Azo-bond reduction | Sulfasalazine | Anti-inflammatory | 5-Aminosalicylic acid and sulphapyridine | Activation of prodrug | Unknown | (Peppercorn and Goldman, 1972) |
Alkene double bond reduction | Digoxin | Cardiac glycoside | Dihydrodigoxin | Reduction of therapeutic efficacy | Eggerthelalenta | (Lindenbaum et al., 1981b; Dobkin et al., 1982; Saha et al., 1983) |
Carbonyl double bond reduction | Tacrolimus | Immuno-suppressant | 9-Hydroxytacrolimus | Low and variable exposure to the immunosuppressant | Faecalibacteriumprausnitzii | (Guo et al., 2019) |
Nitro reduction | Nitrazepam | Hypnotic | 7-Aminonitrazepam | Produces 7-acetylaminonitrazepam having teratogenic potential | Clostridium leptum | (Rafii et al., 1997) |
N-oxide reduction | Loperamide oxide | Anti-diarrheal | Loperamide | Activation of prodrug | Unknown | (Lavrijsen et al., 1995) |
Sulfoxide reduction | Sulindac | Non-steroidal anti-inflammatory drug | Sulindac sulfide | Activation of prodrug | Aerobes Escherichia coli,Enterobacter and anaerobes Clostridia | (Strong et al., 1987) |
Hydrolysis | Sorivudine | Anti-viral | (E)-5-(2-bromovinyl) uracil | Lethal effects due to combination of Sorivudine and 5-fluorouracil | Bacteroides species B. Vulgatus, B.Thetaiotaomicron, B. fragilis, B. uniformis and B. eggerthii | (Nakayama et al., 1997; Okuda et al., 1998) |
Proteolysis | Calcitonin | Synthetic hormone | Unknown | Degradation of peptide drug causing loss of therapeutic efficacy | Unknown | (Sousa et al., 2008) |
De-conjugation | Irinotecan metabolite | Anti-cancer | SN-38 | Intestinal toxicity | Unknown | (Takasuna et al., 1996) |
De-hydroxylation | Levodopa | Anti-parkinsonian | m-Tyramine and m-hydroxyphenyl acetic acid | Reduced therapeutic activity | Unknown | (Sandler et al., 1969; Goldin et al., 1973) |
De-methylation | Imipramine | Tricyclic anti-depressant | Desipramine | Conversion to active metabolite causing variation in response to imipramine therapy | Aerobes Escherichia coli Klebsiella pneumoniae and anaerobes Fusobacterium fusiforme | (Clark et al., 1983) |
Acetylation | 5-Aminosalicylic acid | Metabolite of sulfasalazine | N-Acetyl-5-aminosalicylic acid | Therapeutic inactivation of the drug | Unknown | (Allgayer et al., 1989) |
De-acetylation | Aspirin | Non-steroidal anti-inflammatory drugs and anti-thrombotic | Salicylic acid and hydroxylated salicylic acid | Decrease in anti-thrombotic effect of the drug | Unknown | (Kim IS et al., 2016) |
De-amination | 5-Fluorocytosine | Anti-fungal | 5-Fluorouracil | Possible cause of toxicity of the drug | Unknown | (Harris et al., 1986) |
Oxidation | Lovastatin | HMG-CoA reductase inhibitor | Hydroxylated and hydroxy acid metabolites | Inter-individual variability in pharmacokinetics | Unknown | (Yoo et al., 2014) |
De-nitration | Glyceryl trinitrate | Anti-anginal | Glyceryl-1,3-dinitrate, glyceryl-1,2-dinitrate, glyceryl-1-mononitrate,glyceryl-2-mononitrate | Decrease in the therapeutic activity of the drug | Unknown | (Sousa et al., 2008) |
Thiazole ring opening | Levamisole | Anthelmintic | Levametabol I, II and III | The activity of metabolites not reported | Bacteroidetes and Clostridium spp. under anaerobic conditions | (Shu et al., 1991) |