Drug Interaction Report

MONITOR: The coadministration of diuretics with tetracyclines may result in decreased renal function and abnormalities in electrolytes and acid-base balance. As a class, tetracyclines can cause anti-anabolic effects which have led to increased blood urea nitrogen (BUN), azotemia, acidosis, and hyperphosphatemia. Diuretics have the potential to cause electrolyte and metabolic abnormalities, as well as worsen renal function. When used together, it is possible that these two classes of medications could have additive adverse effects.

MANAGEMENT: Patients on concomitant therapy with tetracycline antibiotics and diuretics should have their renal function and electrolytes monitored closely. The risk of additive adverse effects on the patient's renal function, electrolytes, and acid-base balance differs depending on the type of diuretic being used, the specific tetracycline antibiotic, and the clinical status of the patient. The manufacturer's labeling should be consulted for more specific recommendations.

MONITOR: Although they are frequently combined in clinical practice, diuretics and angiotensin converting enzyme (ACE) inhibitors may have additive effects. Coadministration makes hypotension and hypovolemia more likely than does either drug alone. Some ACE inhibitors may attenuate the increase in the urinary excretion of sodium caused by some loop diuretics. Some patients on diuretics, especially those on dialysis or a dietary salt restriction, may experience acute hypotension with lightheadedness and dizziness after receiving the first dose of the ACE inhibitor. In addition, ACE inhibitors may cause renal insufficiency or acute renal failure in patients with sodium depletion or renal artery stenosis.

MANAGEMENT: Monitoring of blood pressure, diuresis, electrolytes, and renal function is recommended during coadministration. The possibility of first-dose hypotensive effects may be minimized by initiating therapy with small doses of the ACE inhibitor, or either discontinuing the diuretic temporarily or increasing the salt intake approximately one week prior to initiating an ACE inhibitor. Alternatively, the patient may remain under medical supervision for at least two hours after the first dose of the ACE inhibitor, or until blood pressure has stabilized.

ADJUST DOSING INTERVAL: Administration with food, particularly dairy products, significantly reduces tetracycline absorption. The calcium content in some foods can form nonabsorbable chelates with tetracycline.

MANAGEMENT: Tetracycline should be administered one hour before or two hours after meals. Because oral tetracycline has caused rare cases of esophagitis and esophageal ulceration, patients should be advised to take tetracycline with a large glass of water while standing or sitting upright and to avoid laying down immediately afterwards.

GENERALLY AVOID: Moderate-to-high dietary intake of potassium can cause hyperkalemia in some patients who are using angiotensin converting enzyme (ACE) inhibitors. In some cases, affected patients were using a potassium-rich salt substitute. ACE inhibitors can promote hyperkalemia through inhibition of the renin-aldosterone-angiotensin (RAA) system.

MANAGEMENT: It is recommended that patients who are taking ACE inhibitors be advised to avoid moderately high or high potassium dietary intake. Particular attention should be paid to the potassium content of salt substitutes.

MONITOR: Many psychotherapeutic and CNS-active agents (e.g., anxiolytics, sedatives, hypnotics, antidepressants, antipsychotics, opioids, alcohol, muscle relaxants) exhibit hypotensive effects, especially during initiation of therapy and dose escalation. Coadministration with antihypertensives and other hypotensive agents, in particular vasodilators and alpha-blockers, may result in additive effects on blood pressure and orthostasis.

MANAGEMENT: Caution and close monitoring for development of hypotension is advised during coadministration of these agents. Some authorities recommend avoiding alcohol in patients receiving vasodilating antihypertensive drugs. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia. Patients should also avoid driving or operating hazardous machinery until they know how the medications affect them.

MONITOR: Many psychotherapeutic and CNS-active agents (e.g., anxiolytics, sedatives, hypnotics, antidepressants, antipsychotics, opioids, alcohol, muscle relaxants) exhibit hypotensive effects, especially during initiation of therapy and dose escalation. Coadministration with antihypertensives and other hypotensive agents, in particular vasodilators and alpha-blockers, may result in additive effects on blood pressure and orthostasis.

MANAGEMENT: Caution and close monitoring for development of hypotension is advised during coadministration of these agents. Some authorities recommend avoiding alcohol in patients receiving vasodilating antihypertensive drugs. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia. Patients should also avoid driving or operating hazardous machinery until they know how the medications affect them.

GENERALLY AVOID: The oral bioavailability of quinolone and tetracycline antibiotics may be reduced by concurrent administration of preparations containing polyvalent cations such as aluminum, calcium, iron, magnesium, and zinc. Therapeutic failure may result. The proposed mechanism is chelation of quinolone and tetracycline antibiotics by di- and trivalent cations, forming an insoluble complex that is poorly absorbed from the gastrointestinal tract. Reduced gastrointestinal absorption of the cations should also be considered.

MANAGEMENT: Concomitant administration of oral quinolone and tetracycline antibiotics with preparations containing aluminum, calcium, iron, magnesium, and/or zinc salts should generally be avoided. Otherwise, the times of administration should be staggered by as much as possible to minimize the potential for interaction. Quinolones should typically be dosed either 2 to 4 hours before or 4 to 6 hours after polyvalent cation preparations, depending on the quinolone and formulation. Likewise, tetracyclines and polyvalent cation preparations should typically be administered 2 to 4 hours apart. The prescribing information for the antibiotic should be consulted for more specific dosing recommendations.