In studies of dogs, the majority of urinary excretion is through glomerular filtration with some tubular secretion. There is also tubular absorption which is increased with urine acidification. However the activity of nitrofurantoin is also pH dependent and mean inhibitory concentration rises sharply with increased pH above 6. Nitrofurantoin cannot be used to treat infections other than simple cystitis. At the concentrations achieved in urine (>100 μg/mL), nitrofurantoin is a bactericide. It is bacteriostatic against most susceptible organisms at concentrations less than 32 μg/mL.Nitrofurantoin and the quinolone antibiotics are mutually antagonistic in vitro. It is not known whether this is of clinical significance, but the combination should be avoided.Resistance to nitrofurantoin may be chromosomal or plasmid-mediated and involves inhibition of nitrofuran reductase. Acquired resistance in E. coli continues to be rare. Nitrofurantoin and its metabolites are excreted mainly by the kidneys. In renal impairment, the concentration achieved in urine may be subtherapeutic. Nitrofurantoin should not be used in patients with a creatinine clearance of 60 mL/min or less. However, a retrospective chart review may suggest nitrofurantoin is not contraindicated in this population. Mechanism of action
Nitrofurantoin is concentrated in the urine, leading to higher and more effective levels in the urinary tract than in other tissues or compartments. With a 100 mg oral dose, plasma levels are typically less than 1 µg/mL while in the urine it reaches 200 µg/mL.The drug works by damaging bacterial DNA, since its reduced form is highly reactive.
Captopril, sold under the brand name Capoten among others, is an angiotensin-converting enzyme (ACE) inhibitor used for the treatment of hypertension and some types of congestive heart failure. Captopril was the first oral ACE inhibitor found for the treatment of hypertension. It does not cause fatigue as associated with beta-blockers. Due to the adverse drug event of causing hyperkalemia, as seen with most ACE Inhibitors, the medication is usually paired with a diuretic. Captopril was patented in 1976 and approved for medical use in 1980. Structure–activity relationship
Captopril has an L-proline group which allows for it to be more bioavailable within oral formulations. The thiol moiety within the molecule has been associated with two significance adverse effects: the hapten or immune response. This immune response, also known as agranulocytosis, can explain the adverse drug events which may be seen in captopril with the allergic response, which would be: hives, severe stomach pain, difficulty breathing, swelling of the face, lips, tongue or throat.In terms of interaction with the enzyme, the molecules thiol moiety will attach to the binding site of the ACE enzyme. This will inhibit the port at which the angiotensin-1 molecule would normally bind, therefore inhibiting the downstream effects within the renin-angiotensin system. Medical uses
Captoprils main uses are based on its vasodilation and inhibition of some renal function activities. These benefits are most clearly seen in:

Hypertension
Cardiac conditions such as congestive heart failure and after myocardial infarction
Preservation of kidney function in diabetic nephropathy.Additionally, it has shown mood-elevating properties in some patients.