples failed either, they will be categorised as failed samples.
SF, substandard and falsified; UV, ultraviolet.