Paracetamol

Mechanism

The EMA reviewed 42 reports of hepatic reactions with Cimicifuga racemosa; in four well-documented cases there was a temporal relationship, among them one fulminant hepatic failure and two autoimmune hepatitis. Paracetamol is hepatotoxic in a dose-dependent way and its margin narrows with fasting, alcohol use or low body weight. Overlap does not multiply the risk in any established way, but it does complicate attributing the injury when it appears.

Symptoms

Unusual tiredness, persistent nausea, right upper quadrant pain, dark urine, pale stools, jaundice. The EMA states that with these signs black cohosh is stopped and advice sought immediately.

Management

Keep paracetamol within the maximum daily dose in the label and do not extend it without review. Black cohosh is taken for limited periods; if any hepatic sign appears, stop it and request transaminases. In anyone with existing liver disease or on other hepatotoxic drugs, avoid the herb.

Mechanism

Paracetamol does not interact significantly with ciclosporin in short courses. On long-term high-dose use (over 3 g/day for more than 7 days), mild hepatocyte suppression may slightly amplify ciclosporin hepatotoxicity.

Symptoms

Fatigue, nausea, jaundice, elevated liver enzymes. Symptoms with long-term therapy are rare.

Management

Paracetamol remains the analgesic and antipyretic of choice in transplant patients. For chronic need, cap at 2 g/day. Check ALT, AST, GGT monthly. If enzymes rise 2–3-fold above the upper limit, stop paracetamol temporarily.

Mechanism

Paracetamol at doses above 3 g/day for more than 7 days raises INR by 1–1.5 via hepatocyte suppression and weak effect on warfarin metabolism. A single 0.5–1 g dose is safe.

Symptoms

Gum bleeding, epistaxis, bruising without trauma, black or tarry stools, haematuria. Higher risk in older patients, prior peptic ulcer disease, and chronic kidney disease.

Management

Paracetamol remains the analgesic and antipyretic of choice on warfarin, but for chronic use cap at 2 g/day. For full-dose courses longer than 4 days: check INR after a week; if above target, reduce warfarin by 10%.

Mechanism

Paracetamol does not inhibit platelet cyclooxygenase, so it neither competes with acetylsalicylic acid for the binding site nor interferes with cardioprotection, unlike ibuprofen. The paracetamol label proposes it as the alternative to salicylates in anticoagulated patients, with one condition: chronic use above 2 g a day can potentiate acenocoumarol and warfarin.

Symptoms

No symptoms attributable to the pair. With analgesic doses of aspirin the gastrointestinal risk, gum bleeding and bruising remain; at 100 mg the profile is the usual cardioprotective one. If an oral anticoagulant is also on board with chronic paracetamol, INR may rise.

Management

Paracetamol is the analgesic of choice for patients on 100 mg aspirin for cardioprotection: no dose spacing is needed. On oral anticoagulants keep sustained use below 2 g a day, or check INR if more is required.

Mechanism

Paracetamol and bisoprolol are metabolised by different pathways. No direct pharmacokinetic interaction.

Symptoms

The combination usually causes no specific symptoms. Each drug's individual side effects remain.

Management

No dose adjustment needed. Paracetamol remains the analgesic of choice in patients on bisoprolol.

Mechanism

Paracetamol and cetirizine are metabolised by different pathways. No direct pharmacokinetic interaction.

Symptoms

The combination usually causes no specific symptoms. Each drug's individual side effects remain.

Management

No dose adjustment needed. The combination is standard in symptomatic formulations for acute respiratory infections and allergy.

Mechanism

Curcumin (Curcuma longa extract) theoretically weakly inhibits CYP2E1, which produces paracetamol's hepatotoxic metabolite NAPQI. For short paracetamol courses, hepatotoxicity risk may be slightly reduced. Clinical data are limited.

Symptoms

The combination usually causes no specific symptoms. Each drug's individual side effects remain.

Management

No dose adjustment needed. Dietary curcumin (curry, golden milk) does not clinically affect paracetamol metabolism. At supplement doses of curcumin (500–1000 mg/day), no clinically significant interaction has been documented. Paracetamol limit: up to 3 g/day.

Mechanism

Dexketoprofen is an NSAID and paracetamol is not, so the label restriction on combining several NSAIDs does not apply here. The mechanisms differ: peripheral cyclooxygenase inhibition versus central action, which is why the pair is used in moderate acute pain. Neither drug alters the metabolism of the other.

Symptoms

No symptoms specific to the pair. Dexketoprofen brings the gastrointestinal and renal risk of any NSAID: epigastric pain, nausea, black stools, oedema or reduced urine output. Paracetamol brings hepatic risk once the 4 g daily limit is passed.

Management

They can be combined or alternated in acute pain. Dexketoprofen is used in short courses at the lowest effective dose and is not stacked with another NSAID. Paracetamol is counted separately, up to 4 g a day.

Mechanism

Echinacea purpurea modulates CYP1A2 and CYP3A4 in vitro, but the in vivo effect is minimal. No direct pharmacokinetic interaction with paracetamol has been described.

Symptoms

The combination usually causes no specific symptoms. Each drug's individual side effects remain.

Management

No dose adjustment needed. The combination is standard in over-the-counter use for acute respiratory infections. Echinacea's efficacy as an immunostimulant is not confirmed by large randomised trials (Cochrane Review 2014).

Mechanism

St John's wort is a CYP3A4 inducer and a weak CYP2E1 inducer. It may theoretically increase formation of paracetamol's hepatotoxic metabolite NAPQI on long-term combination, but clinical cases are rare.

Symptoms

Fatigue, nausea, jaundice, elevated liver enzymes. Symptoms possible on long-term combination (over 1 month) and high paracetamol dose (over 3 g/day).

Management

For short paracetamol courses (3–7 days), no specific adjustment needed. On long-term combination (St John's wort as phytotherapy for depression), cap paracetamol at 2 g/day. St John's wort has many interactions via CYP3A4 induction (contraceptives, warfarin, SSRIs) — reconsider its use.

Mechanism

Ibuprofen inhibits cyclooxygenase in peripheral tissues, while paracetamol acts mainly centrally and has no appreciable effect on gastric mucosa or platelet aggregation. With different targets, the analgesia adds up: the Cochrane review of single doses in acute postoperative pain found greater relief from the combination than from either drug alone. Paracetamol is not an NSAID, so the ibuprofen label warning against combining several NSAIDs does not apply to it.

Symptoms

The combination adds no symptoms of its own. What shows up after several days belongs to each drug separately: epigastric discomfort, nausea or dark stools from ibuprofen, and liver injury if paracetamol exceeds the 4 g per 24 hours set by the label. That ceiling drops with low body weight, prolonged fasting, regular alcohol use or existing liver disease.

Management

Adults can take them together, or alternate them every 3-4 hours when pain is severe. Daily doses are counted separately for each: paracetamol stays within 4 g per 24 hours, ibuprofen at the lowest effective dose for the shortest time. In children under five with fever, NICE states not to give both at once and to consider alternating only if distress returns before the next dose is due.

Mechanism

Paracetamol and loratadine are metabolised by different pathways. No direct pharmacokinetic interaction.

Symptoms

The combination usually causes no specific symptoms. Each drug's individual side effects remain.

Management

No dose adjustment needed. The combination is standard in symptomatic formulations for acute respiratory infections and allergy.

Mechanism

Neither is an NSAID and their mechanisms do not overlap, so the pair is used to cover peaks of pain or fever by alternating doses. Metamizole induces CYP2B6 and CYP3A4, pathways that do not govern paracetamol metabolism, so the two do not alter each other.

Symptoms

The pair creates no distinct picture. The paracetamol ceiling stays at 4 g a day, and metamizole is limited by haematological risk: recurring fever, sore throat or mouth ulcers during treatment point to agranulocytosis rather than to the infection being treated.

Management

Alternate every 4-6 hours, counting each daily dose separately. Metamizole goes in short courses because of its haematological profile; paracetamol stays under 4 g, and lower with liver disease, low weight or regular alcohol use.

Mechanism

Paracetamol is metabolised by CYP2E1 (5%) and predominantly by glucuronidation; metoprolol by CYP2D6. No direct pharmacokinetic interaction.

Symptoms

The combination usually causes no specific symptoms. Each drug's individual side effects remain.

Management

No dose adjustment needed. Paracetamol remains the analgesic of choice in patients on metoprolol.

Mechanism

No direct pharmacokinetic interaction. Co-administration at standard doses is safe.

Symptoms

The combination usually causes no specific symptoms. Each drug's individual side effects remain.

Management

No dose adjustment needed. Paracetamol remains the analgesic and antipyretic of choice on metronidazole.

Mechanism

Naproxen acts on peripheral cyclooxygenase and has a long half-life, allowing twice-daily dosing; paracetamol works centrally. They share no relevant elimination pathway and do not displace each other from albumin, and the naproxen label reserves its combination warning for other NSAIDs and acetylsalicylic acid.

Symptoms

The pair produces no distinct picture. Naproxen keeps a high gastrointestinal risk because of its long half-life: epigastric pain, dyspepsia, black stools, plus fluid retention and rising blood pressure. Paracetamol adds hepatic risk only above the daily dose.

Management

The combination is acceptable in acute pain and in joint pain when naproxen alone is not enough. Keep a single NSAID, watch blood pressure in hypertensive patients, and consider gastric protection over age 65 or with a history of ulcer.