Chlortetracycline may increase the anticoagulant activities of acenocoumarol. The risk or severity of adverse effects can be increased when chlortetracycline is combined with acitretin, adapalene, or alitretinoin. Aluminum phosphate and aluminum hydroxide can cause decreases in the absorption of chlortetracycline resulting in a reduced serum concentration and potentially a decrease in efficacy. The therapeutic efficacy of mecillinam (amdinocillin), amoxicillin, and ampicillin can be decreased when used in combination with chlortetracycline. Chlortetracycline may increase the neuromuscular blocking activities of atracurium besilate.