B12 deficiency is common in patients on metformin, and should be monitored and supplemented either sublingually or intramuscularly.

The ringing in the ear is tinnitus, which is indicative of ototoxicity. Nausea, metallic taste in mouth, difficulty swallowing and skin reactions are not associated with the development of ototoxicity. 

All of these are potential side effects of ACE (angiotensin-converting enzyme) inhibitors such as enalapril, but angioedema (the swelling of the face, lips, and/or tongue) is a potentially life threatening condition, as swelling can obstruct the airway.

Nausea, vomiting, and diarrhea are common symptoms of digoxin toxicity. Other symptoms may include confusion, anorexia, irregular heartbeat, and palpitations. Tremors, mood swings, and rash are not generally seen with digoxin toxicity. 

Meperidine is contraindicated because in high doses it can form a toxic metabolite that can lead to seizures. All other drugs listed are appropriate for pain control for sickle cell crisis. 

Extrapyramidal side effects generally present as slow or repetitive motions or postures (dystonia), spasm, tremor, slurred speech, slowed thought process, restlessness and anxiety, paranoia, and general overall distress. These effects are caused by antipsychotic drugs that act as dopamine D2 receptor antagonists.

Extrapyramidal side effects are common with typical antipsychotic drugs that act as dopamine D2 receptor antagonists. These include many selective serotonin reuptake inhibitors (SSRI's), serotonin–norepinephrine reuptake inhibitors (SNRI's), and norepinephrine–dopamine reuptake inhibitors (NDRI's), as well as antiemetics such as metclopramide.

Alprazolam is a benzodiazepine and is not associated with extrapyramidal adverse effects.

Chlorpropamide, an antidiabetic medication in the sulfonylurea class, has been associated with drug-induced SIADH (syndrome of inappropriate antidiuretic hormone secretion). This is a rare but serious complication that will generally resolve once drug treatment has stopped. None of the other drugs listed are associated with this side effect. 

Of the drugs listed, the only one associated with this bizarre side effect is rifampicin, a broad spectrum antibiotic used in tuberculosis. Urine, sweat, saliva, or tears may be turned any shade from red to reddish orange.

Gentamicin is an aminoglycoside antibiotic. Most antibiotics in the aminoglycoside class can have significant ototoxic effects. Of these, streptomycin and gentamicin are primarily toxic to the vestubular system, while amikacin, neomycin, dihydrosterptomycin, and kanamicin primarily affect the cochlea. None of the other antibiotics listed are generally associated with ototoxicity.